Novel electrolyte for improving tensile strength and elongation of lithium battery copper foil

Abstract

The invention discloses an electrolyte for improving the tensile strength and elongation of a lithium battery copper foil, which comprises a novel leveling agent, a novel inhibitor, water, copper sulfate, sulfuric acid, an accelerator sodium 3, 3 '-dithiodipropane sulfonate and the like. The electrolyte has higher cathode adsorption efficiency, so that the feeding amount of the inhibitor is reduced, the tensile strength and the ductility of the electroplated copper foil can be improved at the same time through the synergistic effect of the novel inhibitor and the novel leveling agent, and the limitation that only one performance of an existing electrolyte formula can be improved is overcome.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery copper foil electroplating production, and particularly relates to a novel electrolyte for improving the tensile strength and elongation of lithium battery copper foil. BACKGROUND

[0002] The copper foil is an ideal current collector for lithium ion battery negative materials due to its excellent electrical conductivity, mechanical flexibility and suitable electrode potential, and plays a very important role in the whole lithium ion battery industry chain.

[0003] The tensile strength and elongation of lithium battery copper foil are two important technical indicators. The purpose of improving them is to meet the stringent requirements of lithium batteries in the manufacturing and use processes: in the manufacturing end, high tensile strength can avoid the lithium battery copper foil from being pulled apart in high-speed winding, and high elongation can improve the toughness of the lithium battery copper foil to absorb local stress and avoid brittle fracture, thereby improving the production efficiency and yield of the battery; in the use end, high tensile strength can resist the volume expansion stress of active materials (such as graphite or silicon-carbon negative materials) during charging and discharging, and maintain the structural stability, and high elongation can buffer the volume change during the cycle process to prevent the active material from powdering and falling off, thereby significantly improving the cycle life, safety and reliability of the battery.

[0004] In the electroplating production process of lithium battery copper foil, the electrolyte has an important influence on the diffusion and nucleation behavior of copper ions on the cathode surface, and the crystal structure of the copper plating layer, thereby effectively regulating the tensile strength and elongation of the lithium battery copper foil. The electrolyte is composed of multiple components including main salt, accelerator, inhibitor, leveling agent, etc. Among them, the inhibitor is adsorbed on the cathode surface to increase the copper ion nucleation overpotential and refine the crystal grains; the leveling agent is specifically adsorbed on the micro protrusions on the cathode surface, forcing the copper ions to be reduced in the surrounding depressions, thereby leveling the surface of the copper foil. However, the existing inhibitors are mostly molecular compounds, and their limited surface charge density restricts their adsorption efficiency on the cathode surface, so a higher concentration is needed to play a role, increasing the production cost of lithium battery copper foil. The existing leveling agent molecules generally only contain one functional group, and their specific adsorption ability on the cathode surface is also low. Therefore, in order to improve the quality of lithium battery copper foil and reduce the production cost, it is urgent to develop a novel electrolyte containing a new type of inhibitor and leveling agent with strong adsorption ability, which can effectively improve the tensile strength and elongation of the copper foil. SUMMARY

[0005] To solve the above technical problems, the application provides an electrolyte for improving tensile strength and elongation of lithium battery copper foil, and the electrolyte can improve nucleation overpotential of copper ions on the cathode surface, refine and homogenize the copper foil surface grain size and eliminate pinhole phenomenon under the synergistic effect of the new leveler and the new inhibitor, so that the tensile strength and elongation of the lithium battery copper foil are simultaneously improved.

[0006] To achieve the above object, the application provides the technical scheme as follows.

[0007] An electrolyte for improving tensile strength and elongation of lithium battery copper foil, comprising a new type of leveler and a new type of inhibitor.

[0008] The new type of leveler is an organic compound containing amino and sulfydryl, which is preferentially adsorbed on the sharp protrusions on the cathode surface under the action of an electric field, hinders the reduction of copper ions on the sharp protrusions, and forces the deposition of copper ions on the depressions around the protrusions, thereby playing a leveling role on the whole coating. The new type of leveler is one or more of penicillamine, homocysteine, glutathione, 2-aminoethanethiol, mercaptoethylamine, 2-mercaptohistidine, N-acetylcysteine, pantothenic acid and dihydrolipoic acid.

[0009] The new type of inhibitor is an organic compound containing chloride ions and organic cations, wherein the chloride ions provide specific adsorption sites for the accelerator sodium polydithiopropanesulfonate by being pre-adsorbed on the cathode surface, and the two form a surface complex, thereby enhancing the adsorption efficiency of sodium polydithiopropanesulfonate and assisting it to realize rapid and uniform deposition of copper ions. The organic cations form a uniform adsorption layer on the cathode surface, thereby improving the nucleation overpotential of copper ions and refining the grains. The new type of inhibitor is one or more of choline hydrochloride, tetramethylammonium chloride, tetrabutylammonium chloride, benzyltriethylammonium chloride, 1-butyl-3-methylimidazolium chloride, polydiallyldimethylammonium chloride and methyltrioctylammonium chloride.

[0010] The synergistic effect of the new type of inhibitor and the new type of leveler improves the nucleation overpotential of copper ions on the cathode surface in the electroplating process, refines and homogenizes the copper foil surface grain size and eliminates the pinhole phenomenon, thereby achieving the effect of simultaneously improving the tensile strength and elongation of the lithium battery copper foil.

[0011] Preferably, the new type of inhibitor is one of choline hydrochloride, tetrabutylammonium chloride or 1-butyl-3-methylimidazolium chloride.

[0012] Preferably, the new type of leveler is one of penicillamine, 2-aminoethanethiol or 2-thiohistidine.

[0013] Preferably, the electrolyte for improving the tensile strength and elongation of lithium battery copper foil further comprises deionized water, copper sulfate, sulfuric acid, accelerator sodium polydithiopropyl sulfone component.

[0014] Preferably, the concentration of copper sulfate in the electrolyte for improving the tensile strength and elongation of lithium battery copper foil is 225 g / L, the concentration of sulfuric acid is 98 g / L, the concentration of accelerator sodium polydithiopropyl sulfone is 4-10 mg / L, the concentration of new inhibitor is 50-180 mg / L, and the concentration of new leveling agent is 6-20 mg / L.

[0015] Preferably, the concentration of accelerator sodium polydithiopropyl sulfone is 6 mg / L, the concentration of new inhibitor is 100 mg / L, and the concentration of new leveling agent is 12 mg / L.

[0016] The preparation method of the new electrolyte for improving the tensile strength and elongation of lithium battery copper foil as described above: the copper sulfate, sulfuric acid, accelerator sodium polydithiopropyl sulfone, new inhibitor, and new leveling agent are added to deionized water, and constant temperature stirring is performed to obtain a copper foil electrolyte.

[0017] Another object of the present application is to provide the application of the above-mentioned electrolyte for improving the tensile strength and elongation of lithium battery copper foil in the production of copper foil.

[0018] The application as described above is operated by selecting copper foil as anode, titanium foil as cathode, and the above-mentioned electrolyte for improving the tensile strength and elongation of lithium battery copper foil as electrolyte, performing electrodeposition operation, current density is 150-250 mA / cm 2 , plating time is 20-60 s, plating temperature is 55-70 ℃, and then post-processing is performed to obtain the copper foil.

[0019] Preferably, the current density of the plating is 200 mA / cm 2 , the plating time is 40 s, and the plating temperature is 60 ℃.

[0020] Preferably, the post-processing is to sequentially place the copper foil after plating in acetone and ethanol solution for ultrasonic cleaning for 8-12 min, and then heat treatment at a temperature of 150-180 ℃ for 16-20 hours.

[0021] Preferably, the ultrasonic cleaning time is 10 min, the heat treatment temperature is 160 ℃, and the heat treatment time is 18 hours.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] The new inhibitor used in the application is an organic compound containing chloride ions and organic cations. The chloride ions can replace the sodium chloride component in the traditional copper foil plating electrolyte additive, simplifying the electrolyte formula. The organic cations have higher cathode adsorption efficiency due to their own positive charge, compared with the existing molecular type inhibitors which rely on polar functional groups for adsorption, thereby reducing the dosage of the inhibitor. The synergistic effect of the new inhibitor and the new leveler can simultaneously improve the tensile strength and elongation of the copper foil, overcoming the limitation of the existing electrolyte formula which can only improve one of the properties. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 An optical micrograph of the copper foil plated in Example 1 of the application.

[0025] Figure 2 An optical micrograph of the copper foil plated in Example 2 of the application.

[0026] Figure 3 An optical micrograph of the copper foil plated in Example 3 of the application.

[0027] Figure 4 An optical micrograph of the copper foil plated in Comparative Example 1.

[0028] Figure 5 An optical micrograph of the copper foil plated in Comparative Example 2.

[0029] Figure 6 An optical micrograph of the copper foil plated in Comparative Example 3.

[0030] Figure 7 An optical micrograph of the copper foil plated in Comparative Example 4. DETAILED DESCRIPTION

[0031] The application will be described in detail below with reference to the accompanying drawings, but it should be understood that the scope of protection of the application is not limited by the specific embodiments. The raw materials and reagents used in the examples are commercially available unless otherwise specified.

[0032] Example 1

[0033] Take 33.75 g of copper sulfate, 15 g of sulfuric acid, 0.9 mg of sodium polydithiopropane sulfonate, 15 mg of choline hydrochloride and 1.8 mg of penicillamine, add deionized water and dilute to 150 ml, then place in a magnetic stirrer and stir at 60°C for 10 minutes to obtain a copper foil plating electrolyte.

[0034] A copper foil is used as the anode and a titanium foil is used as the cathode in the above obtained copper foil plating electrolyte to complete the assembly of the plating device. The current density used in the plating operation is 200 mA / cm2 The plating time was 40 s, and the plating temperature was 60 °C. During the plating process, copper ions were reduced on the surface of the titanium cathode to form a plated copper foil. The plated copper foil was peeled off from the surface of the titanium cathode, and then sequentially subjected to ultrasonic cleaning in acetone and ethanol solutions for 10 min, and then heat treatment at a temperature of 160 °C for 18 hours. Figure 1 Compared with the comparative example, the plated copper foil prepared in Example 1 had a significantly refined grain size on the surface, was uniform in size, and had no pinhole phenomenon. The tensile strength of the plated copper foil prepared in Example 1 was 558.32 MPa, and the elongation rate was 8.77%, which were significantly higher than those of the comparative example.

[0035] Example 2

[0036] 33.75 g of copper sulfate, 15 g of sulfuric acid, 0.9 mg of sodium polydithiobis propane sulfonate, 15 mg of tetrabutylammonium chloride, and 1.8 mg of 2-aminoethanethiol were taken, deionized water was added and diluted to 150 ml, and then placed in a magnetic stirrer for constant temperature stirring at 60 °C for 10 minutes to obtain a plated copper foil electrolyte.

[0037] The copper foil was used as an anode, and the titanium foil was used as a cathode, and then placed in the plated copper foil electrolyte obtained above to complete the assembly of the plating device. The current density used in the plating operation was 200 mA / cm 2 The plating time was 40 s, and the plating temperature was 60 °C. During the plating process, copper ions were reduced on the surface of the titanium cathode to form a plated copper foil. The plated copper foil was peeled off from the surface of the titanium cathode, and then sequentially subjected to ultrasonic cleaning in acetone and ethanol solutions for 10 min, and then heat treatment at a temperature of 160 °C for 18 hours. Figure 2 Compared with the comparative example, the plated copper foil prepared in Example 2 had a significantly refined grain size on the surface, was uniform in size, and had no pinhole phenomenon. The tensile strength of the plated copper foil prepared in Example 2 was 556.72 MPa, and the elongation rate was 8.76%, which were significantly higher than those of the comparative example.

[0038] Example 3

[0039] 33.75 g of copper sulfate, 15 g of sulfuric acid, 0.9 mg of sodium polydithiobis propane sulfonate, 15 mg of tetrabutylammonium chloride, and 1.8 mg of 2-aminoethanethiol were taken, deionized water was added and diluted to 150 ml, and then placed in a magnetic stirrer for constant temperature stirring at 60 °C for 10 minutes to obtain a plated copper foil electrolyte.

[0040] Copper foil as anode, titanium foil as cathode were placed in the above obtained copper foil electroplating electrolyte, and the assembly of the electroplating device was completed. The current density used in the electroplating operation was 200 mA / cm 2 , the electroplating time was 40 s, and the electroplating temperature was 60 ℃. During the electroplating process, copper ions were reduced on the surface of the titanium cathode to form electroplated copper foil. After the completed electroplated copper foil was peeled off from the surface of the titanium cathode, it was sequentially placed in acetone and ethanol solutions for ultrasonic cleaning for 10 min, and then heat treated at a temperature of 160 ℃ for 18 hours, thereby obtaining the electroplated copper foil. Figure 3 Compared with the comparative example, the surface micro-morphology of the electroplated copper foil prepared in Example 3 showed that the grain size of the electroplated copper foil was significantly refined, uniform in size, and there was no pinhole phenomenon. The tensile strength of the electroplated copper foil prepared in Example 3 was 556.99 MPa, and the elongation rate was 8.04%, which was significantly higher than that of the comparative example.

[0041] Comparative Example 1

[0042] 33.75 g of copper sulfate, 15 g of sulfuric acid, 0.9 mg of sodium polydithiobispropane sulfonate, 15 mg of collagen, and 1.8 mg of hydroxyethyl cellulose were added to deionized water and made up to 150 ml, and placed in a magnetic stirrer for constant temperature stirring at 60 ℃ for 10 minutes to obtain a copper foil electroplating electrolyte.

[0043] Copper foil as anode, titanium foil as cathode were placed in the above obtained copper foil electroplating electrolyte, and the assembly of the electroplating device was completed. The current density used in the electroplating operation was 200 mA / cm 2 , the electroplating time was 40 s, and the electroplating temperature was 60 ℃. During the electroplating process, copper ions were reduced on the surface of the titanium cathode to form electroplated copper foil. After the completed electroplated copper foil was peeled off from the surface of the titanium cathode, it was sequentially placed in acetone and ethanol solutions for ultrasonic cleaning for 10 min, and then heat treated at a temperature of 160 ℃ for 18 hours, thereby obtaining the electroplated copper foil. Figure 4 The surface micro-morphology of the electroplated copper foil prepared in Comparative Example 1 showed that the grain size of the copper foil surface was uneven, and there was a serious pinhole phenomenon. The tensile strength of the electroplated copper foil prepared in Comparative Example 1 was 524.15 MPa, and the elongation rate was 6.85%.

[0044] Comparative Example 2

[0045] 33.75 g of copper sulfate, 15 g of sulfuric acid, 0.9 mg of sodium polydithiobispropane sulfonate, 15 mg of collagen, and 1.8 mg of hydroxyethyl cellulose were added to deionized water and made up to 150 ml, and placed in a magnetic stirrer for constant temperature stirring at 60 ℃ for 10 minutes to obtain a copper foil electroplating electrolyte.

[0046] Copper foil as anode, titanium foil as cathode were placed in the above obtained copper foil electroplating electrolyte, and the assembly of the electroplating device was completed. The current density used in the electroplating operation was 200 mA / cm 2 , the electroplating time was 40 s, and the electroplating temperature was 60 ℃. During the electroplating process, copper ions were reduced on the surface of the titanium cathode to form copper foil. After the copper foil was peeled off from the surface of the titanium cathode, it was sequentially placed in acetone and ethanol solutions for ultrasonic cleaning for 10 min, and then was placed in a temperature of 160 ℃ for heat treatment for 18 hours, and thus the copper foil was obtained. Figure 5 The surface micro-morphology of the copper foil prepared by the method of Comparative Example 2 can be seen. The pinhole phenomenon on the surface of the copper foil disappeared, and the crystal grains were refined compared with Comparative Example 1, but the effect was poorer than that of the inventive example. The tensile strength of the copper foil prepared by the method of Comparative Example 2 was 539.22 MPa, and the elongation rate was 6.79%.

[0047] Comparative Example 3

[0048] 33.75 g of copper sulfate, 15 g of sulfuric acid, 0.9 mg of polydithiodipropyl sulfone sodium, and 15 mg of a new inhibitor choline hydrochloride were added to deionized water and made up to 150 ml, and placed in a magnetic stirrer for constant temperature stirring at 60 ℃ for 10 minutes to obtain a copper foil electroplating electrolyte.

[0049] Copper foil as anode, titanium foil as cathode were placed in the above obtained copper foil electroplating electrolyte, and the assembly of the electroplating device was completed. The current density used in the electroplating operation was 200 mA / cm 2 , the electroplating time was 40 s, and the electroplating temperature was 60 ℃. During the electroplating process, copper ions were reduced on the surface of the titanium cathode to form copper foil. After the copper foil was peeled off from the surface of the titanium cathode, it was sequentially placed in acetone and ethanol solutions for ultrasonic cleaning for 10 min, and then was placed in a temperature of 160 ℃ for heat treatment for 18 hours, and thus the copper foil was obtained. Figure 6 The surface micro-morphology of the copper foil prepared by the method of Comparative Example 3 can be seen. The pinhole phenomenon on the surface of the copper foil disappeared, and the crystal grains were refined compared with Comparative Example 1, and were close to those of Comparative Example 2, but the effect was poorer than that of the inventive example. The tensile strength of the copper foil prepared by the method of Comparative Example 3 was 540.32 MPa, and the elongation rate was 7.02%.

[0050] Comparative Example 4

[0051] 33.75 g of copper sulfate, 15 g of sulfuric acid, 0.9 mg of polydithiodipropyl sulfone sodium, and 1.8 mg of a new leveling agent 2-thiohistidine were added to deionized water and made up to 150 ml, and placed in a magnetic stirrer for constant temperature stirring at 60 ℃ for 10 minutes to obtain a copper foil electroplating electrolyte.

[0052] The copper foil is used as an anode and the titanium foil is used as a cathode to assemble an electroplating device in the above-mentioned electrolyte. The current density used in the electroplating operation is 200 mA / cm 2 , the electroplating time is 40 s, and the electroplating temperature is 60 °C. During the electroplating process, the copper ions are reduced on the surface of the titanium cathode to form an electroplated copper foil. The electroplated copper foil is peeled off from the surface of the titanium cathode and then sequentially cleaned in acetone and ethanol solutions for 10 min under ultrasonic cleaning. Subsequently, the electroplated copper foil is heat-treated at a temperature of 160 °C for 18 hours to obtain the electroplated copper foil. Figure 7 The surface micro-morphology of the electroplated copper foil prepared in Comparative Example 4 can be seen. The pinhole phenomenon on the surface of the copper foil disappears, the crystal grains are slightly refined compared to Comparative Example 1, and are close to Comparative Example 2, but are poorer than the embodiments of the present application. The tensile strength of the electroplated copper foil prepared in Comparative Example 4 is 545.55 MPa, and the elongation is 7.10%.

[0053] Table 1 shows the mechanical properties (tensile strength and elongation) of the electroplated copper foils obtained in each of the embodiments and comparative examples.

[0054] Example Tensile strength / MPa Elongation / % Example 1 558.32 8.77 Example 2 556.72 8.76 Example 3 556.99 8.04 Comparative Example 1 524.15 6.85 Comparative Example 2 539.22 6.79 Comparative Example 3 540.32 7.02 Comparative Example 4 543.42 7.04

[0055] The foregoing description of specific exemplary embodiments of the application is intended to be illustrative only and is not intended to limit the application to the precise forms described. Many modifications and variations are possible in light of the above teachings without departing from the spirit or essential characteristics of the application. The exemplary embodiments are chosen and described in order to explain the principles of the application and its practical application to thereby enable others skilled in the art to best utilize the application and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the application be defined by the claims and their equivalents.

Claims

1. An electrolyte for improving the tensile strength and elongation of lithium-ion battery copper foil, characterized in that: Includes novel leveling agents and novel inhibitors; The novel leveling agent is a class of organic compounds containing amino and thiol groups. The novel leveling agent is one or more of penicillamine, homocysteine, glutathione, 2-aminoethanethiol, mercaptoethylamine, 2-mercaptohistidine, N-acetylcysteine, panteric acid, and dihydrolipoic acid. The novel inhibitor is an organic compound containing both chloride ions and organic cations. The novel inhibitor is one or more of choline hydrochloride, tetramethylammonium chloride, tetrabutylammonium chloride, benzyltriethylammonium chloride, 1-butyl-3-methylimidazolium chloride, polydiallyldimethylammonium chloride, and methyltrioctylammonium chloride.

2. The electrolyte for improving the tensile strength and elongation of lithium-ion battery copper foil according to claim 1, characterized in that: The novel inhibitor is one of choline hydrochloride, tetrabutylammonium chloride, or 1-butyl-3-methylimidazole chloride; the novel leveling agent is one of penicillamine, 2-aminoethanethiol, or 2-thiohistidine.

3. The electrolyte for improving the tensile strength and elongation of lithium-ion battery copper foil according to claim 1, characterized in that: The electrolyte used to improve the tensile strength and elongation of lithium battery copper foil also contains water, copper sulfate, sulfuric acid, and sodium polydithiopropane sulfonate as an accelerator.

4. The electrolyte for improving the tensile strength and elongation of lithium-ion battery copper foil according to claim 3, characterized in that: In the electrolyte used to improve the tensile strength and elongation of lithium-ion battery copper foil, the concentration of copper sulfate is 225 g / L, the concentration of sulfuric acid is 98 g / L, the concentration of the accelerator sodium polydisulfide dipropane sulfonate is 4~10 mg / L, the concentration of the novel inhibitor is 50~180 mg / L, and the concentration of the novel leveling agent is 6~20 mg / L.

5. The electrolyte for improving the tensile strength and elongation of lithium-ion battery copper foil according to claim 4, characterized in that: The concentration of the accelerator sodium polydisulfide dipropane sulfonate is 6 mg / L, the concentration of the novel inhibitor is 100 mg / L, and the concentration of the novel leveling agent is 12 mg / L.

6. The method for preparing the novel electrolyte for improving the tensile strength and elongation of lithium battery copper foil as described in any one of claims 1-5, characterized in that: The copper sulfate, sulfuric acid, accelerator sodium polydisulfide dipropane sulfonate, novel inhibitor, and novel leveling agent are added to water and stirred at a constant temperature to obtain the electrolyte for electroplating copper foil.

7. The application of the novel electrolyte for improving the tensile strength and elongation of lithium-ion battery copper foil as described in any one of claims 1-5, or the electrolyte for improving the tensile strength and elongation of lithium-ion battery copper foil prepared by the method described in claim 6, in the production of electroplated copper foil.

8. The application as described in claim 7, characterized in that: Copper foil was selected as the anode, titanium foil as the cathode, and the electrolyte described above, which improves the tensile strength and elongation of lithium-ion battery copper foil, as the electrolyte for electrodeposition. The current density was 150~250 mA / cm². 2 The electroplating time is 20~60 s, the electroplating temperature is 55~70 ℃, and then post-processing is performed to obtain the final product.

9. The application as described in claim 7, characterized in that: The post-treatment involves placing the electroplated copper foil in acetone and ethanol solutions for ultrasonic cleaning for 8-12 minutes, followed by heat treatment at 150-180°C for 16-20 hours.

10. The application as described in claim 7, characterized in that: The electroplating current density is 200 mA / cm². 2 The electroplating time is 40 s and the electroplating temperature is 60 ℃; the ultrasonic cleaning time is 10 min, the heat treatment temperature is 160 ℃, and the heat treatment time is 18 hours.

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