Method for Detecting Element Concentration Distribution in Cathode Material

Abstract

This application relates to the technical field of chemical element analysis. Specifically, it relates to a method for detecting the elemental concentration distribution in a cathode material. A series of test solutions are prepared by mixing the cathode material containing a reference element and an element to be measured with an inorganic acid. ICP-OES is used to detect the standard working solutions of the reference element and the element to be measured at the analysis lines of the reference element and the element to be measured respectively, and the standard working curves of the reference element and the element to be measured are obtained. The spectral intensities of the reference element and the element to be measured in the test solution are measured by ICP-OES. According to the standard working curves of the reference element and the element to be measured, the concentrations of the reference element and the element to be measured in the test solution are determined, and the concentration distribution curves of the reference element and the element to be measured are obtained. The concentration distribution of the element to be measured in the cathode material is judged according to the correlation between the concentration distribution curve of the reference element and the concentration distribution curve of the element to be measured. The above method has simple operation process, reduces the detection cost and improves the detection accuracy.

Description

Technical Field

[0001] The present application relates to the technical field of chemical element analysis, and more specifically, to a method for detecting the elemental concentration distribution in a cathode material. Background Art

[0002] Lithium-ion batteries have high energy density, charge and discharge efficiency, and discharge platform, and are widely used in mobile devices, power vehicles and other fields. However, lithium-ion batteries still have some potential safety hazards, and it is of great significance to improve their cycle stability and high-temperature stability.

[0003] Coating metal and non-metal compounds (such as magnesium compounds, titanium compounds, boron compounds) on the surface of the cathode material of lithium-ion batteries can effectively inhibit the side reaction between the surface of the cathode material and the electrolyte. Moreover, after doping the above metal and non-metal elements into the cathode material, the atoms can play a supporting role in the crystal lattice, reducing the Li+ / Ni 2+ mixing disorder, effectively increasing the crystal structure stability of the cathode material, and also improving the conductivity of the cathode material. However, when the amount of doped or coated elements is excessive, the conductivity and discharge platform of the cathode material will be reduced. Therefore, it is of great significance to clarify the distribution of added elements in the cathode material to understand the electrochemical performance of the cathode material and guide the improvement direction of its electrochemical performance.

[0004] Currently, the method for analyzing the elemental distribution in particles (such as cathode materials) is usually to perform line scanning on the particle profile with an atom probe. This method requires using a focused ion beam microscope (FEI) or an argon ion cross-section polishing instrument to cut the particle, and then detecting the elemental distribution by X-ray energy spectrum analysis (EDS) line scanning. However, this method has very low detection accuracy for trace elements, a long sample preparation process, and high detection costs. Summary of the Invention

[0005] Based on this, it is necessary to provide a method for detecting the elemental concentration distribution in a cathode material that can simplify the operation process, reduce the detection cost, and improve the detection accuracy.

[0006] The present application provides a method for detecting the elemental concentration distribution in a cathode material, which includes the following steps:

[0007] Mix the cathode material and inorganic acid to prepare a series of test solutions, which are L1, L2, L3,..., L n-1 、L n , a total of n, where n is an integer greater than or equal to 3. The cathode material includes a reference element and a test element; in the n test solutions, the mass percentage content of the cathode material changes in a gradient.

[0008] Using an inductively coupled plasma atomic emission spectrometer, detect the standard working solutions of the reference element and the element to be measured at the analysis lines of the reference element and the element to be measured respectively, and obtain the standard working curves of the reference element and the element to be measured; and

[0009] Introduce a series of the test solutions into an inductively coupled plasma atomic emission spectrometer respectively, measure the spectral intensities of the reference element and the element to be measured in the test solutions, determine the concentrations of the reference element and the element to be measured in the test solutions according to the standard working curves of the reference element and the element to be measured, obtain the concentration distribution curves of the reference element and the element to be measured, and judge the concentration distribution of the element to be measured in the cathode material according to the correlation between the concentration distribution curve of the element to be measured and the concentration distribution curve of the reference element.

[0010] In one embodiment, in the n test solutions, the mass percentage content of the cathode material increases in a gradient manner until the cathode material is completely dissolved.

[0011] In one embodiment, in the test solution with the highest mass percentage content of the cathode material, the cathode material is completely dissolved.

[0012] In one embodiment, the reference element is uniformly distributed in the cathode material.

[0013] In one embodiment, mix n portions of the cathode material with n portions of the inorganic acid respectively to prepare n test solutions;

[0014] Optionally, the volume concentrations of the n portions of the inorganic acid are independently 10% to 100% respectively;

[0015] Optionally, the temperatures for mixing the n portions of the cathode material with the n portions of the inorganic acid are independently 15°C to 90°C respectively, and the mixing times are independently 0.25 h to 6 h respectively.

[0016] In one embodiment, the inorganic acid includes one or more of aqua regia, perchloric acid, hydrochloric acid and nitric acid.

[0017] In one embodiment, the mass of each portion of the cathode material is 0.05 g to 0.5 g.

[0018] In one embodiment, the cathode material is a lithium battery cathode material containing the element to be measured; the reference element is cobalt or nickel; the element to be measured includes one or more of magnesium, titanium, zirconium, aluminum and boron.

[0019] In one embodiment, the analytical line wavelength of the cobalt element is 238.892 nm, the analytical line wavelength of the nickel element is 216.556 nm, and the analytical line wavelengths of the magnesium element, the titanium element, the zirconium element, the aluminum element, and the boron element are 285.213 nm, 336.121 nm, 339.198 nm, 396.152 nm, and 208.959 nm, respectively.

[0020] In one embodiment, after mixing the cathode material and the inorganic acid, a filtering step is further included;

[0021] Optionally, the method adopted for filtering is membrane filtration, wherein the pore size of the membrane is 0.05 μm to 0.5 μm.

[0022] In one embodiment, the operating parameters of the inductively coupled plasma atomic emission spectrometer satisfy at least one of the following conditions:

[0023] (1) The cooling gas, the auxiliary gas, and the carrier gas are all argon with a volume fraction of 99.99%;

[0024] (2) The RF power is 1145 W to 1155 W;

[0025] (3) The atomization pressure is 1.8 MPa to 2.2 MPa, and the atomizer flow rate is 0.5 L / min to 0.8 L / min;

[0026] (4) The sample flushing time is 30 s to 45 s, and the exposure times are 3 to 5 times;

[0027] (5) The auxiliary gas flow rate is 0.5 L / min to 0.9 L / min, the flushing pump speed is 70 rpm to 80 rpm, the analysis pump speed is 45 rpm to 55 rpm, and the pump stabilization time is 4 s to 6 s.

[0028] The method for detecting the element concentration distribution in the cathode material provided by this application determines the concentration distribution of the element to be detected in the cathode material, such as the doping state or coating state of the element to be detected, by comparing the correlation between the concentration distribution curve of the element to be detected and the concentration distribution curve of the reference element (such as cobalt and nickel) based on the characteristic of the uniform distribution of the reference elements (cobalt, nickel, etc.) in the cathode material. Moreover, this method is simple to operate, low in cost, high in precision, and can also perform quantitative analysis. Description of the Drawings

[0029] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0030] Figure 1 Radial distribution diagrams of Mg and Co elements in the positive electrode material particles of Example 1;

[0031] Figure 2 Radial distribution diagrams of Mg and Co elements in the positive electrode material particles of Example 2;

[0032] Figure 3 Radial distribution diagrams of Mg and Co elements in the positive electrode material particles of Example 3;

[0033] Figure 4 Radial distribution diagrams of Mg and Co elements in the positive electrode material particles of Example 4;

[0034] Figure 5 Radial distribution diagrams of Mg and Co elements in the positive electrode material particles of Example 5. Specific Embodiments

[0035] Reference will now be provided in detail to embodiments of the present invention, one or more examples of which are described below. Each example is provided by way of explanation and not limitation of the present invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the scope or spirit of the present invention. For example, features described or illustrated as part of one embodiment can be used in another embodiment to yield a further embodiment.

[0036] Accordingly, it is intended that the present invention cover such modifications and variations that fall within the scope of the appended claims and their equivalents. Other objects, features, and aspects of the present invention are disclosed in or are apparent from the following detailed description. Those of ordinary skill in the art should understand that this discussion is only a description of exemplary embodiments and is not intended to limit the broader aspects of the present invention.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terms used in the description of the present invention herein are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0038] "Analysis line" refers to a term in atomic spectroscopy, which is the spectral line selected for qualitative and quantitative analysis in atomic emission spectroscopy. This spectral line has high sensitivity and strong selectivity.

[0039] This application provides a method for detecting the elemental concentration distribution in a cathode material, which includes the following steps:

[0040] Mix the cathode material with inorganic acid to prepare a series of test solutions, namely L1, L2, L3, ……, L n-1 、L n , a total of n, where n is an integer greater than or equal to 3. The cathode material includes a reference element and a test element; in the n test solutions, the mass percentage content of the cathode material changes in a gradient.

[0041] Use an inductively coupled plasma atomic emission spectrometer to detect the standard working solutions of the reference element and the test element at the analysis lines of the reference element and the test element respectively, to obtain the standard working curves of the reference element and the test element; and

[0042] Introduce a series of the test solutions into the inductively coupled plasma atomic emission spectrometer respectively, measure the spectral line intensities of the reference element and the test element in the test solutions, determine the concentrations of the reference element and the test element in the test solutions according to the standard working curves of the reference element and the test element, obtain the concentration distribution curves of the reference element and the test element, and judge the concentration distribution of the test element in the cathode material according to the correlation between the concentration distribution curve of the test element and the concentration distribution curve of the reference element.

[0043] For the method for detecting the concentration distribution of the test element in the cathode material provided above, based on the known characteristic that the reference element is uniformly distributed in the cathode material, the concentration distribution of the test element in the cathode material is judged by comparing the correlation between the concentration distribution curve of the test element and the concentration distribution curve of the reference element. For example, it can be judged whether the test element is doped in the cathode material or coated on the cathode material according to the strength of the correlation between the concentration distribution curve of the test element and the concentration distribution curve of the reference element, and it can also judge whether the doping is uniform and the coating depth. Moreover, this method is simple to operate, low in cost, high in precision, and can also perform quantitative analysis.

[0044] In some embodiments, the reference elements are uniformly distributed in the cathode material. Then, the volume of the cathode material dissolved in the inorganic acid is positively correlated with the content of the reference elements in the test solution. It can be understood that when the cathode material contacts the inorganic acid, it dissolves layer by layer from the outside to the inside. Accordingly, by detecting the content of the reference elements in the test solution, the concentration distribution curve of the reference elements in the radial direction of the cathode material particles can be obtained. By mapping the concentration of the test solution in the test solution to the concentration distribution curve of the reference elements in the radial direction of the cathode material particles, the concentration distribution of the test elements in the cathode material can be obtained.

[0045] In some embodiments, n can be a natural number greater than or equal to 10, preferably 12.

[0046] In some embodiments, among the n test solutions, the mass percentage content of the cathode material can change in a gradient increasing manner, and in the test solution with the highest mass percentage content of the cathode material, the cathode material is completely dissolved.

[0047] In some embodiments, n portions of the cathode material can be respectively mixed with n portions of inorganic acid to prepare the n test solutions. Specifically, after n portions of the cathode material are respectively mixed with n portions of inorganic acid to obtain n mixtures, when the cathode material is dissolved to different degrees, samples are respectively taken from one of the n mixtures. Through n samplings, n test solutions with different mass contents of the cathode material are obtained. For example, when the cathode material is dissolved by one-tenth, a sample is taken from the first mixture to obtain test solution L1. When the cathode material is dissolved by two-tenths, a sample is taken from the second mixture to obtain test solution L2, and so on, to obtain n test solutions.

[0048] In some embodiments, the n portions of the cathode material are completely the same, and the dissolution depth of the cathode material can be adjusted by the concentration of the inorganic acid, the mixing temperature, and the dissolution time. Specifically, the volume concentrations of the n portions of inorganic acid are respectively independently any value between 10% and 100%. For example, they can also be 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%. The temperatures at which the n portions of the cathode material and the n portions of inorganic acid are mixed can be respectively independently any value between 15°C and 90°C, preferably any value between 25°C and 80°C. The mixing time can be respectively independently any value between 0.25 h and 6 h, preferably any value between 0.5 h and 4 h. The masses of the n portions of the cathode material are the same, specifically any value between 0.05 g and 0.5 g. For example, they can also be 0.08 g, 0.1 g, 0.12 g, 0.15 g, 0.18 g, 0.2 g, 0.25 g, 0.28 g, 0.3 g, 0.4 g. Preferably, the mass of the cathode material is 0.1 g.

[0049] In some embodiments, a mixture of n parts of cathode material and n parts of inorganic acid can be divided into multiple groups. Each group is mixed with different concentrations of inorganic acid or at different temperatures, and then samples are taken from one mixture in each group at different mixing times. Since the dissolution rate of the cathode material is different due to different inorganic acid concentrations and mixing temperatures, multiple test solutions with different mass percentages of cathode material can be obtained at one mixing time point, greatly shortening the detection time and improving the efficiency.

[0050] Specifically, the steps of mixing the cathode material and inorganic acid to prepare a series of test solutions can be as follows:

[0051] Weigh 12 parts of the same mass of cathode material and divide it evenly into the first group and the second group, that is, 6 parts in each group; divide the first group evenly into the third group and the fourth group, that is, 3 parts in each group, and divide the second group evenly into the fifth group and the sixth group, that is, 3 parts in each group;

[0052] Mix the cathode material in the third group with the inorganic acid of the second concentration and stir at the first temperature, mix the cathode material in the fourth group with the inorganic acid of the second concentration and stir at the second temperature, mix the cathode material in the fifth group with the inorganic acid of the first concentration and stir at the first temperature, and mix the cathode material in the sixth group with the inorganic acid of the first concentration and stir at the second temperature. After time t1, take one solution from each of the third, fourth, fifth, and sixth groups and make the volume up to 50 mL respectively; after time t2, take one solution from each of the third, fourth, fifth, and sixth groups and make the volume up to 50 mL respectively; after time t3, take one solution from each of the third, fourth, fifth, and sixth groups and make the volume up to 50 mL respectively.

[0053] Preferably, the first concentration is 15% - 40%, the second concentration is 40% - 80%, and the second concentration is greater than the first concentration; the first temperature is 15°C - 50°C, the second temperature is 50°C - 90°C, and the second temperature is greater than the first temperature; 0.5 h ≤ t1 < t2 < t3 ≤ 6 h, and the stirring times of the three solutions in each of the third, fourth, fifth, and sixth groups are different.

[0054] In some embodiments, after sampling from the mixture of cathode material and inorganic acid, a filtering step is further included; wherein, the filtering method is not limited as long as it can remove the insoluble substances in the test solution. For example, the filtering method used can be membrane filtration, and the pore size of the membrane can be 0.05 μm - 0.5 μm. Preferably, the pore size of the membrane is 0.45 μm.

[0055] In some embodiments, after filtering, a dilution step is further included. Dilution can make the concentration of the test solution within the detection range of ICP - OES.

[0056] In some embodiments, the inorganic acid includes one or more of aqua regia, perchloric acid, hydrochloric acid, and nitric acid, preferably aqua regia, because aqua regia has strong oxidizing and acidic properties and can deeply dissolve the cathode material.

[0057] In some embodiments, the cathode material is a lithium battery cathode material containing the element to be measured.

[0058] Preferably, the lithium cobaltate cathode material containing the element to be measured can be a doped composite material formed by the element to be measured and the lithium battery cathode material or the element to be measured coated on the lithium battery cathode material.

[0059] In some embodiments, the reference element is cobalt or nickel, preferably cobalt; the elements to be measured include one or more of magnesium, titanium, zirconium, aluminum, and boron, preferably magnesium, because magnesium can be completely dissolved without side reactions.

[0060] In some embodiments, the standard working curves of the reference element and the element to be measured are obtained by detecting the standard working solutions of the reference element and the element to be measured. In some embodiments, the preparation methods of the standard working solutions of the reference element and the element to be measured are specifically as follows:

[0061] Provide the standard stock solutions of the reference element and the element to be measured; and

[0062] Dilute the standard stock solution of the reference element to form a series of standard working solutions with gradient changes in the concentration of the reference element, and dilute the standard stock solution of the element to be measured to form a series of standard working solutions with gradient changes in the concentration of the element to be measured.

[0063] Preferably, the methods for preparing the standard stock solutions of the reference element and the element to be measured can be specifically as follows:

[0064] Respectively pipette 1 mL of the national standard solution of the element to be measured with a concentration of 1000 μg / mL and 50 mL of the national standard solution of the reference element with a concentration of 1000 μg / mL into a 100 mL volumetric flask, and prepare a mixed standard solution with a concentration of 10 mg / L of the element to be measured and 500 mg / L of the reference element as the standard stock solution. Then pipette 0 mL, 1 mL, 2 mL, 5 mL, and 10 mL of the standard stock solution into volumetric flasks. Then add 1.75 mL of the national standard Li solution with a concentration of 1000 μg / mL to each volumetric flask, and make up to the scale line with ultrapure water to prepare standard working solutions with concentrations of 0 mg / L, 0.1 mg / L, 0.2 mg / L, 0.5 mg / L, and 1 mg / L of the element to be measured and 0 mg / L, 5 mg / L, 10 mg / L, 25 mg / L, and 50 mg / L of the reference element, respectively.

[0065] In some embodiments, the operating parameters of the inductively coupled plasma atomic emission spectrometer are not limited, and the commonly used operating conditions in the art can be selected. In this application, the ICP-OES operating conditions can be specifically as follows: The cooling gas, auxiliary gas, and carrier gas are all argon with a volume fraction of 99.99%; the RF power is 1145 W to 1155 W; the atomization pressure is 1.8 Mpa to 2.2 Mpa, and the atomizer flow rate is 0.5 L / min to 0.8 L / min; the sample flushing time is 30 s to 45 s, and the exposure times are 3 to 5 times; the auxiliary gas flow rate is 0.5 L / min to 0.9 L / min, the flushing pump speed is 70 rpm to 80 rpm, the analysis pump speed is 45 rpm to 55 rpm, and the pump stabilization time is 5 s.

[0066] Further, the long-wave integration time can be 5 s, and the short-wave integration time can be 15 s.

[0067] Furthermore, the analysis line wavelengths of cobalt element are 238.892 nm, nickel element are 216.556 nm, magnesium element are 285.213 nm, titanium element are 336.121 nm, zirconium element are 339.198 nm, aluminum element are 396.152 nm, and boron element are 208.959 nm.

[0068] The following further elaborates on this application with specific embodiments.

[0069] Example 1

[0070] (1) Acid solution preparation: Take 50 mL of aqua regia and 50 mL of ultrapure water and mix them evenly to obtain a first aqua regia solution with a volume concentration of 50%; take 50 mL of aqua regia and 150 mL of ultrapure water and mix them evenly to obtain a second aqua regia solution with a volume concentration of 25%.

[0071] (2) Sample treatment: Weigh 12 portions of 0.1 g of cathode materials doped with 1100 ppm of Mg element and place them in 12 25-mL beakers, named sample 1 to sample 12 respectively. Pour sample 1 to sample 6 into 10 mL of the first aqua regia solution respectively, and pour sample 7 to sample 12 into 10 mL of the second aqua regia solution respectively. Then place sample 1 to sample 3 and sample 7 to sample 9 on a multi-point intelligent magnetic stirrer and stir at room temperature (25 °C); place sample 4 to sample 6 and sample 10 to sample 12 on a multi-point intelligent magnetic stirrer at 80 °C and stir at a constant temperature.

[0072] After stirring for 1 h, take down sample 1, sample 4, sample 7, and sample 10, make the volume up to 50 mL, and filter through a filter membrane with a pore size of 0.45 μm to obtain cathode material stock solutions 1, stock solution 4, stock solution 7, and stock solution 10.

[0073] After stirring for 2 h, samples 2, 5, 8, and 11 were taken, fixed volume to 50 mL, and filtered through a filter membrane with a pore size of 0.45 μm to obtain the original solutions 2, 5, 8, and 11 of the cathode material;

[0074] After stirring for 4 h, samples 3, 6, 9, and 12 were taken, fixed volume to 50 mL, and filtered through a filter membrane with a pore size of 0.45 μm to obtain the original solutions 3, 6, 9, and 12 of the cathode material;

[0075] (3) Dilution of the original solution: 10 mL of the original solutions 1 to 12 were respectively taken and fixed volume to 50 mL as the dilution solutions 1 to 12; 7 mL of the dilution solutions 1 to 12 were respectively taken and fixed volume to 100 mL as the test solutions 1 to 12, which were the test solutions for Mg element and Co element;

[0076] (4) Preparation of the standard working solution: 1 mL of the national standard single-element solution of Mg with a concentration of 1000 μg / mL and 50 mL of the national standard single-element solution of Co with a concentration of 1000 μg / mL were respectively transferred into a 100-mL volumetric flask, and a mixed standard solution with a Mg element concentration of 10 mg / L and a Co element concentration of 500 mg / L was prepared as the standard stock solution. Then, 0 mL, 1 mL, 2 mL, 5 mL, and 10 mL of the standard stock solution were accurately transferred into volumetric flasks, and 1.75 mL of the national standard Li solution with a concentration of 1000 μg / mL was added to each volumetric flask, and the volume was fixed to the calibration line with ultrapure water to prepare standard working solutions with Mg element concentrations of 0 mg / L, 0.1 mg / L, 0.2 mg / L, 0.5 mg / L, and 1 mg / L, and Co element concentrations of 0 mg / L, 5 mg / L, 10 mg / L, 25 mg / L, and 50 mg / L;

[0077] (5) The standard working solutions containing Mg element and Co element prepared in step (4) are respectively introduced into an inductively coupled plasma atomic emission spectrometer (ICP-OES), ensuring that the correlation coefficients of the standard working solutions of Mg element and Co element reach above 0.999. First, measure the standard working solutions, and then draw the standard working curves of Mg element and Co element respectively according to the known contents of Mg element and Co element in the standard working solutions and the response values of Mg element and Co element measured by ICP-OES. Then, measure the response values of the solutions of Sample 1 to Sample 12, and calculate the concentration values of Mg element and Co element in the standard solution and the concentration values of Mg element and Co element in the solutions of Sample 1 to Sample 12 according to the standard working curves. Among them, the working parameters of ICP-OES are as follows: the RF power value is 1150W; the atomization pressure is 1.8 Mpa - 2.2 Mpa, and the atomizer flow rate is 0.5 L / min; the sample flushing time is 30s, and the exposure is repeated 3 times; the auxiliary gas flow rate is 0.5 L / min; the long-wave integration time is 5s, the short-wave integration time is 15s, the flushing pump speed is 75 rpm, the analysis pump speed is 50 rpm, and the pump stabilization time is 5s; the analysis line of Mg element is 285.213nm, and the analysis line of Co element is 238.892nm;

[0078] (6) Place the test solutions 1 - 12 obtained in step (3) into ICP-OES for testing, measure the spectral intensities of Mg element and Co element contained in the dissolved samples at their respective analysis lines, repeat the measurement 3 times for each sample, and calculate the concentrations of Mg element and Co element in Sample 1 to Sample 12 as shown in Table 1:

[0079] Table 1

[0080]

[0081]

[0082] (7) Calculate the recovery rates of Mg element and Co element in Sample 1 to Sample 12 according to the following formula (1), and the calculation results are shown in Table 2:

[0083] Y i =S i / S max ×100% Formula (1)

[0084] Where i is Sample 1 to Sample 12, S i is the average concentration of Mg element or Co element in Sample i, S max is the concentration of Mg element or Co element after complete dissolution of Sample i, and Y i is the recovery rate corresponding to S i .

[0085] Table 2

[0086] Sample number Mg recovery rate (%) Co recovery rate (%) 1 22.15 16.63 2 32.40 29.54 3 35.03 32.98 4 30.65 30.38 5 35.29 34.29 6 40.89 38.43 7 56.22 52.89 8 85.99 83.20 9 83.36 83.04 10 79.25 79.86 11 100.00 97.02 12 98.77 100.00

[0087] (8) Calculate the distance X from a certain point inside the cathode material particles to the particle center according to the following formula (2) i

[0088] X i = (1 - Y Coi ) 1 / 3 × 100% Formula (2)

[0089] where i is Samples 1 to 12, and X i is the distance X corresponding to the yield of Sample i i . According to the yield data in Table 2 and the formula in step (8), obtain the concentration distribution curves of Mg element and Co element as Figure 1 shown. It is known that Co element is uniformly distributed in the cathode material particles. From Figure 1 it can be seen that the contents of Mg element and Co element show a basically consistent changing trend, and the Pearson correlation coefficient is 0.998. Thus, it can be obtained that Mg element is uniformly doped inside the cathode material particles.

[0090] Example 2

[0091] The detection method in this example is basically the same as that in Example 1, except that: in the sample treatment of step (2), 0.1 g of the cathode material doped with 1100 ppm of Mg element is replaced with 0.1 g of the cathode material coated with 1300 ppm of Mg element. Calculate the concentrations of Mg element and Co element in Samples 1 to 12 as shown in Table 3

[0092] Table 3

[0093]

[0094] Calculate the yields of Mg element and Co element in Samples 1 to 12 according to formula (1), and the calculation results are shown in Table 4

[0095] Table 4

[0096] Sample number Mg recovery rate (%) Co recovery rate (%) 1 99.85 16.95 2 99.92 30.07 3 100 33.20 4 99.85 31.20 5 99.85 34.60 6 99.92 38.87 7 99.85 52.81 8 99.85 80.57 9 99.92 83.73 10 99.85 84.21 11 99.85 99.20 12 100.00 100.00

[0097] Calculate the distance X from a certain point inside the cathode material particles to the particle center according to formula (2) i . According to the yield data in Table 4 and formula (2), obtain the concentration distribution curves of Mg element and Co element as Figure 2 shown. It is known that Co element is uniformly distributed in the cathode material particles. From Figure 2It can be seen that Mg elements are mainly concentrated on the surface more than 94% away from the center of the cathode material particles and exist in a coated state.

[0098] Example 3

[0099] The detection method of this example is basically the same as that of Example 1, except that: in the sample treatment of step (2), 0.1 g of the cathode material doped with 1100 ppm of Mg elements is replaced with 0.1 g of the cathode material doped with 1400 ppm of Mg elements and coated with 1400 ppm of Mg elements at the same time. The concentrations of Mg elements and Co elements in Samples 1 - 12 are calculated as shown in Table 5:

[0100] Table 5

[0101]

[0102] According to formula (1), the recovery rates of Mg elements and Co elements in Samples 1 - 12 are calculated, and the calculation results are shown in Table 6:

[0103] Table 6

[0104]

[0105]

[0106] The distance X from a certain point inside the cathode material particle to the particle center is calculated according to formula (2) i . According to the recovery rate data in Table 6 and formula (2), the concentration distribution curves of Mg elements and Co elements as shown in Figure 3 are obtained. It is known that Co elements are evenly distributed in the cathode material particles. From Figure 3 it can be seen that in the range of about 0% - 94% from the center of the cathode material particles, Mg elements are evenly doped; in the range of about 94% - 100% from the center of the cathode material particles, Mg elements mainly exist in a coated state.

[0107] Example 4

[0108] The detection method of this example is basically the same as that of Example 1, except that: in the sample treatment of step (2), 0.1 g of the cathode material doped with 1100 ppm of Mg elements is replaced with 0.05 g of the cathode material doped with 1100 ppm of Mg elements. The concentrations of Mg elements and Co elements in Samples 1 - 12 are calculated as shown in Table 7:

[0109] Table 7

[0110]

[0111] According to formula (1), the recovery rates of Mg elements and Co elements in Samples 1 - 12 are calculated, and the calculation results are shown in Table 8:

[0112] Table 8

[0113]

[0114]

[0115] Calculate the distance X from a certain point inside the cathode material particles to the particle center according to formula (2). i Based on the yield data in Table 8 and formula (2), we obtain the Mg element and Co element concentration distribution curves as shown in Figure 4 Figure [not provided]. It can be seen that due to the reduction of the sample mass, the error in the sample preparation process is amplified; at the same time, due to the too low concentration of the test solution, the detection accuracy of the ICP instrument is also affected.

[0116] Example 5

[0117] The detection method in this example is basically the same as that in Example 1, except that: replace the first aqua regia solution with a volume concentration of 50% and the second aqua regia solution with a volume concentration of 25% in step (1) as follows: take 50 mL of aqua regia and mix it evenly with 200 mL of ultrapure water to obtain the first aqua regia solution with a volume concentration of 20%; take 50 mL of aqua regia and mix it evenly with 450 mL of ultrapure water to obtain the second aqua regia solution with a volume concentration of 10%.

[0118] Calculate the concentrations of Mg element and Co element in Samples 1 - 12 as shown in Table 9:

[0119] Table 9

[0120]

[0121] Calculate the yields of Mg element and Co element in Samples 1 - 12 according to formula (1), and the calculation results are shown in Table 10:

[0122] Table 10

[0123] Sample number Mg recovery rate (%) Co recovery rate (%) 1 3.15 3.25 2 2.24 3.16 3 5.63 5.32 4 4.51 5.26 5 9.69 9.58 6 10.32 10.26 7 21.41 20.12 8 23.84 23.96 9 26.01 25.33 10 30.58 30.22 11 34.99 35.81 12 41.33 40.32

[0124] Calculate the distance X from a certain point inside the cathode material particles to the particle center according to formula (2). i Based on the yield data in Table 10 and formula (2), we obtain the Mg element and Co element concentration distribution curves as shown in Figure 5 Figure [not provided]. It can be seen that due to the use of acids with lower concentrations, the samples cannot be completely dissolved, so only data near the particle surface can be obtained.

[0125] In summary, the detection method provided by the present invention can accurately and quantitatively detect the concentration distribution of the elements to be measured in the cathode material, and thus can judge the distribution and existence form (doping or coating, etc.) of the elements to be measured in the cathode material.

[0126] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as falling within the scope described in this specification.

[0127] The above-described embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed. However, it should not be construed as a limitation on 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 these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A method for detecting the elemental concentration distribution in a cathode material, characterized in that, It includes the following steps: A series of test solutions are prepared by mixing a cathode material with an inorganic acid. The test solutions are L1, L2, L3, ……, L n-1 , L n , a total of n, where n is an integer greater than or equal to 3. The cathode material includes a reference element and a test element; in the n test solutions, the mass percentage content of the cathode material changes in a gradient manner; the inorganic acid includes one or more of aqua regia, perchloric acid, hydrochloric acid, and nitric acid; wherein, the reference element is uniformly distributed in the cathode material; the cathode material is a lithium battery cathode material containing a test element; the reference element is cobalt or nickel; the test element includes one or more of magnesium, titanium, zirconium, aluminum, and boron; Using an inductively coupled plasma atomic emission spectrometer to detect the standard working solutions of the reference element and the element to be measured at the analysis lines of the reference element and the element to be measured respectively, so as to obtain the standard working curves of the reference element and the element to be measured; and Introducing a series of the test solutions into the inductively coupled plasma atomic emission spectrometer respectively, measuring the spectral intensities of the reference element and the element to be measured in the test solutions, determining the concentrations of the reference element and the element to be measured in the test solutions according to the standard working curves of the reference element and the element to be measured, obtaining the concentration distribution curves of the reference element and the element to be measured, and judging the concentration distribution of the element to be measured in the cathode material by comparing the correlation between the concentration distribution curve of the element to be measured and the concentration distribution curve of the reference element; wherein, the concentration distribution of the element to be measured in the cathode material is the doping state or the coating state of the element to be measured.

2. The method for detecting the elemental concentration distribution in the positive electrode material according to claim 1, wherein In the test solution with the highest mass percentage of the cathode material, the cathode material is completely dissolved.

3. The method for detecting the elemental concentration distribution in the positive electrode material according to claim 1, characterized in that, Mixing n portions of the cathode material with n portions of the inorganic acid respectively to prepare n test solutions.

4. The method for detecting the elemental concentration distribution in the positive electrode material according to claim 3, wherein The volume concentrations of the n portions of the inorganic acid are independently 10% - 100% respectively.

5. The method for detecting the elemental concentration distribution in the positive electrode material according to claim 3, wherein The temperatures for mixing the n portions of the cathode material with the n portions of the inorganic acid are independently 15°C - 90°C respectively, and the mixing times are independently 0.25 h - 6 h respectively.

6. The method for detecting the elemental concentration distribution in the cathode material according to claim 3, characterized in that, The mass of each portion of the cathode material is 0.05 g - 0.5 g.

7. The method for detecting the elemental concentration distribution in the cathode material according to claim 1, wherein The analysis line wavelength of the cobalt element is 238.892 nm, the analysis line wavelength of the nickel element is 216.556 nm, and the analysis line wavelengths of the magnesium element, the titanium element, the zirconium element, the aluminum element and the boron element are 285.213 nm, 336.121 nm, 339.198 nm, 396.152 nm and 208.959 nm respectively.

8. The method for detecting the elemental concentration distribution in the cathode material according to any one of claims 1 to 7, characterized in that, After mixing the cathode material and the inorganic acid, it further includes a filtering step; wherein, the filtering method used is membrane filtration, and the pore size of the filter membrane is 0.05 μm - 0.5 μm.

9. The method for detecting the elemental concentration distribution in the cathode material according to any one of claims 1 to 7, characterized in that, The working parameters of the inductively coupled plasma atomic emission spectrometer satisfy at least one of the following conditions: (1) The cooling gas, the auxiliary gas and the carrier gas are all argon with a volume fraction of 99.99%; (2) The RF power is 1145 W - 1155 W; (3) The atomization pressure is 1.8 MPa - 2.2 MPa, and the atomizer flow rate is 0.5 L / min - 0.8 L / min; (4) The sample flushing time is 30 s - 45 s, and the exposure times are 3 - 5 times; (5) The auxiliary gas flow rate is 0.5 L / min - 0.9 L / min, the flushing pump speed is 70 rpm - 80 rpm, the analysis pump speed is 45 rpm - 55 rpm, and the pump stabilization time is 4 s - 6 s.

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