Method for measuring content of impurity elements in carbon-coated copper foil coating layer

Abstract

The application provides a method for determining the content of impurity elements in a carbon-coated copper foil coating layer, and belongs to the technical field of lithium ion batteries. The method for determining the content of impurity elements in the carbon-coated copper foil coating layer comprises the following steps: firstly, dissolving the carbon-coated copper foil by using a digestion agent to measure the mass proportion a of impurity elements in the carbon-coated copper foil, and meanwhile, performing a process blank test to measure the mass proportion b of impurity elements in the process blank sample of the carbon-coated copper foil; secondly, taking another matrix copper foil which is the same as the matrix copper foil in the carbon-coated copper foil or taking the matrix copper foil in the carbon-coated copper foil after calcination, dissolving the matrix copper foil by using a digestion agent to measure the mass proportion c of impurity elements in the matrix copper foil, and meanwhile, performing a process blank test to measure the mass proportion d of impurity elements in the process blank sample of the matrix copper foil; and finally, combining formula (1) to calculate the mass proportion e of impurity elements in the coating layer of the carbon-coated copper foil. The method for determining the content of impurity elements in the carbon-coated copper foil coating layer can accurately test the content of each element in the carbon-coated copper foil coating layer.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a method for determining the content of impurity elements in a carbon-coated copper foil coating. Background Technology

[0002] In recent years, lithium-ion batteries have been widely used in the field of rechargeable batteries due to their advantages such as high energy density, long lifespan, and environmental friendliness. The main materials of a lithium-ion battery include four parts: the positive electrode, the negative electrode, the separator, and the electrolyte. The negative electrode further includes the negative electrode current collector and the negative electrode active material coated on the surface of the current collector. Currently, carbon-coated copper foil is commonly used as the negative electrode current collector. The substrate of the carbon-coated copper foil is copper foil, coated with pre-dispersed conductive carbon black or carbon-coated particles. This reduces the resistance between the current collector and the electrode material, improves the adhesion of the electrode material to the current collector, and thus improves the battery's energy density and rate performance.

[0003] For example, patent application CN107749479A discloses a carbon-coated copper foil negative electrode sheet and a power battery containing the negative electrode sheet. The carbon-coated copper foil negative electrode sheet includes a copper foil (2) and a negative electrode material coating (1). A carbon coating layer (3) is provided on both surfaces of the copper foil, and the negative electrode material coating is provided on the surface of the carbon coating layer. The preparation method of the carbon-coated copper foil negative electrode sheet includes the following steps: 1) Copper foil pretreatment: pre-etching the copper foil; 2) Coating carbon slurry: preparing carbon slurry, coating the carbon slurry onto the pre-etched copper foil, and curing to form a carbon coating layer; 3) Coating negative electrode slurry: preparing negative electrode slurry, coating the negative electrode slurry onto the surface of the carbon coating layer, and curing to form a negative electrode material coating layer; 4) Rolling: rolling the copper foil after step 3) to obtain the carbon-coated copper foil negative electrode sheet. For example, patent application CN106252666A discloses a method for preparing a negative electrode current collector for a lithium-ion battery, including the following steps: selecting copper foil, coating both sides of the copper foil with a carbon coating layer, wherein the thickness of the copper foil is 8-15 μm, the double-layer thickness of the carbon coating layer is 1.5-3.5 μm, and the single-sided areal density of the carbon coating layer is 0.5-0.7 g / m³. 2 .

[0004] In lithium-ion batteries, the content of impurity elements needs to be kept below specified levels. Excessive levels can negatively impact battery performance, especially during long cycles and at low temperatures. For example, excessive amounts of impurity elements such as Fe, Cr, Ni, and Zn can easily be reduced and aggregate into elemental metals during cycling, potentially puncturing the separator and causing a short circuit between the positive and negative electrodes. This leads to a decrease in battery capacity, and in extreme cases, can even cause battery fires and explosions, endangering lives and property. Therefore, it is necessary to control the content of impurity elements in the raw materials and battery structure of lithium-ion batteries.

[0005] Carbon-coated copper foil is a crucial component in lithium-ion battery materials. It comes into close contact with the negative electrode active material and significantly impacts its performance. Therefore, controlling the impurity element content of the coating layer in carbon-coated copper foil is a vital part of lithium-ion battery production. Current technologies typically measure the impurity elements in the conductive paste forming the coating layer, neglecting the potential introduction of impurities during the subsequent coating preparation process. Therefore, it is necessary to measure the impurity element content of the coating layer after preparation to verify the product's quality. Additionally, some technologies directly measure the overall impurity element content of the carbon-coated copper foil, but this method does not eliminate the influence of impurities in the base copper foil and cannot accurately control the impurity element content of the coating layer. Summary of the Invention

[0006] This invention is based on the inventor's discovery and understanding of the following facts and problems: The inventor had previously attempted to scrape off the coating layer from carbon-coated copper foil to determine the content of impurity elements in the coating powder. However, since the thickness of current carbon-coated copper foil is generally 5-8 μm, and the thickness of the coating layer is only about 1 μm, and the coating layer is in close contact with the substrate copper foil, it is easy to scrape off the substrate copper foil during the coating layer scraping process, mistakenly including impurities from the substrate copper foil in the coating layer, resulting in inaccurate determination results of the impurity element content in the coating layer. Therefore, there is an urgent need to design a method for determining the impurity element content of the coating layer of carbon-coated copper foil.

[0007] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention proposes a method for determining the impurity element content in a carbon-coated copper foil coating.

[0008] This invention provides a method for determining the impurity element content in a carbon-coated copper foil coating, comprising the following steps:

[0009] S1. Weigh out carbon-coated copper foil with a mass of m1;

[0010] S2. Dissolve the carbon-coated copper foil using a digesting agent, then dilute and bring to a fixed volume to obtain the carbon-coated copper foil test solution; simultaneously, dissolve the blank sample from the carbon-coated copper foil process using a digesting agent, then dilute and bring to a fixed volume to obtain the blank test solution from the carbon-coated copper foil process.

[0011] S3. Weigh out a base copper foil with a mass of m2, wherein the base copper foil is the same as the base copper foil in the carbon-coated copper foil;

[0012] S4. Dissolve the substrate copper foil using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate copper foil test solution; simultaneously, dissolve the substrate copper foil process blank sample using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate copper foil process blank test solution.

[0013] S5. The concentrations of impurity elements in the blank test solution of the carbon-coated copper foil process, the blank test solution of the substrate copper foil process, the test solution of the carbon-coated copper foil, and the test solution of the substrate copper foil are determined using an inductively coupled plasma atomic emission spectrometer. Then, the mass percentages of impurity elements in the carbon-coated copper foil (a), the blank test solution of the carbon-coated copper foil process (b), the substrate copper foil (c), and the blank test solution of the substrate copper foil process (d) are obtained according to the standard curve. Finally, the mass percentage of impurity elements in the coating layer of the carbon-coated copper foil (e) is calculated according to formula (1).

[0014] e={(ab)×m1-(cd)×m2} / (m1-m2) (1)

[0015] In this context, m1 and m2 are in g; a, b, c, d, and e are all in ppm.

[0016] The advantages and technical effects of the method for determining the impurity element content of carbon-coated copper foil coating layer of the present invention are as follows: The method of the present invention can accurately test the content of each element in the carbon-coated copper foil coating layer, which is crucial for raw material production, lithium battery incoming material monitoring, mechanism analysis, etc.

[0017] Preferably, the base copper foil in step S3 has the same area, thickness, volume, density, mass, manufacturer, and production batch as the base copper foil in the carbon-coated copper foil.

[0018] Preferably, the digesting agent in steps S2 and S4 comprises a mixture of nitric acid solution and sulfuric acid solution.

[0019] Preferably, the mass concentration of the nitric acid solution is 60 wt% or more, the mass concentration of the sulfuric acid solution is 95 wt% or more, and the volume ratio of the nitric acid solution to the sulfuric acid solution is (2-10):(8-10).

[0020] Preferably, the dissolution is carried out at 160-400°C in steps S2 and S4.

[0021] Preferably, the blank sample of the carbon-coated copper foil process in step S2 and the blank sample of the substrate copper foil process in step S4 include deionized water, distilled water or ultrapure water.

[0022] Preferably, the test conditions for the inductively coupled plasma atomic emission spectrometer in step S5 are as follows: plasma flow rate of 12-15 L / min, nebulizing gas flow rate of 0.6-0.8 L / min, pump speed of 1.5 mL / min, delay time of 40-60 s, number of tests of 2-4, and nebulizer back pressure of 280-320 kPa.

[0023] Preferably, the impurity element includes at least one selected from Fe, Cr, Ni, Zn, Li, P, Al, S, Ti, V, Si, B, Pb, Ca, Na, and K.

[0024] In addition, the present invention also provides another method for determining the impurity element content of carbon-coated copper foil coating, comprising the following steps:

[0025] S1. Weigh out carbon-coated copper foil with a mass of m1;

[0026] S2. Dissolve the carbon-coated copper foil using a digesting agent, then dilute and bring to a fixed volume to obtain the carbon-coated copper foil test solution; simultaneously, dissolve the blank sample from the carbon-coated copper foil process using a digesting agent, then dilute and bring to a fixed volume to obtain the blank test solution from the carbon-coated copper foil process.

[0027] S3. Weigh out a carbon-coated copper foil with a mass of m1, and calcine the carbon-coated copper foil to obtain the base copper foil in the carbon-coated copper foil. The mass of the base copper foil is recorded as m2.

[0028] S4. Dissolve the substrate copper foil using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate copper foil test solution; simultaneously, dissolve the substrate copper foil process blank sample using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate copper foil process blank test solution.

[0029] S5. The concentrations of impurity elements in the blank test solution of the carbon-coated copper foil process, the blank test solution of the substrate copper foil process, the test solution of the carbon-coated copper foil, and the test solution of the substrate copper foil are determined using an inductively coupled plasma atomic emission spectrometer. Then, the mass percentages of impurity elements in the carbon-coated copper foil (a), the blank test solution of the carbon-coated copper foil process (b), the substrate copper foil (c), and the blank test solution of the substrate copper foil process (d) are obtained according to the standard curve. Finally, the mass percentage of impurity elements in the coating layer of the carbon-coated copper foil (e) is calculated according to formula (1).

[0030] e={(ab)×m1-(cd)×m2} / (m1-m2) (1)

[0031] In this context, m1 and m2 are in g; a, b, c, d, and e are all in ppm.

[0032] The advantages and technical effects of the method for determining the impurity element content of carbon-coated copper foil coating layer of the present invention are as follows: The method of the present invention can accurately test the content of each element in the carbon-coated copper foil coating layer, which is crucial for raw material production, lithium battery incoming material monitoring, mechanism analysis, etc.

[0033] Preferably, in step S3, the carbon-coated copper foil is calcined at 350-900°C for 8-24 hours.

[0034] Preferably, the carbon-coated copper foil is calcined before being wiped and blown clean.

[0035] Preferably, the digesting agent in steps S2 and S4 comprises a mixture of nitric acid solution and sulfuric acid solution.

[0036] Preferably, the mass concentration of the nitric acid solution is 60 wt% or more, the mass concentration of the sulfuric acid solution is 95 wt% or more, and the volume ratio of the nitric acid solution to the sulfuric acid solution is (2-10):(8-10).

[0037] Preferably, the dissolution is carried out at 160-400°C in steps S2 and S4.

[0038] Preferably, the blank sample of the carbon-coated copper foil process in step S2 and the blank sample of the substrate copper foil process in step S4 include deionized water, distilled water or ultrapure water.

[0039] Preferably, the test conditions for the inductively coupled plasma atomic emission spectrometer in step S5 are as follows: plasma flow rate of 12-15 L / min, nebulizing gas flow rate of 0.6-0.8 L / min, pump speed of 1.5 mL / min, delay time of 40-60 s, number of tests of 2-4, and nebulizer back pressure of 280-320 kPa.

[0040] Preferably, the impurity element includes at least one selected from Fe, Cr, Ni, Zn, Li, P, Al, S, Ti, V, Si, B, Pb, Ca, Na, and K. Detailed Implementation

[0041] The present invention is described in detail below. The embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0042] First aspect

[0043] The first aspect of this invention provides a method for determining the impurity element content of a carbon-coated copper foil coating, comprising the following steps:

[0044] S1. Weigh out carbon-coated copper foil with a mass of m1;

[0045] S2. Dissolve the carbon-coated copper foil using a digesting agent, then dilute and bring to a fixed volume to obtain the carbon-coated copper foil test solution; simultaneously, dissolve the blank sample from the carbon-coated copper foil process using a digesting agent, then dilute and bring to a fixed volume to obtain the blank test solution from the carbon-coated copper foil process.

[0046] S3. Weigh out a base copper foil with a mass of m2, wherein the base copper foil is the same as the base copper foil in the carbon-coated copper foil;

[0047] S4. Dissolve the substrate copper foil using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate copper foil test solution; simultaneously, dissolve the substrate copper foil process blank sample using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate copper foil process blank test solution.

[0048] S5. The concentrations (mass concentration or molar concentration) of impurity elements in the blank test solution of the carbon-coated copper foil process, the blank test solution of the substrate copper foil process, the test solution of the carbon-coated copper foil, and the test solution of the substrate copper foil are determined using an inductively coupled plasma atomic emission spectrometer. Then, the mass percentages of impurity elements in the carbon-coated copper foil (a), the blank test solution of the carbon-coated copper foil process (b), the blank test solution of the substrate copper foil (c), and the blank test solution of the substrate copper foil process (d) are obtained according to the standard curve. Finally, the mass percentage of impurity elements in the coating layer of the carbon-coated copper foil (e) is calculated according to formula (1).

[0049] e={(ab)×m1-(cd)×m2} / (m1-m2) (1)

[0050] In this context, m1 and m2 are in g; a, b, c, d, and e are all in ppm.

[0051] Working principle: This invention first uses a digesting agent to dissolve the carbon-coated copper foil. The mass percentage (a) of impurity elements in the carbon-coated copper foil is measured using inductively coupled plasma atomic emission spectrometry (ICP-AES) and a standard curve. Simultaneously, a process blank is prepared, and the mass percentage (b) of impurity elements in the blank sample of the carbon-coated copper foil is measured in the same manner. Then, another base copper foil identical to the base copper foil in step S1 is taken and dissolved again using a digesting agent. The mass percentage (c) of impurity elements in this base copper foil is measured using ICP-AES and a standard curve. Simultaneously, a process blank is prepared, and the mass percentage (d) of impurity elements in the blank sample of the base copper foil is measured in the same manner. Finally, the mass percentage (e) of impurity elements in the coating layer of the carbon-coated copper foil is calculated using formula (1). Compared to the method of scraping the coating layer from the carbon-coated copper foil and then measuring the impurity element content, the method of this invention provides more accurate and effective test results.

[0052] Preferably, the base copper foil in step S3 has the same area, thickness, volume, density, mass, manufacturer, and production batch as the base copper foil in the carbon-coated copper foil. This ensures that the impurity element content of the base copper foil taken in step S3 is exactly the same as that of the carbon-coated copper foil in step S1, which helps to improve the accuracy of the test results of the method for determining the impurity element content of the carbon-coated copper foil coating layer.

[0053] Preferably, the digesting agent in steps S2 and S4 comprises a mixture of nitric acid solution and sulfuric acid solution. In step S2, the combined action of nitric acid and sulfuric acid dissolves the carbon-coated copper foil. Although only the base copper foil is used in step S4, the digesting agent is the same as that in step S2, in order to improve the accuracy of the test results.

[0054] More preferably, the nitric acid solution has a mass concentration of 60 wt% or higher, the sulfuric acid solution has a mass concentration of 95 wt% or higher, and the volume ratio of the nitric acid solution to the sulfuric acid solution is (2-10):(8-10). When the concentrations and volume ratios of the nitric acid and sulfuric acid solutions are within the above ranges, the digesting agent can completely dissolve the carbon-coated copper foil and the base copper foil, thereby improving the accuracy of the test results for the impurity element content of the carbon-coated copper foil coating and avoiding the problem of low test results for the impurity element content of the carbon-coated copper foil coating due to incomplete carbon dissolution. More preferably, the nitric acid solution has a mass concentration of 64-66 wt%, and the sulfuric acid solution has a mass concentration of 98 wt% or higher.

[0055] Preferably, dissolution in steps S2 and S4 is carried out at 160-400℃. In steps S2 and S4, the digesting agent is dissolved by a digestion reaction on the carbon-coated copper foil or the base copper foil. Heating conditions are beneficial for increasing the rate of the digestion reaction, shortening the dissolution time, and improving testing efficiency. It is understood that a microwave digestion apparatus could also be used for dissolution in steps S2 and S4, but microwave digestion apparatuses are expensive instruments, which is not conducive to reducing the cost of testing auxiliary materials.

[0056] Preferably, the blank samples of the carbon-coated copper foil process in step S2 and the blank samples of the substrate copper foil process in step S4 include deionized water, distilled water, or ultrapure water. In step S2, except for using water instead of the carbon-coated copper foil, the other conditions are consistent with the preparation process of the test solution for the carbon-coated copper foil. In step S4, except for using water instead of the substrate copper foil, the other conditions are consistent with the preparation process of the test solution for the substrate copper foil. The process blanks are used to eliminate the influence of the digesting agent and the testing instrument on the test solutions for the carbon-coated copper foil and the substrate copper foil, thereby improving the accuracy of the test results for the impurity element content of the carbon-coated copper foil coating.

[0057] Preferably, the testing conditions for the inductively coupled plasma atomic emission spectrometer in step S5 are as follows: plasma flow rate of 12-15 L / min, nebulizing gas flow rate of 0.6-0.8 L / min, pump speed of 1.5 mL / min, delay time of 40-60 s, number of tests of 2-4, and nebulizer back pressure of 280-320 kPa. Testing the inductively coupled plasma atomic emission spectrometer under these conditions can improve the accuracy of the impurity concentration test results in the corresponding test liquid and process blank test liquid, thereby improving the accuracy of the impurity element content test results in the carbon-coated copper foil coating layer.

[0058] It should be noted that the impurity elements mentioned in this invention include at least one of Fe, Cr, Ni, Zn, Li, P, Al, S, Ti, V, Si, B, Pb, Ca, Na, and K. The types of impurity elements monitored need to be determined based on the types of impurities that may be introduced into the carbon-coated copper foil production environment.

[0059] Second aspect

[0060] A second aspect of the present invention provides a method for determining the impurity element content of a carbon-coated copper foil coating, comprising the following steps:

[0061] S1. Weigh out carbon-coated copper foil with a mass of m1;

[0062] S2. Dissolve the carbon-coated copper foil using a digesting agent, then dilute and bring to a fixed volume to obtain the carbon-coated copper foil test solution; simultaneously, dissolve the blank sample from the carbon-coated copper foil process using a digesting agent, then dilute and bring to a fixed volume to obtain the blank test solution from the carbon-coated copper foil process.

[0063] S3. Weigh out a carbon-coated copper foil with a mass of m1, and calcine the carbon-coated copper foil to obtain the base copper foil in the carbon-coated copper foil. The mass of the base copper foil is recorded as m2.

[0064] S4. Dissolve the substrate copper foil using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate copper foil test solution; simultaneously, dissolve the substrate copper foil process blank sample using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate copper foil process blank test solution.

[0065] S5. The concentrations (mass concentration or molar concentration) of impurity elements in the blank test solution of the carbon-coated copper foil process, the blank test solution of the substrate copper foil process, the test solution of the carbon-coated copper foil, and the test solution of the substrate copper foil are determined using an inductively coupled plasma atomic emission spectrometer. Then, the mass percentages of impurity elements in the carbon-coated copper foil (a), the blank test solution of the carbon-coated copper foil process (b), the blank test solution of the substrate copper foil (c), and the blank test solution of the substrate copper foil process (d) are obtained according to the standard curve. Finally, the mass percentage of impurity elements in the coating layer of the carbon-coated copper foil (e) is calculated according to formula (1).

[0066] e={(ab)×m1-(cd)×m2} / (m1-m2) (1)

[0067] In this context, m1 and m2 are in g; a, b, c, d, and e are all in ppm.

[0068] Working Principle: This invention first uses a digesting agent to dissolve the carbon-coated copper foil. The mass percentage (a) of impurity elements in the carbon-coated copper foil is measured using inductively coupled plasma atomic emission spectrometry (ICP-AES) and a standard curve. Simultaneously, a process blank is prepared, and the mass percentage (b) of impurity elements in the blank sample is measured in the same manner. Then, the same carbon-coated copper foil as in step S1 is taken and calcined to obtain the base copper foil. The base copper foil is again dissolved using a digesting agent, and the mass percentage (c) of impurity elements in the base copper foil is measured using ICP-AES and a standard curve. Simultaneously, a process blank is prepared, and the mass percentage (d) of impurity elements in the blank sample is measured in the same manner. Finally, the mass percentage (e) of impurity elements in the coating layer of the carbon-coated copper foil is calculated using formula (1). Compared to the method of scraping the coating layer from the carbon-coated copper foil and then measuring the impurity element content, the method of this invention provides more accurate and effective test results.

[0069] Preferably, in step S3, the carbon-coated copper foil is calcined at 350-900℃ for 8-24 hours. It should be noted that the coatings used in related technologies generally contain more than 90wt% nano-graphite, SP, and / or carbon nanotubes, as well as a portion of PVDF. The thermal decomposition temperature of PVDF is 316℃, while the melting point of the base copper foil is 1083℃. Therefore, to ensure complete ashing of the coating without affecting the base copper foil, a calcination temperature of 350-900℃ is preferred. After calcination, PVDF decomposes into HF gas and C-containing gas, which will not affect the accuracy of the test results. It is understood that if the binder used in the coating is another type of binder besides PVDF, the calcination temperature in step S3 can be determined based on the thermal decomposition temperature of that binder.

[0070] Under the aforementioned temperature conditions and for the specified time, the coating layer in the carbon-coated copper foil can be completely ashed, resulting in the base copper foil without any visible residue. If the calcination temperature is too low, the PVDF in the coating layer may not reach its decomposition temperature, leading to residue and negatively impacting the accuracy of test results. If the calcination temperature is too high, it wastes energy and poses certain risks. Furthermore, copper's melting point is 1083℃, therefore the calcination temperature is preferably no higher than 900℃. If the calcination time is too short, complete ashing of the coating layer is not recommended, further hindering the accuracy of test results. If the calcination time is too long, it increases the testing time and wastes testing resources.

[0071] Preferably, after calcining the carbon-coated copper foil, wiping and blowing can remove residual metal oxides from the coating layer, further improving the accuracy of the test results.

[0072] Preferably, the digesting agent in steps S2 and S4 comprises a mixture of nitric acid solution and sulfuric acid solution. In step S2, nitric acid can be used to dissolve the base copper foil, while nitric acid and sulfuric acid work together to dissolve the coating layer in the carbon-coated copper foil. Although only the base copper foil is used in step S4, the digesting agent is the same as that in step S2, in order to improve the accuracy of the test results.

[0073] More preferably, the nitric acid solution has a mass concentration of 60 wt% or higher, the sulfuric acid solution has a mass concentration of 95 wt% or higher, and the volume ratio of the nitric acid solution to the sulfuric acid solution is (2-10):(8-10). Having the concentrations and volume ratios of the nitric acid and sulfuric acid solutions within these ranges is beneficial for improving the solubility of the carbon-coated copper foil and the base copper foil, thereby improving the accuracy of the test results for the impurity element content of the carbon-coated copper foil coating and avoiding the problem of low test results for the impurity element content of the carbon-coated copper foil coating due to incomplete carbon dissolution. Even more preferably, the nitric acid solution has a mass concentration of 64-66 wt%, and the sulfuric acid solution has a mass concentration of 98 wt% or higher.

[0074] Preferably, dissolution in steps S2 and S4 is carried out at 160-400℃. In steps S2 and S4, the digesting agent is dissolved by a digestion reaction on the carbon-coated copper foil or the base copper foil. Heating conditions are beneficial for increasing the rate of the digestion reaction, shortening the dissolution time, and improving testing efficiency. It is understood that a microwave digestion apparatus could also be used for dissolution in steps S2 and S4, but microwave digestion apparatuses are expensive instruments, which is not conducive to reducing the cost of testing auxiliary materials.

[0075] Preferably, the blank samples of the carbon-coated copper foil process in step S2 and the blank samples of the substrate copper foil process in step S4 include deionized water, distilled water, or ultrapure water. In step S2, except for using water instead of the carbon-coated copper foil, the other conditions are consistent with the preparation process of the test solution for the carbon-coated copper foil. In step S4, except for using water instead of the substrate copper foil, the other conditions are consistent with the preparation process of the test solution for the substrate copper foil. The process blanks are used to eliminate the influence of the digesting agent and the testing instrument on the test solutions for the carbon-coated copper foil and the substrate copper foil, thereby improving the accuracy of the test results for the impurity element content of the carbon-coated copper foil coating.

[0076] Preferably, the testing conditions for the inductively coupled plasma atomic emission spectrometer in step S5 are as follows: plasma flow rate of 12-15 L / min, nebulizing gas flow rate of 0.6-0.8 L / min, pump speed of 1.5 mL / min, delay time of 40-60 s, number of tests of 2-4, and nebulizer back pressure of 280-320 kPa. Testing the inductively coupled plasma atomic emission spectrometer under these conditions can improve the accuracy of the impurity concentration test results in the corresponding test liquid and process blank test liquid, thereby improving the accuracy of the impurity element content test results in the carbon-coated copper foil coating layer.

[0077] It should be noted that the impurity elements mentioned in this invention include at least one of Fe, Cr, Ni, Zn, Li, P, Al, S, Ti, V, Si, B, Pb, Ca, Na, and K. The types of impurity elements monitored need to be determined based on the types of impurities that may be introduced into the carbon-coated copper foil production environment.

[0078] The present invention will now be described in detail with reference to the embodiments.

[0079] Example 1

[0080] A method for determining the impurity element content in a carbon-coated copper foil coating includes the following steps:

[0081] (1) Weigh m1 = 0.1 ± 0.0010 g of carbon-coated copper foil (manufacturer: Jiangxi Copper, grade: 1+6+1) using a ten-thousandth balance and place it in a 100 mL beaker.

[0082] (2) Add 2 mL of nitric acid solution (64 wt%, GR) and 8 mL of sulfuric acid solution (98 wt%, GR) to the beaker in step (1). Heat the solution at 180°C on a graphite heating plate until it reduces to 4 mL. Then transfer the solution to a 100 mL glass volumetric flask and record it as the carbon-coated copper foil test solution.

[0083] (3) At the same time, a process blank is made by replacing the carbon-coated copper foil with the same mass of deionized water as in step (1) and placing it in a 100mL beaker.

[0084] (4) Add 2 mL of nitric acid solution (64 wt%, GR) and 8 mL of sulfuric acid solution (98 wt%, GR) to the beaker in step (3), heat it at 180°C on a graphite heating plate until it reduces to 4 mL, then transfer it to a 100 mL glass volumetric flask and record it as the blank test solution for the carbon-coated copper foil process.

[0085] (5) Weigh the base copper foil (manufacturer: Jiangxi Copper, grade 1+6+1) that is identical to the base copper foil in the carbon-coated copper foil in step (1) in terms of area, thickness, volume, density, mass, manufacturer and production batch, using a ten-thousandth balance, and place it in a 100mL beaker. Record the mass of the base copper foil as m2, and the unit is g.

[0086] (6) Add 2 mL of nitric acid solution (64 wt%, GR) and 8 mL of sulfuric acid solution (98 wt%, GR) to the beaker in step (5), heat it at 180°C on a graphite heating plate until it reduces to 4 mL, then transfer it to a 100 mL glass volumetric flask and record it as the test solution of the copper foil matrix.

[0087] (7) At the same time, a process blank is made by replacing the base copper foil with the same mass of deionized water as the base copper foil in step (5) and placing it in a 100mL beaker.

[0088] (8) Add 2 mL of nitric acid solution (64 wt%, GR) and 8 mL of sulfuric acid solution (98 wt%, GR) to the beaker in step (7), heat it at 180°C on a graphite heating plate until it reduces to 4 mL, then transfer it to a 100 mL glass volumetric flask and record it as the blank test solution for the copper foil substrate process.

[0089] (9) Turn on the inductively coupled plasma atomic emission spectrometer, set the plasma flow rate to 15 L / min, the nebulizer gas flow rate to 0.8 L / min, the pump speed to 1.5 mL / min, the delay time to 45 s, the number of tests to 2, and the nebulizer back pressure to 300 MPa. Take different volumes of gradient concentration standard solutions of multi-metal elements (Fe, Cr, Ni, Zn) and prepare standard solutions of 1.0 μg / mL, 2.0 μg / mL, 5.0 μg / mL, 10.0 μg / mL, and 15.0 μg / mL respectively to obtain the standard curves of multi-metal elements (Fe, Cr, Ni, Zn), and fit the standard curve equations. The linearity is ≥0.999.

[0090] (10) Under the same test conditions as in step (9), the mass concentration of impurity metal elements in the blank test solution of carbon-coated copper foil, the blank test solution of base copper foil, the test solution of carbon-coated copper foil, and the test solution of base copper foil were determined by inductively coupled plasma atomic emission spectrometry. Then, according to the standard curve of step (9), the mass percentage a of impurity metal elements in the carbon-coated copper foil in step (1), the mass percentage b of impurity metal elements in the blank test solution of carbon-coated copper foil in steps (3) and (4), the mass percentage c of impurity metal elements in the base copper foil in step (5), and the mass percentage d of impurity metal elements in the blank test solution of base copper foil in steps (7) and (8), respectively, were obtained.

[0091] (11) Calculate the mass percentage e of each impurity metal element in the carbon-coated copper foil coating layer according to formula (1), in ppm.

[0092] e={(ab)×m1-(cd)×m2} / (m1-m2) (1).

[0093] Step (1) requires 6 parallel samples, labeled #1, #2, #3, #4, #5, and #6 respectively. The content of the corresponding impurity elements in these 6 groups is tested, and the test results are shown in Table 1-3.

[0094] Table 1. Mass percentage of impurity elements in carbon-coated copper foil

[0095] Serial Number <![CDATA[Mass m1 (g)]]> Fe Cr Ni Zn Process blank / 0.002 0 0.001 0.001 #1 0.1001 10.208 10.996 8.146 19.586 #2 0.0992 10.599 11.588 8.116 21.796 #3 0.1006 10.301 10.336 7.811 21.203 #4 0.1007 10.848 11.347 7.974 21.458 #5 0.1002 10.986 11.456 8.306 21.137 #6 0.1001 10.508 10.579 8.415 21.346 average value / 10.575 11.050 8.128 21.088 Standard deviation / 0.303 0.505 0.219 0.772 COV (%) / 2.9％ 4.6％ 2.7％ 3.7％

[0096] Table 2. Mass percentage of impurity elements in the base copper foil

[0097] Serial Number <![CDATA[Mass m2 (g)]]> Fe Cr Ni Zn Process blank / 0.002 0.001 0.001 0 #1 0.0959 10.265 11.235 8.146 20.176 #2 0.0952 10.658 11.834 8.099 22.463 #3 0.0959 10.334 10.568 7.823 21.948 #4 0.0963 10.908 11.614 7.966 22.176 #5 0.0957 11.075 11.732 8.325 21.846 #6 0.0956 10.573 10.836 8.431 22.063 average value / 10.636 11.303 8.132 21.779 Standard deviation / 0.316 0.515 0.224 0.813 COV (%) / 3.0％ 4.6％ 2.8％ 3.7％

[0098] Table 3. Mass percentage of impurity elements in carbon-coated copper foil coating layer (e)

[0099] Serial Number Fe Cr Ni Zn #1 8.906 5.539 8.146 6.114 #2 9.195 5.733 8.521 5.921 #3 9.628 5.602 7.566 6.002 #4 9.535 5.503 8.149 5.744 #5 9.093 5.586 7.902 6.059 #6 9.127 5.119 8.075 6.114 average value 9.247 5.514 8.060 5.992 Standard deviation 0.277 0.209 0.315 0.142 COV (%) 3.0％ 3.8％ 3.9％ 2.4％

[0100] The values ​​in Table 3, i.e., the content of impurity elements in the carbon-coated copper foil coating, can be calculated from the data in Tables 1 and 2 using formula (1). The covariance (COV) of the impurity elements in groups #1-#6 in Tables 1 and 2 is <5%, and the COV of the impurity elements in groups #1-#6 obtained after calculation in Table 3 is <5%, indicating that the test method is very stable and the test results are accurate and effective.

[0101] Example 2

[0102] A method for determining the impurity element content in a carbon-coated copper foil coating includes the following steps:

[0103] (1) Weigh m1 = 0.1 ± 0.0010 g of carbon-coated copper foil (manufacturer: Jiangxi Copper, grade: 1+6+1) using a ten-thousandth balance and place it in a 100 mL beaker.

[0104] (2) Add 2 mL of nitric acid solution (64 wt%, GR) and 8 mL of sulfuric acid solution (98 wt%, GR) to the beaker in step (1). Heat the solution at 180°C on a graphite heating plate until it reduces to 4 mL. Then transfer the solution to a 100 mL glass volumetric flask and record it as the test solution coated with carbon copper foil.

[0105] (3) At the same time, a process blank is made by replacing the carbon-coated copper foil with the same mass of deionized water as in step (1) and placing it in a 100mL beaker.

[0106] (4) Add 2 mL of nitric acid solution (64 wt%, GR) and 8 mL of sulfuric acid solution (98 wt%, GR) to the beaker in step (3), heat it at 180°C on a graphite heating plate until it reduces to 4 mL, then transfer it to a 100 mL glass volumetric flask and record it as the blank test solution for the carbon-coated copper foil process.

[0107] (5) Weigh out a carbon-coated copper foil of the same mass as in step (1) with mass m1, put it into a muffle furnace, calcine the carbon-coated copper foil at 900℃ for 12h, take it out and cool it to room temperature in a desiccator to obtain the base copper foil in the carbon-coated copper foil. Weigh the mass of the base copper foil using a ten-thousandth balance and record it as m2, g. Place the base copper foil in a 100mL beaker.

[0108] (6) Add 2 mL of nitric acid solution (64 wt%, GR) and 8 mL of sulfuric acid solution (98 wt%, GR) to the beaker in step (5), heat it at 180°C on a graphite heating plate until it reduces to 4 mL, then transfer it to a 100 mL glass volumetric flask and record it as the test solution of the copper foil matrix.

[0109] (7) At the same time, a process blank is made by replacing the base copper foil with the same mass of deionized water as the base copper foil in step (5) and placing it in a 100mL beaker.

[0110] (8) Add 2 mL of nitric acid solution (64 wt%, GR) and 8 mL of sulfuric acid solution (98 wt%, GR) to the beaker in step (7), heat it at 180°C on a graphite heating plate until it reduces to 4 mL, then transfer it to a 100 mL glass volumetric flask and record it as the blank test solution for the copper foil substrate process.

[0111] (9) Turn on the inductively coupled plasma atomic emission spectrometer, set the plasma flow rate to 15 L / min, the nebulizer gas flow rate to 0.8 L / min, the pump speed to 1.5 mL / min, the delay time to 45 s, the number of tests to 2, and the nebulizer back pressure to 300 kPa. Take different volumes of gradient concentration standard solutions of multi-metal elements (Fe, Cr, Ni, Zn) and prepare standard solutions of 1.0 μg / mL, 2.0 μg / mL, 5.0 μg / mL, 10.0 μg / mL, and 15.0 μg / mL respectively to obtain the standard curves of multi-metal elements (Fe, Cr, Ni, Zn), and fit the standard curve equations. The linearity is ≥0.999.

[0112] (10) Under the same test conditions as in step (9), the mass concentration of impurity metal elements in the blank test solution of carbon-coated copper foil, the blank test solution of base copper foil, the test solution of carbon-coated copper foil, and the test solution of base copper foil were determined by inductively coupled plasma atomic emission spectrometry. Then, according to the standard curve of step (9), the mass percentage a of impurity metal elements in the carbon-coated copper foil in step (1), the mass percentage b of impurity metal elements in the blank test solution of carbon-coated copper foil in steps (3) and (4), the mass percentage c of impurity metal elements in the base copper foil in step (5), and the mass percentage d of impurity metal elements in the blank test solution of base copper foil in steps (7) and (8), respectively, were obtained.

[0113] (11) Calculate the mass percentage e of each impurity metal element in the carbon-coated copper foil coating layer according to formula (1), in ppm.

[0114] e={(ab)×m1-(cd)×m2} / (m1-m2) (1).

[0115] Step (1) requires 6 parallel samples, labeled #1, #2, #3, #4, #5, and #6 respectively. The content of the corresponding impurity elements in these 6 groups is tested, and the test results are shown in Table 4-6.

[0116] Table 4. Mass percentage of impurity elements in carbon-coated copper foil

[0117] Serial Number <![CDATA[Mass m1 (g)]]> Fe Cr Ni Zn Process blank / 0.003 0 0 0.001 #1 0.1001 10.121 11.827 8.362 23.124 #2 0.1001 10.732 10.696 7.584 24.386 #3 0.1003 10.575 10.974 7.702 23.049 #4 0.1001 10.656 11.422 8.158 23.145 #5 0.1004 10.519 11.731 7.673 23.174 #6 0.1008 10.103 11.179 8.247 22.163 average value / 10.451 11.305 7.954 23.174 Standard deviation / 0.272 0.439 0.339 0.709 COV (%) / 2.6％ 3.9％ 4.3％ 3.1％

[0118] Table 5. Mass percentage of impurity elements in the base copper foil

[0119] Serial Number <![CDATA[Mass m2 (g)]]> Fe Cr Ni Zn Process blank / 0.001 0 0 0.001 #1 0.0956 10.207 12.137 8.367 23.948 #2 0.0955 10.845 10.969 7.594 25.279 #3 0.0958 10.669 11.235 7.685 23.847 #4 0.0954 10.734 11.743 8.192 24.001 #5 0.0958 10.619 12.064 7.658 24.019 #6 0.0961 10.184 11.469 8.258 22.972 average value / 10.543 11.603 7.959 24.011 Standard deviation / 0.280 0.463 0.349 0.737 COV (%) / 2.7％ 4.0％ 4.4％ 3.1％

[0120] Table 6. Mass percentage of impurity elements in carbon-coated copper foil coating layer (e)

[0121] Serial Number Fe Cr Ni Zn #1 8.294 5.241 8.256 5.619 #2 8.386 5.028 7.376 5.847 #3 8.574 5.418 8.064 6.060 #4 9.073 4.906 7.468 5.770 #5 8.436 4.796 7.985 5.576 #6 8.447 5.249 8.022 5.622 average value 8.535 5.106 7.862 5.749 Standard deviation 0.279 0.236 0.354 0.184 COV (%) 3.3％ 4.6％ 4.5％ 3.2％

[0122] The values ​​in Table 6, i.e., the content of impurity elements in the carbon-coated copper foil coating, can be calculated from the data in Tables 4 and 5 using formula (1). The COV of impurity elements in groups #1-#6 in Tables 4 and 5 is less than 5%, and the COV of impurity elements in groups #1-#6 in Table 6 after calculation is also less than 5%, indicating that the test method is very stable and the test results are accurate and effective.

[0123] Comparative Example 1

[0124] A method for determining the impurity element content in a carbon-coated copper foil coating includes the following steps:

[0125] (1) Weigh m1 = 0.1 ± 0.0010 g of carbon-coated copper foil (manufacturer: Jiangxi Copper, grade: 1+6+1) using a ten-thousandth balance. Scrape off the coating layer on the carbon-coated copper foil with a scraper. Weigh the mass m3 of the scraped coating powder using a ten-thousandth balance. Then place the coating powder in a 100 mL beaker.

[0126] (2) Add 2 mL of nitric acid solution (64 wt%, GR) and 8 mL of sulfuric acid solution (98 wt%, GR) to the beaker in step (1). Heat the solution at 180°C on a graphite heating plate until it reduces to 4 mL. Then transfer the solution to a 100 mL glass volumetric flask and record it as the test solution with carbon-coated copper foil coating.

[0127] (3) At the same time, a process blank is made by replacing the coating powder with deionized water of the same mass as the coating powder in step (1) and placing it in a 100mL beaker.

[0128] (4) Add 2 mL of nitric acid solution (64 wt%, GR) and 8 mL of sulfuric acid solution (98 wt%, GR) to the beaker in step (3), heat it at 180°C on a graphite heating plate until it reduces to 4 mL, then transfer it to a 100 mL glass volumetric flask and record it as the blank test solution for the carbon copper foil coating process.

[0129] (5) Turn on the inductively coupled plasma atomic emission spectrometer, set the plasma flow rate to 15 L / min, the nebulizer gas flow rate to 0.8 L / min, the pump speed to 1.5 mL / min, the delay time to 45 s, the number of tests to 2, and the nebulizer back pressure to 300 MPa. Take different volumes of gradient concentration standard solutions of multi-metal elements (Fe, Cr, Ni, Zn) and prepare standard solutions of 1.0 μg / mL, 2.0 μg / mL, 5.0 μg / mL, 10.0 μg / mL, and 15.0 μg / mL respectively to obtain the standard curves of multi-metal elements (Fe, Cr, Ni, Zn), and fit the standard curve equations. The linearity is ≥0.999.

[0130] (6) Under the same test conditions as in step (5), inductively coupled plasma atomic emission spectrometry is used to determine the mass concentration of impurity metal elements in the blank test solution and the test solution of the carbon-coated copper foil coating layer, respectively. Then, according to the standard curve of step (5), the mass ratio f of impurity metal elements in the carbon-coated copper foil coating layer in step (1) is obtained, with the unit being ppm. The mass ratio g of impurity metal elements in the blank test solution of the carbon-coated copper foil coating layer in steps (3) and (4) is obtained, with the unit being ppm.

[0131] (7) Calculate the actual mass percentage h of each impurity metal element in the carbon-coated copper foil coating layer according to formula (2), in ppm.

[0132] h = fg (2).

[0133] Step (1) requires 6 parallel samples, labeled #1, #2, #3, #4, #5, and #6 respectively. The content of the corresponding impurity elements in these 6 groups is tested, and the test results are shown in Table 7.

[0134] Table 7. Mass percentage of impurity elements in carbon-coated copper foil coating layer (h)

[0135] Serial Number Fe (ppm) Cr (ppm) Ni (ppm) Zn (ppm) #1 12.068 6.495 8.893 7.063 #2 10.894 8.295 8.756 6.463 #3 11.354 8.546 8.007 5.194 #4 11.034 8.434 10.145 6.746 #5 12.746 7.729 10.068 5.964 #6 11.943 7.673 9.639 5.816 average value 11.673 7.862 9.251 6.208 Standard deviation 0.707 0.762 0.841 0.682 COV (%) 6.1％ 9.7％ 9.1％ 11.0％

[0136] The content of impurity elements in groups #1-#6 in Table 7 is higher than that in Examples 1-2, and the COV of impurity elements in groups #1-#6 is >5%, indicating that the accuracy and stability of the test method are poor. This may be due to the inevitable scraping of the base copper foil when scraping the coating powder, which leads to the introduction of impurity elements into the base copper foil.

[0137] Comparative Example 2

[0138] A method for determining the impurity element content of carbon-coated copper foil includes the following steps:

[0139] (1) Weigh m1 = 0.1 ± 0.0010 g of carbon-coated copper foil (manufacturer: Jiangxi Copper, grade 1+6+1) using a ten-thousandth balance and place it in a 100 mL beaker.

[0140] (2) Add 10 mL of nitric acid solution (64 wt%, GR) to the beaker in step (1), heat it at 180 °C on a graphite heating plate until it reduces to 4 mL, filter it, transfer it to a 100 mL glass volumetric flask, and record it as the test solution coated with carbon copper foil.

[0141] (3) At the same time, a process blank is made by replacing the carbon-coated copper foil with the same mass of deionized water as in step (1) and placing it in a 100mL beaker.

[0142] (4) Add 10 mL of nitric acid solution (64 wt%, GR) to the beaker in step (3), heat it at 180 °C on a graphite heating plate until it reduces to 4 mL, then transfer it to a 100 mL glass volumetric flask and record it as the blank test solution for the carbon-coated copper foil process.

[0143] (5) Turn on the inductively coupled plasma atomic emission spectrometer, set the plasma flow rate to 15 L / min, the nebulizer gas flow rate to 0.8 L / min, the pump speed to 1.5 mL / min, the delay time to 45 s, the number of tests to 2, and the nebulizer back pressure to 300 kPa. Take different volumes of gradient concentration standard solutions of multi-metal elements (Fe, Cr, Ni, Zn) and prepare standard solutions of 1.0 μg / mL, 2.0 μg / mL, 5.0 μg / mL, 10.0 μg / mL, and 15.0 μg / mL respectively to obtain the standard curves of multi-metal elements (Fe, Cr, Ni, Zn), and fit the standard curve equations. The linearity is ≥0.999.

[0144] (6) Under the same test conditions as in step (5), inductively coupled plasma atomic emission spectrometry is used to measure the impurity metal elements in the blank test solution and the test solution of the carbon-coated copper foil in the carbon-coated copper foil process, respectively. Then, according to the standard curve in step (5), the mass percentage a of the impurity metal elements in the carbon-coated copper foil in step (1) is obtained, in ppm, and the mass percentage b of the impurity metal elements in the blank test solution of the carbon-coated copper foil in step (3) is obtained, in ppm.

[0145] (7) Calculate the actual mass percentage i of each impurity metal element in the carbon-coated copper foil according to formula (2), in ppm.

[0146] i = ab (2).

[0147] Step (1) requires 6 parallel samples, labeled #1, #2, #3, #4, #5, and #6 respectively. The content of the corresponding impurity elements in these 6 groups is tested, and the test results are shown in Table 8.

[0148] Table 8. Mass percentage of impurity elements in carbon-coated copper foil

[0149] Serial Number Fe (ppm) Cr (ppm) Ni (ppm) Zn (ppm) #1 8.167 10.093 6.673 18.062 #2 9.334 11.296 6.954 19.446 #3 10.028 9.896 7.365 17.243 #4 8.139 10.374 8.037 18.02 #5 8.627 11.234 7.009 19.403 #6 8.633 12.082 8.224 19.832 average value 8.821 10.829 7.377 18.668 Standard deviation 0.733 0.845 0.627 1.031 COV (%) 8.3％ 7.8％ 8.5％ 5.5％

[0150] In Table 8, the contents of impurity elements Fe and Ni in groups #1-#6 are all lower than those in Example 1, while the contents of Cr and Zn are significantly higher than those in Example 1. Furthermore, the test deviation (COV) for impurity elements in groups #1-#6 is >5%, indicating that the test method has poor accuracy and stability. The lower Fe content is due to the use of nitric acid alone for digestion, which dissolves the base copper foil but does not completely digest the coating layer. The lower Ni content is because, although the amount of Ni dissolved in the coating layer is constant, the mass of the carbon-coated copper foil in the test object is larger than that of the coating layer in Example 1, thus reducing the Ni proportion. The higher Cr and Zn contents are due to the failure to remove the influence of the base copper foil, leading to a large amount of Cr and Zn dissolving from the base copper foil. Therefore, the method for determining the impurity element content of the carbon-coated copper foil in this comparative example is completely incomparable to the method for determining the impurity element content of the carbon-coated copper foil coating layer in Example 1 and cannot be used to determine the impurity element content in the coating layer.

[0151] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0152] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for determining the impurity element content in a carbon-coated copper foil coating, characterized in that, Includes the following steps: S1. Weigh out carbon-coated copper foil with a mass of m1; S2. Dissolve the carbon-coated copper foil using a digesting agent, then dilute and bring to a fixed volume to obtain the carbon-coated copper foil test solution; simultaneously, dissolve the blank sample from the carbon-coated copper foil process using a digesting agent, then dilute and bring to a fixed volume to obtain the blank test solution from the carbon-coated copper foil process. S3. Weigh out a base copper foil with a mass of m2, wherein the base copper foil is the same as the base copper foil in the carbon-coated copper foil; S4. Dissolve the substrate copper foil using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate copper foil test solution; simultaneously, dissolve the substrate copper foil process blank sample using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate copper foil process blank test solution; wherein, the digesting agent in steps S2 and S4 is a mixture of nitric acid solution and sulfuric acid solution; the carbon-coated copper foil process blank sample in step S2 and the substrate copper foil process blank sample in step S4 are deionized water, distilled water or ultrapure water; S5. The concentrations of impurity elements in the blank test solution of the carbon-coated copper foil process, the blank test solution of the substrate copper foil process, the test solution of the carbon-coated copper foil, and the test solution of the substrate copper foil are determined by inductively coupled plasma atomic emission spectrometry. Then, the mass percentages of impurity elements in the carbon-coated copper foil (a), the blank test solution of the carbon-coated copper foil process (b), the substrate copper foil (c), and the blank test solution of the substrate copper foil process (d) are obtained according to the standard curve. Then, the mass percentage of impurity elements in the coating layer of the carbon-coated copper foil (e) is calculated according to formula (1). e ={(ab)×m1-(cd)×m2} / (m1- m2) (1) In this context, m1 and m2 are in g; a, b, c, d, and e are all in ppm.

2. The method for determining the impurity element content of the carbon-coated copper foil coating layer according to claim 1, characterized in that, The base copper foil mentioned in step S3 has the same area, thickness, volume, density, mass, manufacturer, and production batch as the base copper foil in the carbon-coated copper foil.

3. The method for determining the impurity element content of the carbon-coated copper foil coating layer according to claim 1, characterized in that, Replace step S3 with: weigh a carbon-coated copper foil with a mass of m1, calcine the carbon-coated copper foil to obtain the base copper foil in the carbon-coated copper foil, and record the mass of the base copper foil as m2.

4. The method for determining the impurity element content of the carbon-coated copper foil coating layer according to claim 3, characterized in that, In step S3, the carbon-coated copper foil is calcined at 350-900℃ for 8-24 hours.

5. The method for determining the impurity element content of the carbon-coated copper foil coating layer according to claim 3, characterized in that, The carbon-coated copper foil is calcined, then wiped and blown clean.

6. The method for determining the impurity element content of the carbon-coated copper foil coating layer according to claim 1 or 3, characterized in that, The nitric acid solution has a mass concentration of 60 wt% or more, the sulfuric acid solution has a mass concentration of 95 wt% or more, and the volume ratio of the nitric acid solution to the sulfuric acid solution is (2-10):(8-10).

7. The method for determining the impurity element content of the carbon-coated copper foil coating layer according to claim 1 or 3, characterized in that, Dissolution is carried out at 160-400℃ in steps S2 and S4.

8. The method for determining the impurity element content of the carbon-coated copper foil coating layer according to claim 1 or 3, characterized in that, The test conditions for the inductively coupled plasma atomic emission spectrometer in step S5 are as follows: plasma flow rate of 12-15 L / min, nebulizer gas flow rate of 0.6-0.8 L / min, pump speed of 1.5 mL / min, delay time of 40-60 s, number of tests of 2-4, and nebulizer back pressure of 280-320 kPa.

9. The method for determining the impurity element content of the carbon-coated copper foil coating layer according to claim 1 or 3, characterized in that, The impurity elements include at least one of Fe, Cr, Ni, Zn, Li, P, Al, S, Ti, V, Si, B, Pb, Ca, Na, and K.