Low-temperature high-current copper electroplating solution and application thereof in preparation of composite current collector

Abstract

The application relates to the technical field of battery materials, in particular to a low-temperature high-current copper electroplating solution which is composed of a base solution and an additive, the base solution is composed of the following substances with the following concentrations: 60-120 g / L of copper ions, 120-200 g / L of sulfuric acid and 30-80 ppm of chloride ions; and the additive is composed of the following substances with the following concentrations: 0.5-5 mg / L of an accelerator, 50-300 mg / L of an inhibitor, 5-50 mg / L of a leveling agent, 1-30 mg / L of a stress regulator and 1-10 mg / L of a grain refiner. 2 The application realizes 5-20 A / dm 2 high-current density electroplating under the condition of 15-30 DEG C low temperature, avoids the deformation of a polymer substrate caused by high-temperature electroplating, cooperatively regulates the copper deposition process through multiple additives, obtains a thick copper layer with low internal stress, low roughness and good bonding force with the polymer substrate, and solves the problems of large copper layer stress and easy cracking and falling under high-current electroplating.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a low-temperature high-current copper plating solution and its application in the preparation of composite current collectors. Background Technology

[0002] Composite current collectors (such as PET / PP-copper composite films) are key materials for improving the energy density and safety of lithium-ion batteries. The core technical challenge lies in how to deposit a thick copper layer (>1.5μm) on a polymer film with a low softening point and high coefficient of thermal expansion, possessing high conductivity, high adhesion, low stress, and high thermal stability. Existing technologies suffer from the following problems: 1. High current density is used to improve electroplating efficiency, but this requires a high electroplating bath temperature. Typically, at a current density of 5A / dm², the electroplating bath temperature should not be lower than 50℃. However, high electroplating bath temperatures can cause thermal deformation of the polymer substrate, affecting the uniformity of electroplating and the performance of the current collector. 2. High current density electroplating increases the roughness of the coating, further leading to stress concentration. 3. The coefficient of thermal expansion of copper is much lower than that of the polymer substrate. During electroplating and battery cycling, thermal stress caused by temperature changes can easily lead to cracking, warping, or detachment of the copper layer.

[0003] Therefore, developing an electroplating technology that can achieve high current density deposition at low temperatures and obtain a thick copper layer with low internal stress and thermal expansion matching the polymer substrate is key to promoting the industrialization of composite current collectors. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a low-temperature, high-current copper plating solution, comprising a base solution and additives. The base solution consists of the following concentrations of substances: 60-120 g / L copper ions, 120-200 g / L sulfuric acid, and 30-80 ppm chloride ions. The additives consist of the following concentrations of substances: 0.5-5 mg / L accelerator, 50-300 mg / L inhibitor, 5-50 mg / L leveling agent, 1-30 mg / L stress modifier, and 1-10 mg / L grain refiner.

[0005] In the copper plating solution of this invention, a higher concentration of copper ions in the base solution can improve the conductivity of the plating solution, reduce concentration polarization under high current density, and provide a sufficient copper source for high current deposition. Sulfuric acid, as a strong electrolyte, further enhances the conductivity of the plating solution, while a suitable range of chloride ions can work synergistically with other additives to regulate the copper deposition process. Specifically, the copper ion donor in this invention is one of copper sulfate, copper methanesulfonate, or copper fluoroborate.

[0006] This invention utilizes a combination of various additives to enable high current density electroplating in the electroplating solution under low temperature conditions, while simultaneously obtaining a uniform, low-stress copper plating layer. Specifically, the accelerator is one of sodium dithiopropane sulfonate (SPS), sodium 3-mercapto-1-propanesulfonate (MPS), or 3,3'-thiobis(1-propanesulfonic acid) (TDPS). The accelerator can accelerate the copper deposition reaction at low temperatures and ensure deposition efficiency under high current density. The inhibitor is polyethylene glycol or polypropylene glycol. The inhibitor is adsorbed on the substrate surface to inhibit the excessively rapid deposition of copper and avoid abnormal grain growth. The leveling agent is an imidazole or pyridine nitrogen-containing heterocyclic compound. The leveling agent can effectively reduce the roughness of the coating under high current deposition and ensure that the coating is uniform and flat. The stress modifier is a mercapto compound or a polyamine compound. It can regulate the growth direction of copper grains, reduce the internal stress of the coating, and avoid cracking and warping of the copper layer. The grain refiner is an organic sulfide or polyol. The grain refiner can refine the copper grains, improve the adhesion between the coating and the substrate, and obtain a copper layer that is more compatible with the thermal expansion properties of the polymer substrate.

[0007] This invention also provides the application of the low-temperature, high-current copper plating solution in the preparation of composite current collectors, specifically providing a method for preparing composite current collectors, using the above-mentioned copper plating solution as the electroplating electrolyte, including the following steps:

[0008] 1) The polymer substrate is cleaned, subjected to plasma surface roughening, Sn sensitization and Pd activation treatment, and a conductive seed layer is formed by chemical plating or magnetron sputtering.

[0009] 2) Place the polymer substrate treated in step 1) into the copper plating solution for copper plating. Control the plating parameters as follows: plating solution temperature 15~30℃, current density 5~20A / dm², plating time 30~120s to obtain copper-plated polymer substrate.

[0010] 3) The copper-plated polymer substrate obtained in step 2) is washed with water, passivated and subjected to anti-oxidation treatment, and dried at a low temperature below 60°C to obtain the composite current collector.

[0011] In step 1) of the method of this invention, the polymer substrate is made of PET or PP. These two materials have good insulation and mechanical stability, and are inexpensive, making them suitable as the substrate for composite current collectors. The conductive seed layer ensures the conductivity of the initial electroplating without excessively increasing the thickness of the inactive layer, which is beneficial for improving the overall energy density of the battery. In the method of this invention, the thickness of the conductive seed layer is controlled between 0.05 and 0.2 μm. In step 3), low-temperature drying further avoids deformation of the polymer substrate caused by high temperatures. A gradient drying mode is used to gradually remove moisture from the coating, preventing rapid evaporation of moisture from causing internal stress in the coating.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention achieves high current density electroplating of 5~20A / dm² at low temperature of 15~30℃ by using an electroplating solution with specific components and concentration ratios, avoiding deformation of polymer substrate caused by high temperature electroplating; by synergistically regulating the copper deposition process with multiple additives, a thick copper layer with low internal stress, low roughness and good adhesion to the polymer substrate is obtained, solving the problem of high stress and easy cracking and peeling of copper layer under high current electroplating. The prepared composite current collector has stable performance and is suitable for large-scale industrial production. When applied to lithium-ion batteries, it can effectively improve the energy density and safety performance of the battery. Detailed Implementation

[0013] The present invention will be described below with reference to examples. These examples are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0014] I. Preparation of copper plating solution

[0015] Prepare copper plating solutions #1 to #4 according to the substances and proportions in Table 1.

[0016] Table 1. Copper plating solution ratio

[0017]

[0018] II. Electroplating copper for current collector preparation

[0019] Example 1

[0020] A method for preparing a copper-plated PET current collector involves electroplating copper onto a PET substrate using a No. 1 copper plating solution. The specific steps are as follows:

[0021] 1. A PET substrate with a thickness of 4.5 μm is sequentially cleaned, subjected to plasma surface roughening, Sn sensitization and Pd activation treatment, and a conductive seed layer with a thickness of 0.1 μm is formed by chemical plating.

[0022] 2. Place the PET substrate treated in step 1 into copper plating solution #1 for copper plating. Control the plating parameters as follows: plating solution temperature is 20℃, and current density is 12.5A / dm³. 2 The electroplating time is 75 seconds, resulting in a copper-plated PET substrate;

[0023] 3. The copper-plated PET substrate is washed with water and passivated for oxidation resistance. Then, starting from 60°C, the temperature is reduced by 5°C and kept at that temperature for 10 minutes at a time. The substrate is then dried at a low temperature until it reaches 20°C, at which point the copper-plated PET current collector is obtained.

[0024] Example 2

[0025] A method for preparing a copper-plated PP current collector involves electroplating copper onto a PP substrate using a No. 2 copper plating solution. The specific steps are as follows:

[0026] 1. A PP substrate with a thickness of 4μm is sequentially cleaned, subjected to plasma surface roughening, Sn sensitization and Pd activation treatment, and a conductive seed layer with a thickness of 0.05μm is formed by magnetron sputtering.

[0027] 2. Place the PP substrate treated in step 1 into copper plating solution #2 for copper plating. Control the plating parameters as follows: plating solution temperature is 15℃, and current density is 5A / dm³. 2 The electroplating time is 120s, resulting in copper-plated PP substrate;

[0028] 3. The copper-plated PP substrate is washed with water and passivated for oxidation resistance. Then, it is subjected to gradient low-temperature drying starting from 55°C and kept at 5°C for 10 minutes at a time. After cooling to room temperature, the copper-plated PP current collector is obtained.

[0029] Example 3

[0030] A method for preparing a copper-plated PET current collector involves electroplating copper onto a PET substrate using a No. 3 copper plating solution. The specific steps are as follows:

[0031] 1. A PET substrate with a thickness of 5μm is sequentially cleaned, subjected to plasma surface roughening, Sn sensitization and Pd activation treatment, and a conductive seed layer with a thickness of 0.2μm is formed by chemical plating.

[0032] 2. Place the PET substrate treated in step 1 into copper plating solution #3 for copper plating. Control the plating parameters as follows: plating solution temperature is 30℃, and current density is 20A / dm³. 2 The electroplating time is 30 seconds, resulting in a copper-plated PET substrate;

[0033] 3. The copper-plated PET substrate is washed with water and passivated for oxidation resistance. Then, it is subjected to gradient low-temperature drying starting from 58°C and kept at 5°C for 10 minutes at a time. After cooling to room temperature, the copper-plated PET current collector is obtained.

[0034] Example 4

[0035] A method for preparing a copper-plated PP current collector involves electroplating copper onto a PP substrate using a No. 4 copper plating solution. The specific steps are as follows:

[0036] 1. A PP substrate with a thickness of 4.2 μm was sequentially cleaned, subjected to plasma surface roughening, Sn sensitization and Pd activation treatment, and a conductive seed layer with a thickness of 0.12 μm was formed by magnetron sputtering.

[0037] 2. Place the PP substrate treated in step 1 into copper plating solution #4 for copper plating. Control the plating parameters as follows: plating solution temperature is 25℃, and current density is 15A / dm³. 2The electroplating time is 60 seconds, resulting in a copper-plated PP substrate;

[0038] 3. The copper-plated PP substrate is washed with water and passivated for oxidation resistance. Then, it is dried in a gradient low temperature manner, starting from 50°C and maintaining the temperature for 10 minutes at a time of 5°C decrease. After cooling to room temperature, the copper-plated PP current collector is obtained.

[0039] Comparative Example 1

[0040] The difference from Example 1 is that the electroplating temperature is 55°C, otherwise they are the same.

[0041] Comparative Example 2

[0042] The difference from Example 1 is that the copper plating solution does not contain mercaptoethylamine, but all other aspects are the same.

[0043] Comparative Example 3

[0044] The difference from Example 1 is that the copper plating solution does not contain sorbitol, but all other aspects are the same.

[0045] Comparative Example 4

[0046] The difference from Example 3 is that the current density is 3A / dm. 2 The electroplating time is 500 seconds, and everything else is the same.

[0047] III. Testing

[0048] Table 2 shows the test indicators of the current collectors obtained in the examples and comparative examples. The data in Table 2 shows that the copper-plated current collectors prepared in Examples 1-4 have a more uniform copper layer thickness, all exceeding 1.5 μm, lower roughness, and higher adhesion between the copper layer and the substrate. Simultaneously, the internal stress is significantly lower than that of the comparative examples. Specifically, in Comparative Example 1, due to the use of high-temperature electroplating at 55℃, slight thermal deformation occurred in the PET substrate, leading to a decrease in the uniformity of the copper layer thickness, an increase in roughness, and a significant reduction in adhesion. Comparative Example 2, without the addition of a stress modifier, resulted in a significant increase in the internal stress of the copper layer. Comparative Example 3, without the addition of a grain refiner, had larger copper grain sizes, resulting in a decrease in adhesion between the copper layer and the substrate, and also higher internal stress. Comparative Example 4 used low-current-density electroplating, which, although achieving a qualified plating layer, required more than ten times the electroplating time of Example 3, resulting in low production efficiency and failing to meet industrialization requirements. The test results confirm that the copper plating solution of this invention can achieve high-current-density electroplating under low-temperature conditions, and the performance of the prepared composite current collector is superior to existing processes, meeting the application requirements of lithium-ion batteries.

[0049] Table 2. Current collector performance test results for both examples and comparative examples

[0050]

[0051] Standard 1, Internal stress testing: ASTM B636 / B636M-15 (2021) "Standard method for measuring internal stress in metallic coatings using a spiral shrinkage tester";

[0052] 2. Peel strength test: GB / T 5270-2005 "Review of test methods for adhesion strength of electrodeposited and chemically deposited metal coatings on metal substrates";

[0053] 3. Grain size detection: GB / T 31568-2015 "Determination of grain size of thermal barrier ZrO2 coating by Scherrer formula".

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-temperature, high-current copper plating solution, wherein the copper plating solution is composed of a base solution and additives, characterized in that, The base solution is composed of the following substances at concentrations: 60-120 g / L copper ions, 120-200 g / L sulfuric acid, and 30-80 ppm chloride ions; The additive consists of the following substances at the following concentrations: 0.5-5 mg / L of accelerator, 50-300 mg / L of inhibitor, 5-50 mg / L of leveling agent, 1-30 mg / L of stress modifier, and 1-10 mg / L of grain refiner.

2. The low-temperature, high-current copper plating solution according to claim 1, characterized in that, The copper ion donor is one of copper sulfate, copper methanesulfonate, or copper fluoroborate; the chloride ion donor is copper chloride or hydrochloric acid.

3. The low-temperature, high-current copper plating solution according to claim 1, characterized in that, The accelerator is one of sodium dithiopropane sulfonate, sodium 3-mercapto-1-propanesulfonate, or 3,3'-thiobis(1-propanesulfonic acid).

4. The low-temperature, high-current copper plating solution according to claim 1, characterized in that, The inhibitor is polyethylene glycol or polypropylene glycol.

5. The low-temperature, high-current copper plating solution according to claim 1, characterized in that, The leveling agent is an imidazole or pyridine nitrogen-containing heterocyclic compound.

6. The low-temperature, high-current copper plating solution according to claim 1, characterized in that, The stress modifier is a thiol compound or a polyamine compound.

7. The low-temperature, high-current copper plating solution according to claim 1, characterized in that, The grain refiner is an organic sulfide or a polyol.

8. A method for preparing a composite current collector, using the low-temperature high-current copper plating solution according to any one of claims 1 to 7 as the electrolyte, characterized in that, Includes the following steps: 1) The polymer substrate is cleaned, subjected to plasma surface roughening, Sn sensitization and Pd activation treatment, and a conductive seed layer is formed by chemical plating or magnetron sputtering. 2) Place the polymer substrate treated in step 1) into an electroplating solution for copper electroplating, controlling the electroplating parameters as follows: electroplating solution temperature 15~30℃, current density 5~20A / dm³. 2 The electroplating time is 30~120s to obtain a copper-plated polymer substrate; 3) The copper-plated polymer substrate obtained in step 2) is washed with water, passivated and subjected to anti-oxidation treatment, and dried at a low temperature below 60°C to obtain the composite current collector.

9. The method according to claim 8, characterized in that, In step 1), the polymer substrate is made of PET or PP; the thickness of the conductive seed layer is 0.05~0.2μm.

10. The method according to claim 8, characterized in that, In step 3), low-temperature drying is a drying mode with a decreasing gradient.

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