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

Abstract

The application provides a method for determining the content of impurity elements in a carbon-coated aluminum 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 aluminum foil coating layer comprises the following steps: firstly, dissolving the carbon-coated aluminum foil by using a digestion agent to measure the mass proportion a of impurity elements in the carbon-coated aluminum 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 aluminum foil; secondly, taking another matrix aluminum foil which is the same as the matrix aluminum foil in the carbon-coated aluminum foil or taking the matrix aluminum foil in the carbon-coated aluminum foil after calcination, dissolving the matrix aluminum foil by using the digestion agent to measure the mass proportion c of impurity elements in the matrix aluminum 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 aluminum foil; and finally, combining formula (1) to calculate the mass proportion e of impurity elements in the coating layer of the carbon-coated aluminum foil. The method for determining the content of impurity elements in the carbon-coated aluminum foil coating layer can accurately test the content of each element in the carbon-coated aluminum 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 aluminum 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 lithium-ion batteries include four parts: positive electrode, negative electrode, separator, and electrolyte. The positive electrode includes the positive electrode current collector and the positive electrode active material coated on the surface of the positive electrode current collector. Currently, the positive electrode current collector is usually made of carbon-coated aluminum foil.

[0003] For example, patent application CN106602076A discloses carbon-coated aluminum foil, its preparation method, and its application. This carbon-coated aluminum foil consists of an aluminum foil and a Super P conductive layer, a graphene conductive layer, and a mixed conductive layer sequentially disposed along at least one surface of the aluminum foil. The mixed conductive layer contains at least two conductive agents selected from VGCF, CNT, and Super P. Another example is patent application CN113054198A, which discloses a carbon-coated aluminum foil, its preparation method, and its application. This carbon-coated aluminum foil includes an aluminum foil substrate and a carbon coating layer; the carbon coating layer is obtained by coating and curing a composite slurry; the composite slurry, by mass percentage, comprises: 20-25% binder, 5-10% conductive agent, 0.3-0.8% calcium hydroxide, and the balance being solvent; the solid content of the composite slurry is 12-13%; and the pH of the composite slurry is 3-5.

[0004] As can be seen, the substrate of carbon-coated aluminum foil is aluminum foil, and the aluminum foil is coated with well-dispersed conductive carbon black or carbon-coated particles. Carbon-coated aluminum foil is mainly used in lithium iron phosphate power batteries and has advantages such as improving battery energy density, suppressing battery polarization, reducing battery internal resistance, increasing battery cycle life, and improving battery material processing performance.

[0005] In lithium-ion batteries, the content of impurity elements must 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 Ni, Mn, Mg, and Cr can easily be reduced and aggregated 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 lithium-ion battery raw materials and battery structures.

[0006] Carbon-coated aluminum foil is a crucial component in lithium-ion battery materials. It comes into close contact with the positive electrode active material and significantly impacts its performance. Therefore, controlling the impurity element content of the coating layer in carbon-coated aluminum 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 determine the product's quality. Additionally, some technologies directly measure the overall impurity element content of the carbon-coated aluminum foil, but this method does not eliminate the influence of impurities in the base aluminum foil and cannot accurately monitor the impurity element content of the coating layer. Summary of the Invention

[0007] 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 aluminum foil to determine the content of impurity elements in the coating powder. However, since the thickness of current carbon-coated aluminum foil is generally 8-15 μm, and the thickness of the coating layer is only about 1 μm, and the coating layer is in close contact with the substrate aluminum foil, it is easy to scrape off the substrate aluminum foil during the coating layer scraping process, mistakenly including impurities from the substrate aluminum 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 aluminum foil.

[0008] 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 aluminum foil coating.

[0009] This invention provides a method for determining the impurity element content in the coating layer of carbon-coated aluminum foil, comprising the following steps:

[0010] S1. Weigh out carbon-coated aluminum foil with a mass of m1;

[0011] S2. Dissolve the carbon-coated aluminum foil using a digesting agent, then dilute and bring to a fixed volume to obtain the carbon-coated aluminum foil test solution; simultaneously, dissolve the blank sample from the carbon-coated aluminum foil process using a digesting agent, then dilute and bring to a fixed volume to obtain the blank test solution from the carbon-coated aluminum foil process.

[0012] S3. Weigh out a base aluminum foil with a mass of m2, wherein the base aluminum foil is the same as the base aluminum foil in the carbon-coated aluminum foil;

[0013] S4. Dissolve the substrate aluminum foil using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate aluminum foil test solution; simultaneously, dissolve the substrate aluminum foil process blank sample using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate aluminum foil process blank test solution;

[0014] S5. The concentrations of impurity elements in the blank test solution of the carbon-coated aluminum foil process, the blank test solution of the substrate aluminum foil process, the test solution of the carbon-coated aluminum foil, and the test solution of the substrate aluminum foil are determined using an inductively coupled plasma atomic emission spectrometer. Then, the mass percentages of impurity elements in the carbon-coated aluminum foil (a), the blank test solution of the carbon-coated aluminum foil process (b), the substrate aluminum foil (c), and the blank test solution of the substrate aluminum 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 aluminum foil (e) is calculated according to formula (1).

[0015] e={(ab)×m1-(cd)×m2} / (m1-m2) (1)

[0016] In this context, m1 and m2 are in g; a, b, c, d, and e are all in ppm.

[0017] The advantages and technical effects of the method for determining the impurity element content of the carbon-coated aluminum 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 aluminum foil coating layer, which is crucial for raw material production, lithium battery incoming material monitoring, mechanism analysis, etc.

[0018] Preferably, the base aluminum foil in step S3 has the same area, thickness, volume, density, mass, manufacturer, and production batch as the base aluminum foil in the carbon-coated aluminum foil.

[0019] Preferably, the digesting agent in steps S2 and S4 comprises a mixture of hydrochloric acid solution, nitric acid solution and sulfuric acid solution.

[0020] Preferably, the hydrochloric acid solution has a mass concentration of 35 wt% or more, 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 hydrochloric acid solution, the nitric acid solution, and the sulfuric acid solution is (2-8):(2-8):(8-10).

[0021] Preferably, the dissolution is carried out at 160-400°C in steps S2 and S4.

[0022] Preferably, the blank sample of the carbon-coated aluminum foil process in step S2 and the blank sample of the substrate aluminum foil process in step S4 include deionized water, distilled water or ultrapure water.

[0023] 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.

[0024] Preferably, the impurity element includes at least one selected from Ni, Mn, Mg, Cr, Li, Fe, P, Cu, Zn, S, Ti, V, Si, B, Pb, Ca, Na, and K.

[0025] In addition, the present invention also provides another method for determining the impurity element content of carbon-coated aluminum foil coating, comprising the following steps:

[0026] S1. Weigh out carbon-coated aluminum foil with a mass of m1;

[0027] S2. Dissolve the carbon-coated aluminum foil using a digesting agent, then dilute and bring to a fixed volume to obtain the carbon-coated aluminum foil test solution; simultaneously, dissolve the blank sample from the carbon-coated aluminum foil process using a digesting agent, then dilute and bring to a fixed volume to obtain the blank test solution from the carbon-coated aluminum foil process.

[0028] S3. Weigh out a carbon-coated aluminum foil with a mass of m1, and calcine the carbon-coated aluminum foil to obtain the base aluminum foil in the carbon-coated aluminum foil. The mass of the base aluminum foil is recorded as m2.

[0029] S4. Dissolve the substrate aluminum foil using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate aluminum foil test solution; simultaneously, dissolve the substrate aluminum foil process blank sample using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate aluminum foil process blank test solution;

[0030] S5. The concentrations of impurity elements in the blank test solution of the carbon-coated aluminum foil process, the blank test solution of the substrate aluminum foil process, the test solution of the carbon-coated aluminum foil, and the test solution of the substrate aluminum foil are determined using an inductively coupled plasma atomic emission spectrometer. Then, the mass percentages of impurity elements in the carbon-coated aluminum foil (a), the blank test solution of the carbon-coated aluminum foil process (b), the substrate aluminum foil (c), and the blank test solution of the substrate aluminum 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 aluminum foil (e) is calculated according to formula (1).

[0031] e={(ab)×m1-(cd)×m2} / (m1-m2) (1)

[0032] In this context, m1 and m2 are in g; a, b, c, d, and e are all in ppm.

[0033] The advantages and technical effects of the method for determining the impurity element content of the carbon-coated aluminum 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 aluminum foil coating layer, which is crucial for raw material production, lithium battery incoming material monitoring, mechanism analysis, etc.

[0034] Preferably, in step S3, the carbon-coated aluminum foil is calcined at 350-600°C for 8-24 hours.

[0035] Preferably, the carbon-coated aluminum foil is calcined before being wiped and blown clean.

[0036] Preferably, the digesting agent in steps S2 and S4 comprises a mixture of hydrochloric acid solution, nitric acid solution and sulfuric acid solution.

[0037] Preferably, the hydrochloric acid solution has a mass concentration of 35 wt% or more, 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 hydrochloric acid solution, the nitric acid solution, and the sulfuric acid solution is (2-8):(2-8):(8-10).

[0038] Preferably, the dissolution is carried out at 160-400°C in steps S2 and S4.

[0039] Preferably, the blank sample of the carbon-coated aluminum foil process in step S2 and the blank sample of the substrate aluminum foil process in step S4 include deionized water, distilled water or ultrapure water.

[0040] 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.

[0041] Preferably, the impurity element includes at least one selected from Ni, Mn, Mg, Cr, Li, Fe, P, Cu, Zn, S, Ti, V, Si, B, Pb, Ca, Na, and K. Detailed Implementation

[0042] The present invention will now be described in detail. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0043] First aspect

[0044] The first aspect of this invention provides a method for determining the impurity element content of a carbon-coated aluminum foil coating, comprising the following steps:

[0045] S1. Weigh out carbon-coated aluminum foil with a mass of m1;

[0046] S2. Dissolve the carbon-coated aluminum foil using a digesting agent, then dilute and bring to a fixed volume to obtain the carbon-coated aluminum foil test solution; simultaneously, dissolve the blank sample from the carbon-coated aluminum foil process using a digesting agent, then dilute and bring to a fixed volume to obtain the blank test solution from the carbon-coated aluminum foil process.

[0047] S3. Weigh out a base aluminum foil with a mass of m2, wherein the base aluminum foil is the same as the base aluminum foil in the carbon-coated aluminum foil;

[0048] S4. Dissolve the substrate aluminum foil using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate aluminum foil test solution; simultaneously, dissolve the substrate aluminum foil process blank sample using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate aluminum foil process blank test solution;

[0049] S5. The concentrations (mass concentration or molar concentration) of impurity elements in the blank test solution of the carbon-coated aluminum foil process, the blank test solution of the substrate aluminum foil process, the test solution of the carbon-coated aluminum foil, and the test solution of the substrate aluminum foil are measured using an inductively coupled plasma atomic emission spectrometer. Then, the mass percentages of impurity elements in the carbon-coated aluminum foil process blank sample (a), the carbon-coated aluminum foil process blank sample (b), the substrate aluminum foil process blank sample (c), and the substrate aluminum foil process blank sample (d) are obtained according to the standard curve. Finally, the mass percentage of impurity elements in the coating layer of the carbon-coated aluminum foil (e) is calculated according to formula (1).

[0050] e={(ab)×m1-(cd)×m2} / (m1-m2) (1)

[0051] In this context, m1 and m2 are in g; a, b, c, d, and e are all in ppm.

[0052] Working principle: This invention first uses a digesting agent to dissolve the carbon-coated aluminum foil. The mass percentage (a) of impurity elements in the carbon-coated aluminum 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 aluminum foil is measured in the same manner. Then, another base aluminum foil identical to the base aluminum foil used in step S1 is taken and dissolved again using a digesting agent. The mass percentage (c) of impurity elements in this base aluminum 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 aluminum foil is measured in the same manner. Finally, the mass percentage (e) of impurity elements in the coating layer of the carbon-coated aluminum foil is calculated using formula (1). Compared to the method of scraping the coating layer from the carbon-coated aluminum foil and then measuring the impurity element content, the measurement method of this invention provides more accurate and effective test results.

[0053] Preferably, the base aluminum foil in step S3 has the same area, thickness, volume, density, mass, manufacturer, and production batch as the base aluminum foil in the carbon-coated aluminum foil. This ensures that the impurity element content of the base aluminum foil taken in step S3 is exactly the same as the impurity element content of the carbon-coated aluminum 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 aluminum foil coating.

[0054] Preferably, the digesting agent in steps S2 and S4 comprises a mixture of hydrochloric acid solution, nitric acid solution, and sulfuric acid solution. In step S2, the hydrochloric acid is mainly used to dissolve the base aluminum foil in the carbon-coated aluminum foil, while the nitric acid and sulfuric acid are mainly used to dissolve the coating layer in the carbon-coated aluminum foil. Although only the base aluminum 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.

[0055] More preferably, the hydrochloric acid solution has a mass concentration of 35 wt% or higher, the nitric acid solution has a mass concentration of 60 wt% or higher, and the sulfuric acid solution has a mass concentration of 95 wt% or higher, with a volume ratio of (2-8):(2-8):(8-10). When the concentrations and volume ratios of the hydrochloric acid, nitric acid, and sulfuric acid solutions are within the above ranges, the digesting agent can completely dissolve the carbon-coated aluminum foil and the base aluminum foil, thereby improving the accuracy of the test results for the impurity element content of the carbon-coated aluminum foil coating and avoiding the problem of low test results for the impurity element content of the carbon-coated aluminum foil coating due to incomplete carbon dissolution. Further preferably, the hydrochloric acid solution has a mass concentration of 36-68%, 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.

[0056] Preferably, dissolution in steps S2 and S4 is carried out at 160-400℃. In steps S2 and S4, the digesting agent dissolves through a digestion reaction on the carbon-coated aluminum foil or the base aluminum 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.

[0057] Preferably, the blank samples of the carbon-coated aluminum foil process in step S2 and the blank samples of the substrate aluminum 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 aluminum foil, all other conditions are consistent with the preparation process of the test solution for the carbon-coated aluminum foil. In step S4, except for using water instead of the substrate aluminum foil, all other conditions are consistent with the preparation process of the test solution for the substrate aluminum 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 aluminum foil and the substrate aluminum foil, thereby improving the accuracy of the test results for the impurity element content of the carbon-coated aluminum foil coating.

[0058] 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 aluminum foil coating layer.

[0059] It should be noted that the impurity elements mentioned in this invention include at least one of Ni, Mn, Mg, Cr, Li, Fe, P, Cu, Zn, 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 aluminum foil production environment.

[0060] Second aspect

[0061] A second aspect of the present invention provides a method for determining the impurity element content of a carbon-coated aluminum foil coating, comprising the following steps:

[0062] S1. Weigh out carbon-coated aluminum foil with a mass of m1;

[0063] S2. Dissolve the carbon-coated aluminum foil using a digesting agent, then dilute and bring to a fixed volume to obtain the carbon-coated aluminum foil test solution; simultaneously, dissolve the blank sample from the carbon-coated aluminum foil process using a digesting agent, then dilute and bring to a fixed volume to obtain the blank test solution from the carbon-coated aluminum foil process.

[0064] S3. Weigh out a carbon-coated aluminum foil with a mass of m1, and calcine the carbon-coated aluminum foil to obtain the base aluminum foil in the carbon-coated aluminum foil. The mass of the base aluminum foil is recorded as m2.

[0065] S4. Dissolve the substrate aluminum foil using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate aluminum foil test solution; simultaneously, dissolve the substrate aluminum foil process blank sample using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate aluminum foil process blank test solution;

[0066] S5. The concentrations (mass concentration or molar concentration) of impurity elements in the blank test solution of the carbon-coated aluminum foil process, the blank test solution of the substrate aluminum foil process, the test solution of the carbon-coated aluminum foil, and the test solution of the substrate aluminum foil are measured using an inductively coupled plasma atomic emission spectrometer. Then, the mass percentages of impurity elements in the carbon-coated aluminum foil process blank sample (a), the carbon-coated aluminum foil process blank sample (b), the substrate aluminum foil process blank sample (c), and the substrate aluminum foil process blank sample (d) are obtained according to the standard curve. Finally, the mass percentage of impurity elements in the coating layer of the carbon-coated aluminum foil (e) is calculated according to formula (1).

[0067] e={(ab)×m1-(cd)×m2} / (m1-m2) (1)

[0068] In this context, m1 and m2 are in g; a, b, c, d, and e are all in ppm.

[0069] Working principle: This invention first uses a digesting agent to dissolve the carbon-coated aluminum foil. The mass percentage (a) of impurity elements in the carbon-coated aluminum 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 aluminum foil is measured in the same manner. Then, the same carbon-coated aluminum foil as in step S1 is taken and calcined to obtain the base aluminum foil. The base aluminum foil is again dissolved using a digesting agent, and the mass percentage (c) of impurity elements in the base aluminum 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 aluminum foil is measured in the same manner. Finally, the mass percentage (e) of impurity elements in the coating layer of the carbon-coated aluminum foil is calculated using formula (1). Compared to the method of scraping the coating layer from the carbon-coated aluminum foil and then measuring the impurity element content, the measurement method of this invention provides more accurate and effective test results.

[0070] Preferably, in step S3, the carbon-coated aluminum foil is calcined at 350-600℃ 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 aluminum foil is 660℃. Therefore, to ensure complete ashing of the coating without affecting the base aluminum foil, a calcination temperature of 350-600℃ 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.

[0071] Calcination for the specified time at the temperatures described above can completely ashing the coating layer in the carbon-coated aluminum foil, resulting in the base aluminum 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, energy is wasted. Furthermore, since the melting point of the base aluminum foil is 660°C, the calcination temperature is preferably no higher than 600°C. 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.

[0072] Preferably, calcining the carbon-coated aluminum foil followed by wiping and blowing can remove residual metal oxides from the coating layer, further improving the accuracy of the test results.

[0073] Preferably, the digesting agent in steps S2 and S4 comprises a mixture of hydrochloric acid solution, nitric acid solution, and sulfuric acid solution. In step S2, the hydrochloric acid is mainly used to dissolve the base aluminum foil in the carbon-coated aluminum foil, while the nitric acid and sulfuric acid are mainly used to dissolve the coating layer in the carbon-coated aluminum foil. Although only the base aluminum 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.

[0074] More preferably, the hydrochloric acid solution has a mass concentration of 35 wt% or higher, the nitric acid solution has a mass concentration of 60 wt% or higher, and the sulfuric acid solution has a mass concentration of 95 wt% or higher. The volume ratio of the hydrochloric acid solution, the nitric acid solution, and the sulfuric acid solution is (2-8):(2-8):(8-10). Having the concentrations and volume ratios of the hydrochloric acid solution, nitric acid solution, and sulfuric acid solution within the above ranges is beneficial for improving the solubility of the carbon-coated aluminum foil and the base aluminum foil, thereby improving the accuracy of the test results for the impurity element content of the carbon-coated aluminum foil coating layer and avoiding the problem of low test results for the impurity element content of the carbon-coated aluminum foil coating layer due to incomplete carbon dissolution. Even more preferably, the hydrochloric acid solution has a mass concentration of 36-68%, 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.

[0075] Preferably, dissolution in steps S2 and S4 is carried out at 160-400℃. In steps S2 and S4, the digesting agent dissolves through a digestion reaction on the carbon-coated aluminum foil or the base aluminum 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.

[0076] Preferably, the blank samples of the carbon-coated aluminum foil process in step S2 and the blank samples of the substrate aluminum 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 aluminum foil, all other conditions are consistent with the preparation process of the test solution for the carbon-coated aluminum foil. In step S4, except for using water instead of the substrate aluminum foil, all other conditions are consistent with the preparation process of the test solution for the substrate aluminum 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 aluminum foil and the substrate aluminum foil, thereby improving the accuracy of the test results for the impurity element content of the carbon-coated aluminum foil coating.

[0077] 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 aluminum foil coating layer.

[0078] It should be noted that the impurity elements mentioned in this invention include at least one of Ni, Mn, Mg, Cr, Li, Fe, P, Cu, Zn, 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 aluminum foil production environment.

[0079] The present invention will now be described in detail with reference to the embodiments.

[0080] Example 1

[0081] A method for determining the impurity element content in a carbon-coated aluminum foil coating includes the following steps:

[0082] (1) Weigh m1 = 0.1 ± 0.0010 g of carbon-coated aluminum foil (manufacturer: Wuxing Aluminum Industry, grade: 1+13+1) using a ten-thousandth balance and place it in a 100 mL beaker.

[0083] (2) Add 2 mL of hydrochloric acid solution (37 wt%, GR), 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 on a graphite heating plate at 180°C until it reduces to 4 mL. Then transfer the solution to a 100 mL glass volumetric flask and record it as the carbon-coated aluminum foil test solution.

[0084] (3) At the same time, a process blank is made by replacing the carbon-coated aluminum foil with the same mass of deionized water as in step (1) and placing it in a 100mL beaker.

[0085] (4) Add 2 mL of hydrochloric acid solution (37 wt%, GR), 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 the solution on a graphite heating plate at 180°C until it reduces to 4 mL. Then transfer the solution to a 100 mL glass volumetric flask and record it as the blank test solution for the carbon-coated aluminum foil process.

[0086] (5) Weigh the same base aluminum foil (manufacturer: Wuxing Aluminum Industry, grade: 1+13+1) as the base aluminum foil in the carbon-coated aluminum foil in step (1) using a ten-thousandth balance. Place it in a 100mL beaker. Record the mass of the base aluminum foil as m2, and the unit is g.

[0087] (6) Add 2 mL of hydrochloric acid solution (37 wt%, GR), 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 the solution on a graphite heating plate at 180°C until it reduces to 4 mL. Then transfer the solution to a 100 mL glass volumetric flask and record it as the substrate aluminum foil test solution.

[0088] (7) At the same time, a process blank is made by replacing the base aluminum foil with the same mass of deionized water as the base aluminum foil in step (5) and placing it in a 100mL beaker.

[0089] (8) Add 2 mL of hydrochloric acid solution (37 wt%, GR), 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 the solution on a graphite heating plate at 180°C until it reduces to 4 mL. Then transfer the solution to a 100 mL glass volumetric flask and record it as the blank test solution for the aluminum foil substrate process.

[0090] (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 (Ni, Mn, Mg, Cr) 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 standard curves of multi-metal elements (Ni, Mn, Mg, Cr), and fit the standard curve equations. The linearity is ≥0.999.

[0091] (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 aluminum foil, the blank test solution of base aluminum foil, the test solution of carbon-coated aluminum foil, and the test solution of base aluminum 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 carbon-coated aluminum foil in step (1), the mass percentage b of impurity metal elements in the blank test solution of carbon-coated aluminum foil in steps (3) and (4), the mass percentage c of impurity metal elements in base aluminum foil in step (5), and the mass percentage d of impurity metal elements in the blank test solution of base aluminum foil in steps (7) and (8), respectively, were obtained.

[0092] (11) Calculate the mass percentage e of each impurity metal element in the carbon-coated aluminum foil coating layer according to formula (1), in ppm.

[0093] e={(ab)×m1-(cd)×m2} / (m1-m2) (1).

[0094] 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.

[0095] Table 1. Mass percentage of impurity elements in carbon-coated aluminum foil

[0096] Serial Number <![CDATA[Mass m1 (g)]]> Ni (ppm) Mn (ppm) Mg (ppm) Cr (ppm) Process blank / 0.004 0 0 0 #1 0.1002 21.952 26.542 12.832 12.485 #2 0.1005 22.098 24.982 11.876 12.867 #3 0.1001 21.896 27.071 12.573 11.684 #4 0.1004 22.483 26.473 12.049 12.816 #5 0.1005 22.451 27.556 11.997 12.824 #6 0.1000 21.473 26.437 12.068 12.283 average value / 22.059 26.510 12.233 12.493 Standard deviation / 0.379 0.866 0.379 0.459 COV (%) / 1.7％ 3.3％ 3.1％ 3.7％

[0097] Table 2. Mass percentage of impurity elements in the base aluminum foil

[0098] Serial Number <![CDATA[Mass m2 (g)]]> Ni (ppm) Mn (ppm) Mg (ppm) Cr (ppm) Process blank / 0.002 0 0 0 #1 0.0971 22.457 27.042 13.065 12.691 #2 0.0973 22.484 25.347 12.047 13.033 #3 0.0972 22.379 27.581 12.808 11.871 #4 0.0975 23.025 26.995 12.285 13.048 #5 0.0972 23.009 28.178 12.234 13.051 #6 0.0970 21.918 26.893 12.268 12.471 average value / 22.545 27.006 12.451 12.694 Standard deviation / 0.419 0.946 0.394 0.468 COV (%) / 1.9％ 3.5％ 3.2％ 3.7％

[0099] Table 3. Mass percentage of impurity elements in the coating layer of carbon-coated aluminum foil (e)

[0100] Serial Number Ni (ppm) Mn (ppm) Mg (ppm) Cr (ppm) #1 6.644 11.386 5.769 6.241 #2 6.967 10.674 5.173 6.360 #3 6.783 11.113 5.220 5.833 #4 7.020 11.581 5.316 6.197 #5 6.986 10.318 5.429 6.533 #6 7.085 11.693 5.601 6.204 average value 6.914 11.127 5.418 6.228 Standard deviation 0.166 0.539 0.231 0.232 COV (%) 2.4％ 4.8％ 4.3％ 3.7％

[0101] The values ​​in Table 3, i.e., the content of impurity elements in the carbon-coated aluminum foil coating layer, 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.

[0102] Example 2

[0103] A method for determining the impurity element content in a carbon-coated aluminum foil coating includes the following steps:

[0104] (1) Weigh m1 = 0.1 ± 0.0010 g of carbon-coated aluminum foil (manufacturer: Wuxing Aluminum Industry, grade: 1+13+1) using a ten-thousandth balance and place it in a 100 mL beaker.

[0105] (2) Add 2 mL of hydrochloric acid solution (37 wt%, GR), 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 on a graphite heating plate at 180°C until it reduces to 4 mL. Then transfer the solution to a 100 mL glass volumetric flask and record it as the carbon-coated aluminum foil test solution.

[0106] (3) At the same time, a process blank is made by replacing the carbon-coated aluminum foil with the same mass of deionized water as in step (1) and placing it in a 100mL beaker.

[0107] (4) Add 2 mL of hydrochloric acid solution (37 wt%, GR), 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 the solution on a graphite heating plate at 180°C until it reduces to 4 mL. Then transfer the solution to a 100 mL glass volumetric flask and record it as the blank test solution for the carbon-coated aluminum foil process.

[0108] (5) Weigh out a carbon-coated aluminum foil of the same mass as in step (1) with mass m1, put it into a muffle furnace, calcine the carbon-coated aluminum foil at 600℃ for 12h, take it out and cool it to room temperature in a desiccator to obtain the base aluminum foil in the carbon-coated aluminum foil. Weigh the mass of the base aluminum foil using a ten-thousandth balance and record it as m2 in g. Place the base aluminum foil in a 100mL beaker.

[0109] (6) Add 2 mL of hydrochloric acid solution (37 wt%, GR), 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 the solution on a graphite heating plate at 180°C until it reduces to 4 mL. Then transfer the solution to a 100 mL glass volumetric flask and record it as the substrate aluminum foil test solution.

[0110] (7) At the same time, a process blank is made by replacing the base aluminum foil with the same mass of deionized water as the base aluminum foil in step (5) and placing it in a 100mL beaker.

[0111] (8) Add 2 mL of hydrochloric acid solution (37 wt%, GR), 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 the solution on a graphite heating plate at 180°C until it reduces to 4 mL. Then transfer the solution to a 100 mL glass volumetric flask and record it as the blank test solution for the aluminum foil substrate process.

[0112] (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 (Ni, Mn, Mg, Cr) 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 standard curves of multi-metal elements (Ni, Mn, Mg, Cr), and fit the standard curve equations. The linearity is ≥0.999.

[0113] (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 aluminum foil, the blank test solution of base aluminum foil, the test solution of carbon-coated aluminum foil, and the test solution of base aluminum 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 carbon-coated aluminum foil in step (1), the mass percentage b of impurity metal elements in the blank test solution of carbon-coated aluminum foil in steps (3) and (4), the mass percentage c of impurity metal elements in base aluminum foil in step (5), and the mass percentage d of impurity metal elements in the blank test solution of base aluminum foil in steps (7) and (8), respectively, were obtained.

[0114] (11) Calculate the mass percentage e of each impurity metal element in the carbon-coated aluminum foil coating layer according to formula (1), in ppm.

[0115] e={(ab)×m1-(cd)×m2} / (m1-m2) (1).

[0116] 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.

[0117] Table 4. Mass percentage of impurity elements in carbon-coated aluminum foil

[0118] Serial Number <![CDATA[Mass m1 (g)]]> Ni (ppm) Mn (ppm) Mg (ppm) Cr (ppm) Process blank / 0.002 0 0.001 0 #1 0.0999 20.626 25.004 12.766 11.348 #2 0.1002 21.624 24.182 12.417 12.519 #3 0.1 20.678 23.924 13.632 11.292 #4 0.0995 20.784 23.499 13.183 11.343 #5 0.1003 22.051 25.258 13.626 11.421 #6 0.0989 22.074 25.427 12.879 11.812 average value / 21.306 24.549 13.084 11.623 Standard deviation / 0.689 0.788 0.488 0.478 COV (%) / 3.2％ 3.2％ 3.7％ 4.1％

[0119] Table 5. Mass percentage of impurity elements in the base aluminum foil

[0120] Serial Number <![CDATA[Mass m2 (g)]]> Ni (ppm) Mn (ppm) Mg (ppm) Cr (ppm) Process blank / 0.002 0 0.001 0 #1 0.0956 21.283 25.732 13.123 11.557 #2 0.0958 22.358 24.721 12.784 12.808 #3 0.0951 21.442 24.554 14.091 11.549 #4 0.0944 21.59 24.129 13.663 11.638 #5 0.0957 22.824 25.864 14.071 11.674 #6 0.0948 22.782 25.989 13.238 12.053 average value / 22.047 25.165 13.495 11.880 Standard deviation / 0.693 0.792 0.534 0.491 COV (%) / 3.1％ 3.1％ 4.0％ 4.1％

[0121] Table 6. Mass percentage of impurity elements in carbon-coated aluminum foil coating layer (e)

[0122] Serial Number Ni (ppm) Mn (ppm) Mg (ppm) Cr (ppm) #1 6.019 11.850 4.829 6.701 #2 5.643 12.447 4.426 6.227 #3 5.850 11.697 4.724 6.304 #4 5.865 11.838 4.298 5.883 #5 5.969 12.651 4.368 6.158 #6 5.704 12.432 4.578 6.240 average value 5.842 12.152 4.537 6.252 Standard deviation 0.146 0.403 0.210 0.265 COV (%) 2.5％ 3.3％ 4.6％ 4.2％

[0123] The values ​​in Table 6, i.e., the content of impurity elements in the carbon-coated aluminum foil coating layer, 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.

[0124] Comparative Example 1

[0125] A method for determining the impurity element content in a carbon-coated aluminum foil coating includes the following steps:

[0126] (1) Weigh m1 = 0.1 ± 0.0010 g of carbon-coated aluminum foil (manufacturer: Wuxing Aluminum Industry, grade: 1+13+1) using a ten-thousandth balance. Scrape off the coating layer on the carbon-coated aluminum 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.

[0127] (2) Add 2 mL of hydrochloric acid solution (37 wt%, GR), 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 aluminum foil coating.

[0128] (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.

[0129] (4) Add 2 mL of hydrochloric acid solution (37 wt%, GR), 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 the solution on a graphite heating plate at 180°C until it reduces to 4 mL. Then transfer the solution to a 100 mL glass volumetric flask and record it as the blank test solution for the carbon aluminum foil coating process.

[0130] (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 (Ni, Mn, Mg, Cr) 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 (Ni, Mn, Mg, Cr), and fit the standard curve equations. The linearity is ≥0.999.

[0131] (6) Under the same test conditions as in step (5), the mass concentration of impurity metal elements in the blank test liquid and the test liquid of the carbon-coated aluminum foil coating layer are determined by inductively coupled plasma atomic emission spectrometry. Then, according to the standard curve of step (5), the mass ratio f of impurity metal elements in the carbon-coated aluminum 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 liquid of the carbon-coated aluminum foil coating layer in steps (3) and (4) is obtained, with the unit being ppm.

[0132] (7) Calculate the actual mass percentage h of each impurity metal element in the carbon-coated aluminum foil coating layer according to formula (2), in ppm.

[0133] h = fg (2).

[0134] 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.

[0135] Table 7. Mass percentage of impurity elements in the coating layer of carbon-coated aluminum foil (h)

[0136] Serial Number Ni (ppm) Mn (ppm) Mg (ppm) Cr (ppm) #1 7.024 13.275 5.994 7.084 #2 7.198 14.008 5.137 6.563 #3 7.882 13.129 5.087 7.342 #4 8.014 13.680 5.473 6.943 #5 7.637 15.176 5.208 6.567 #6 7.812 13.069 5.334 6.018 average value 7.595 13.764 5.372 6.753 Standard deviation 0.398 0.797 0.335 0.470 COV (%) 5.2％ 5.8％ 6.2％ 7.0％

[0137] In Table 7, the contents of impurity elements Ni, Mn, and Cr in groups #1-#6 are all higher than those in Examples 1-2, and the COV of impurity elements in groups #1-#6 is >5%, indicating that the test method has poor accuracy and stability. This may be due to the inevitable scraping of the base aluminum foil when scraping the coating powder, which introduces impurity elements into the base aluminum foil.

[0138] Comparative Example 2

[0139] A method for determining the impurity element content of carbon-coated aluminum foil includes the following steps:

[0140] (1) Weigh m1 = 0.1 ± 0.0010 g of carbon-coated aluminum foil (manufacturer: Wuxing Aluminum Industry, grade: 1+13+1) using a ten-thousandth balance and place it in a 100 mL beaker.

[0141] (2) Add 10 mL of hydrochloric acid solution (37 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 carbon-coated aluminum foil test solution.

[0142] (3) At the same time, a process blank is made by replacing the carbon-coated aluminum foil with the same mass of deionized water as in step (1) and placing it in a 100mL beaker.

[0143] (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 aluminum foil process.

[0144] (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 (Ni, Mn, Mg, Cr) 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 (Ni, Mn, Mg, Cr), and fit the standard curve equations. The linearity is ≥0.999.

[0145] (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 liquid and the test liquid of the carbon-coated aluminum foil coating process, respectively. Then, according to the standard curve of step (5), the mass percentage a of the impurity metal elements in the carbon-coated aluminum foil in step (1) is obtained, with the unit being ppm, and the mass percentage b of the impurity metal elements in the blank test liquid of the carbon-coated aluminum foil in step (3) is obtained, with the unit being ppm.

[0146] (7) Calculate the actual mass percentage i of each impurity metal element in the carbon-coated aluminum foil according to formula (2), in ppm.

[0147] i = ab (2).

[0148] 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.

[0149] Table 8. Mass percentage of impurity elements in carbon-coated aluminum foil

[0150] Serial Number Ni (ppm) Mn (ppm) Mg (ppm) Cr (ppm) #1 19.386 19.176 10.102 8.769 #2 23.467 16.023 10.943 7.551 #3 21.146 17.428 9.117 7.038 #4 21.743 19.994 9.864 8.165 #5 19.917 18.32 8.62 9.007 #6 21.005 18.367 9.735 8.724 average value 21.111 18.218 9.730 8.209 Standard deviation 1.440 1.382 0.804 0.777 COV (%) 6.8％ 7.6％ 8.3％ 9.5％

[0151] In Table 8, the contents of impurity elements in groups #1-#6 are all higher than those in Example 1, and the COV of impurity elements in groups #1-#6 is >5%, indicating that the accuracy and stability of this test method are poor. The reasons for this are mainly twofold: First, the influence of the substrate aluminum foil was not removed, leading to the dissolution of impurities in the substrate aluminum foil. This method is completely incomparable to the method for determining the impurity element content in the carbon-coated aluminum foil coating layer in Example 1 and cannot be used to determine the impurity element content in the coating layer. Second, although hydrochloric acid was used alone for digestion, while dissolving the substrate aluminum foil, the carbon in the coating layer was not completely digested, resulting in lower test results and larger test deviations.

[0152] 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.

[0153] 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 aluminum foil coating, characterized in that, Includes the following steps: S1. Weigh out carbon-coated aluminum foil with a mass of m1; S2. Dissolve the carbon-coated aluminum foil using a digesting agent, then dilute and bring to a fixed volume to obtain the carbon-coated aluminum foil test solution; simultaneously, dissolve the blank sample from the carbon-coated aluminum foil process using a digesting agent, then dilute and bring to a fixed volume to obtain the blank test solution from the carbon-coated aluminum foil process. S3. Weigh out a base aluminum foil with a mass of m2, wherein the base aluminum foil is the same as the base aluminum foil in the carbon-coated aluminum foil; S4. Dissolve the substrate aluminum foil using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate aluminum foil test solution; simultaneously, dissolve the substrate aluminum foil process blank sample using the digesting agent, then dilute and bring to a fixed volume to obtain the substrate aluminum foil process blank test solution; wherein, the digesting agent in steps S2 and S4 includes a mixture of hydrochloric acid solution, nitric acid solution and sulfuric acid solution; S5. The concentrations of impurity elements in the blank test solution of the carbon-coated aluminum foil process, the blank test solution of the substrate aluminum foil process, the test solution of the carbon-coated aluminum foil, and the test solution of the substrate aluminum foil are determined by inductively coupled plasma atomic emission spectrometry. Then, the mass percentages of impurity elements in the carbon-coated aluminum foil (a), the blank test solution of the carbon-coated aluminum foil process (b), the substrate aluminum foil (c), and the blank test solution of the substrate aluminum 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 aluminum 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 aluminum foil coating layer according to claim 1, characterized in that, The base aluminum foil mentioned in step S3 has the same area, thickness, volume, density, mass, manufacturer, and production batch as the base aluminum foil in the carbon-coated aluminum foil.

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

4. The method for determining the impurity element content of the carbon-coated aluminum foil coating layer according to claim 3, characterized in that, In step S3, the carbon-coated aluminum foil is calcined at 350-600℃ for 8-24 hours.

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

6. The method for determining the impurity element content of the carbon-coated aluminum foil coating layer according to claim 1 or 3, characterized in that, In steps S2 and S4, the mass concentration of the hydrochloric acid solution is 35 wt% or more, 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 hydrochloric acid solution, the nitric acid solution, and the sulfuric acid solution is (2-8):(2-8):(8-10).

7. The method for determining the impurity element content of the carbon-coated aluminum 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 aluminum foil coating layer according to claim 1 or 3, characterized in that, The blank sample for the carbon-coated aluminum foil process in step S2 and the blank sample for the substrate aluminum foil process in step S4 include deionized water, distilled water, or ultrapure water.

9. The method for determining the impurity element content of the carbon-coated aluminum 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.

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