Method for detecting metallic foreign matter in electrode active material

Abstract

The present invention relates to a method for detecting metallic foreign matter in an electrode active material, comprising: a first step of mixing an electrode active material with an aqueous nitric acid solution to form a metallic foreign matter extraction solution; a second step of selectively precipitating metallic foreign matter from the metallic foreign matter extraction solution to obtain a precipitate; and a third step of measuring the content of metallic foreign matter in the precipitate.

Description

Technical Field

[0001] The present invention relates to a method for detecting metal foreign substances in an electrode active material, and more particularly to a method for detecting fine metal foreign substances of 40 μm or less that are difficult to remove in advance and quantitatively analyzing their content.

Background Art

[0002] Metal foreign substances contained in the electrode active material among secondary battery materials are deposited from the surface of the negative electrode by repeating charging and discharging to form an internal short circuit, which can cause capacity reduction, low voltage failure, and / or fire. Therefore, for quality control of secondary batteries, it is necessary to measure and evaluate the amount of metal foreign substances in the electrode active material and manage the amount of foreign substances.

[0003] Conventionally, a method has been used in which metal foreign substances in the electrode active material are removed using a magnetic separator, or the content of metal foreign substances in the electrode active material is measured by ICP (inductively coupled plasma) analysis and managed so that their content is within a predetermined range. However, such conventional methods have a problem that it is difficult to detect metal foreign substances with a small particle size or a small content. Specifically, in the case of metal foreign substances with a particle size as small as 40 μm or less, it is difficult to perform prior removal using a magnetic separator, and when the content is as low as less than 1 ppm, the matrix effect due to the electrode active material components acts greatly, and it is also difficult to measure the content by ICP analysis.

[0004] Therefore, in order to manage the amount of metal foreign substances in the electrode active material, there is a need to develop a method for detecting fine metal foreign substances and quantitatively analyzing their content.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention aims to solve the above problems and provides a detection method that can quantitatively detect the amount of extremely small amounts of fine metallic foreign matter contained in an electrode active material. [Means for solving the problem]

[0006] In one embodiment, the present invention provides a method for detecting metal foreign matter in an electrode active material, comprising: a first step of mixing an electrode active material with an aqueous nitric acid solution to form a metal foreign matter extraction solution; a second step of selectively precipitating metal foreign matter in the metal foreign matter extraction solution; and a third step of measuring the content of metal foreign matter in the precipitate.

[0007] Here, the electrode active material may contain metallic foreign matter with a particle size of 40 μm or less, and the metallic foreign matter may be one or more selected from the group consisting of Cu, Zn, Al, Ti, Sn, Pb and their alloys.

[0008] Furthermore, the electrode active material may also be a positive electrode active material, where the positive electrode active material is D 50 The particle size may be 1 to 40 μm.

[0009] On the other hand, the first step is preferably carried out under conditions where the solubility of the metallic foreign matter is 80% or more and the solubility of the metal component of the electrode active material is 50% or less. Specifically, the first step may be carried out by dissolving the electrode active material in an aqueous nitric acid solution having a nitric acid concentration of 20 to 40% by weight, and then stirring at room temperature for 1 to 30 hours.

[0010] On the other hand, the second step may also be carried out by adjusting the pH of the metal foreign matter extraction solution, for example, by adding ammonia water to the metal foreign matter extraction solution to adjust the pH of the metal foreign matter extraction solution to 4.8 to 6.5.

[0011] Next, the third step may be carried out by dissolving the precipitate with acid and then measuring the content of the dissolved metal foreign matter using the inductively coupled plasma (ICP) method.

[0012] Here, the acid may include hydrochloric acid, nitric acid, hydrogen peroxide, or a mixture thereof, and it is preferable that it includes one or more of hydrochloric acid and nitric acid, and hydrogen peroxide. [Effects of the Invention]

[0013] The detection method according to the present invention selectively dissolves metallic foreign matter from the electrode active material using an aqueous nitric acid solution to form a metallic foreign matter extraction solution, selectively precipitates the metallic foreign matter from the metallic foreign matter extraction solution to obtain a precipitate, and then measures the content of the metallic foreign matter contained in the precipitate. This minimizes the matrix effect of the metal component of the electrode active material, and allows for quantitative analysis of the amount of metallic foreign matter contained at a particle size of 40 μm or less and a content of less than 1 ppm. Specifically, according to the detection method of the present invention, the metal component of the electrode active material is removed in two steps and the metallic foreign matter is concentrated, so the matrix effect due to the metal component of the active material is reduced, the detection limit of metallic foreign matter is lowered, and detection at the ppb level becomes possible.

[0014] Furthermore, in the detection method of the present invention, since a step is taken to remove the metal component of the electrode active material, a larger amount of electrode active material can be added to the same volume of nitric acid aqueous solution compared to the production of conventional ICP analytical solutions. After concentrating the metal foreign matter by precipitation, it is redissolved in acid to produce the ICP analytical solution, so the amount of electrode active material sample that can be analyzed per unit volume of the final ICP analytical solution is increased compared to conventional methods. Therefore, using the method of the present invention, metal foreign matter that is unevenly distributed in the electrode active material can be easily detected. [Brief explanation of the drawing]

[0015] [Figure 1] This is a diagram illustrating the detection method of the present invention. [Figure 2] This photograph shows the metal foreign matter extraction solution (a) and the sample solution (b) obtained by dissolving the precipitate in acid in Example 1. [Modes for carrying out the invention]

[0016] The present invention will be described in detail below.

[0017] The inventors of this invention have conducted extensive research to control metallic foreign matter in electrode active materials that affects the performance and safety of batteries. As a result, they have discovered that trace amounts of metallic foreign matter in electrode active materials can be quantitatively detected by mixing the electrode active material with an aqueous nitric acid solution to form a metallic foreign matter extraction solution, selectively precipitating the metallic foreign matter from the extraction solution to obtain a precipitate, and then measuring the content of the metallic foreign matter in the precipitate. This has led to the completion of the present invention.

[0018] Specifically, the method for detecting metallic foreign matter in an electrode active material according to the present invention includes a first step of mixing the electrode active material with an aqueous nitric acid solution to form a metallic foreign matter extraction solution, a second step of selectively precipitating metallic foreign matter from the metallic foreign matter extraction solution to obtain a precipitate, and a third step of measuring the content of metallic foreign matter in the precipitate.

[0019] The method for detecting metallic foreign matter in electrode active materials according to the present invention will be described in detail below.

[0020] (1) First step: Metal foreign matter extraction solution formation step First, the electrode active material and nitric acid aqueous solution are mixed to selectively dissolve the metallic foreign matter and form a metallic foreign matter extraction solution (first step).

[0021] Here, the electrode active material may contain metallic foreign matter with a particle size of 40 μm or less, and the metallic foreign matter may be one or more selected from the group consisting of Cu, Zn, Al, Ti, Sn, Pb and their alloys, and is preferably Cu, Zn or a combination thereof, and more preferably Cu.

[0022] The electrode active material may be a positive electrode active material or a negative electrode active material, and is preferably a positive electrode active material. On the other hand, the positive electrode active material is D 50 The particle size may be 1 to 40 μm, and is preferably 1 to 25 μm.

[0023] The first step is for extracting metal foreign substances contained in the positive electrode active material, and an aqueous nitric acid solution is used as the extraction solvent. Specifically, the first step may be performed by a method in which the aqueous nitric acid solution and the electrode active material are mixed and then stirred for a predetermined time so that the metal foreign substances in the electrode active material are eluted.

[0024] In order to increase the extraction rate of the metal foreign substances, the first step is preferably performed under the condition that the solubility of the metal foreign substances is 80% or more and the solubility of the metal components (for convenience, referred to as "electrode active material metal components") constituting the electrode active material, such as Ni, Co, Mn, Al, etc., is 50% or less. The solubility of the metal foreign substances and the solubility of the electrode active material metal components vary depending on the concentration of the aqueous nitric acid solution, the elution time, and the elution temperature. Therefore, by appropriately adjusting the concentration of the aqueous nitric acid solution and the metal ion elution conditions used according to the type of metal foreign substances to be detected, the solubility of the metal foreign substances and the solubility of the electrode active material metal components can be adjusted.

[0025] For example, when the metal foreign substance to be detected is copper (Cu), it is preferable to use an aqueous nitric acid solution with a nitric acid concentration of 20 to 40% by weight. When the concentration of the aqueous nitric acid solution satisfies the above range, the solubility of copper increases, the solubility of transition metals relatively decreases, and the extraction rate of copper increases.

[0026] Also, when the metal foreign substance to be detected is copper (Cu), the electrode active material is dissolved in the aqueous nitric acid solution, and then stirring is performed for 1 hour to 30 hours, preferably 5 hours to 30 hours, more preferably 5 hours to 25 hours under normal temperature conditions, for example, temperature conditions of 10°C to 30°C, to elute the metal foreign substances. When the elution temperature and the elution time satisfy the above range, the solubility of copper in the aqueous nitric acid solution with respect to the electrode active material metal components increases, and the proportion of copper in the extraction solution increases.

[0027] The type of the metal foreign substances to be detected is different, the concentration of the aqueous nitric acid solution and the elution conditions also differ accordingly.

[0028] After extracting metallic foreign matter from the electrode active material using the method described above, a solution containing metallic foreign matter is obtained by separating the solution using methods such as centrifugation.

[0029] When metal is eluted by utilizing the difference in solubility between the electrode active material metal component and the metal foreign matter, as in the present invention, the amount of electrode active material metal component eluted can be minimized. Specifically, by using the method described above, the amount of electrode active material metal component contained in the extraction solution can be reduced to a level of 1 / 2 to 1 / 3 or less of the amount contained in the electrode active material.

[0030] (2) Second step: Selective sedimentation step Next, the metal foreign matter contained in the metal foreign matter extraction solution obtained in the first step is selectively precipitated to obtain a precipitate (second step).

[0031] The second step is for separating the metal foreign matter from the metal foreign matter extraction solution by precipitation, and may be carried out, for example, by adjusting the pH of the metal foreign matter extraction solution.

[0032] The metal foreign matter extraction solution obtained in the first step contains not only metal foreign matter but also electrode active material metal components such as Ni, Co, and Mn. Therefore, in order to accurately measure the content of metal foreign matter, it is necessary to separate the metal foreign matter to be detected from the electrode active material metal components. To this end, in the present invention, the metal foreign matter to be detected is selectively precipitated by adjusting the pH of the metal foreign matter extraction solution. Here, the pH adjustment of the metal foreign matter extraction solution may be performed, for example, by adding a basic solution such as ammonia water to the metal foreign matter extraction solution. On the other hand, as the ammonia water, an aqueous ammonia solution with an ammonia concentration of 1 to 20 wt%, preferably 1 to 15 wt%, and more preferably 5 to 15 wt%, can be used.

[0033] On the other hand, the pH of the metal foreign matter extraction solution can be adjusted to increase the selective precipitation rate of the metal foreign matter to be detected. For example, if the metal foreign matter to be extracted is copper, it is preferable to adjust the pH of the metal foreign matter extraction solution to 4.8 to 6.5. When the pH of the metal foreign matter extraction solution is within the above range, the selective precipitation rate of copper increases, allowing for effective separation of the electrode active material metal component from copper. By minimizing the content of electrode active material metal in the precipitate, the matrix effect of the electrode active material metal component can be minimized when measuring the metal foreign matter content. If the pH of the metal foreign matter extraction solution exceeds 6.5, the electrode active material metal component precipitates together with copper, and if the pH is less than 4.8, the precipitation rate of copper decreases, making it difficult to reduce the matrix effect of the electrode active material metal component when measuring the metal foreign matter content.

[0034] On the other hand, the pH range of the metal foreign matter extraction solution in this step is not limited to the above range. If the type of metal foreign matter to be detected is different, the pH range of the metal foreign matter extraction solution can be adjusted so that the metal foreign matter precipitates selectively.

[0035] As described above, when the pH of the metal foreign matter extraction solution is adjusted to selectively precipitate the metal foreign matter, the content of the electrode active material metal component in the precipitate can be reduced to a level of 1 / 20 or less of the content contained in the electrode active material. This minimizes the matrix effect of the electrode active material metal component when measuring the metal foreign matter content, and allows for the quantitative measurement of even extremely small amounts of metal foreign matter contained at ppb levels.

[0036] After selectively precipitating the metal foreign matter using the method described above, the precipitate is separated from the metal foreign matter extraction solution by methods such as centrifugation, and then dried to obtain the precipitate.

[0037] (3) Third step: Step to measure the amount of metallic foreign matter Next, the content of metallic foreign matter in the precipitate is measured (third step). Here, the content of metallic foreign matter may be measured, for example, by the inductively coupled plasma (ICP) method.

[0038] Here, the measurement of the metallic foreign matter content using the inductively coupled plasma (ICP) method may be performed by dissolving the precipitate with acid to prepare a sample solution, and then measuring the metallic foreign matter content in the sample solution using an inductively coupled plasma emission spectrometer (ICP-OES), an inductively coupled plasma atomic emission spectrometer (ICP-AES), or an inductively coupled plasma mass spectrometer (ICP-MS).

[0039] Here, the acid may include hydrochloric acid, nitric acid, hydrogen peroxide, or a mixture thereof, and it is preferable that it includes one or more of hydrochloric acid and nitric acid, and hydrogen peroxide.

[0040] As described above, the second step results in a very low level of metal components in the electrode active material contained in the precipitate, less than 1 / 20th of the amount contained in the electrode active material. This creates an environment where the matrix effect from the metal components of the electrode active material is minimized. Therefore, even the content of metal impurities present in extremely small amounts at the ppb level can be analyzed by the ICP method.

[0041] Figure 1 discloses a diagram illustrating a method for detecting metallic foreign matter in electrode active materials according to the present invention. As shown in Figure 1, according to the method of the present invention, by going through each step, the proportion of the electrode active material metal component in the sample to be measured decreases and the proportion of metallic foreign matter such as Cu increases, thereby minimizing the matrix effect of the electrode active material metal component and enabling quantitative detection of trace amounts of metallic foreign matter.

[0042] The present invention will be described in more detail below with reference to specific examples.

[0043] Example 1 A metal foreign matter extraction solution was prepared by adding 0.23 mg of copper particles to 10.8 g of positive electrode active material (NCM811), then adding 50 mL of a 20 wt% aqueous nitric acid solution, stirring at 300 rpm at room temperature for 24 hours, and then centrifuging at 8000 rpm for 10 minutes.

[0044] Ten g of the aforementioned metal foreign matter extraction solution was taken, and the Cu content in the metal foreign matter extraction solution was then measured using an ICP-OES instrument. Figure 2(a) is a photograph of the collected metal foreign matter extraction solution.

[0045] Next, 10 g of metal foreign matter extraction solution was mixed with 13 wt% aqueous ammonia until the pH reached 6.5, and the mixture was stirred for 20 minutes to precipitate copper. The precipitate and solution were then separated by centrifugation. The obtained precipitate was dried, and the dried precipitate was then dissolved in a mixed solvent of 2 mL of hydrochloric acid and 0.5 mL of hydrogen peroxide to prepare a sample solution. The Cu content in the sample solution was measured using an ICP-OES instrument. Figure 2(b) is a photograph of the sample solution prepared by dissolving the precipitate in acid.

[0046] The recovery rate of Cu was measured by calculating the percentage of Cu content in the precipitate relative to the Cu content in the measured metal foreign matter extraction solution. The measurement results are shown in [Table 1] below.

[0047] Example 2 The recovery rate of Cu was measured in the same manner as in Example 1, except that 13 wt% aqueous ammonia was added to the metal foreign matter extraction solution during copper precipitation until the pH reached 5.6. The measurement results are shown in Table 1 below.

[0048] Example 3 The recovery rate of Cu was measured in the same manner as in Example 1, except that 13 wt% aqueous ammonia was added to the metal foreign matter extraction solution during copper precipitation until the pH reached 4.8. The measurement results are shown in Table 1 below.

[0049] [Table 1]

[0050] From Table 1 above, it can be confirmed that when ammonia water is added to the non-magnetic material extraction solution to adjust the pH to 4.8-6.5, more than 90% of the copper in the non-magnetic material extraction solution precipitates.

[0051] Example 4 A metal foreign matter extraction solution was prepared by adding 0.23 mg of copper particles to 10.8 g of positive electrode active material (NCM811), then adding 50 mL of a 20 wt% aqueous nitric acid solution, stirring at 300 rpm at room temperature for 24 hours, and then centrifuging at 8000 rpm for 10 minutes.

[0052] Next, 10 g of the metal foreign matter extraction solution was mixed with 13 wt% aqueous ammonia until the pH reached 5.6, then stirred for 1 hour and maintained for 23 hours to precipitate copper. The precipitate and solution were then separated by centrifugation. The obtained precipitate was dried, and the dried precipitate was then dissolved in a mixed solvent of 2 mL of hydrochloric acid and 0.5 mL of hydrogen peroxide to prepare a sample solution. The Cu content in the sample solution was measured using an ICP-OES instrument, and the Cu content per 1 kg of positive electrode active material (in mg / kg) was then calculated using the measured Cu content. The measurement results are shown in Table 2 below.

[0053] Example 5 A metal foreign matter extraction solution was prepared by adding 100 mL of a 20 wt% aqueous nitric acid solution to 20 g of positive electrode active material (NCM811), stirring at 300 rpm at room temperature for 24 hours, and then centrifuging at 8000 rpm for 10 minutes.

[0054] Next, 43 g of the metal foreign matter extraction solution was mixed with 13 wt% aqueous ammonia until the pH reached 5, then stirred for 1 hour and maintained for 23 hours to precipitate copper. The precipitate and solution were then separated by centrifugation. The obtained precipitate was dried, and the dried precipitate was then dissolved in a mixed solvent of 2 mL of hydrochloric acid and 0.5 mL of hydrogen peroxide to prepare a sample solution. The Cu content in the sample solution was measured using an ICP-OES instrument, and the Cu content per 1 kg of positive electrode active material (in mg / kg) was then calculated using the measured Cu content. The measurement results are shown in Table 2 below.

[0055] Example 6 A metal foreign matter extraction solution was prepared by adding 100 mL of a 20 wt% aqueous nitric acid solution to 20 g of positive electrode active material (NCM811), stirring at 300 rpm at room temperature for 24 hours, and then centrifuging at 8000 rpm for 10 minutes.

[0056] Next, 0.5 μg of Cu (equivalent to 0.06 mg per 1 kg of positive electrode active material) was added to 43 g of metal foreign matter extraction solution. Then, 13 wt% aqueous ammonia was added until the pH reached 5, and the mixture was stirred for 1 hour. The mixture was maintained for 23 hours to precipitate the copper, and the precipitate was then separated from the solution by centrifugation. The obtained precipitate was dried, and the dried precipitate was then dissolved in a mixed solvent of 2 mL of hydrochloric acid and 0.5 mL of hydrogen peroxide to prepare a sample solution. The Cu content in the sample solution was measured using an ICP-OES instrument, and the Cu content per 1 kg of positive electrode active material (in mg / kg) was calculated using the measured Cu content. The measurement results are shown in Table 2 below.

[0057] [Table 2]

[0058] In Example 4, a sample was prepared by mixing 0.23 mg of Cu with 10.8 g of positive electrode active material. Therefore, the Cu concentration per kg of positive electrode active material was approximately 21 mg / kg. The value measured by the method of the present invention was 20.1 mg / kg, confirming that the measured value is almost the same as the actual amount of Cu mixed. Furthermore, comparing Example 5 and Example 6, it can be confirmed that the difference between the measured value in Example 5 and the measured value in Example 6 corresponds to the amount of Cu added in Example 6. This demonstrates that the content of metallic foreign matter can be measured relatively accurately using the method of the present invention.

[0059] Furthermore, the measurement values ​​shown in Table 2 confirm that the method of the present invention can quantitatively detect metallic foreign matter present in extremely small amounts at the ppb level.

Claims

1. The first step involves mixing the electrode active material with an aqueous nitric acid solution to form a metal foreign matter extraction solution, A second step involves selectively precipitating the metal foreign matter from the aforementioned metal foreign matter extraction solution to obtain a precipitate, A method for detecting metallic foreign matter in an electrode active material, comprising a third step of measuring the content of metallic foreign matter in the precipitate.

2. The method for detecting metallic foreign matter in an electrode active material according to claim 1, wherein the electrode active material contains metallic foreign matter with a particle size of 40 μm or less.

3. The method for detecting metallic foreign matter in an electrode active material according to claim 2, wherein the metallic foreign matter is one or more selected from the group consisting of Cu, Zn, Al, Ti, Sn, Pb and their alloys.

4. The method for detecting a metallic foreign substance in an electrode active material according to claim 1, wherein the first step is performed under the condition that the solubility of the metallic foreign substance is 80% or more and the solubility of the metallic component of the electrode active material is 50% or less.

5. The method for detecting metallic foreign matter in an electrode active material according to claim 1, wherein the concentration of nitric acid in the aqueous nitric acid solution is 20 to 40% by weight.

6. The first step is to dissolve the electrode active material in an aqueous nitric acid solution having a nitric acid concentration of 20 to 40% by weight, and then stir at room temperature for 1 to 30 hours, the method for detecting metallic foreign matter in an electrode active material according to claim 1.

7. The method for detecting metallic foreign matter in an electrode active material according to claim 1, wherein the second step is performed by adjusting the pH of the metallic foreign matter extraction solution.

8. The method for detecting metallic foreign matter in an electrode active material according to claim 7, wherein ammonia water is added to the metallic foreign matter extraction solution to adjust the pH of the metallic foreign matter extraction solution to 4.8 to 6.

5.

9. The method for detecting metallic foreign matter in an electrode active material according to claim 1, wherein the second step further comprises separating the precipitate from the metallic foreign matter extraction solution by centrifugation and then drying it.

10. The third step is performed by dissolving the precipitate with acid and then measuring the content of the dissolved metallic foreign matter by inductively coupled plasma (ICP) method, as described in claim 1.

11. The method for detecting metallic foreign matter in an electrode active material according to claim 10, wherein the acid includes hydrochloric acid, nitric acid, hydrogen peroxide, or a mixture thereof.

12. The method for detecting metallic foreign matter in an electrode active material according to claim 10, wherein the acid comprises one or more of hydrochloric acid and nitric acid and hydrogen peroxide.

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