Method for making fluorescence analysis working curve for determining ferrophosphorus content and application

Abstract

The invention relates to a method for making a fluorescence analysis working curve for measuring ferrophosphorus content and application, and the making method comprises the following steps: weighing iron phosphate or lithium iron phosphate powder with known A element content, dividing the powder into at least three parts, respectively adding a solid diluent, and uniformly mixing, preparing standard samples with gradient change of the content of the element A, and respectively tabletting; measuring the fluorescence intensity of the element A in each standard sample and the fluorescence intensity of the target scattered rays in one-to-one correspondence with each standard sample by adopting an XRF (X-Ray Fluorescence) which generates X-rays through the target, and obtaining the ratio of the fluorescence intensity of the element A in each standard sample to the fluorescence intensity of the corresponding target scattered rays, namely an intensity ratio; associating the content and strength ratio of the element A in each standard sample, and performing linear fitting to form a strength ratio-content working curve of the element A; wherein the element A is iron or phosphorus. The working curve is high in sensitivity, and the accuracy of analyzing the content of the target element based on the working curve is high, and the stability is good.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery element analysis, and particularly to a method for preparing a fluorescence analysis working curve for determining the contents of iron and phosphorus elements in lithium iron phosphate as the cathode material of a lithium battery and its production raw material iron phosphate, and an application thereof. Background Art

[0002] The high-speed development of the electric vehicle industry is inseparable from the support of high-performance power batteries. The battery with lithium iron phosphate (LiFePO4, abbreviated as LFP) as the cathode material is one of the main types of current power batteries, and currently accounts for about 70% in the domestic market; while iron phosphate (FePO4, abbreviated as FP) is one of the main production raw materials of lithium iron phosphate. Iron and phosphorus are the main components of iron phosphate and lithium iron phosphate, and the contents of iron and phosphorus and the iron / phosphorus ratio directly affect the performance of the battery. Therefore, it is crucial to accurately determine the iron and phosphorus contents in iron phosphate or lithium iron phosphate.

[0003] Currently, the commonly used methods in the industry for determining the iron and phosphorus contents in iron phosphate or lithium iron phosphate are mostly chemical analysis methods (such as GB / T30835-2014, GB / T 33822-2017, HG / T 4701-2021). The process of analyzing the iron and phosphorus element contents by these methods includes steps such as accurate weighing of samples, chemical digestion treatment, volume fixing, titration, precipitation, filtration, drying, and weighing. The operation process is complex and cumbersome, time-consuming, requires high skills of operators, and strong acids and other chemicals need to be consumed during the analysis process, which is likely to cause secondary environmental pollution.

[0004] Compared with the commonly used chemical analysis methods in the industry, X-ray fluorescence spectrometry is a method with simple sample preparation, non-destructive to samples, fast analysis speed, without the need to use toxic and polluting reagents, and without a complex and time-consuming pretreatment process, and can be used to test the iron and phosphorus element contents in iron phosphate or lithium iron phosphate. This method relies on the working curve established by the content of specific elements in the standard sample and the fluorescence intensity. After measuring the fluorescence intensity of specific elements in the sample to be measured, the content of this element can be obtained through the working curve. However, due to the stable structure of iron phosphate or lithium iron phosphate, the iron and phosphorus contents are relatively fixed and cannot form a content gradient, so it is difficult to prepare a suitable working curve. And even if a working curve can be prepared, the prepared working curve has poor linearity (as shown in Figure 1-2 ), resulting in low sensitivity and poor applicability of the working curve, thus limiting the application of X-ray fluorescence spectrometry in determining the iron and phosphorus element contents in iron phosphate or lithium iron phosphate. Summary of the Invention

[0005] Based on this, the object of the present invention is, on the one hand, to provide a method for making a fluorescence analysis working curve for determining the content of ferrophosphorus, which has the advantages of high accuracy and good stability of the analysis results.

[0006] A method for making a fluorescence analysis working curve for determining the content of ferrophosphorus includes the following steps:

[0007] Weigh ferric phosphate or lithium iron phosphate powder with a known content of element A, divide it into at least three parts, then add a solid diluent to each part and mix evenly to prepare standard samples with a gradient change in the content of element A, and then press tablets for each standard sample; use XRF that generates X-rays through a target to measure the fluorescence intensity of element A in each standard sample, as well as the fluorescence intensity of the scattered rays of the corresponding target for each standard sample, and calculate the ratio between the fluorescence intensity of element A in each standard sample and the fluorescence intensity of the scattered rays of the corresponding target, which is the intensity ratio; correlate the content of element A in each standard sample with the obtained intensity ratio and perform linear fitting to form a working curve of element A with the content of element A as the abscissa and the intensity ratio as the ordinate; wherein, the element A is iron or phosphorus.

[0008] The analysis method for determining the content of iron and phosphorus elements in ferric phosphate or lithium iron phosphate of the present invention first uses a solid diluent to perform solid dilution on standard samples with known iron and phosphorus element contents to form a content gradient, and based on the discovered trend that the characteristic spectra of iron and phosphorus elements change with the dilution degree and the trend of the change of the scattered rays of the corresponding target show a specific inverse relationship, calculate the ratio between the fluorescence intensity ratio of iron and phosphorus elements and the fluorescence intensity of the scattered rays of the target to obtain the intensity ratio, so as to form a working curve reflecting the functional relationship between the intensity ratio and the content, and solve the problems of difficulty in forming a content gradient for ferric phosphate / lithium iron phosphate and poor curve sensitivity when making the working curves of iron and phosphorus elements.

[0009] Further, the particle size of the solid diluent is 2 - 15 μm.

[0010] Further, the solid diluent is composed of carbon, hydrogen and oxygen.

[0011] Further, the solid diluent is starch or methylcellulose.

[0012] Further, the solid diluent is carbon powder or boric acid.

[0013] Further, the target is any one of rhodium, tungsten, molybdenum or silver.

[0014] Further, the scattered rays of the target are inelastic scattered rays or elastic scattered rays of the target.

[0015] On the other hand, the present invention also provides an application of a method for making a fluorescence analysis working curve for measuring the content of ferrophosphorus, which is used for measuring the content of element A in iron phosphate or lithium iron phosphate, wherein the element A is iron or phosphorus, and the method includes the following steps: making the working curve of element A by any one of the above-mentioned making methods; pressing the powder of the iron phosphate or lithium iron phosphate to be measured into a tablet to form a sample to be measured; measuring the intensity ratio of element A in the sample to be measured; and obtaining the content of element A in the sample to be measured through the working curve of element A.

[0016] Further, the measured intensity ratio of element A in the sample to be measured is the ratio obtained by calculating the fluorescence intensity of element A in the sample to be measured measured by the XRF and the fluorescence intensity of the scattered rays of the target material corresponding to the sample to be measured.

[0017] For better understanding and implementation, the present invention will be described in detail below with reference to the accompanying drawings. Description of the Drawings

[0018] Figure 1 It is the intensity-content working curve of iron element made by the traditional method;

[0019] Figure 2 It is the intensity-content working curve of phosphorus element made by the traditional method;

[0020] Figure 3 It is the comparison diagram of the change of the characteristic spectrum lines of iron and phosphorus elements in iron phosphate and the inelastic scattered rays of the target material in the embodiment of the present invention;

[0021] Figure 4 It is the comparison diagram of the change of the characteristic spectrum lines of iron and phosphorus elements in lithium iron phosphate and the inelastic scattered rays of the target material in the embodiment of the present invention;

[0022] Figure 5 It is the physical diagram of the standard sample formed by pressing the iron phosphate powder with borate edging in the embodiment of the present invention;

[0023] Figure 6 It is the intensity ratio-content working curve of iron element prepared in the embodiment of the present invention;

[0024] Figure 7 It is the intensity ratio-content working curve of phosphorus element prepared in the embodiment of the present invention;

[0025] Figure 8 It is the comparison diagram of the intensity ratio-content working curve of iron element prepared in the embodiment of the present invention and the intensity ratio-content working curve of iron element prepared in the comparative example;

[0026] Figure 9It is a comparison chart of the phosphorus element intensity ratio - content working curve obtained in the embodiment of the present invention and the phosphorus element intensity ratio - content working curve obtained in the comparative example;

[0027] Figure 10 It is the characteristic spectrum line of the phosphorus element and the characteristic spectrum line of the calcium element measured by using calcium carbonate as a solid diluent in the comparative example of the present invention;

[0028] Figure 11 It is based on Figure 6 The error value of the analysis result of the iron element intensity ratio - content working curve and the error value of the analysis result of the iron element intensity - content working curve based on Figure 1 Comparison chart;

[0029] Figure 12 It is based on Figure 7 The error value of the analysis result of the phosphorus element intensity ratio - content working curve and the error value of the analysis result of the phosphorus element intensity - content working curve based on Figure 2 Comparison chart. Specific embodiments

[0030] It should be clear that the described embodiments are only part of the embodiments of the present application, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts belong to the scope protected by the embodiments of the present application.

[0031] Traditionally, when making a working curve for X-ray fluorescence spectrometry analysis, samples with a content gradient are usually used. The fluorescence intensity of the target analysis element of the test sample is measured, and the functional relationship between the content and the intensity is established using the least squares method, which is the working curve. However, since the content points of iron phosphate and lithium iron phosphate have extremely small fluctuations and cannot form a content gradient, it is very difficult to make a working curve. The inventor of the present invention uses a solid diluent to mix and dilute the iron phosphate or lithium iron phosphate sample for making the working curve to form a series of standard samples with a content gradient of the target analysis element. However, during this process, although the solid dilution can form a content gradient, the slope of the obtained intensity - content working curve is small and the intercept is large. As Figure 1 And Figure 2As shown, in the intensity-content working curve, the intensity increase of the target analysis element is relatively small, so that the corresponding increase ratio of the unit content of the target analysis element is also relatively small. Here, the intensity increase = (the intensity maximum value - the intensity minimum value in the same intensity-content working curve) / the intensity minimum value; and the increase ratio of the unit content = the intensity increase / (the content maximum value - the content minimum value in the same intensity-content working curve). Thus, even if there are large changes in the content of the target analysis element in the test sample, the material or shape of the sample, the corresponding intensity change is not obvious, the sensitivity is low, so it is easy to cause errors in the analysis results when using this working curve to test, and the content of the target analysis element cannot be accurately measured, and the applicability is poor.

[0032] In the research and analysis of using XRF that generates primary X-rays through a rhodium target to determine the iron and phosphorus content in iron phosphate, the inventors of the present invention found that when starch is used as a solid diluent to form a series of standard samples, the trend of the characteristic spectral line FeKa of the iron element changing with the dilution degree in each standard sample is significantly inversely proportional to the trend of the inelastic scattered ray RhKaC of the corresponding target material rhodium changing (as Figure 3 shown), that is, when there is no dilution (i.e., FP-100%), the fluorescence intensity of FeKa of the iron element is the maximum value, while the fluorescence intensity of RhKaC of the target material rhodium is the minimum value. As the dilution degree continuously increases, the fluorescence intensity of FeKa of the iron element gradually decreases, while the fluorescence intensity of RhKaC of the target material rhodium gradually increases, that is, the higher the dilution degree of the standard sample, the lower the fluorescence intensity of its FeKa, and the higher the fluorescence intensity of RhKaC. Similarly, as Figure 3 shown, the trend of the characteristic spectral line PKa of the phosphorus element changing with the dilution degree is also exactly opposite to the trend of the inelastic scattered ray RhKaC of the corresponding target material rhodium changing, that is, the higher the dilution degree of the standard sample, the lower the fluorescence intensity of its PKa, and the higher the fluorescence intensity of RhKaC. And in lithium iron phosphate, as Figure 4 shown, the trend of the characteristic spectral lines of iron and phosphorus elements changing with the dilution degree is also in the same specific relationship as described above with the trend of the inelastic scattered rays of the corresponding target material rhodium changing.

[0033] Based on the above inverse relationship between the changing trends of the characteristic spectral lines of iron and phosphorus elements and the changing trend of the inelastic scattered ray intensity of the target material rhodium, if the ordinate of the working curve uses the fluorescence intensity (I FeKa 、I PKa) The ratio to the fluorescence intensity of the inelastic scattered rays of the target material can amplify the correspondence between the fluorescence intensity of the target analysis element and its content value through the fluorescence intensity of the inelastic scattered rays of the target material, making the increase ratio per unit content in the formed intensity ratio - content working curve larger. In this way, when the content of the target test element in the sample, the material or shape of the sample changes slightly, using the variable form of the intensity ratio can more sensitively reflect these changes, so as to accurately measure the contents of iron and phosphorus elements.

[0034] Based on this, an embodiment of the present invention provides a method for making a fluorescence analysis working curve for measuring the contents of iron and phosphorus. The working curves of iron and phosphorus elements prepared thereby have high sensitivity. Based on this working curve, the contents of iron and phosphorus elements in iron phosphate or lithium iron phosphate can be analyzed, and the analysis results have high accuracy and good stability.

[0035] The following takes the determination of the iron element content in iron phosphate as an example to specifically illustrate the method for making the working curve of the present invention. The making method includes the following steps:

[0036] S11: Weigh iron phosphate powder with a known iron element content and divide it into five portions. Then, add different amounts of solid diluent to each portion so that the total mass of each portion is the same (for example, the first portion of iron phosphate powder is 9 g and 1 g of solid diluent is added, the second portion of iron phosphate powder is 8 g and 2 g of solid diluent is added, the third portion of iron phosphate powder is 7 g and 3 g of solid diluent is added, and so on), and mix them evenly respectively to prepare standard samples with gradient changes in iron element contents of 90%, 80%, 70%, 60% and 50%. Then, use boric acid to edge and press each standard sample into a Figure 5 flaky structure as shown;

[0037] Specifically, to obtain the iron element content in the iron phosphate powder, iron phosphate powder with a known iron element content can be directly purchased; or it can be determined by the test methods disclosed in standards such as GB / T33822 - 2017 and HG / T4701 - 2021. Since the test methods are prior arts, they will not be elaborated here in detail;

[0038] The number of standard samples should be at least three. In this embodiment, the number of standard samples is five; of course, the more the number of standard samples, the higher the accuracy of the working curve; and when the number of standard samples is less than three, the prepared working curve may have a large error.

[0039] The particle size of the solid diluent is 2 - 15 μm. It can be starch or methyl cellulose that only contains three elements of carbon, hydrogen and oxygen, or carbon powder that only contains carbon element, or light matrix substances such as boric acid. The constituent elements of these materials are not within the scope of XRF testing and have little absorption of the fluorescence of the target analysis element. In this embodiment, starch is used as the solid diluent. The average particle size of starch is 3 - 4 μm, which is close to the average particle sizes of iron phosphate and lithium iron phosphate (the average particle size of iron phosphate is 3 μm). Therefore, when mixed with iron phosphate, it can be better mixed evenly. In addition, starch is only composed of three elements of carbon, hydrogen and oxygen, and these elements are not within the scope of XRF testing (the general XRF vacuum atmosphere testing range is Na - U), and no fluorescence spectrum peaks will be generated, so it will not form overlapping interference on the determination of iron and phosphorus elements. In addition, the mass absorption coefficients of the constituent elements carbon, hydrogen and oxygen of the solid diluent are small, and the absorption ability of fluorescence is weak, so it has little influence on the target analysis element in the standard sample.

[0040] S12: The fluorescence intensity of iron element in each standard sample is measured by XRF that generates primary X-rays through a target, and the fluorescence intensity of the scattered rays of the target corresponding to each standard sample one by one is obtained. The ratio between the fluorescence intensity of iron element in each standard sample and the fluorescence intensity of the scattered rays of the corresponding target is the intensity ratio.

[0041] Specifically, XRF that generates primary X-rays through a target is used to measure the fluorescence intensity of iron element in each standard sample. The XRF used in this embodiment is specifically an EDX-7200 series instrument. Of course, in addition to using an EDX-7200 series instrument, other XRFs of the same type that generate primary X-rays through a target can also be used.

[0042] The XRF used in this embodiment mainly includes an X-ray tube, a target and a detector. Among them, the material of the target is specifically rhodium. Of course, targets such as tungsten, molybdenum and silver can also be used. The working principle of XRF is: primary X-rays are generated by bombarding the target through the X-ray tube. The primary X-rays irradiate the standard sample, and the constituent elements of the standard sample are excited to generate their respective characteristic fluorescent X-rays. For example, iron phosphate is excited to generate fluorescent X-rays of iron element and phosphorus element. The fluorescent X-rays complete photoelectric conversion in the detector, convert the optical signal into an electrical signal, and through circuit processing and software calculation, respectively form the characteristic spectral line FeKa of iron element and the characteristic spectral line PKa of phosphorus element, and then the fluorescence intensity I of the fluorescent X-rays of iron element is obtained. FeKa And the fluorescence intensity I of the fluorescent X-rays of phosphorus element PKa ;

[0043] Meanwhile, the primary X-rays generated by the ray tube bombarding the target irradiate the standard sample, generating scattered rays of the target. The scattered rays include elastic scattered rays RhKa and inelastic scattered rays RhKaC. The fluorescence intensity of RhKa and RhKaC is related to the material of the standard sample. Among them, the fluorescence intensity of RhKaC of the standard sample with a light matrix material is large. When the material changes, the fluorescence intensity of RhKaC also changes accordingly. Through the detector, photoelectric conversion is completed, and the fluorescence intensity I of the inelastic scattered rays RhKaC of the rhodium target can be obtained. RhKaC ;

[0044] Then, by calculating the fluorescence intensity I FeKa of the fluorescent X-rays of the iron element in each standard sample and the fluorescence intensity I RhKaC of the inelastic scattered rays of the corresponding rhodium target, the intensity ratio I FeRatio , I FeRatio = I FeKa / I RhKaC .

[0045] Of course, since the fluorescence intensity of the elastic scattered rays RhKa of the target also changes with the change of the material of the standard sample, therefore, the fluorescence intensity I FeKa of the fluorescent X-rays of the iron element can also be taken and the fluorescence intensity I RhKa of the elastic scattered rays of the corresponding rhodium target, forming an intensity ratio. However, compared with the elastic scattered rays RhKa of the target, the inelastic scattered rays RhKaC of the target have better stability.

[0046] S13: Correlate the iron element content in each standard sample with the obtained intensity ratio and perform linear fitting to form an iron element working curve with the iron element content as the abscissa and the intensity ratio as the ordinate;

[0047] There is a specific inverse relationship between the trend of the characteristic spectral line FeKa of the iron element changing with the dilution degree and the trend of the change of the inelastic scattered rays RhKaC of the corresponding rhodium target. Calculate the ratio of the measured fluorescence intensity of the iron element to the fluorescence intensity of the inelastic scattered rays of the rhodium target to obtain the intensity ratio; Correlate the iron element content of each standard sample with the intensity ratio and perform linear fitting to prepare an iron element working curve as shown in Figure 6 with the iron element content as the abscissa and the intensity ratio as the ordinate.

[0048] The method for making the phosphorus element working curve is the same as the method for making the above iron element working curve, so it will not be elaborated here. Through the manufacturing method of the above embodiments, a phosphorus element working curve as shown in Figure 7 with the phosphorus element content as the abscissa and the intensity ratio as the ordinate can be prepared.

[0049] From Figure 6 andFigure 7 It can be seen that in the intensity ratio - content working curves obtained through the above embodiments, the increases in the intensity ratios of the target analysis elements are all relatively large, so that the increase ratios of the corresponding target analysis elements per unit content are also relatively large. Here, the increase in intensity ratio = (the maximum intensity ratio - the minimum intensity ratio in the same intensity ratio - content working curve) / the minimum intensity ratio; and the increase ratio per unit content = the increase in intensity ratio / (the maximum content - the minimum content in the same intensity ratio - content working curve). Thus, when there are slight changes in the content of the target analysis element in the sample to be tested, the material or shape of the sample, the corresponding change in the intensity ratio is also obvious, with high sensitivity. Therefore, the accuracy of analyzing the content of the target analysis element in the sample to be tested using this intensity ratio - content working curve is high.

[0050] Here, it should be noted that the selection of the solid diluent in the above embodiments of the present invention is closely related to the finally obtained high - sensitivity intensity ratio - content working curves of iron and phosphorus elements: in addition to the fact that the particle size of starch is close to that of iron phosphate, enabling better mixing of starch and iron phosphate, and the constituent elements of starch itself do not cause overlapping interference to the target analysis elements (iron, phosphorus), the density of starch is small. After mixing with iron phosphate or lithium iron phosphate, the average density of each standard sample formed becomes smaller and the matrix becomes lighter. Since the amount of X - rays reaching the detector is related to the matrix composition of the sample (here referring to each standard sample), the lighter the matrix of the sample, the stronger the fluorescence signal generated after the primary X - rays irradiate the sample matrix, and at the same time, the change in the inelastic scattered ray RhKaC of the target material also becomes larger. And precisely because the change in the inelastic scattered ray RhKaC of the target material rhodium is large, the inverse relationship between the trend of the characteristic spectral lines of the target analysis elements (iron, phosphorus) in each standard sample changing with the dilution degree and the trend of the change in the inelastic scattered ray of the target material rhodium can be clearly shown. Furthermore, based on this inverse relationship, the working curve can be corrected by calculating the intensity ratio between the fluorescence intensity of the target analysis elements (iron, phosphorus) and the fluorescence intensity of the inelastic scattered ray of the target material rhodium, forming an intensity ratio - content working curve, thereby improving the sensitivity of the working curve.

[0051] In addition, due to the low density and small mass absorption coefficient of starch, starch absorbs less fluorescence excited after the standard sample is irradiated by the primary X - rays, that is, it has less influence on the fluorescence intensity of the target analysis elements. Furthermore, the corresponding relationship between the intensity ratio calculated by the ratio of the fluorescence intensity of the target analysis elements (iron, phosphorus) to the fluorescence intensity of the inelastic scattered ray of the target material rhodium and the content of the target analysis elements (iron, phosphorus) is more accurate. Therefore, the analysis effect of the content of the target analysis elements (iron, phosphorus) can be improved.

[0052] The beneficial effects of using starch as a solid diluent in the embodiments of the present invention for making an intensity ratio - content working curve are further illustrated by the following comparative example.

[0053] The difference between the comparative example and the example of the present invention lies only in that: the solid diluent in the comparative example is calcium carbonate, and the other steps are exactly the same as those in the above example.

[0054] Please refer to Figure 8-9 , Figure 8-9 , which respectively show the working curves of iron element intensity ratio - content and phosphorus element intensity ratio - content prepared from the examples of the present invention and the comparative example. As Figure 8-9 can be seen, whether it is the working curve of iron element or phosphorus element, the linear relationship of the test points of each standard sample in the examples of the present invention is better than that of the comparative example. Therefore, the obtained working curve can more accurately reflect the content of iron element and phosphorus element. In addition, as Figure 9 shown, the working curve of the comparative example intersects the vertical axis in the upper half axis. That is, when the phosphorus element content is 0 in the working curve of the comparative example, the intensity ratio can still be detected, indicating that there are elements in the sample that interfere with the intensity of the phosphorus element spectral peak. After analysis, it is found that this is because the spectral peak of the characteristic spectral line CaKaESC of calcium element in calcium carbonate significantly interferes with the characteristic spectral line Pka of phosphorus element: as Figure 10 shown, in the calcium carbonate sample without phosphorus element, a CaKaESC spectral peak will be generated at the position where the characteristic spectral line Pka of phosphorus element is located. Therefore, when the standard sample contains calcium carbonate, when calculating the fluorescence intensity of the characteristic spectral line Pka of phosphorus element in the standard sample, the CaKaESC spectral peak will also be included in the calculated value of the fluorescence intensity of Pka, resulting in an increase in the fluorescence intensity of Pka, which also makes it possible to detect the intensity ratio when the phosphorus element content is 0. It can be seen that using calcium carbonate as the solid diluent will affect the accuracy of the production of the phosphorus element working curve. Compared with calcium carbonate, using starch as the solid diluent in the examples of the present invention can avoid the influence of the constituent elements of the solid diluent itself on the analysis result, thereby ensuring the accuracy of the analysis result.

[0055] Furthermore, when preparing the sample of the test sample into a tablet, it is easy to have defects such as uneven shape, thickness, and surface flatness of the analysis surface, or cracks on the surface of the analysis surface. These defects often lead to a decrease in the fluorescence intensity of the target analysis element and the fluorescence intensity of the background scattered rays of the target material. Therefore, when analyzing the content of the target analysis element in the test sample using the intensity - content working curve, the measured content of the target element is often on the low side, thus further increasing the error between the content analysis value measured based on the intensity - content working curve and the actual content value.

[0056] While the fluorescence intensity of the target analysis element decreases due to the existence of the above-mentioned defects, the fluorescence intensity of the scattered rays of the target material also decreases. When calculating the intensity ratio by taking the ratio between the fluorescence intensity of the target analysis element and the fluorescence intensity of the scattered rays of the target material, the changes caused by the defects resulting from tablet pressing are weakened or even offset. Thus, the errors introduced due to the inconsistent shape, thickness, and surface flatness of the sample to be measured can be reduced or even avoided. Therefore, when analyzing the content of the target analysis element in the sample to be measured using the intensity ratio-content working curve, the measured content of the target element is closer to the actual value.

[0057] The present invention also provides an analytical method for determining the phosphorus iron content based on the iron element working curve prepared above. Taking the determination of the iron element content in iron phosphate as an example, the analytical method includes the following steps:

[0058] S1: Prepare the iron element working curve as shown in Figure 6 by the above preparation method;

[0059] S2: Determine the iron element content;

[0060] S21: Press the iron phosphate powder to be measured into a tablet to form a sample to be measured;

[0061] Use boric acid to edge and press the iron phosphate powder to be measured into a sheet-like structure to form a sample to be measured;

[0062] S22: Measure the intensity ratio of the iron element in the sample to be measured;

[0063] Use XRF same as in step S12 to measure the fluorescence intensity of the characteristic spectrum line of the iron element in the sample to be measured, and the fluorescence intensity of the inelastic scattered rays of the target material corresponding to the sample to be measured, and calculate the ratio between the fluorescence intensity of the characteristic spectrum line of the iron element in the sample to be measured and the fluorescence intensity of the corresponding inelastic scattered rays of the target material.

[0064] S23: Obtain the iron element content of the sample to be measured through the iron element working curve;

[0065] According to the obtained intensity ratio of the iron element, obtain the corresponding iron element content through the iron element working curve.

[0066] Similarly, when determining the phosphorus element content in lithium iron phosphate, first prepare the phosphorus element working curve (as shown in Figure 7As shown, the intensity ratio of phosphorus element in the sample to be measured is then measured by XRF and calculated. Then, according to the obtained intensity ratio of phosphorus element, the corresponding content of phosphorus element is obtained through the working curve of phosphorus element. Since the principle and steps of measuring the content of phosphorus element are the same as those of measuring the content of iron element above, no repeated description will be given here. For measuring the contents of iron and phosphorus elements in lithium iron phosphate, since its principle and steps are also the same as those of measuring the contents of iron and phosphorus elements in lithium iron phosphate above, no repeated description will be given here either.

[0067] Verification of test results

[0068] (1) Accuracy test

[0069] To verify the accuracy of the analysis method based on the working curve prepared according to the above embodiments of the present invention, 8 different samples of iron phosphate to be measured are taken, and then the analysis values obtained by analyzing using the working curve prepared according to the embodiments of the present invention are compared with the analysis values obtained by chemical analysis. Among them, the chemical method is carried out with reference to standards such as GB / T 33822-2017 and HG / T 4701-2021. The statistical analysis results are shown in Table 1:

[0070] Table 1 Unit: wt / %

[0071]

[0072] The data in the above table show that in the analysis results of the contents of Fe and P in the iron phosphate sample to be measured based on the working curve prepared according to the embodiments of the present invention, the analysis error of Fe is better than 0.152%, and the analysis error of P is better than 0.074%. It can be seen that the results of the contents of Fe and P obtained by the analysis method based on the working curve prepared according to the present invention are highly consistent with the results of the contents of Fe and P obtained by chemical analysis.

[0073] (2) Short-term stability test

[0074] To test the short-term stability of the analysis method based on the working curve prepared according to the above embodiments of the present invention, under repeatability conditions, a pressed tablet of iron phosphate powder with borate edging is used to form an iron phosphate sample to be measured, and the same iron phosphate sample to be measured is continuously analyzed 10 times using the working curve prepared according to the above embodiments of the present invention. The statistical analysis results are shown in Table 2:

[0075] Table 2 Unit: wt / %

[0076]

[0077]

[0078] Note: AVE represents the average value; SD represents the standard deviation; RSD represents the relative standard deviation

[0079] The data in the above table show that in the 10 consecutive analysis results of Fe and P elements in the iron phosphate sample to be measured based on the working curve prepared according to the above embodiments of the present invention, the RSD value of the analysis precision of Fe is better than 0.089%, and the R value is better than 0.100%; the RSD value of the analysis precision of P is better than 0.091%, and the R value is better than 0.061%. It can be seen that the short-term stability of the analysis method based on the working curve prepared according to the present invention is good.

[0080] (3) Long-term stability test

[0081] To test the long-term stability of the analysis method based on the working curve prepared according to the above embodiments of the present invention, the iron phosphate powder tablets are pressed with the same boric acid edging to form an iron phosphate sample to be measured. The working curve prepared in the above embodiments of the present invention is used to analyze the iron phosphate sample to be measured. After the analysis is completed, it is taken out, and after an interval of more than 1 hour, it is put into the XRF again, and analyzed by the same method. 10 analyses are completed within 2 adjacent days, and the statistical analysis results are shown in Table 3:

[0082] Table 3 Unit: wt / %

[0083]

[0084] Note: AVE represents the average value; SD represents the standard deviation; RSD represents the relative standard deviation

[0085] The data in the above table show that in the 10 consecutive analysis results of Fe and P elements in the iron phosphate sample to be measured based on the working curve prepared according to the above embodiments of the present invention, the RSD value of the analysis precision of Fe is better than 0.119%, and the R value is better than 0.116%; the RSD value of the analysis precision of P is better than 0.169%, and the R value is better than 0.100%. It can be seen that the long-term stability of the analysis method based on the working curve prepared according to the present invention is good.

[0086] (4) Parallel sample stability test

[0087] To test the parallel sample stability of the analysis method based on the working curve prepared according to the above embodiments of the present invention, 3 different iron phosphate powders are taken, and 10 parallel samples are pressed for each iron phosphate powder with boric acid edging to form samples to be measured. Then, the working curve prepared in the above embodiments of the present invention is used to analyze the parallel samples to be measured respectively, and the statistical analysis results are shown in Table 4:

[0088] Table 4 Unit: wt / %

[0089]

[0090] Note: AVE represents the average value; SD represents the standard deviation; RSD represents the relative standard deviation

[0091] The data in the above table show that in the results of analyzing the Fe and P contents in the iron phosphate samples based on the working curve prepared according to the above embodiments of the present invention, the RSD value of the analysis precision of Fe is better than 0.129%, and the R value is better than 0.149%; the RSD value of the analysis precision of P is better than 0.141%, and the R value is better than 0.087%.

[0092] In addition, the analysis results of Fe and P for the 3 iron phosphate samples to be measured in the above table meet the requirements of the 2 - time parallel analysis errors of Fe and P in the standard HG / T 4701 - 2021 "Iron Phosphate for Batteries" (0.3% and 0.2% respectively); the absolute differences among the 10 independent analysis results of the 3 iron phosphate samples to be measured in the above table are all less than the error requirements. It can be seen that the analysis results of the analysis method based on the working curve prepared according to the present invention meet the requirements of the above - mentioned standard.

[0093] (5) Comparative analysis of the intensity ratio - content working curve and the intensity - content working curve

[0094] To compare the accuracy of the analysis method based on the intensity ratio - content working curve prepared according to the above embodiments of the present invention with the accuracy of the analysis method based on the intensity - content working curve, 16 different iron phosphate powders were taken, and then the analysis values obtained by analyzing with the intensity ratio - content working curve shown in Figure 6 and Figure 7 and the analysis values obtained by analyzing with the intensity - content working curve shown in Figure 1 and Figure 2 were respectively compared with the analysis values obtained by the chemical method. Among them, the chemical method was carried out with reference to standards such as GB / T 33822 - 2017 and HG / T 4701 - 2021. The statistical analysis results are shown in Table 5:

[0095] Table 5 Unit: wt / %

[0096]

[0097] Figure 11-12 The comparison chart drawn based on the analysis results in Table 5, where Figure 11-12 the position at the 0 of the vertical coordinate represents 0 error compared with the chemical analysis value. As can be seen from Figure 11-12 , compared with the analysis values obtained based on the intensity - content working curve, the error between the analysis values obtained based on the intensity ratio - content working curve prepared according to the embodiments of the present invention and the chemical analysis values is smaller, and the fluctuation range of the curve is also smaller, with better stability. It can be seen that the analysis results based on the intensity ratio - content working curve prepared according to the embodiments of the present invention are significantly better than the analysis results obtained by analyzing with the intensity - content working curve.

[0098] Compared with the prior art, the method for making a fluorescence analysis working curve for determining the content of ferrophosphorus in the present invention first uses a solid diluent to perform solid dilution on a standard sample with known iron and phosphorus element contents to form a content gradient, and based on the fact that the trend of the characteristic spectral lines of iron and phosphorus elements changing with the dilution degree is in a specific inverse relationship with the change trend of the scattered rays of the corresponding target material, calculates the ratio between the fluorescence intensity ratio of iron and phosphorus elements and the fluorescence intensity of the scattered rays of the target material to obtain an intensity ratio, so as to form an intensity ratio - content working curve, solving the problems that it is difficult to form a content gradient for iron phosphate / lithium iron phosphate and the curve sensitivity is poor when making the working curves of iron and phosphorus elements; then based on the prepared working curve, the contents of iron and phosphorus elements can be obtained by measuring the intensity ratio of iron and phosphorus elements in the sample to be measured. The whole process will not damage the sample and will not cause secondary pollution. It has a fast analysis speed, low cost, simple operation, and high accuracy and good stability of the analysis results. In the face of occasions where the sample analysis volume is large and the time requirement is urgent, only one working curve needs to be made, and multiple analyses can be carried out, with high analysis efficiency.

[0099] The above-described embodiments merely represent several implementation manners of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and the present invention also intends to include these modifications and deformations.

Claims

1. A method for making a fluorescence analysis working curve for determining the content of ferrophosphorus, characterized in that: It includes the following steps: Weigh ferric phosphate or lithium iron phosphate powder with a known content of element A, divide it into at least three portions, then add a solid diluent to each portion and mix evenly to prepare standard samples with a gradient change in the content of element A. Then, press tablets from each standard sample; Use XRF that generates X-rays through a target to measure the fluorescence intensity of element A in each standard sample, as well as the fluorescence intensity of the scattered rays of the target corresponding to each standard sample one by one, and calculate the ratio between the fluorescence intensity of element A in each standard sample and the fluorescence intensity of the scattered rays of the corresponding target, which is the intensity ratio; Relate the content of element A in each standard sample to the obtained intensity ratio and perform linear fitting to form a working curve of element A with the content of element A as the abscissa and the intensity ratio as the ordinate; Wherein, the element A is iron or phosphorus.

2. The method for making a fluorescence analysis working curve for measuring the content of phosphorus and iron according to claim 1, wherein: The particle size of the solid diluent is 2 - 15 μm.

3. The method for making a fluorescence analysis working curve for measuring the content of phosphorus and iron according to claim 2, wherein: The solid diluent is composed of carbon, hydrogen, and oxygen.

4. The method for making a fluorescence analysis working curve for measuring the content of phosphorus and iron according to claim 3, wherein: The solid diluent is starch or methyl cellulose.

5. The method for making a fluorescence analysis working curve for measuring the content of phosphorus and iron according to claim 2, wherein: The solid diluent is carbon powder or boric acid.

6. The method for making a fluorescence analysis working curve for measuring the content of phosphorus and iron according to claim 1, wherein: The target is any one of rhodium, tungsten, molybdenum, palladium, or silver.

7. The method for making a fluorescence analysis working curve for measuring the content of phosphorus and iron according to claim 1, wherein: The scattered rays of the target are the inelastic scattered rays or the elastic scattered rays of the target.

8. Application of a method for making a fluorescence analysis working curve for determining the content of ferrophosphorus, characterized in that: For measuring the content of element A in ferric phosphate or lithium iron phosphate, wherein the element A is iron or phosphorus, it includes the following steps: Make the working curve of element A by the making method according to any one of claims 1 - 7; Press the powder of the ferric phosphate or lithium iron phosphate to be measured into a tablet to form a sample to be measured; Measure the intensity ratio of element A in the sample to be measured; Obtain the content of element A in the sample to be measured through the working curve of element A.

9. The application of the method for making a fluorescence analysis working curve for measuring the content of phosphorus and iron according to claim 8, wherein: The measured intensity ratio of element A in the sample to be measured is the ratio calculated from the fluorescence intensity of element A measured in the sample to be measured by using the XRF and the fluorescence intensity of the scattered rays of the target corresponding to the sample to be measured, which is the ratio between the fluorescence intensity of element A in the sample to be measured and the fluorescence intensity of the scattered rays of the corresponding target.

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