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 dissolving an electrode active material in a nitric acid aqueous solution to form a metallic foreign matter extraction solution, a second step of plating the metallic foreign matter in the metallic foreign matter extraction solution onto an electrode, and a third step of measuring the content of the metallic foreign matter plated onto the electrode.

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 through charging and discharging to form an internal short circuit, which can cause a decrease in capacity, 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 mass of the foreign substances.

[0003] Therefore, 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 analysis and managed so that these contents are within a predetermined range. However, such a conventional method has a problem that it is difficult to detect metal foreign substances with a small particle size. Specifically, in the case of metal foreign substances with a particle size as small as 40 μm or less, it is difficult to remove them in advance 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, there is a need to develop a method that can detect fine non-magnetic metal foreign substances and quantitatively analyze their content in order to manage the amount of metal foreign substances in the electrode active material.

Summary of the Invention

Problems to be Solved by the Invention

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

[0006] In one aspect, the present invention provides a method for detecting metal foreign matter in an electrode active material, comprising: a first step of dissolving an electrode active material in an aqueous nitric acid solution to form a metal foreign matter extraction solution; a second step of plating the metal foreign matter in the metal foreign matter extraction solution onto an electrode; and a third step of measuring the content of the metal foreign matter plated on the electrode.

[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 Cu.

[0008] Furthermore, the electrode active material can be a positive electrode active material, where the positive electrode active material is D 50 The particle size can be between 1 and 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 can be carried out by dissolving the electrode active material in an aqueous nitric acid solution with a nitric acid concentration of 20 to 40% by weight, and then stirring at room temperature for 20 hours or more.

[0010] On the other hand, the second step can be carried out by immersing the electrode in the metal foreign matter extraction solution and then applying a current such that the transition metal in the electrode active material is not reduced, and the metal foreign matter to be extracted is reduced, where the electrode can be a carbon electrode.

[0011] Next, the third step can be carried out by dissolving the metal foreign matter plated on the electrode with acid, and then measuring the content of the dissolved metal foreign matter by the inductively coupled plasma (ICP) method, or by the anodic stripping voltammetry method.

[0012] When using the ICP method, the acid may include hydrochloric acid, nitric acid, hydrogen peroxide, or a mixture thereof, and preferably may include 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 recovers metallic foreign matter from the electrode active material using an aqueous nitric acid solution, and then extracts the metallic foreign matter from the electrode active material by an electrochemical method so that the metallic foreign matter is selectively plated onto the electrode. By measuring the amount of metallic foreign matter plated onto the electrode, the matrix effect of the metallic components of the electrode active material is minimized, and the amount of metallic foreign matter contained in the electrode active material with a particle size of 40 μm or less and a content of less than 1 ppm can be quantitatively analyzed. [Modes for carrying out the invention]

[0014] The present invention will be described in detail below.

[0015] The inventors of this invention have diligently conducted research on managing metallic foreign matter in electrode active materials, which affects the performance and safety of batteries. As a result, they have discovered that by selectively recovering metallic foreign matter from the electrode active material using an aqueous nitric acid solution, plating the electrode with the metallic foreign matter, and then measuring the amount of metallic foreign matter plated onto the electrode, the matrix effect of the metallic components of the electrode active material can be minimized, and the amount of metallic foreign matter contained at a particle size of 40 μm or less and a content of less than 1 ppm can be quantitatively detected, thus completing the present invention.

[0016] Specifically, the method for detecting metallic foreign matter in an electrode active material according to the present invention includes a first step of dissolving the electrode active material in an aqueous nitric acid solution to form a metallic foreign matter extraction solution, a second step of plating the metallic foreign matter in the metallic foreign matter extraction solution onto an electrode, and a third step of measuring the content of the metallic foreign matter plated onto the electrode.

[0017] The method for detecting metallic foreign matter in electrode active materials according to the present invention will be described in detail below.

[0018] (1) First step: Metal foreign matter dissolution step First, the electrode active material is dissolved in an aqueous nitric acid solution to dissolve metallic foreign matter and form a metallic foreign matter extraction solution (Step 1).

[0019] 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, Ti, Sn, Pb, and alloys thereof, and preferably Cu.

[0020] The electrode active material can be a positive electrode active material or a negative electrode active material, and preferably a positive electrode active material. On the other hand, the positive electrode active material is D 50 However, the particle size can be 1 to 40 μm, preferably 1 to 25 μm.

[0021] The first step is for selectively extracting metallic foreign matter contained in the positive electrode active material, and an aqueous nitric acid solution is used as the extraction solvent. Specifically, the first step can be carried out by adding the electrode active material to the aqueous nitric acid solution and stirring for a predetermined time so that the metal in the electrode active material is dissolved.

[0022] In order to increase the extraction rate of metal foreign substances, the first step is preferably carried out under the condition that the solubility of the metal foreign substances is 80% or more and the solubility of the metal components constituting the electrode active material (for convenience, referred to as "electrode active material metal components"), 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 nitric acid aqueous solution, the elution time, and the elution temperature. Therefore, by appropriately adjusting the concentration of the nitric acid aqueous solution used and the elution conditions of the metal ions 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.

[0023] For example, when the metal foreign substance to be detected is copper (Cu), it is preferable to use a nitric acid aqueous solution with a nitric acid concentration of 20 to 40% by weight. This is because when the concentration of the nitric acid aqueous solution satisfies the above range, the solubility of copper increases, the solubility of transition metals becomes relatively low, and the copper extraction rate increases.

[0024] Also, when the metal foreign substance to be detected is copper (Cu), after dissolving the electrode active material in the nitric acid aqueous solution, it is preferable to perform stirring for 1 hour or more, preferably 1 hour to 30 hours, under normal temperature conditions, for example, at a temperature of 10°C to 30°C, to elute the metal foreign substances. When the elution temperature and time satisfy the above range, the solubility of copper in the nitric acid aqueous solution with respect to the electrode active material metal components increases, and the ratio of copper in the extraction solution can increase.

[0025] However, when the type of metal foreign substance to be detected changes, the concentration of the nitric acid aqueous solution and the elution conditions may also change accordingly.

[0026] After extracting the metal foreign substances in the electrode active material by the method as described above, the solution containing the metal foreign substances is separated by a method such as centrifugation to obtain a metal foreign substance extraction solution.

[0027] As in the present invention, when metal is eluted using the difference between the solubility of the metal component of the electrode active material and the solubility of metallic foreign matter, the amount of eluted electrode active material metal component 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.

[0028] (2) Second step: Plating step Next, the metal foreign matter contained in the metal foreign matter extraction solution obtained in the first step is plated onto the electrode (second step).

[0029] The second step is for selectively extracting metallic foreign matter from a metallic foreign matter extraction solution, and can be performed, for example, by immersing an electrode in the metallic foreign matter extraction solution and applying an electric current to the electrode. Here, the electric current can be applied such that it has a potential difference in which the metallic component of the electrode active material is not reduced, but the metallic foreign matter to be extracted is reduced, and the electrode can be a carbon electrode. Here, the potential difference changes depending on the type of metallic foreign matter, and can be appropriately adjusted according to the type of metallic foreign matter to be detected.

[0030] 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 amount of metal foreign matter, it is necessary to separate the metal foreign matter to be detected from the electrode active material metal components.

[0031] Therefore, in this invention, a current is applied to the extraction solution within a voltage range in which the metal foreign matter to be detected is reduced, so that the metal foreign matter is reduced and deposited on the electrode (positive electrode) and forms a plating layer, thereby separating the metal foreign matter from the extraction solution. In this way, when separating metal foreign matter by electroplating, only the metal foreign matter is selectively reduced and deposited on the plating layer, creating an environment that is not affected by the matrix effect of the metal components of the electrode active material, and the content of even extremely small amounts of metal foreign matter contained at the ppb level can be quantitatively measured.

[0032] (3) Third step: Step to measure the amount of metallic foreign matter Next, the content of the metallic foreign matter plated on the electrode is measured (third step). Here, the content of the metallic foreign matter can be measured by an electrochemical analysis method such as inductively coupled plasma (ICP) or anodic stripping voltammetry.

[0033] Here, the measurement of the metallic foreign matter content using the inductively coupled plasma (ICP) method can be performed by first dissolving the metallic foreign matter plated on the electrode with acid to prepare a sample solution, and then measuring the metallic foreign matter content in the sample solution using an inductively coupled plasma atomic emission spectrometer (ICP-OES), an inductively coupled plasma atomic emission spectrometer (ICP-AES), or an inductively coupled plasma mass spectrometer (ICP-MS).

[0034] Here, the acid may include hydrochloric acid, nitric acid, hydrogen peroxide, or a mixture thereof, and preferably may include one or more of hydrochloric acid and nitric acid, and hydrogen peroxide.

[0035] As described above, in the plating layer obtained in the second step, only metallic impurities are selectively reduced and deposited, creating an environment that is not affected by the matrix effect of the electrode active material's metal components. Therefore, even the content of metallic impurities present at extremely small amounts (ppb levels) can be analyzed by the ICP method.

[0036] On the other hand, the measurement of the metallic foreign matter content using the anode stripping voltammetry method can be performed by applying a potential difference of opposite polarity to the potential difference applied in the second step to an electrode plated with the metallic foreign matter, thereby ionizing the metallic foreign matter in the plating layer, and measuring the amount of current generated in this process to determine the metallic foreign matter content.

[0037] As described above, when measuring the content of metallic foreign matter by electrochemical methods, the content can be easily measured without the need for any additional processing steps for content measurement.

[0038] The present invention will be described in more detail below with reference to specific examples.

[0039] Example 1 10 g of positive electrode active material (NCM811) was mixed with 50 mL of a 20 wt% aqueous nitric acid solution. The mixture was stirred at room temperature at 300 rpm for 24 hours, and then centrifuged at 8000 rpm for 10 minutes to produce metal foreign matter extraction solution A.

[0040] Eight ml of the aforementioned metal foreign matter extraction solution A was placed in an electrochemical cell to form a three-electrode system consisting of a glass carbon electrode as the working electrode, a silver chloride electrode (Ag / AgCl) as the reference electrode, and a platinum wire (Pt wire) as the counter electrode.

[0041] Subsequently, -0.2V was applied to the glass carbon electrode for a total of 120 seconds to plate the metal in metal foreign matter extraction solution A. During this time, the solution was stirred using a stirrer at a speed of 300 rpm for 60 seconds while plating was performed, and for the remaining 60 seconds, the stirrer was stopped to allow the solution to reach equilibrium.

[0042] Example 2 Except for mixing approximately 10 g of positive electrode active material (NCM811) with 0.11 mg of copper particles, metal foreign matter extraction solution B was prepared using the same process as in Example 1, and then plating was performed.

[0043] Example 3 Except for mixing approximately 10 g of positive electrode active material (NCM811) with 0.13 mg of copper particles, metal foreign matter extraction solution C was prepared using the same process as in Example 1, and then plating was performed.

[0044] Experimental Example 1 After taking 10g of each of the metal foreign matter extraction solutions A to C prepared in Examples 1 to 3, the Cu content was measured using ICP-OES equipment. The measurement results are shown in Table 1.

[0045] Experimental Example 2 After plating was completed in Examples 1-3, the stripping charge was measured while oxidizing the metal by applying a voltage of 0.3V (Anodic Stripping Voltammetry; ASV). The measurement results are shown in Table 1 below.

[0046] [Table 1]

[0047] Referring to Table 1, in the case of the metal foreign matter extraction solution of Example 1, in which no further metal foreign matter (Cu) was added, a very small amount of metal foreign matter was present in the positive electrode active material, making it impossible to measure the amount of metal foreign matter by the ICP-OES method. However, as in the method of the present invention, it can be confirmed that quantification is possible when measured by the ASV method after plating. On the other hand, in the cases of Examples 2 and 3, when the metal foreign matter (Cu) content was increased by further addition of metal foreign matter, it became possible to measure the amount of metal foreign matter by the ICP-OES method. As shown in Table 1, it can be confirmed that as the amount of metal foreign matter measured by the ICP-OES method increases, the Charge value measured by the ASV method also increases. This indicates that the Charge value measured by the ASV method can represent the amount of metal foreign matter. Therefore, it can be seen that the method of the present invention makes it possible to quantify even a very small amount of metal foreign matter that cannot be measured by the ICP method.

Claims

1. The first step involves dissolving the electrode active material in an aqueous nitric acid solution to form a metal foreign matter extraction solution, The second step involves plating the metal foreign matter in the metal foreign matter extraction solution onto an electrode, A method for detecting metallic foreign matter in an electrode active material, comprising a third step of measuring the amount of metallic foreign matter plated on the electrode.

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 having a particle size of 40 μm or less.

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

4. The first step is performed under the condition that the solubility of the metallic foreign matter is 80% or more and the solubility of the metallic component of the electrode active material is 50% or less, as described in claim 1, for detecting metallic foreign matter in an electrode active material.

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

6. The first step is performed 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 20 hours or more, as described in claim 1, for the method of detecting metallic foreign matter in an electrode active material.

7. The method for detecting a metal foreign substance in an electrode active material according to claim 1, wherein the second step is performed by immersing the electrode in the metal foreign substance extraction solution and then applying a current such that the metal component of the electrode active material is not reduced and the metal foreign substance to be extracted is reduced, resulting in a potential difference.

8. The method for detecting metallic foreign matter in an electrode active material according to claim 7, wherein the electrode is a carbon electrode.

9. The third step is performed by dissolving the metal foreign matter plated on the electrode with acid, and then measuring the content of the dissolved metal foreign matter by inductively coupled plasma, as described in claim 1.

10. The method for detecting metallic foreign matter in an electrode active material according to claim 9, wherein the acid comprises hydrochloric acid, nitric acid, hydrogen peroxide, or a mixture thereof.

11. The method for detecting metallic foreign matter in an electrode active material according to claim 9, wherein the acid comprises one or more of hydrochloric acid and nitric acid and hydrogen peroxide.

12. The third step is performed by anode stripping voltammetry, the method for detecting metallic foreign matter in an electrode active material according to claim 1.

Images