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 metallic foreign matter in an electrode active material, and more particularly to a method for detecting fine metallic foreign matter of 40 μm or less that is difficult to remove in advance, and quantitatively analyzing the content thereof. [Background technology]

[0002] Metallic particles contained in the electrode active material of secondary battery materials are precipitated from the surface of the negative electrode during charging and discharging, forming an internal short circuit, which can lead to reduced capacity, low voltage failure, and / or fire. Therefore, for quality control of secondary batteries, it is necessary to measure and evaluate the amount of metallic particles in the electrode active material and manage the mass of the particles.

[0003] Therefore, conventional methods have been used to remove metallic contaminants from electrode active materials using a magnetic separator, or to measure the content of metallic contaminants in electrode active materials using ICP analysis and maintain the content within a specified range. However, these conventional methods have the problem of difficulty in detecting metallic contaminants with small particle sizes. Specifically, it is difficult to remove metallic contaminants with particle sizes of 40 μm or less using a magnetic separator in advance, and when the content is low, at less than 1 ppm, the matrix effect of the electrode active material components is significant, making it difficult to measure the content using ICP analysis.

[0004] Therefore, there is a need to develop a method for detecting minute non-magnetic metallic particles and quantitatively analyzing their content in order to control the amount of metallic particles in the electrode active material. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention is intended to solve the above-mentioned problems, and aims 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 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.

[0007] Here, the electrode active material may contain metallic foreign matter having a particle size of 40 μm or less, and the metallic foreign matter may be Cu.

[0008] The electrode active material may be a positive electrode active material, and the positive electrode active material may be a 50 can be 1 to 40 μm.

[0009] Meanwhile, the first step is preferably carried out under conditions where the solubility of the metal 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 a nitric acid aqueous solution having a nitric acid concentration of 20 to 40% by weight, and then stirring the solution at room temperature for 20 hours or more.

[0010] Meanwhile, the second step may be performed by immersing an electrode in the foreign metal extracting solution and then applying a current to create a potential difference such that the transition metal in the electrode active material is not reduced but the foreign metal to be extracted is reduced, and the electrode may be a carbon electrode.

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

[0012] When the ICP method is used, 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 impurities from an electrode active material using a nitric acid solution and then electrochemically plates the metallic impurities onto an electrode. By extracting the metallic impurities from the electrode active material and then measuring the amount of the metallic impurities plated onto the electrode, the matrix effect of the metal components of the electrode active material can be minimized, and the amount of metallic impurities with a particle size of 40 μm or less and a content of less than 1 ppm can be quantitatively analyzed. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be specifically described below.

[0015] The present inventors have conducted extensive research into the management of foreign metal particles in electrode active materials that affect the performance and safety of batteries. As a result, they have discovered that by selectively recovering foreign metal particles in electrode active materials using an aqueous nitric acid solution, plating the foreign metal particles onto an electrode, and then measuring the amount of foreign metal particles plated onto the electrode, it is possible to minimize the matrix effect of the metal components of the electrode active material and quantitatively detect the amount of foreign metal particles with a particle size of 40 μm or less and contained at a content of less than 1 ppm, thereby 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 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.

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

[0018] (1) First step: Metallic foreign matter elution step First, the electrode active material is dissolved in a nitric acid aqueous solution to elute the foreign metals, thereby forming a foreign metal extract solution (first step).

[0019] Here, the electrode active material may contain metallic foreign matter having 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 may preferably be Cu.

[0020] The electrode active material may be a positive electrode active material or a negative electrode active material, and preferably may be a positive electrode active material. 50 The thickness can be 1 to 40 μm, preferably 1 to 25 μm.

[0021] The first step is for selectively extracting metal foreign matters contained in the positive electrode active material, and uses a nitric acid aqueous solution as an extraction solvent. Specifically, the first step may be performed by adding the electrode active material to the nitric acid aqueous solution and stirring for a predetermined time to allow the metals in the electrode active material to elute.

[0022] To increase the extraction rate of metallic foreign matter, 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 components constituting the electrode active material, such as Ni, Co, Mn, and Al (for convenience, referred to as "metal components of the electrode active material") is 50% or less. The solubility of the metallic foreign matter and the solubility of the metal components of the electrode active material vary depending on the concentration of the nitric acid aqueous solution, the elution time, and the elution temperature. Therefore, the solubility of the metallic foreign matter and the solubility of the metal components of the electrode active material can be adjusted by appropriately adjusting the concentration of the nitric acid aqueous solution used and the elution conditions for metal ions depending on the type of metallic foreign matter to be detected.

[0023] For example, if the metal foreign matter 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 wt %. When the concentration of the aqueous nitric acid solution satisfies this range, the solubility of copper increases, while the solubility of transition metals decreases relatively, resulting in an increased copper extraction rate.

[0024] Furthermore, when the foreign metal substance to be detected is copper (Cu), it is preferable to dissolve the electrode active material in an aqueous nitric acid solution and then elute the foreign metal substance by stirring for at least 1 hour, preferably 1 hour to 30 hours, at room temperature, for example, at a temperature of 10° C. to 30° C. When the elution temperature and time satisfy the above ranges, the solubility of copper in the aqueous nitric acid solution increases relative to the metal component of the electrode active material, and the proportion of copper in the extraction solution can be increased.

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

[0026] After extracting the foreign metals from the electrode active material using the above method, the solution containing the foreign metals is separated by a method such as centrifugation to obtain a foreign metal extract solution.

[0027] When metals are extracted using the difference in solubility between the metal component of the electrode active material and the metal foreign matter, as in the present invention, the content of the extracted metal component of the electrode active material can be minimized. Specifically, by using the above method, the content of the metal component of the electrode active material contained in the extraction solution can be reduced to a level of 1 / 2 to 1 / 3 or less of the content contained in the electrode active material.

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

[0029] The second step is for selectively extracting metallic particles from the metallic particle extraction solution, and can be performed, for example, by immersing an electrode in the metallic particle extraction solution and applying a current to the electrode. Here, the current can be applied so as to create a potential difference such that the metal component of the electrode active material is not reduced but the metallic particles to be extracted are reduced, and the electrode can be a carbon electrode. Here, the potential difference varies depending on the type of metallic particle, and can be appropriately adjusted depending on the type of metallic particle to be detected.

[0030] The metal impurity extraction solution obtained in the first step contains not only the metal impurities but also metal components of the electrode active material such as Ni, Co, and Mn. Therefore, in order to accurately measure the content of the metal impurities, it is necessary to separate the metal impurities to be detected from the metal components of the electrode active material.

[0031] Therefore, in the present invention, a current is applied to the extraction solution within a voltage range in which the foreign metals to be detected are reduced, causing the foreign metals to be reduced and deposited on the electrode (positive electrode) to form a plating layer, thereby separating the foreign metals from the extraction solution. When separating foreign metals using electroplating in this manner, only the foreign metals are selectively reduced and deposited on the plating layer, creating an environment free from the matrix effect of the metal components of the electrode active material, allowing for quantitative measurement of even very small amounts of foreign metals contained at the ppb level.

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

[0033] Here, the measurement of the content of metal foreign matter using the inductively coupled plasma (ICP) method can be performed by dissolving the metal foreign matter plated on an electrode in acid to prepare a sample solution, and then measuring the content of the metal foreign matter in the sample solution using an inductively coupled plasma optical 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 mentioned above, the plating layer obtained in the second step has only metallic impurities selectively reduced and deposited, creating an environment that is free from the matrix effect of the metal components of the electrode active material. Therefore, even trace amounts of metallic impurities at the ppb level can be analyzed using the ICP method.

[0036] Meanwhile, the measurement of the content of foreign metal particles using the anodic stripping voltammetry method can be performed by applying a potential difference of opposite polarity to the potential difference applied in the second step to the electrode plated with the foreign metal particles to ionize the foreign metal particles in the plating layer, and measuring the amount of current generated during this process to determine the content of the foreign metal particles.

[0037] As described above, when the content of metallic foreign matter is measured by an electrochemical method, the content can be easily measured without a separate processing step for measuring the content.

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

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

[0040] 8 ml of the metal foreign body extraction solution A was placed in an electrochemical cell, and a three-electrode system was constructed, consisting of a glassy carbon electrode as the working electrode, a silver chloride electrode (Ag / AgCl) as the reference electrode, and a platinum wire as the counter electrode.

[0041] Thereafter, a voltage of −0.2 V was applied to the glass carbon electrode for a total of 120 seconds to plate the metal in the foreign metal extracting solution A. For 60 seconds, plating was performed while stirring the solution at 300 rpm using a stirrer, and for the remaining 60 seconds, the stirrer was stopped to allow the solution to reach equilibrium.

[0042] Example 2 A foreign metal extracting solution B was prepared in the same manner as in Example 1, except that 0.11 mg of copper particles was mixed with about 10 g of the positive electrode active material (NCM811), and plating was performed.

[0043] Example 3 A foreign metal extracting solution C was prepared in the same manner as in Example 1, except that 0.13 mg of copper particles was mixed with about 10 g of the positive electrode active material (NCM811), and plating was performed.

[0044] Experimental Example 1 10 g of each of the foreign metal extract solutions A to C prepared in Examples 1 to 3 was collected and the Cu content was measured using an ICP-OES device. The measurement results are shown in Table 1.

[0045] Experimental Example 2 After plating was completed in Examples 1 to 3, a voltage of 0.3 V was applied to oxidize the metal, and the stripping charge was measured (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 additional metal foreign matter (Cu) was added, the amount of metal foreign matter in the positive active material was so small that it was impossible to measure using ICP-OES. However, it can be confirmed that quantification is possible when measuring using the ASV method after plating, as in the method of the present invention. On the other hand, in Examples 2 and 3, when the additional metal foreign matter (Cu) was added to increase the content of metal foreign matter, it was possible to measure the amount of metal foreign matter using ICP-OES. As shown in Table 1, it can be confirmed that as the amount of metal foreign matter measured using ICP-OES increases, the charge value measured using the ASV method also increases. This indicates that the charge value measured using the ASV method can represent the amount of metal foreign matter. Therefore, it can be seen that the method of the present invention can quantify the amount of metal foreign matter that is not measured using the ICP method.

Claims

1. A first step of dissolving an electrode active material in a nitric acid aqueous solution to form a metal foreign matter extraction solution; a second step of plating the foreign metal particles in the foreign metal particle extraction solution onto an electrode; and a third step of measuring the content of the 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 diameter of 40 μm or less.

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

4. 2. The method for detecting metallic foreign matter in an electrode active material according to claim 1, wherein the first step is performed under conditions in which 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.

5. 2. 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. 2. The method for detecting metallic foreign matter in an electrode active material according to claim 1, wherein the first step is carried out by dissolving the electrode active material in a nitric acid aqueous solution having a nitric acid concentration of 20 to 40 wt %, and then stirring the solution at room temperature for 20 hours or more.

7. 2. The method for detecting metallic foreign matter in an electrode active material according to claim 1, wherein the second step is performed by applying a current so as to create a potential difference after immersing the electrode in the metallic foreign matter extraction solution such that the metal component of the electrode active material is not reduced but the metallic foreign matter to be extracted is reduced.

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. 2. The method for detecting metallic foreign matter in an electrode active material according to claim 1, wherein the third step is performed by dissolving the metallic foreign matter plated on the electrode with an acid and then measuring the content of the dissolved metallic foreign matter by an inductively coupled plasma method.

10. The method for detecting metallic foreign matter in an electrode active material according to claim 9, wherein the acid includes 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 includes at least one of hydrochloric acid and nitric acid, and hydrogen peroxide.

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

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