KR20130018523A - Analysis method of metal impurity by electrochemical method - Google Patents

Abstract

PURPOSE: A method for analyzing metallic foreign materials by an electrochemical method is provided to freely increase the size of a working electrode according to mass produced scales of a secondary battery, thereby enhancing the reliability of an analysis result. CONSTITUTION: A method for analyzing metallic foreign materials by an electrochemical method is as follows. A battery cell including a working electrode is manufactured. Voltage is applied to the working electrode so that metallic foreign materials included in raw materials for a secondary cell has a chemical reaction. Changes in the voltage flowing in a reference electrode are measured so that the metallic foreign materials are analyzed. [Reference numerals] (AA) Current(1e-4A); (BB) Voltage(V)

Description

Analysis method of metal foreign matter by electrochemical method {Analysis Method of Metal Impurity By Electrochemical Method}

The present invention relates to a method for analyzing metal foreign matters by an electrochemical method, and more particularly, after manufacturing a battery cell including a working electrode composed of only a secondary battery raw material and a binder, and included in the secondary battery raw material. The present invention relates to a method for analyzing a metal foreign material, wherein the metal foreign material is analyzed by applying a voltage to the working electrode so as to cause an electrochemical reaction and measuring a change in current flowing to the reference electrode.

As the price of energy sources increases due to the depletion of fossil fuels, and the interest of environmental pollution is increasing, the demand for environmentally friendly alternative energy sources becomes an indispensable factor for future life. As demand increases, demand for secondary batteries as energy sources is rapidly increasing, and in recent years, the use of secondary batteries as power sources for electric vehicles (EVs) and hybrid electric vehicles (HEVs) has been realized.

Rechargeable charging and discharging of the secondary battery is performed by an electrochemical reaction between the positive electrode active material and the negative electrode active material.

The positive electrode mixture includes a positive electrode active material, a binder, a conductive material, and an additive (hereinafter, referred to as a raw material for a secondary battery). In the raw material for the secondary battery, metal foreign substances that can freely participate in the electrochemical reaction of the secondary battery are generally mixed. have. In particular, the conductive material generally includes a metal foreign material that can participate in the electrochemical reaction of the secondary battery as described above and a metal element present in the conductive material.

However, such a metal foreign matter has a problem of causing a low voltage of the secondary battery by freely participating in the electrochemical reaction of the secondary battery.

Conventionally, inductively coupled plasma (ICP, Inductively Coupled Plasma) method is used to analyze metal foreign substances in the secondary battery raw materials as described above. Not only does not represent the entire lot of the secondary battery of the mass production scale, but in the case of the Atomic Emission Spectroscopy (ICP-AES) analysis, a large amount of metal foreign matters during the pretreatment of the samples at a high temperature of 900 ℃ Since it is very likely to be lost, there is a problem that the reliability of the accurate analysis results is poor.

Accordingly, there is a high need for a method for analyzing metal foreign matters that can reliably detect the detection results of metal foreign matters contained in a secondary battery of a mass production scale.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

After extensive research and various experiments, the inventors of the present application confirmed that only the metal components participating in the actual electrochemical reaction can be analyzed in a secondary battery of mass production using the voltammetry. Reached.

Specifically, in the method of analyzing a foreign substance in a metal according to the present invention, after manufacturing a battery cell including a working electrode composed of only a raw material for a secondary battery and a binder, the foreign metal contained in the raw material for the secondary battery undergoes an electrochemical reaction. Analyzing the metal foreign matter by applying a voltage to the working electrode to measure the change in the current flowing to the reference electrode.

The analysis method according to the present invention is to analyze the metal oxide using the oxidation reaction of the metal foreign matters, the metal foreign matters are oxidized at the intrinsic oxidation potential to generate a current.

The above metal foreign matters are metal foreign substances which cause oxidation at 3.50 to 4.00 V, specifically, copper (Cu) which causes oxidation at 3.60 to 3.75 V or iron (Fe) which causes oxidation at 3.75 to 3.90 V. Can be.

As described above, different types of metal foreign matters may be analyzed by comparing the measured voltage at which the metal foreign matter is oxidized and current starts to flow with the intrinsic oxidation potential of the metal foreign matter.

In addition, when the amount of the metal foreign matter reacts to increase the amount of current flowing through the active oxidation reaction, and the metal foreign matters are different from each other inherent oxidation potential, the current of the intrinsic oxidation potential of the metal foreign matter. It is also possible to analyze the relative content of different metal foreign bodies by measuring the strength.

The above qualitative analysis and quantitative analysis may be performed by voltammetry, for example, linear voltametry or cyclic voltametry, wherein the boost is linear ( linear) and the slower the boosting speed, the more advantageous it is for the detection of metal foreign matter, but preferably 0.1 to 20 mV / s, more preferably 1 to 5 mV / s.

Therefore, the analysis method according to the present invention can freely adjust the size of the working electrode according to the mass production scale of the secondary battery, thereby increasing the size of the sample used in one test, that is, the working electrode to increase the reliability of the analysis results In addition, the correlation between the metal foreign matters included in the secondary battery and the low voltage failure rate of the secondary battery can be analyzed significantly.

Specifically, the working electrode composed of only the secondary battery raw material and the binder refers to a dry electrode applied to a current collector by applying a slurry made by mixing an electrode mixture composed of only the secondary battery raw material and the binder to a solvent such as NMP.

In one embodiment of the present invention, the secondary battery raw material may be made of a conductive material only, the electrode mixture may include a conductive material of 40% to 99.5% by weight based on the total weight of the electrode mixture. have.

The current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the current collector include, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or the surface of aluminum or stainless steel. Surface treated with carbon, nickel, titanium, silver, or the like can be used.

In addition, the current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is added to the binder in an amount of 1 to 30% by weight, based on the total weight of the mixture containing the cathode active material, as a component that assists in bonding between the active material and the conductive agent and bonding to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, and various copolymers.

The reference electrode may be lithium (Li) metal or silver (Ag), and the battery cell may be a two-electrode cell consisting of a working electrode / reference electrode or a three-electrode cell consisting of a working electrode / cathode / reference electrode.

The negative electrode is prepared by, for example, applying a negative electrode mixture containing a negative electrode active material on a negative electrode current collector and then drying it. The negative electrode active material is, for example, carbon such as non-graphitized carbon or graphite carbon. ; Li _x Fe ₂ O ₃ (0 ≦ _x ≦ 1), Li _x WO ₂ (0 ≦ _x ≦ 1), Sn _x Me _1-x Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me' Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen, 0 <x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, Bi ₂ O ₅ and the like; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and examples thereof include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

Since the structure and manufacturing method of the two-electrode cell, the three-electrode cell are known to those skilled in the art, detailed description thereof will be omitted below.

As described above, the analysis method according to the present invention can freely adjust the size of the working electrode according to the mass production scale of the secondary battery, the size of the sample used in one test, that is, the size of the working electrode to increase the analysis result Not only can the reliability be improved, but also the correlation between the metal foreign matters included in the secondary battery and the low voltage failure rate of the secondary battery can be analyzed significantly.

1 is a result of analyzing the electrode cell of Example 1 of the present invention using the cyclic voltammetry;
2 is a result of analyzing the electrode cell of Example 2 of the present invention using the cyclic voltammetry;
3 is a diagram illustrating these together after the charging currents of the graphs of FIGS. 1 and 2 are corrected to be the same;
4 is a result of analyzing the electrode cells of Examples 3 and 4 of the present invention using the cyclic voltammetry;
5 is a graph showing the correlation between the low voltage failure rate and the metal foreign matter content when the electrode cells of Examples 1 and 2 of the present invention are analyzed by cyclic voltammetry (CV);
6 is a graph showing the correlation between the low voltage failure rate and the metal foreign matter content when the electrode cells of Examples 1 to 2 of the present invention are analyzed by the ICP-AES method;
7 is a graph showing the correlation between the low voltage failure rate and the metal foreign matter content when the electrode cells of Examples 1 to 2 of the present invention are analyzed by the ICP-MS method.

Hereinafter, the present invention is further described, but the scope of the present invention is not limited thereto.

&Lt; Example 1 >

As a conductive material, carbon black (C2515) having the highest low voltage failure rate and a binder were mixed at a weight ratio of 1: 1, and put into NMP to prepare a slurry. The slurry was coated on an aluminum current collector, followed by rolling and drying to prepare a working electrode. An electrode cell was fabricated using the carbonate electrolyte in which 1 mol of LiPF ₆ was dissolved as the working electrode, the reference metal, and the silver metal as the electrolyte.

<Example 2>

An electrode cell was fabricated in the same manner as in Example 1 except that carbon black (D2137) having the lowest low voltage failure rate was used as the conductive material.

<Example 3>

As a conductive material, carbon black (C2515) having the highest low voltage failure rate and a binder were mixed at a weight ratio of 95: 5, and put into NMP to prepare a slurry. The slurry was coated on an aluminum current collector, followed by rolling and drying to prepare a working electrode. An electrode cell was prepared using the carbonate electrolyte in which 1 mol of LiPF ₆ was dissolved as the working electrode, the reference electrode, and lithium metal as the electrolyte.

<Example 4>

An electrode cell was fabricated in the same manner as in Example 3 except that carbon black (D2137) having the lowest low voltage failure rate was used as the conductive material.

&Lt; Comparative Example 1 &

0.313 g of carbon black (C2515) of Example 1 was placed in a 25 mL beaker and weighed. Distilled water: 13 mL of a mixed solution having a volume ratio of 4: 3: 1 by 60% HNO ₃ : H ₂ O ₂ was added to carbon black (C2515). Sonication for 30 minutes, heated for 6 hours at a temperature of 140 ℃, cooled for 10 minutes at room temperature, and filtered under reduced pressure.

After filtration and washing with 2% nitric acid solution, the filtrate was placed in a 25 mL volumetric flask and filled with 2% nitric acid solution, and an appropriate amount was taken to prepare a sample for ICP analysis.

Comparative Example 2

A sample was prepared in the same manner as in Comparative Example 1 except that carbon black (D2137) having the lowest low voltage failure rate was used as the conductive material.

<Experimental Example 1>

Cyclic current analysis was performed using the electrode cells of Examples 1 and 2, and the results are shown in FIGS. 1 and 2. 1 and 2 together, it can be seen that the graph pattern of Example 1 and the graph pattern of Example 2 are different from each other at 1.2V.

In FIG. 1, the peak near 1.2 V is estimated to be the result of an increase in the amount of current due to the oxidation reaction of the metal foreign matters contained in the carbon black C2515 having the highest low voltage failure rate.

FIG. 3 is a diagram illustrating the graphs of FIGS. 1 and 2 after correcting the charging current to be the same, and together. Referring to FIG. 3, it can be seen that the peak of Example 1 is higher than that of Example 2 at 1.2V.

From the above results, it can be seen that the conductive material C2515 of Example 1 contains a larger amount of metal foreign matter than the conductive material D2137 of Example 2.

<Experimental Example 2>

Cyclic current analysis was performed using the electrode cells of Examples 3 and 4, and the results are shown in FIG.

Referring to FIG. 4, it can be seen that the graph pattern of Example 1 and the graph pattern of Example 2 are different from each other.

Specifically, it can be seen that the current profile is different from about 3.75 to 4.0 V, and the oxidation reaction to the metal foreign material occurs from around 3.75 V.

Comparative Example 1

ICP-AES (Atomic Emission Spectroscopy) analysis was performed using the samples of Comparative Examples 1 and 2, and the results are shown in FIG. 6. Referring to FIG. 6, it can be seen that the ICP-AES analysis has a limit in determining a correlation between a low voltage failure rate and a content of a copper foreign material.

Comparative Example 2

ICP-MS (Mess Spectroscopy) analysis was performed using the samples of Comparative Examples 1 and 2. The detection sensitivity within the limit of quantification of copper (0.1 ppm) was not possible even with the ICP-MS analysis, which was superior to the ICP-AES. (Fig. 7)

On the other hand, when the electrode cells of Examples 1 and 2 of the present invention are analyzed by cyclic voltammetry (CV), FIG. 5 illustrates a correlation between a low voltage failure rate and a metal foreign matter content. When compared with, the cyclic voltammetry method can be compared with the ICP-AES method and ICP-MS method, it can be seen that the correlation between the low-voltage defect rate and the content of the foreign matter of copper significantly.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (17)

After manufacturing a battery cell including a working electrode consisting of a raw material for the secondary battery and only the binder, and applying a voltage to the working electrode so that the metal foreign matter contained in the secondary battery raw material to cause an electrochemical reaction, as a reference electrode A method for analyzing a metal foreign material, wherein the metal foreign material is analyzed by measuring a change in a flowing current. The method of claim 1, wherein the secondary battery raw material is a conductive material. The method of claim 2, wherein the working electrode is an electrode coated with a slurry prepared by mixing an electrode mixture composed of only a conductive material and a binder in a solvent and dried on a current collector. The method of claim 2, wherein the electrode mixture contains 40 wt% to 99.5 wt% of a conductive material based on the total weight of the electrode mixture. The method of claim 1, wherein the reference electrode is made of Li metal. The method of claim 1, wherein the battery cell is a two-electrode cell consisting of a working electrode and a reference electrode. The method of claim 1, wherein the battery cell is a three-electrode cell consisting of a working electrode / cathode / reference electrode. The method of claim 1, wherein the electrochemical reaction of the metal foreign material is an oxidation reaction. The method of claim 8, wherein the metal foreign material is Cu. 10. The method of claim 9, wherein the Cu is oxidized at 3.60 to 3.75V. The method of claim 8, wherein the metal foreign material is Fe. 12. The method of claim 11, wherein the Fe is oxidized at 3.75 to 3.90V. The method of claim 1, wherein the analysis of the metal foreign material is a qualitative analysis of analyzing different types of metal foreign matters by measuring a voltage through which a current flows and comparing the metal foreign matters with an intrinsic potential causing an electrochemical reaction. Method of analysis. The method of claim 13, wherein the qualitative analysis is performed by voltammetry. 15. The method of claim 14, wherein the voltammetry is linear volatmetry or cyclic voltametry. The method of claim 15, wherein the step-up is linear when the voltammetry is measured and the step-up speed is 0.1 to 20 mV / s. The method of claim 16, wherein the boosting speed is 1 to 5 mV / s.

Images