Highly heat-resistant antioxidant liquid for lithium battery copper foil

Abstract

To provide highly heat-resistant antioxidant liquid for a lithium battery copper foil capable of solving cost increase and a sewage treatment problem while effectively improving heat-resistant temperature.SOLUTION: Antioxidant liquid for a lithium battery copper foil contains hexavalent chromium and a heteroatom-containing organic substance in which a heteroatom contains N, O, S or P.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an antioxidant solution for lithium battery copper foil, and more particularly to a highly heat-resistant antioxidant solution for lithium battery copper foil. [Background technology]

[0002] Most conventional oxidation prevention treatments for copper foils for lithium batteries involve immersing the copper foil in a hexavalent chromium solution and electroplating it to form a passivation layer on the surface of the copper foil to prevent oxidation, and the heat resistance temperature of this is approximately 150°C. To reach temperatures above 210°C, a heat-resistant composite metal layer is usually formed using chromium in addition to nickel, zinc, or other metal elements.

[0003] As applications such as electric vehicles are rapidly developing, users' requirements for lithium battery performance are also increasing. To improve the safety of lithium batteries and prevent overcharging, the reactivity between the electrodes and electrolyte increases, resulting in rapid heat release. As a result, high-temperature oxidation can cause copper foil peeling, lithium dendrite formation, and destruction of the insulating film, ultimately leading to battery explosions. Therefore, it is necessary to increase the heat resistance temperature of copper foil.

[0004] However, in conventional technology, various metal elements are added to a hexavalent chromium electroplating solution to form a composite metal oxidation prevention layer. Although this can improve the heat resistance temperature, adding too many heavy metals not only increases costs but also makes sewage treatment difficult and affects the battery performance of the copper foil.

[0005] Based on the above, it is an urgent goal for those skilled in the art to develop a highly heat-resistant antioxidant solution for lithium battery copper foil that can effectively improve the heat resistance temperature while solving the problems of increased costs and sewage treatment. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention provides a highly heat-resistant antioxidant solution for lithium battery copper foil, which can effectively improve the heat resistance temperature while solving the problems of increased costs and sewage treatment. [Means for solving the problem]

[0007] The antioxidant solution for lithium battery copper foil of the present invention contains hexavalent chromium and a heteroatom-containing organic substance, and the heteroatom contains N, O, S, or P.

[0008] In one embodiment of the present invention, the content of hexavalent chromium is 50 ppm to 500 ppm, and the content of heteroatom-containing organic matter is 3,000 ppm to 60,000 ppm, based on the total weight of the antioxidant solution for lithium battery copper foil.

[0009] In one embodiment of the present invention, sources of hexavalent chromium include chromium trioxide and chromates and dichromates.

[0010] In one embodiment of the present invention, the heteroatom-containing organic compound comprises benzotriazole, 2-mercaptobenzothiazole nitrogen-containing azole, hydroxyethylenediphosphonic acid, aminotrimethylenephosphonic acid, sodium ethylenediaminetetramethylenephosphonate, ethylenediaminetetraacetic acid, sodium gluconate, sodium potassium tartrate, or a water-soluble siloxane.

[0011] In one embodiment of the present invention, the nitrogen-containing azole comprises an aminotriazole or an aminotetrazole. [Effects of the Invention]

[0012] Based on the above, the present invention provides a highly heat-resistant antioxidant solution for lithium battery copper foil. The addition of heteroatom-containing organic compounds forms coordinate bonds with vacant copper orbitals, forming a dense antioxidant layer on the copper foil surface, preventing oxidative discoloration even at temperatures as high as 210°C. [Brief explanation of the drawings]

[0013] [Figure 1]FIG. 1 is an equivalent circuit diagram used for fitting. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described in detail, but these embodiments are merely examples and the present invention is not limited to these.

[0015] In this specification, ranges expressed as "from one value to another value" are generalizations intended to avoid listing every single value within the range in the specification. Thus, the recitation of a particular numerical range includes any number within that range and any smaller numerical range defined by that number, just as if that number and smaller numerical range were recited in the specification.

[0016] The present invention provides a highly heat-resistant antioxidant solution for lithium battery copper foil, which contains hexavalent chromium and a heteroatom-containing organic substance, where the heteroatom includes N, O, S, or P. Based on the total weight of the antioxidant solution for lithium battery copper foil, the content of the hexavalent chromium is, for example, 50 ppm to 1500 ppm, and the content of the heteroatom-containing organic substance is, for example, 3000 ppm to 60000 ppm.

[0017] In this embodiment, the source of hexavalent chromium may include chromium trioxide, chromate, and dichromate. The heteroatom-containing organic compound may include benzotriazole or a derivative thereof, 2-mercaptobenzothiazole, a nitrogen-containing azole, hydroxyethylenediphosphonic acid, aminotrimethylenephosphonic acid, sodium ethylenediaminetetramethylenephosphonate, ethylenediaminetetraacetic acid or a derivative thereof, sodium gluconate, sodium potassium tartrate, or a water-soluble siloxane. The nitrogen-containing azole may include aminotriazole or aminotetrazole.

[0018] The present invention also provides a method for treating copper foil for lithium batteries with high heat resistance and antioxidant properties, using the aforementioned high heat resistance antioxidant solution for lithium battery copper foil, comprising the following steps: First, electrolytic copper foil is washed and air-dried, and then impregnated or electroplated with the high heat resistance antioxidant solution of the present invention. The impregnation time is, for example, 1 to 20 seconds, and the electroplating conditions are, for example, 0.1 ASD to 4 ASD. The foil is then wrung, air-dried, and wound up. In this embodiment, the thickness of the organic antioxidant layer formed on the copper foil surface is, for example, 10 to 300 nm, and the organic antioxidant layer can be formed on both opposing surfaces of the copper foil.

[0019] After the oxidation prevention treatment of copper foil is completed, its heat resistance is tested. The copper foil is placed in a circulating oven at different temperatures and baked for 10 minutes. The highest temperature at which the color difference (△E) after baking does not exceed 8 is the heat resistance temperature.

[0020] Color difference(△E ab ) is calculated by measuring the L, a, and b values ​​of the copper foil before and after firing using a spectrophotometer and using the following formula.

number

[0021] Copper foil for lithium batteries treated with the formulation of the present invention does not oxidize and discolor even at high temperatures of 180°C to 250°C.

[0022] The highly heat-resistant antioxidant solution for lithium battery copper foil of the present invention will be described in detail below with reference to experimental examples, although the present invention is not limited to these examples.

[0023] Experimental example

[0024] The following experimental example was specially prepared to demonstrate that copper foil treated with the high heat resistant antioxidant solution of the present invention has superior lithium battery performance compared to conventional hexavalent chromium formulations.

[0025] Example 1

[0026] The plating solution on the original foil was washed with pure water and air-dried, after which it was immersed for 8 seconds in an antioxidant solution containing 390 ppm of hexavalent chromium and 7000 ppm of heteroatom-containing organic matter. The hexavalent chromium was derived from potassium dichromate, and the heteroatom-containing organic matter included 5-aminotetrazole and disodium ethylenediaminetetraacetate. The current was 0.17 amperes per square decimeter (A / dm 2 These were electroplated using a current density of 1000 kJ / cm2 for 0.5 seconds to form a heat-resistant anti-oxidation layer on the copper foil surface. Testing showed that the heat resistance was 210°C for 10 minutes.

[0027] Example 2

[0028] The plating solution on the original foil was washed with pure water and air-dried, after which it was immersed for 8 seconds in an antioxidant solution containing 390 ppm of hexavalent chromium and 16,000 ppm of heteroatom-containing organic matter. The hexavalent chromium was derived from potassium dichromate, and the heteroatom-containing organic matter included 5-aminotetrazole, disodium ethylenediaminetetraacetate, and ethylenediaminetetramethylenephosphonic acid. The current density was 0.17 amperes per square decimeter (A / dm 2 These were electroplated using a current density of 1000 kJ / cm2 for 0.5 seconds to form a heat-resistant anti-oxidation layer on the copper foil surface. Testing showed that the heat resistance was 210°C for 10 minutes.

[0029] Example 3

[0030] The plating solution on the original foil was washed with pure water and air-dried, after which it was immersed for 8 seconds in an antioxidant solution containing 390 ppm of hexavalent chromium and 56,000 ppm of heteroatom-containing organic matter. The hexavalent chromium was derived from potassium dichromate, and the heteroatom-containing organic matter included 5-aminotetrazole and potassium sodium tartrate. The current was 0.17 amperes per square decimeter (A / dm 2 These were electroplated using a current density of 0.5 seconds to form a heat-resistant oxidation-resistant layer on the copper foil surface. Testing showed that the heat resistance was 250°C for 10 minutes.

[0031] Comparative Example 1

[0032] The plating solution on the original foil was washed with pure water and air-dried, after which it was immersed for 8 seconds in an antioxidant solution containing 988 ppm of hexavalent chromium. Here, the hexavalent chromium was derived from potassium dichromate and had a current of 0.17 amperes per square decimeter (A / dm 2 These were electroplated using a current density of 1000 kJ / cm2 for 0.5 seconds to form a heat-resistant anti-oxidation layer on the copper foil surface. Testing showed that the heat resistance was 150°C for 10 minutes.

[0033] From the heat resistance test described above, it can be seen that the heat resistance temperature of Examples 1 to 3 treated with the antioxidant solution of the present invention is improved compared to Comparative Example 1 which used a conventional hexavalent chromium compound, and that the heat resistance is more preferable.

[0034] Comparison of copper foil battery performance for lithium batteries

[0035] The lithium battery copper foils of Example 1 and Comparative Example 1 were combined with commercially available negative electrode materials to prepare negative electrodes, and CR2032 button batteries were assembled and analyzed for their electrical performance, such as AC impedance and cycle life.

[0036] The button battery is manufactured as follows. First, a uniform negative electrode slurry with a solid phase composition of 92 wt% graphite (FMGP-A, Nakahata Carbon Chemical Co., Ltd.), 5% polyvinylidene fluoride (PVDF 5130), and 3% conductive carbon black (Super P), containing NMP as a solvent, was prepared. The negative electrode slurry was then applied to a copper foil for lithium batteries at a wet film thickness of 200 μm and a coating speed of 2 mm / s. After application was complete, the negative electrode was first dried in an oven at 60°C and then vacuum-dried in an oven at 120°C. The dried negative electrode was then dried to a compressed density of 1.3 (g / cm). 3The battery was then rolled to a thickness of 13 mm and cut into circular electrode pieces with a diameter of 13 mm. Next, a CR2032 button battery was assembled by arranging the bottom cover, lithium metal sheet, PE insulating film, negative electrode sheet, gasket, and lead in this order from bottom to top, and pouring in 1M LiPF6in EC:DEC (1:1) electrolyte. The top cover was then placed on the battery and the battery was pressure-sealed using a sealing machine to complete the battery assembly.

[0037] After the battery was assembled, it was validated by performing three charge and discharge cycles at a current of 0.1 C. The discharge mode was constant current-constant voltage (CC-CV), the charge mode was constant current, and the operating voltage range was 10 mV to 2 V.

[0038] The batteries of Comparative Example 1 and Example 1 were subjected to AC impedance analysis and fitted with an equivalent circuit diagram (FIG. 1). As can be seen from the results in Table 1 below, the charge transfer resistance (R3) of Example 1 is superior to that of Comparative Example 1.

[0039] [Table 1]

[0040] A cycle life test was conducted on the batteries of Comparative Example 1 and Example 1, and charge / discharge cycles were performed at a current of 1 C. Here, the discharge mode was constant current-constant voltage (CC-CV), the charge mode was constant current, and the operating voltage range was 10 mV to 2 V. The cycle life was the number of cycles when the capacity of the lithium battery decreased to 80% of the initial capacity, and the test results are shown in Table 2 below.

[0041] [Table 2]

[0042] In summary, the present invention provides a highly heat-resistant antioxidant solution for lithium battery copper foil. The addition of a heteroatom-containing organic substance forms coordinate bonds with vacant copper orbitals, forming a dense antioxidant layer on the copper foil surface. This prevents the copper foil from oxidizing and discoloring even at temperatures as high as 210°C, effectively improving its heat resistance. Thus, copper foil treated with the antioxidant solution of the present invention exhibits superior lithium battery performance compared to conventional copper foils containing hexavalent chromium. Furthermore, the highly heat-resistant antioxidant solution of the present invention uses a heteroatom-containing organic substance instead of the heavy metals used in conventional technology. Therefore, not only can the heat resistance be effectively improved, but costs and sewage treatment issues can also be resolved. [Industrial Applicability]

[0043] The highly heat-resistant antioxidant solution for lithium battery copper foil of the present invention can be applied to the lithium battery industry.

Claims

1. Hexavalent chromium, a heteroatom-containing organic compound, wherein the heteroatom includes N, O, S, or P; Antioxidant for lithium battery copper foil.

2. The antioxidant solution for lithium battery copper foil contains hexavalent chromium in an amount of 50 ppm to 1500 ppm and heteroatom-containing organic matter in an amount of 3000 ppm to 60000 ppm based on the total weight of the antioxidant solution for lithium battery copper foil. The antioxidant solution for lithium battery copper foil according to claim 1.

3. Sources of the hexavalent chromium include chromium trioxide, chromates, and dichromates. The antioxidant solution for lithium battery copper foil according to claim 1.

4. The heteroatom-containing organic substance includes benzotriazole, 2-mercaptobenzothiazole, nitrogen-containing azole, hydroxyethylenediphosphonic acid, aminotrimethylenephosphonic acid, sodium ethylenediaminetetramethylenephosphonate, ethylenediaminetetraacetic acid, sodium gluconate, sodium potassium tartrate, or water-soluble siloxane. The antioxidant solution for lithium battery copper foil according to claim 1.

5. The nitrogen-containing azole includes an aminotriazole or an aminotetrazole. The antioxidant solution for lithium battery copper foil according to claim 4.

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