Method for detecting content of free elements in lithium iron phosphate and application of method

Abstract

The invention relates to the field of battery detection, in particular to a method for detecting the content of free elements in lithium iron phosphate and application of the method, and the method comprises the following steps: (S.1) mixing a lithium iron phosphate sample with a solvent, and standing; (S.2) sampling and filtering the mixed solution at a plurality of time points in the standing process to obtain filtrate; (S.3) testing the content of target free elements in the filtrate at each time point; and (S.4) drawing a content-time relation curve by taking the standing time as an abscissa and the element content as an ordinate, and obtaining a linear equation through linear fitting, the intercept of the linear equation being the content of the target free element in the lithium iron phosphate. Compared with the prior art, the method has the advantages that the contribution of free elements and material body dissolved elements is effectively separated through a time sequence sampling and linear fitting method, the problem that the test result of a conventional method is too high is solved, the measured value is closer to the real content, and reliable data support is provided for material quality control.

Description

Technical Field

[0001] This invention relates to the field of battery testing, and more particularly to a method for detecting the content of free elements in lithium iron phosphate. Background Technology

[0002] Lithium iron phosphate (LFP), as a cathode material for lithium-ion batteries, is widely used in electric vehicles and energy storage due to its high safety, good cycle performance, and environmental friendliness. The electrochemical performance of LFP materials is highly dependent on their chemical composition, especially the content and forms of key elements such as iron, lithium, and phosphorus. These parameters directly affect the battery's capacity, stability, and lifespan. Therefore, developing accurate and efficient methods for testing elemental content is crucial for the quality control, process optimization, and performance evaluation of LFP materials. Currently, various methods exist in the industry for testing the elemental content of LFP, but all have certain limitations and cannot meet the ever-increasing demands of material analysis.

[0003] Early potentiometric titration methods, commonly used in chemical analysis, involved treating samples with acid solutions followed by titration with reagents such as potassium dichromate to determine iron content. While this method could provide total elemental data, it was cumbersome, with a testing cycle of 5 to 7 hours, and involved toxic reagents such as potassium dichromate and stannous chloride. This not only posed a high operational risk but also easily introduced human error, making high-throughput detection difficult. Furthermore, potentiometric titration only provides total elemental information and cannot distinguish between different forms of elements in the material, such as lattice-intercalated elements and free elements. Free elements (such as lithium or phosphorus not involved in the lattice structure) may originate from synthesis residues or degradation products, and their content fluctuations directly affect the battery's interfacial stability and cycle performance. Therefore, relying solely on total elemental analysis often fails to comprehensively assess material defects.

[0004] To overcome the shortcomings of potentiometric titration, inductively coupled plasma optical emission spectrometry (ICP-OES) has been increasingly introduced into the elemental analysis of lithium iron phosphate. For example, one existing method (refer to CN113533309A) involves digesting the lithium iron phosphate sample with an acid solution, heating and filtering, adding a yttrium internal standard solution, and then using ICP-OES to determine the iron content, employing a radial observation mode to reduce the dilution factor. This method avoids toxic reagents and improves detection efficiency, but its core focus remains on total elemental determination. Furthermore, the digestion process can completely dissolve the bulk material, leading to mixing of free elements with lattice elements, making the test results unable to reflect the true content of free elements. Simultaneously, high dilution (e.g., 10,000-fold dilution) may amplify errors and affect accuracy, especially for low-content components. Another existing technology (refer to CN116519415A) targets carbon-coated lithium iron phosphate, removing the carbon layer through high-temperature sintering followed by acid digestion to test for impurity metal elements such as sodium and potassium. While this method effectively eliminates carbon interference, the pretreatment is complex, and being based on the same digestion principle, it cannot avoid the problem of morphological differentiation. These methods all obtain the total elemental content through destructive pretreatment, neglecting the specific effects that free elements may have on battery performance. For example, free lithium may trigger electrolyte decomposition or electrode interface side reactions, thereby accelerating capacity decay.

[0005] In summary, existing testing methods share several drawbacks: First, they rely on acid digestion or harsh chemical treatments, which destroy the original morphology of the sample and lead to the loss of information on free elements. Second, the testing targets are mostly limited to total content or impurities, lacking specific detection methods for free elements. Third, even with high-precision instruments such as ICP-OES, the contribution of free elements cannot be separated due to limitations in the method's principles. This results in blind spots in material evaluation, particularly in the optimization of lithium iron phosphate synthesis processes and failure analysis, where it is difficult to accurately identify the risks posed by free elements. For example, excessively high free lithium content may indicate unbalanced synthesis conditions, but existing methods cannot provide specific data, thus limiting the fine-tuning of material properties. Therefore, there is an urgent need in this field for a new method that can non-destructively or with minimal interference test the free element content in lithium iron phosphate. This method should possess high accuracy, simplicity, and compatibility with existing analytical platforms to fill the technological gap. Summary of the Invention

[0006] This application aims to overcome the shortcomings of existing methods for detecting free elements in lithium iron phosphate, which result in overestimation of the actual free element content. Therefore, it provides a method for detecting the free element content in lithium iron phosphate to overcome the above-mentioned deficiencies.

[0007] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a method for detecting the content of free elements in lithium iron phosphate, comprising the following steps: (S.1) Mix the lithium iron phosphate sample with the solvent and let it stand; (S.2) At multiple time points during the settling process, the mixed solution is sampled and filtered to obtain the filtrate; (S.3) Test the content of the target free elements in the filtrate at each time point; (S.4) Plot the content-time relationship curve with the standing time as the abscissa and the element content as the ordinate, and obtain the linear equation through linear fitting. The intercept of the linear equation is the content of the target free element in lithium iron phosphate.

[0008] In the field of lithium-ion battery cathode materials, quality control of lithium iron phosphate is crucial, as the content of free elements (such as lithium and phosphorus) directly affects the battery's interface stability and cycle life. However, as shown in the background section, conventional detection methods such as potentiometric titration or inductively coupled plasma optical emission spectrometry (ICP-OES) based on acid digestion have inherent limitations. While they can determine the total elemental content, they cannot distinguish between the contributions of free elements and dissolved elements in the bulk material. This systematic error limits the accuracy of material process optimization and failure analysis, becoming a long-standing technical challenge in this field.

[0009] Based on the aforementioned problems, this invention re-examines the dissolution kinetics of free elements in solvents from the fundamental principles of physicochemical processes. This invention recognizes that free elements begin to dissolve upon contact with the solvent, while the dissolution of bulk elements in the material gradually becomes apparent with prolonged settling time; the two differ on a time scale. This discovery guides the technical solution of this invention towards non-destructive time-series analysis: that is, by mixing the sample with a solvent (such as water), allowing it to stand, and taking samples at multiple time points for testing, the changing trend of element content over time is recorded.

[0010] Specifically, this invention achieves gentle sample processing and multi-timepoint data acquisition through steps (S.1) to (S.3), avoiding the confusion caused by a single test. Furthermore, in step (S.4), mathematical tools are introduced to linearly fit the content-time relationship, using the intercept to characterize the element content at time zero, i.e., the initial dissolution amount of free elements, thereby effectively separating the interference from bulk dissolution. This design not only avoids the matrix effect introduced by acid digestion or the impurity risks from filtration, but also focuses the test target on free components through kinetic analysis, demonstrating a precise grasp of the essence of the problem.

[0011] Furthermore, the application of linear fitting in this invention stems from experimental observations of approximately linear growth in dissolution curves. The intercept has a clear physical meaning and is easily implemented using conventional instruments (such as ICP-OES). Compared to existing techniques that rely on complex pretreatment or internal standard methods to correct for total content, this invention directly analyzes the free contribution through mathematical means, avoiding additional reagents or equipment modifications and significantly improving the method's universality and cost-effectiveness. Simultaneously, the multi-timepoint sampling design ensures the reliability of the fitting, while steps such as settling and filtration employ routine laboratory procedures, lowering the implementation threshold and facilitating standardization and promotion.

[0012] Ultimately, compared to existing technologies, this solution brings synergistic improvements in several technical aspects. First, testing accuracy is significantly improved. Because the contribution of free elements to bulk dissolution is effectively separated, the measurement results are closer to the true values, providing a reliable basis for material quality assessment. Second, the method is simple to operate, has good repeatability, and requires no toxic reagents or specialized equipment, reducing human error and costs. Furthermore, the method has good scalability, applicable not only to the detection of free elements such as lithium and phosphorus in lithium iron phosphate but also to similar cathode materials (such as lithium manganese iron phosphate), providing the industry with a universal and efficient solution. Overall, this invention, by introducing the time dimension into the detection process and cleverly combining it with mathematical modeling, solves the long-standing problem of inaccurate measurement of free element content in a simple way.

[0013] Preferably, the lithium iron phosphate sample in step (S.1) is in powder form.

[0014] Further preferably, the ratio of the lithium iron phosphate sample mass to the solvent volume is 1g:100mL.

[0015] Preferably, the standing time in step (S.1) is at room temperature, and the standing time ranges from 30 minutes to 240 minutes.

[0016] Preferably, the plurality of time points mentioned in step (S.2) includes at least three different time points.

[0017] Preferably, the sampling and filtration in step (S.2) are performed using a syringe or pipette, and the samples are filtered using a filter membrane or filter paper.

[0018] Preferably, the content of the target free element in step (S.3) is tested using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0019] Preferably, the target free element includes at least one of lithium and phosphorus.

[0020] Preferably, the correlation coefficient R of the linear fitting described in step (S.4) is... 2Not less than 0.95.

[0021] Preferably, the method is applicable to the detection of free elements in lithium manganese iron phosphate or similar lithium-ion battery cathode materials.

[0022] Secondly, the present invention also relates to the application of the aforementioned detection method in quality control during the production process of lithium-ion battery cathode materials, wherein the synthesis process parameters are adjusted in real time by detecting the content of free elements in order to optimize the electrochemical performance of the cathode material.

[0023] Therefore, the present invention has the following beneficial effects: (1) Compared with the prior art, the detection accuracy of the present invention is significantly improved. By using time series sampling and linear fitting methods, the contribution of free elements and dissolved elements in the material bulk is effectively separated, which solves the problem of the test results being too high by conventional methods, making the measured value closer to the true content, and providing reliable data support for material quality control. (2) The operation method is simple and has good repeatability. The whole process does not require complicated pretreatment processes, and only involves routine operations such as settling, filtering and ICP-OES testing. It is easy to standardize and implement. Parallel experiments show that the linear fitting correlation coefficient R 2 The values ​​were all no less than 0.95, with minimal deviation, which verified the robustness of the method. (3) It has a wide range of applications. It is not only applicable to the detection of free elements such as lithium and phosphorus in lithium iron phosphate powder, but can also be extended to similar cathode materials such as lithium manganese iron phosphate, and has strong industrial versatility. (4) The detection cost is low, requiring only common laboratory equipment such as quartz beakers and ICP-OES instruments, without the need for special and expensive instruments, which is conducive to large-scale promotion and application; (5) Overall, the method has been optimized in terms of accuracy, operability, universality and economy, providing an efficient solution for the quality control of lithium-ion battery cathode materials. Attached Figure Description

[0024] Figure 1 This is the linear fitting result of parallel sample 1 in Example 1.

[0025] Figure 2 This is the linear fitting result of parallel sample 2 in Example 1. Detailed Implementation

[0026] The present invention will be further described below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0027] Example 1 This embodiment provides a method for detecting the content of free elements in lithium iron phosphate, and the specific steps are as follows: (S.1) Weigh 1.000g of commercially available lithium iron phosphate powder and place it in a 250mL clean quartz beaker. Add 100mL of ultrapure water and stir with a glass rod for 2 minutes to ensure uniform dispersion of the sample. Allow the mixture to stand at room temperature (25℃) for a total of 30 minutes.

[0028] (S.2) At 10, 20 and 30 minutes after the start of standing, take 5 mL of solution with a 10 mL disposable sterile syringe, filter immediately through a 0.22 μm polyethersulfone filter membrane, and collect the filtrate in a 15 mL centrifuge tube.

[0029] (S.3) The content of Li and P elements in the filtrate at each time point was tested using an inductively coupled plasma optical emission spectrometer (ICP-OES) to complete the test of parallel sample 1; (S.4) Repeat the steps (S.1)-(S.3) to complete the sampling, filtering and ICP-oes test under the same conditions, and complete the test of parallel sample 2.

[0030] The test results for parallel sample 1 are shown in Table 1 below: Table 1 Settling time (min) Li content (ug / ml) P content (ug / ml) 30 4.706 18.082 60 6.132 21.539 90 7.052 23.503 120 7.565 24.982 240 9.021 27.522 .

[0031] The data in Table 1 were subjected to linear fitting, and the fitting results are as follows: Figure 1 As shown, the linear fitting results indicate that the linear equation for the Li element is y = 1.0063x + 3.8763, with coefficients R0... 2 =0.977. Therefore, the intercept 3.8763 ug / ml is the free Li content in lithium iron phosphate. The linear equation for P element is y = 2.2323x + 16.429, with coefficient R... 2 =0.980. Therefore, the intercept of 16.429 ug / ml is the free phosphorus content in lithium iron phosphate.

[0032] The test results for parallel sample 2 are shown in Table 2 below: Table 1 Settling time (min) Li content (ug / ml) P content (ug / ml) 30 4.433 18.111 60 6.349 21.434 90 7.148 23.291 120 7.938 24.676 240 9.109 27.402 .

[0033] The data in Table 2 were subjected to linear fitting, and the fitting results are as follows: Figure 2 As shown, the linear fitting results indicate that the linear equation for the Li element is y = 1.0941x + 3.7131, with coefficients R0... 2 =0.968. Therefore, the intercept 3.713 ug / ml is the free Li content in lithium iron phosphate; the linear equation for P element is y = 2.1824x + 16.436, with coefficient R 2 =0.980. Therefore, the intercept of 16.436 ug / ml is the free phosphorus content in lithium iron phosphate.

[0034] The test results of the two sets of parallel samples above show that the contents of Li and P elements both show a significant linear increasing trend with the extension of standing time, and the coefficient R 2 All values ​​were above 0.95, indicating a good linear relationship and verifying the rationality of the testing principle of this invention. Meanwhile, the deviations in the free Li and P element contents (intercept values) of the two parallel samples were extremely small. The free Li contents were 3.8763 ug / ml and 3.713 ug / ml, respectively, and the free P contents were 16.429 ug / ml and 16.436 ug / ml, respectively. This demonstrates that the detection method has good repeatability and reliability, and can accurately determine the content of free elements in lithium iron phosphate.

[0035] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A method for detecting the content of free elements in lithium iron phosphate, characterized in that, Includes the following steps: (S.1) Mix the lithium iron phosphate sample with the solvent and let it stand; (S.2) At multiple time points during the settling process, the mixed solution is sampled and filtered to obtain the filtrate; (S.3) Test the content of the target free elements in the filtrate at each time point; (S.4) Plot the content-time relationship curve with the standing time as the abscissa and the element content as the ordinate, and obtain the linear equation through linear fitting. The intercept of the linear equation is the content of the target free element in lithium iron phosphate.

2. The detection method according to claim 1, characterized in that, The lithium iron phosphate sample mentioned in step (S.1) is in powder form.

3. The detection method according to claim 1 or 2, characterized in that, The solvent mentioned in step (S.1) is water.

4. The detection method according to claim 1 or 2, characterized in that, The standing time mentioned in step (S.1) is at room temperature and the standing time ranges from 30 minutes to 240 minutes.

5. The detection method according to claim 1, characterized in that, The multiple time points mentioned in step (S.2) include at least three different time points.

6. The detection method according to claim 1, characterized in that, The sampling and filtration described in step (S.2) are performed using a syringe or pipette and filtered using a filter membrane or filter paper.

7. The detection method according to claim 1, characterized in that, The content of the target free element in step (S.3) is tested using inductively coupled plasma atomic emission spectrometry (ICP-AES).

8. The detection method according to claim 1 or 7, characterized in that, The target free element includes at least one of lithium and phosphorus.

9. The detection method according to claim 1, characterized in that, The correlation coefficient R of the linear fit described in step (S.4) 2 Not less than 0.

95.

10. The application of the detection method as described in any one of claims 1-9 in quality control during the production process of lithium-ion battery cathode materials.

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