Method for measuring ion content in positive electrode material

Abstract

The application provides a method for determining the ion content in a positive electrode material, which adopts ion chromatography to determine the peak area of each ion in the ion mixed standard solution in the positive electrode material, and establishes a standard curve. The ions include at least one of lithium ions, nickel ions, cobalt ions and manganese ions. The positive electrode material sample is detected by ion chromatography. The ion chromatography is used to detect the ions in the positive electrode material, the detection precision is high, the reproducibility is good, the RSD of the repeated test results of the same sample is less than 0.3%, which is much better than the existing methods such as ICP-OES, and can meet the high-precision quality control requirements in the production process of the positive electrode material. The detection parameters have a wide adjustable range, the parameters such as the proportion of the mobile phase, the column temperature and the flow rate can be adjusted according to the type of the sample to be detected, the detection requirements of various lithium ion battery positive electrode materials are met, and the application range is wide.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery testing technology, specifically to a method for determining the ion content in a cathode material. Background Technology

[0002] The intrinsic electrochemical properties (such as reversible capacity, cycle stability, and thermal safety) of lithium-ion cathode materials (e.g., NCM, LCO) are fundamentally determined by the integrity and order of their crystal structure. Therefore, it is necessary to perform precise and rapid quantitative analysis of the absolute content and proportions of the major elements Li, Ni, Co, and Mn. However, current testing methods are of low precision, cumbersome, and require individual testing of each element. Summary of the Invention

[0003] To address at least one of the above-mentioned technical problems, embodiments of this application provide a method for determining the ion content in a cathode material.

[0004] This application provides a method for determining the ion content in a cathode material, comprising dissolving a cathode material sample of mass m in acid and heating it, then adding water to bring the volume to V1 to obtain a primary dilution. The primary dilution (volume V2) is then diluted with water to bring the volume to V3 to obtain a secondary dilution. Ion chromatography is used to determine the peak area of ​​each ion in the mixed standard solution of the cathode material, establishing a standard curve and calibrating the chromatograph. The ions include at least one of lithium ions, nickel ions, cobalt ions, and manganese ions. The filtrate obtained after filtering the secondary dilution is used as the cathode material test solution and detected using the calibrated chromatograph. The concentration of the analyte element in the cathode material test solution is calculated as c using the standard curve. x The concentration of the analyte in the cathode material sample is calculated using the following formula: .

[0005] The ion chromatography method uses an acid-bonded silica column. The mobile phase includes a first mobile phase and a second mobile phase. The first mobile phase is at least one of nitric acid or methanesulfonic acid, with a concentration of 1 mmol / L to 10 mmol / L and a flow rate of 0.8 mL / min to 1.5 mL / min. The detector is a conductivity detector. The injection volume is 1.5 μL to 25 μL. The column temperature is 20℃ to 40℃.

[0006] This application utilizes ion chromatography to detect ions in cathode materials, achieving high detection accuracy and good reproducibility. The RSD of repeated tests on the same sample is <0.3%, significantly superior to existing methods such as ICP-OES, meeting the high-precision quality control requirements of cathode material production. The detection parameters have a wide adjustable range; parameters such as mobile phase ratio, column temperature, and flow rate can be adjusted according to the type of sample, adapting to the detection needs of various lithium-ion battery cathode materials and making it widely applicable.

[0007] In some embodiments of this application, the acid-bonded filler used in the silica gel column includes at least one of carboxyl and phosphine groups.

[0008] In some embodiments of this application, filtration uses a filter membrane with a diameter of 0.2 μm to 0.25 μm.

[0009] In some embodiments of this application, the cathode material includes one of ternary materials (NCM) and lithium cobalt oxide (LCO).

[0010] In some embodiments of this application, the acid used for dissolution includes at least one of hydrochloric acid, nitric acid, and sulfuric acid.

[0011] In some embodiments of this application, the volume V1 is from 50 mL to 250 mL, and the ratio of m to V1 is from 0.01 g / mL to 0.2 g / mL.

[0012] In some embodiments of this application, the volume ratio of volume V2 to volume V3 is 1:10 to 1:50.

[0013] In some embodiments of this application, the heating temperature is from 150°C to 350°C.

[0014] In some embodiments of this application, the second mobile phase is one or more of tartaric acid, oxalic acid, oxalic acid, citric acid, diaminopropionic acid (DAP), and 2,6-pyridinedicarboxylic acid (PDCA), and the concentration of the second mobile phase is from 1 mmol / L to 10 mmol / L.

[0015] In some embodiments of this application, the ion-mixed standard solution comprises: lithium: 1 μg / mL to 30 μg / mL; nickel: 2 μg / mL to 200 μg / mL; cobalt: 1 μg / mL to 100 μg / mL; and manganese: 1 μg / mL to 100 μg / mL. Attached Figure Description

[0016] Figure 1 This is a standard chromatogram of the ternary material prepared in Example 1 of this application.

[0017] Figure 2This is a standard chromatogram of lithium cobalt oxide prepared in Example 2 of this application. Detailed Implementation

[0018] The technical solutions in the embodiments of this application are described clearly and in detail below. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0019] Precise lithium content is fundamental to ensuring high capacity and initial charge-discharge efficiency of cathode materials. Excess or insufficient lithium will block lithium-ion diffusion channels, leading to capacity decay, increased impedance, and deterioration of cycle performance. Furthermore, in ternary materials (NCM), the ratio of nickel, cobalt, and manganese directly controls the material's energy density, rate performance, structural stability, and production cost. Therefore, accurate and rapid quantitative analysis of the absolute content and ratio of major elements (Li, Ni, Co, and Mn) is crucial throughout the entire process of research, development, production, and quality control of lithium-ion battery cathode materials.

[0020] Currently, the mainstream testing methods for lithium, nickel, cobalt, and manganese in the industry mainly include ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry), atomic absorption spectrometry, XRF (X-ray Fluorescence Spectrometry), and chemical titration. Among them, ICP-OES and atomic absorption spectrometry can analyze four elements simultaneously, but this method is more suitable for the analysis of trace elements. When testing major elements with high content in cathode materials, the detection results fluctuate greatly. Even when ICP-OES uses the internal standard method, the relative standard deviation (RSD) of the test results is around 0.5%-1%, which cannot meet the current high-precision quality control requirements of lithium-ion cathode materials. Although the detection stability of XRF and chemical titration can reach RSD < 0.4%, XRF cannot achieve quantitative detection of lithium, and chemical titration has a cumbersome operation process, requiring individual testing of each element, resulting in long detection cycles, low efficiency, and inability to achieve simultaneous determination of multiple elements.

[0021] In view of this, embodiments of this application provide a method for determining the ion content in a cathode material that can simultaneously perform multi-element detection, is simple, has a short detection cycle, and is highly efficient, including the following steps: S1. Dissolve the positive electrode material sample with mass m in acid, heat it, and add water to make up to volume V1 to obtain a first dilution solution.

[0022] Specifically, a positive electrode material sample with mass m is dissolved in acid and then heated to digest to about 5 mL to completely digest the positive electrode material sample and remove excess acid. The digestion solution is then transferred to a volumetric flask with ultrapure water and diluted to volume V1 to obtain a first dilution solution.

[0023] In some embodiments, the cathode material includes one of ternary materials (NCM) and lithium cobalt oxide (LCO).

[0024] In some embodiments, the acid includes at least one of hydrochloric acid, nitric acid, and sulfuric acid.

[0025] In some embodiments, the volume V1 is from 50 mL to 250 mL, and the ratio of m to V1 is from 0.01 g / mL to 0.2 g / mL.

[0026] In some embodiments, the heating temperature is from 150°C to 350°C.

[0027] S2. Add water to the first dilution solution with a volume of V2 and bring the volume to V3 to obtain the second dilution solution.

[0028] In some embodiments, the volume ratio of volume V2 to volume V3 is 1:10 to 1:50.

[0029] S3. The peak area of ​​each ion in the mixed standard solution of cathode material ions is determined by ion chromatography, a standard curve is established and the chromatograph is calibrated. The ions in the mixed standard solution of cathode material ions include at least one of lithium ions, nickel ions, cobalt ions and manganese ions.

[0030] Specifically, in some embodiments, the ion content of the cathode material ion mixed standard solution includes: lithium: 1 μg / mL to 30 μg / mL; nickel: 2 μg / mL to 200 μg / mL; cobalt: 1 μg / mL to 100 μg / mL; and manganese: 1 μg / mL to 100 μg / mL.

[0031] In some embodiments, the lithium, cobalt, nickel or manganese solution is a stock solution of a certified reference material with a concentration of 1000 μg / mL. A mixed standard solution of cathode material ions is prepared using the stock solutions of the above elements. The prepared standard solutions are injected sequentially in order of increasing concentration for testing. A standard curve is plotted, and linear regression is performed to obtain the regression equation. The standard curve equation is as follows.

[0032] Standard curve equation: y = kx + b in: y represents the peak area of ​​the substance to be measured, in μS·min / cm; x represents the concentration of the standard solution, in μg / mL; k is the slope of the standard curve; b is the x-intercept of the standard curve.

[0033] In some embodiments, the peak area y of ions in the test solution of the positive electrode material is measured by an instrument, and c is calculated by substituting y into the standard curve equation. x =(yb) / k, c x That is, how many micrograms of the target ion are contained in each 1 mL of the positive electrode material test solution.

[0034] S4. The filtrate obtained after filtering the secondary dilution solution is used as the test solution for the positive electrode material and detected using a calibrated chromatograph. The concentration of the analyte element in the test solution for the positive electrode material is calculated as c using the standard curve. x The concentration of the analyte in the cathode material sample is calculated using the following formula: .

[0035] The ion chromatography method uses an acid-bonded silica column. The mobile phase includes a first mobile phase and a second mobile phase. The first mobile phase is at least one of nitric acid or methanesulfonic acid, with a concentration of 1 mmol / L to 10 mmol / L and a flow rate of 0.8 mL / min to 1.5 mL / min. The detector is a conductivity detector. The injection volume is 1.5 μL to 25 μL. The column temperature is 20℃ to 40℃.

[0036] In some embodiments, the chromatographic column is a Metrosep C6-250 / 4.0 silica matrix bonded acid group chromatographic column.

[0037] In some embodiments, filtration uses a filter membrane with a diameter of 0.2 μm to 0.25 μm. Preferably, a filter membrane with a diameter of 0.22 μm is used for filtration.

[0038] In some embodiments, the second mobile phase is one or more selected from tartaric acid, oxalic acid, oxalic acid, citric acid, diaminopropionic acid (DAP), and 2,6-pyridinedicarboxylic acid (PDCA), and the concentration of the second mobile phase is from 1 mmol / L to 10 mmol / L. The addition of the second mobile phase can improve the elution of excess element ions. Preferably, oxalic acid is used as the second mobile phase.

[0039] In some embodiments, the acid-bonded filler used in the silica gel column includes at least one of carboxyl and phosphine groups. Preferably, a filler bonded with carboxyl groups is used.

[0040] This application utilizes ion chromatography to detect ions in cathode materials, achieving high detection accuracy and good reproducibility. The RSD of repeated tests on the same sample is <0.3%, significantly superior to existing methods such as ICP-OES, meeting the high-precision quality control requirements of cathode material production. The detection parameters have a wide adjustable range; parameters such as mobile phase ratio, column temperature, and flow rate can be adjusted according to the type of sample, adapting to the detection needs of various lithium-ion battery cathode materials and making it widely applicable.

[0041] The following specific examples further illustrate the method for determining the ion content in the aforementioned cathode material.

[0042] The lithium ion, nickel ion, cobalt ion, and manganese ion standard stock solutions used in the following embodiments of the present invention are all commercially available certified standard substances with a concentration of 1000 μg / mL; the hydrochloric acid, nitric acid, oxalic acid, and other reagents used are all of analytical grade or higher purity; the resistivity of the ultrapure water used is greater than 18.2 MΩ·cm; the ion chromatograph used is equipped with a conductivity detector and a continuous automatic membrane regeneration suppressor, and the chromatographic column is a Metrosep C6-250 / 4.0 silica matrix column with bonded carboxyl groups.

[0043] Example 1 This embodiment measures the content of lithium, nickel, cobalt, and manganese ions in ternary cathode materials. The specific steps are as follows: S1. Sample Pretreatment: Accurately weigh 0.5 g of the ternary material sample into a beaker using a 0.01 g / mL balance, add 15 mL of hydrochloric acid, place on a hot plate, and heat at 250 °C to digest to near dryness, ensuring complete digestion and removal of excess acid; transfer the digestion solution to a 100 mL volumetric flask with ultrapure water, dilute to volume, and mix well to obtain a primary dilution; accurately transfer 2 mL of the primary dilution solution to a 100 mL volumetric flask using a 2 mL pipette, dilute to volume with ultrapure water, and mix well to obtain a secondary dilution; filter the secondary dilution solution into a sample tube using a 0.22 μm disposable filter membrane to obtain the cathode material test solution, ready for analysis.

[0044] S2. Preparation of a series of mixed standard solutions: Transfer 2 mL of lithium standard stock solution, 20 mL of nickel standard stock solution, 5 mL of cobalt standard stock solution, and 5 mL of manganese standard stock solution to 200 mL volumetric flasks, dilute to volume with ultrapure water, and shake well to obtain standard solution 1; Transfer 50 mL, 20 mL, 10 mL, and 5 mL of standard solution 1 to a series of 100 mL volumetric flasks, dilute to volume with ultrapure water, and shake well to obtain standard solutions 2, 3, 4, and 5. The concentrations of each standard solution are shown in Table 1 below.

[0045] Table 1 Concentration of Standard Solutions for Ternary Materials S3. Establishment of Standard Curve: A series of mixed standard solutions were injected sequentially in ascending order of concentration. Ion chromatography was used for detection. A standard curve was plotted with the mass concentration of each ion in the standard solution as the abscissa and the peak area as the ordinate: y = kx + b. The ion chromatography detection conditions were as follows: mobile phase: 1.8 mmol / L nitric acid and 2.25 mmol / L oxalic acid; column temperature: 30 ℃; flow rate: 0.9 mL / min; injection volume: 10 μL; detector: conductivity detector.

[0046] S4. Sample Testing: Preheat the instrument according to the ion chromatography detection conditions described above. After the instrument baseline noise stabilizes, enter the sample information, sequentially inject the cathode material test solution, and record the chromatogram (e.g., ...). Figure 1 The peak areas of each ion (as shown) are used to calculate the concentration of each ion in the cathode material sample solution by substituting the peak areas into the standard curve in step S3. The content of each ion in the sample is calculated according to the above formula of the present invention.

[0047] Table 2. Concentration results of 20 parallel tests on ternary material samples. Table 3. Retention time results of 20 parallel tests on ternary material samples. The results above show that the RSD of the 20 parallel tests of lithium, nickel, cobalt and manganese in the ternary material in this embodiment is all within 0.3%, the range of retention time of each ion is all within 0.03 min, the ratio of the molar amount of lithium to the total molar amount of transition metal elements (Li / Me) is greater than 1.17, the separation stability is excellent, the retention time interval of each component is greater than 1.5 min, there is no matrix interference, and the detection accuracy and stability meet the quality control requirements of cathode materials.

[0048] Example 2 This embodiment measures the lithium and cobalt ion content in lithium cobalt oxide cathode materials. The specific steps are as follows: S1. Sample Pretreatment: Accurately weigh 0.5 g of lithium cobalt oxide sample into a beaker using a 0.01 g / mL balance, add 15 mL of aqua regia (1:1 volume ratio), place on a heated plate, and heat at 250 °C to digest to near dryness, ensuring complete digestion and removal of excess acid. Transfer the digestion solution to a 100 mL volumetric flask with ultrapure water, dilute to volume, and mix well to obtain a primary dilution. Accurately transfer 2 mL of the primary dilution solution to a 100 mL volumetric flask using a 2 mL pipette, dilute to volume with ultrapure water, and mix well to obtain a secondary dilution. Filter the secondary dilution solution into a sample tube using a 0.22 μm disposable filter membrane to obtain the cathode material test solution, ready for analysis.

[0049] S2. Preparation of a series of mixed standard solutions: Transfer 2 mL of lithium standard stock solution and 20 mL of cobalt standard stock solution to 200 mL volumetric flasks, dilute to volume with ultrapure water, and shake well to obtain standard solution 1; transfer 50 mL, 20 mL, 10 mL, and 5 mL of standard solution 1 to a series of 100 mL volumetric flasks, dilute to volume with ultrapure water, and shake well to obtain standard solutions 2, 3, 4, and 5. The concentrations of each standard solution are shown in Table 4 below.

[0050] Table 4 Concentration of Lithium Cobalt Oxide Series Mixed Standard Solutions S3. Establishment of Standard Curve: A series of mixed standard solutions were injected sequentially in ascending order of concentration. Ion chromatography was used for detection. A standard curve was plotted with the mass concentration of each ion in the standard solution as the x-axis and the peak area as the y-axis. The ion chromatography detection conditions were as follows: mobile phase: 1.8 mmol / L nitric acid + 2.25 mmol / L oxalic acid; column temperature: 30 ℃; flow rate: 0.9 mL / min; injection volume: 10 μL; detector: conductivity detector.

[0051] S4. Sample Testing: Preheat the instrument according to the ion chromatography detection conditions described above. After the instrument baseline noise stabilizes, enter the sample information, sequentially inject the cathode material test solution, and record the chromatogram (see...). Figure 2 The peak area of ​​each ion is calculated and then converted into the standard curve in step S3 to obtain the concentration of each ion to be tested in the positive electrode material sample solution. The content of each ion in the sample is calculated according to the above formula of the present invention.

[0052] The same lithium cobalt oxide sample was subjected to 18 parallel tests according to the above method to verify the stability of the method. The test results are shown in Tables 5 and 6 below.

[0053] Table 5. Concentration results of 18 parallel tests for lithium cobalt oxide samples. Table 6. Retention time results of 18 parallel tests on lithium cobalt oxide samples. As can be seen from the above results, the RSD of the 18 parallel tests of lithium and cobalt in lithium cobalt oxide in this embodiment is all within 0.2%, the range of retention time of each ion is all within 0.04 min, the separation stability is excellent, the retention time interval of each component is >5 min, there is no matrix interference, and the detection accuracy and stability are excellent.

[0054] Example 3 The difference from Example 1 is that the mobile phase composition in step S3 is changed to 0.9 mmol / L nitric acid and 3.25 mmol / L oxalic acid, while other parameters and operating methods are the same as in Example 1.

[0055] Example 4 The difference from Example 1 is that the mobile phase composition in step S3 is changed to 2.766 mmol / L nitric acid and 1.25 mmol / L oxalic acid, while the other parameters and operating methods are the same as in Example 1.

[0056] Example 5 The difference from Example 1 is that the mobile phase composition in step S3 is changed to 3.665 mmol / L nitric acid and 2.25 mmol / L oxalic acid, while other parameters and operating methods are the same as in Example 1.

[0057] Example 6 The difference from Example 1 is that the mobile phase composition in step S3 is changed to 0.916 mmol / L nitric acid and 2.25 mmol / L oxalic acid, while other parameters and operating methods are the same as in Example 1.

[0058] Using the mobile phase components from Examples 1, 3 to 6, the same ternary material sample was tested according to step S4, and the retention time of each ion was recorded. The test results are shown in Table 7 below.

[0059] Table 7 Mobile phase concentration and ion separation status The results above show that, with a constant hydrogen ion concentration, adjusting the oxalic acid concentration does not significantly change the retention time of lithium ions. Nickel, cobalt, and manganese ions form complexes with oxalic acid, thus accelerating elution. As the oxalic acid concentration increases, the retention times of nickel, cobalt, and manganese ions decrease. Conversely, with a constant oxalic acid concentration, increasing the hydrogen ion concentration shortens the retention times of lithium, nickel, cobalt, and manganese ions. Except for Example 3, the retention time differences for lithium, nickel, cobalt, and manganese ions in the other examples are all above 0.9 min, demonstrating excellent separation performance and enabling effective separation and accurate quantification of each ion.

[0060] Example 7 The difference from Example 1 is that the column temperature in step S3 is changed to 20 °C, while the other parameters and operating methods are the same as in Example 1.

[0061] Example 8 The difference from Example 1 is that the column temperature in step S3 is changed to 40 °C, while the other parameters and operating methods are the same as in Example 1.

[0062] Example 9 The difference from Example 1 is that the flow rate in step S3 is changed to 0.8 mL / min, while the other parameters and operating methods are the same as in Example 1.

[0063] Example 10 The difference from Example 1 is that the flow rate in step S3 is changed to 0.8 mL / min, while the other parameters and operating methods are the same as in Example 1.

[0064] Using the column parameters from Examples 1, 7 to 10, the same ternary material sample was tested according to step S4, and the retention time of each ion was recorded. The test results are shown in Table 8 below.

[0065] Table 8. Flow rate, column temperature, and separation of ions. The results above show that increasing the column temperature slightly prolongs the retention times of lithium, cobalt, manganese, and nickel ions, indicating that the adsorption reaction of these four ions on the chromatographic column is endothermic. Increasing the flow rate shortens the retention times of the four ions. In the above examples, the retention time differences of lithium, nickel, cobalt, and manganese ions are all greater than 1.5 min, demonstrating excellent separation performance. This indicates that the detection method of the present invention can achieve effective separation and accurate quantification of each ion within a column temperature range of 20 ℃ to 40 ℃ and a flow rate range of 0.8 mL / min to 1.0 mL / min, exhibiting a wide adjustable parameter range and strong adaptability.

[0066] As can be seen from the above embodiments, the determination method provided by the present invention can realize the simultaneous determination of lithium, nickel, cobalt and manganese ions in cathode materials. The detection result RSD < 0.3%, with high detection accuracy, good reproducibility, excellent separation effect, and simple operation process. It solves the problems of insufficient accuracy, cumbersome operation and inability to simultaneously determine multiple elements in existing detection methods, and can meet the quality control needs of the entire process of lithium-ion battery cathode material research and development and production.

[0067] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for determining the ion content in a cathode material, characterized in that, include: A positive electrode material sample with mass m was dissolved in acid and heated. Water was then added to bring the volume to V1 to obtain a first dilution solution. The first dilution solution with a volume of V2 is diluted with water to a final volume of V3 to obtain the second dilution solution; The peak area of ​​each ion in the mixed standard solution of the cathode material was determined by ion chromatography to establish a standard curve and calibrate the chromatograph. The ions include at least one of lithium ions, nickel ions, cobalt ions and manganese ions. The filtrate obtained after filtering the secondary dilution solution was used as the test solution for the cathode material and detected using the calibrated chromatograph. The concentration of the analyte element in the test solution was calculated as c using the standard curve. x The concentration of the analyte in the cathode material sample is calculated using the following formula: ； The ion chromatography method employs an acid-bonded silica column. The mobile phase includes a first mobile phase and a second mobile phase. The first mobile phase is at least one of nitric acid or methanesulfonic acid, with a concentration of 1 mmol / L to 10 mmol / L and a flow rate of 0.8 mL / min to 1.5 mL / min. The detector is a conductivity detector. The injection volume is 1.5 μL to 25 μL, and the column temperature is 20℃ to 40℃.

2. The method for determining the ion content in the cathode material according to claim 1, characterized in that, The silica gel column uses acid-bonded fillers, including at least one of carboxyl and phosphine groups.

3. The method for determining the ion content in the cathode material according to claim 1, characterized in that, The filtration uses a filter membrane with a diameter of 0.2 μm to 0.25 μm.

4. The method for determining the ion content in the cathode material according to claim 1, characterized in that, The cathode material includes one of ternary materials (NCM) and lithium cobalt oxide (LCO).

5. The method for determining the ion content in the cathode material according to claim 1, characterized in that, The acid used for dissolving the acid includes at least one of hydrochloric acid, nitric acid, and sulfuric acid.

6. The method for determining the ion content in the cathode material according to claim 1, characterized in that, The volume V1 is 50 mL to 250 mL, and the ratio of m to V1 is 1:100 to 1:

500.

7. The method for determining the ion content in the cathode material according to claim 1, characterized in that, The volume ratio of volume V2 to volume V3 is 1:10 to 1:

50.

8. The method for determining the ion content in the cathode material according to claim 1, characterized in that, The heating temperature is between 150°C and 350°C.

9. The method for determining the ion content in the cathode material according to claim 1, characterized in that, The second mobile phase is one or more of tartaric acid, oxalic acid, oxalic acid, citric acid, diaminopropionic acid (DAP), and 2,6-pyridinedicarboxylic acid (PDCA), and the concentration of the second mobile phase is from 1 mmol / L to 10 mmol / L.

10. The method for determining the ion content in the cathode material according to claim 1, characterized in that, The ion-mixed standard solution comprises: Lithium: 1 μg / mL to 30 μg / mL; Nickel: 2 μg / mL to 200 μg / mL; Cobalt: 1 μg / mL to 100 μg / mL; Manganese: 1 μg / mL to 100 μg / mL.

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