Highly flexible tinned round copper wire and method for making same

Abstract

This invention relates to the field of conductor materials technology, specifically disclosing a high-flexibility tin-plated round copper wire and its preparation method. The tin-plated round copper wire comprises, from the inside out, a copper substrate, a buffer interface layer, and a composite tin layer; wherein the copper substrate is a round copper wire activated by a rare earth activating solution; the buffer interface layer is formed by impregnating the surface of the copper substrate with a buffer layer solution containing modified graphene oxide and then heat-treating; the composite tin layer is formed by electrodeposition on the surface of the buffer interface layer with a composite electrolyte containing thiolized carbon nanotubes. This invention also discloses a method for preparing the high-flexibility tin-plated round copper wire, which includes pretreatment, rare earth activation, buffer interface layer construction, electrodeposition of the composite tin layer, and gradient annealing. The tin-plated round copper wire obtained by this invention has high interfacial adhesion, good plating flexibility, and is not easily cracked or peeled off, making it suitable for continuous production.

Description

Technical Field

[0001] This invention relates to the field of conductor materials technology, and more specifically, to a highly flexible tin-plated round copper wire and its preparation method. Background Technology

[0002] Round copper wire, due to its excellent electrical and thermal conductivity and processing properties, is widely used in electronics, electrical engineering, cable manufacturing, connectors, terminals, winding wires, and wiring harnesses for new energy vehicles. To improve the corrosion resistance, weldability, and surface stability of round copper wire, a tin layer is usually plated onto its surface, resulting in tin-plated round copper wire. Tin-plated round copper wire often undergoes mechanical processing such as bending, twisting, winding, and crimping during subsequent use. Therefore, in addition to requiring good conductivity and adhesion of the plating, it also needs high flexibility and crack resistance.

[0003] However, existing tin-plated round copper wires still have shortcomings in practical applications. On the one hand, the interfacial bonding between the copper substrate and the tin plating mainly relies on mechanical adhesion and conventional metallurgical bonding. During repeated bending or deformation, stress concentration easily occurs at the interface, leading to plating cracking, peeling, or even delamination, affecting the reliability of the product. On the other hand, traditional tin plating itself has limited toughness, and micro-defects or residual internal stress are easily generated within the plating. Under complex stress conditions, this can easily induce crack initiation and propagation, making it difficult to meet the requirements of high flexibility and high reliability applications.

[0004] Therefore, there is an urgent need to develop a high-flexibility tin-plated round copper wire with stable interface bonding, high coating flexibility, excellent bending resistance, and suitable for continuous production, as well as its preparation method. Summary of the Invention

[0005] To address the problems of insufficient interfacial bonding, poor coating flexibility, and easy cracking and peeling during bending or torsion in existing tin-plated round copper wires, this invention provides a highly flexible tin-plated round copper wire and its preparation method.

[0006] In a first aspect, the present invention provides a highly flexible tin-plated round copper wire, employing the following technical solution: A highly flexible tin-plated round copper wire comprises, from the inside out: a copper substrate, a buffer interface layer, and a composite tin layer; The copper substrate is a round copper wire activated by a rare earth activating solution; the buffer interface layer is formed by impregnating the surface of the copper substrate with a buffer layer solution containing modified graphene oxide and then heat-treating it; the composite tin layer is formed by electrodeposition on the surface of the buffer interface layer with a composite electrolyte containing thiolated carbon nanotubes.

[0007] Preferably, the preparation method of the rare earth activation solution includes the following steps: Ammonium citrate and glycine were added to deionized water and stirred until homogeneous. The mixture was then heated to 45-55°C, and lanthanum chloride hexahydrate and cerium chloride hexahydrate were added. The mixture was stirred until homogeneous, and the pH of the system was adjusted to 3.5-4.5 to obtain the rare earth activation solution.

[0008] Preferably, the mass ratio of ammonium citrate, glycine, lanthanum chloride hexahydrate, cerium chloride hexahydrate, and deionized water is 7:3-4:0.9-1.1:0.9-1.1:100.

[0009] Preferably, the term "uniform stirring" refers to stirring for 20-25 minutes at room temperature and a speed of 350-450 rpm.

[0010] Preferably, the term "continued stirring until uniform" refers to continuing stirring for 40-50 minutes at a temperature of 45-55℃ and a rotation speed of 350-450 rpm.

[0011] Preferably, the method for preparing the modified graphene oxide includes the following steps: A1. Add graphene oxide powder to deionized water and sonicate to obtain a suspension. Under stirring, add 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to the suspension and stir to react. After the reaction is completed, an activated suspension is obtained. A2. Under nitrogen protection, furfurylamine was added to the activated suspension and stirred to react. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain modified graphene oxide.

[0012] Preferably, in step A1, the mass ratio of graphene oxide powder, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide and deionized water is 1:2.5-3:1.5-2:280-300.

[0013] Preferably, the ultrasonic treatment in step A1 refers to ultrasonic treatment for 35-45 minutes under the conditions of frequency 25-35kHz and power 200-300W.

[0014] Preferably, the stirring reaction in step A1 refers to stirring the reaction at room temperature and a speed of 450-550 rpm for 1.5-2 hours.

[0015] Preferably, the mass ratio of furfurylamine to activated suspension in step A2 is 4-5:100.

[0016] Preferably, the stirring reaction in step A2 refers to stirring the reaction at room temperature and a speed of 450-550 rpm for 8-10 hours.

[0017] Preferably, in step A2, the centrifugation, washing, and drying process refers to: centrifuging at 8000-10000 rpm for 5-10 minutes, washing the precipitate 3-4 times each with deionized water and anhydrous ethanol, and then drying at 50-60℃ for 12-16 hours.

[0018] Preferably, the method for preparing the buffer layer solution containing modified graphene oxide includes the following steps: Modified graphene oxide and anhydrous DMF were mixed evenly, and bismaleimide and γ-mercaptopropyltrimethoxysilane were added and stirred evenly to obtain a buffer layer solution containing modified graphene oxide.

[0019] Preferably, the mass ratio of the modified graphene oxide, bismaleimide, γ-mercaptopropyltrimethoxysilane and anhydrous DMF is 1:4.5-5.5:1-1.5:90-100.

[0020] Preferably, the term "uniform stirring" refers to stirring for 1.5-2 hours at room temperature and a speed of 550-650 rpm.

[0021] Preferably, the method for preparing the thiolized carbon nanotubes includes the following steps: B1. Mix multi-walled carbon nanotubes and deionized water, add sodium dodecylbenzenesulfonate, and sonicate to obtain a carbon nanotube suspension. B2. Add cysteine ​​to the carbon nanotube suspension, stir evenly, heat to 70-80℃, add hydrogen peroxide, stir to react, and after the reaction is completed, centrifuge, wash and dry to obtain thiolized carbon nanotubes.

[0022] Preferably, in step B1, the mass ratio of multi-walled carbon nanotubes, sodium dodecylbenzenesulfonate, and deionized water is 1:0.8-1.2:280-300.

[0023] Preferably, the ultrasonic treatment in step B1 refers to ultrasonic treatment for 50-60 minutes at a frequency of 25-35kHz and a power of 250-350W.

[0024] Preferably, the mass ratio of cysteine, hydrogen peroxide, and carbon nanotube suspension in step B2 is 2-3:4-6:100.

[0025] Preferably, the term "stirring evenly" in step B2 refers to stirring for 20-25 minutes at room temperature and a speed of 350-450 rpm.

[0026] Preferably, the stirring reaction in step B2 refers to stirring the reaction for 3-4 hours at a temperature of 70-80℃ and a rotation speed of 400-600 rpm.

[0027] Preferably, in step B2, the centrifugation, washing, and drying process refers to: centrifuging at 9000-10000 rpm for 5-10 minutes, washing the precipitate 3-5 times each with deionized water and anhydrous ethanol, and then drying at 60-70℃ for 12-14 hours.

[0028] Preferably, the preparation method of the composite electrolyte containing thiolized carbon nanotubes includes the following steps: C1. Thiolized carbon nanotubes and deionized water are mixed, alkyl glycosides are added, and the mixture is ultrasonically treated to obtain a nano slurry. C2. Mix methanesulfonic acid and deionized water, add tin methanesulfonate, and stir until homogeneous to obtain MSA base solution; C3. Under stirring, the nano-slurry is added to the MSA base solution. After stirring evenly, ascorbic acid is added and stirring is continued to be evenly mixed to obtain a composite electrolyte containing thiolized carbon nanotubes.

[0029] Preferably, in step C1, the mass ratio of thiolated carbon nanotubes, alkyl glycosides and deionized water is 1:0.8-1.2:280-300.

[0030] Preferably, the ultrasonic treatment in step C1 refers to ultrasonic treatment for 30-40 minutes under the conditions of frequency 25-35kHz and power 200-300W.

[0031] Preferably, in step C2, the mass ratio of methanesulfonic acid, tin methanesulfonate, and deionized water is 8-10:30-32:60-64.

[0032] Preferably, the term "stirring evenly" in step C2 refers to stirring for 30-40 minutes at room temperature and a speed of 300-500 rpm.

[0033] Preferably, in step C3, the mass ratio of nano-slurry, MSA base liquid, and ascorbic acid is 2-3:100:0.1-0.2.

[0034] Preferably, in step C3, the rotation speed of adding the nano-slurry while stirring is 400-600 rpm.

[0035] Preferably, in step C3, "stirring evenly" means stirring for 30-40 minutes at room temperature and a speed of 400-600 rpm, followed by stirring for another 20-30 minutes.

[0036] Secondly, this invention provides a method for preparing highly flexible tin-plated round copper wire, employing the following technical solution: A method for preparing highly flexible tin-plated round copper wire includes the following preparation steps: S1. After pretreatment, the round copper wire is immersed in rare earth activation solution for impregnation treatment, and then dried with hot air to obtain a copper matrix. S2. After immersing the copper substrate in a buffer layer solution containing modified graphene oxide, remove it and perform heat treatment to form a buffer interface layer, thus obtaining modified copper wire. S3. Using modified copper wire as the cathode and a high-purity tin plate with a polypropylene anode bag as the anode, the copper wire is placed in a composite electrolyte containing thiolated carbon nanotubes for electrodeposition treatment to form a composite tin layer. Then, it is subjected to gradient annealing to obtain a highly flexible tin-plated round copper wire.

[0037] Preferably, the pretreatment in step S1 refers to: first immersing the round copper wire in an alkaline degreasing solution at 45-55℃ for 2-3 minutes; then cleaning it with deionized water; then activating the water-washed round copper wire in a sulfuric acid solution with a mass fraction of 5-8% for 20-30 seconds; and finally cleaning it again with deionized water.

[0038] Preferably, the immersion treatment in step S1 refers to immersion at a temperature of 30-40℃ for 50-60 seconds.

[0039] Preferably, the hot air drying in step S1 refers to drying with hot air at a temperature of 45-55℃ for 15-25 seconds until there are no obvious liquid droplets on the surface.

[0040] Preferably, the immersion time in the buffer layer solution containing modified graphene oxide in step S2 is 50-60 seconds.

[0041] Preferably, the heat treatment in step S2 refers to heat treatment at a temperature of 90-100℃ for 20-30 minutes.

[0042] Preferably, the thickness of the buffer interface layer in step S2 is 0.2-0.5 μm.

[0043] Preferably, the electrodeposition process in step S3 refers to: using pulsed electrodeposition, performing electrodeposition for 8-10 minutes under the conditions of a temperature of 25-35℃, a duty cycle of 35-45%, a current density of 3-4A / dm², and a pulse frequency of 150-200Hz.

[0044] Preferably, in step S3, gradient annealing refers to: heating to 90-100℃ at a heating rate of 3-4℃ / min and holding for 8-12min, then heating to 115-125℃ and holding for 8-12min, then heating to 130-135℃ and holding for 3-5min, and then cooling to room temperature.

[0045] Preferably, the thickness of the composite tin layer in step S3 is 4-6 μm.

[0046] In summary, the present invention has the following beneficial effects: 1. This invention constructs a buffer interface layer between the copper substrate and the composite tin layer, which is composed of modified graphene oxide, bismaleimide and γ-mercaptopropyltrimethoxysilane. This significantly improves the interfacial bonding force between the copper substrate and the tin plating layer. At the same time, the buffer interface layer is used to relieve stress under external force, thereby effectively reducing the risk of cracking and peeling of the plating layer during bending and torsion, and improving the flexibility and structural stability of the tin-plated round copper wire.

[0047] 2. This invention introduces thiolized carbon nanotubes into a composite electrolyte and uses electrodeposition to deposit them in synergistic with the tin plating layer. This allows the thiolized carbon nanotubes to be dispersed in the composite tin layer, thereby improving the density, toughness, and crack resistance of the tin plating layer. It also inhibits the initiation and propagation of microcracks in the plating layer during repeated bending, further enhancing the bending resistance and service life of the tin-plated round copper wire.

[0048] 3. This invention activates round copper wire with rare earth activating solution, and combines it with electrodeposition treatment with methanesulfonic acid system and gradient annealing process. On the one hand, it can effectively improve the active state of the copper substrate surface and improve the deposition uniformity of subsequent buffer interface layer and composite tin layer. On the other hand, it can reduce the internal stress of the coating and promote the stability of the interface structure, so that the obtained high-flexibility tin-plated round copper wire has good coating adhesion, surface quality, electrical properties and processing adaptability.

[0049] 4. By using tin methanesulfonate electrolyte and a high-purity tin plate with a polypropylene anode bag as the anode for electrodeposition, this invention can effectively maintain the stability of tin ion concentration in the electrolyte, reduce the introduction of impurities and the adverse effects of anode mud on the coating quality, thereby improving the deposition stability, consistency and surface quality of the composite tin layer, which is beneficial for continuous production and industrial applications. Detailed Implementation

[0050] The present invention will be further described in detail below with reference to the embodiments.

[0051] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0052] The key raw materials used in this invention are sourced from the following sources: Graphene oxide powder: Brand: Xianfeng Nano, Model: XFQ022, provided by Jiangsu Xianfeng Nanomaterials Technology Co., Ltd. Lanthanum chloride hexahydrate: CAS No.: 17272-45-6, provided by Shanghai Maclean Biochemical Technology Co., Ltd. Cerium chloride hexahydrate: CAS No.: 16651-27-7, provided by Shanghai Maclean Biochemical Technology Co., Ltd. Bismaleimide: CAS No.: 13676-54-5, provided by Hubei Chuanhe Chemical Co., Ltd.; γ-Mercaptopropyltrimethoxysilane: CAS No.: 4420-74-0, provided by Hubei Changfu Chemical Co., Ltd.; Multi-walled carbon nanotubes: Brand: Carbon Peak, Model: TF-210, provided by Shandong Carbon Peak New Material Technology Co., Ltd. Alkyl glycoside: Brand: FC, Item No.: 1214, provided by Shanghai Fuqi Industry & Trade Co., Ltd. High-purity tin plate: thickness: 1mm, provided by Zhongyan Metal Materials; Round copper wire: Brand: Guangqian Copper Industry, wire diameter: 0.2mm, provided by Zhejiang Guangqian Copper Industry Co., Ltd.; Alkaline degreasing agent: Model: XH6211PC9YGO, provided by Tengyi Material Supply Station, Xigong District, Luoyang City.

[0053] Examples 1-3 provide a highly flexible tin-plated round copper wire and its preparation method.

[0054] Example 1 The preparation method of rare earth activation solution includes the following steps: The mass ratio of ammonium citrate, glycine, lanthanum chloride hexahydrate, cerium chloride hexahydrate, and deionized water was controlled at 7:3:0.9:0.9:100. Ammonium citrate and glycine were added to deionized water and stirred for 25 minutes at room temperature and 350 rpm. The temperature was then raised to 45°C, and lanthanum chloride hexahydrate and cerium chloride hexahydrate were added. The mixture was stirred for another 50 minutes at 45°C and 350 rpm. The pH of the system was adjusted to 3.5 using a 5% hydrochloric acid solution to obtain the rare earth activation solution. The preparation method of modified graphene oxide includes the following steps: A1. The mass ratio of graphene oxide powder, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, and deionized water was controlled at 1:2.5:1.5:280. Graphene oxide powder was added to deionized water and ultrasonically treated for 45 min at a frequency of 25 kHz and a power of 200 W to obtain a suspension. 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide were added to the suspension at a speed of 450 rpm. The mixture was stirred at room temperature and a speed of 450 rpm for 2 h. After the reaction was completed, an activated suspension was obtained. A2. Controlling the mass ratio of furfurylamine to activated suspension to 4:100, furfurylamine was added to activated suspension under nitrogen protection. The mixture was stirred at room temperature and 450 rpm for 10 h. After the reaction was completed, the mixture was centrifuged at 8000 rpm for 10 min. The precipitate was washed three times each with deionized water and anhydrous ethanol and then dried at 50℃ for 16 h to obtain modified graphene oxide. A method for preparing a buffer layer solution containing modified graphene oxide includes the following steps: The mass ratio of modified graphene oxide, bismaleimide, γ-mercaptopropyltrimethoxysilane and anhydrous DMF was controlled at 1:4.5:1:90. The modified graphene oxide and anhydrous DMF were mixed evenly, and bismaleimide and γ-mercaptopropyltrimethoxysilane were added. The mixture was stirred for 2 hours at room temperature and 550 rpm to obtain a buffer layer solution containing modified graphene oxide. The preparation method of thiolized carbon nanotubes includes the following steps: B1. Control the mass ratio of multi-walled carbon nanotubes, sodium dodecylbenzenesulfonate and deionized water to 1:0.8:280. Mix multi-walled carbon nanotubes and deionized water, add sodium dodecylbenzenesulfonate, and sonicate for 60 min at a frequency of 25 kHz and a power of 250 W to obtain a carbon nanotube suspension. B2. The mass ratio of cysteine, hydrogen peroxide and carbon nanotube suspension was controlled at 2:4:100. Cysteine ​​was added to the carbon nanotube suspension and stirred for 25 min at room temperature and 350 rpm. The temperature was raised to 70℃, and 30% hydrogen peroxide was added. The mixture was stirred for 4 h at 70℃ and 400 rpm. After the reaction was completed, the mixture was centrifuged at 9000 rpm for 10 min. The precipitate was washed three times each with deionized water and anhydrous ethanol and then dried at 60℃ for 14 h to obtain thiolized carbon nanotubes. A method for preparing a composite electrolyte containing thiolated carbon nanotubes includes the following steps: C1. Control the mass ratio of thiolized carbon nanotubes, alkyl glycosides and deionized water to 1:0.8:280. Mix the thiolized carbon nanotubes and deionized water, add the alkyl glycosides, and sonicate for 40 min at a frequency of 25 kHz and a power of 200 W to obtain nano-slurry. C2. Control the mass ratio of methanesulfonic acid, tin methanesulfonate and deionized water to 8:30:60. Mix methanesulfonic acid and deionized water, add tin methanesulfonate, and stir for 40 minutes at room temperature and 300 rpm to obtain MSA base solution. C3. Control the mass ratio of nano-slurry, MSA base solution and ascorbic acid to 2:100:0.1. Add nano-slurry to MSA base solution at 400 rpm. Stir for 40 min at room temperature and 400 rpm. Then add ascorbic acid and continue stirring for 30 min to obtain composite electrolyte containing thiolized carbon nanotubes. A method for preparing highly flexible tin-plated round copper wire includes the following preparation steps: S1. Immerse the round copper wire in an alkaline degreasing solution at 45℃ for 3 minutes; then clean it with deionized water; then activate the washed round copper wire in a 5% sulfuric acid solution for 30 seconds; finally clean it again with deionized water to obtain pretreated copper wire. Immerse the pretreated copper wire in a rare earth activation solution at 30℃ for 60 seconds, then remove it and dry it with hot air at 45℃ for 25 seconds until there are no obvious liquid droplets on the surface to obtain a copper substrate. S2. Immerse the copper substrate in a buffer layer solution containing modified graphene oxide for 50 seconds, then remove it and heat-treat it at 90℃ for 30 minutes to form a buffer interface layer with a thickness of 0.2μm, thus obtaining the modified copper wire. S3. Using modified copper wire as the cathode and a high-purity tin plate with a polypropylene anode bag as the anode, the electrodeposition is carried out in a composite electrolyte containing thiolized carbon nanotubes. Pulse electrodeposition is performed at a temperature of 25℃, a duty cycle of 35%, a current density of 3A / dm², and a pulse frequency of 150Hz for 10 minutes to form a composite tin layer with a thickness of 4μm. The temperature is then increased to 90℃ at a heating rate of 3℃ / min and held for 12 minutes, then increased to 115℃ and held for 12 minutes, then increased to 130℃ and held for 5 minutes, and then cooled to room temperature to obtain a highly flexible tin-plated round copper wire.

[0055] Example 2 The preparation method of rare earth activation solution includes the following steps: The mass ratio of ammonium citrate, glycine, lanthanum chloride hexahydrate, cerium chloride hexahydrate, and deionized water was controlled at 7:3.5:1:1:100. Ammonium citrate and glycine were added to deionized water and stirred for 22.5 min at room temperature and 400 rpm. The temperature was then raised to 50°C, and lanthanum chloride hexahydrate and cerium chloride hexahydrate were added. The mixture was stirred for another 45 min at 50°C and 400 rpm. The pH of the system was adjusted to 4 using a 5% hydrochloric acid solution to obtain the rare earth activation solution. The preparation method of modified graphene oxide includes the following steps: A1. The mass ratio of graphene oxide powder, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, and deionized water was controlled at 1:2.8:1.8:290. Graphene oxide powder was added to deionized water and ultrasonically treated for 40 min at a frequency of 30 kHz and a power of 250 W to obtain a suspension. 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide were added to the suspension at a speed of 500 rpm. The mixture was stirred at room temperature and a speed of 500 rpm for 1.75 h. After the reaction was completed, an activated suspension was obtained. A2. Controlling the mass ratio of furfurylamine to activated suspension at 4.5:100, furfurylamine was added to activated suspension under nitrogen protection, and the reaction was stirred at room temperature and 500 rpm for 9 h. After the reaction was completed, the mixture was centrifuged at 9000 rpm for 7.5 min. The precipitate was washed 4 times each with deionized water and anhydrous ethanol, and then dried at 55℃ for 14 h to obtain modified graphene oxide. A method for preparing a buffer layer solution containing modified graphene oxide includes the following steps: The mass ratio of modified graphene oxide, bismaleimide, γ-mercaptopropyltrimethoxysilane and anhydrous DMF was controlled at 1:5:1.25:95. The modified graphene oxide and anhydrous DMF were mixed evenly, and bismaleimide and γ-mercaptopropyltrimethoxysilane were added. The mixture was stirred at room temperature and 600 rpm for 1.75 h to obtain a buffer layer solution containing modified graphene oxide. The preparation method of thiolized carbon nanotubes includes the following steps: B1. Control the mass ratio of multi-walled carbon nanotubes, sodium dodecylbenzene sulfonate and deionized water to 1:1:290. Mix multi-walled carbon nanotubes and deionized water, add sodium dodecylbenzene sulfonate, and sonicate for 55 minutes at a frequency of 30kHz and a power of 300W to obtain a carbon nanotube suspension. B2. The mass ratio of cysteine, hydrogen peroxide, and carbon nanotube suspension was controlled at 2.5:5:100. Cysteine ​​was added to the carbon nanotube suspension and stirred at room temperature and 400 rpm for 22.5 min. The temperature was raised to 75℃, and 30% hydrogen peroxide was added. The mixture was stirred at 75℃ and 500 rpm for 3.5 h. After the reaction was completed, the mixture was centrifuged at 9500 rpm for 7.5 min. The precipitate was washed 4 times each with deionized water and anhydrous ethanol and then dried at 65℃ for 13 h to obtain thiolized carbon nanotubes. A method for preparing a composite electrolyte containing thiolated carbon nanotubes includes the following steps: C1. Control the mass ratio of thiolized carbon nanotubes, alkyl glycosides and deionized water to 1:1:290. Mix the thiolized carbon nanotubes and deionized water, add the alkyl glycosides, and sonicate for 35 min at a frequency of 30 kHz and a power of 250 W to obtain nano slurry. C2. Control the mass ratio of methanesulfonic acid, tin methanesulfonate and deionized water to 9:31:62. Mix methanesulfonic acid and deionized water, add tin methanesulfonate, and stir for 35 minutes at room temperature and 400 rpm to obtain MSA base solution. C3. Control the mass ratio of nano-slurry, MSA base solution and ascorbic acid to 2.5:100:0.15. Add nano-slurry to MSA base solution at 500 rpm. Stir for 35 min at room temperature and 500 rpm. Then add ascorbic acid and continue stirring for 25 min to obtain composite electrolyte containing thiolized carbon nanotubes. A method for preparing highly flexible tin-plated round copper wire includes the following preparation steps: S1. Immerse the round copper wire in an alkaline degreasing solution at 50℃ for 2.5 min; then clean it with deionized water; then activate the water-washed round copper wire in a 7% sulfuric acid solution for 25 s; finally clean it again with deionized water to obtain pretreated copper wire. Immerse the pretreated copper wire in a rare earth activation solution at 35℃ for 55 s, then remove it and dry it with hot air at 50℃ for 20 s until there are no obvious droplets on the surface to obtain a copper substrate. S2. The copper substrate is immersed in a buffer layer solution containing modified graphene oxide for 55 seconds and then removed. It is then heat-treated at 95°C for 25 minutes to form a buffer interface layer with a thickness of 0.35 μm, thus obtaining the modified copper wire. S3. Using modified copper wire as the cathode and a high-purity tin plate with a polypropylene anode bag as the anode, the electrodeposition is carried out in a composite electrolyte containing thiolized carbon nanotubes. Pulse electrodeposition is performed at a temperature of 30℃, a duty cycle of 40%, a current density of 3.5A / dm², and a pulse frequency of 180Hz for 9 minutes to form a composite tin layer with a thickness of 5μm. The temperature is then increased to 95℃ at a heating rate of 3.5℃ / min and held for 10 minutes, then increased to 120℃ and held for 10 minutes, and then increased to 132℃ and held for 4 minutes. Finally, the temperature is cooled to room temperature to obtain a highly flexible tin-plated round copper wire.

[0056] Example 3 The preparation method of rare earth activation solution includes the following steps: The mass ratio of ammonium citrate, glycine, lanthanum chloride hexahydrate, cerium chloride hexahydrate, and deionized water was controlled at 7:4:1.1:1.1:100. Ammonium citrate and glycine were added to deionized water and stirred for 20 minutes at room temperature and 450 rpm. The temperature was then raised to 55°C, and lanthanum chloride hexahydrate and cerium chloride hexahydrate were added. The mixture was stirred for another 40 minutes at 55°C and 450 rpm. The pH of the system was adjusted to 4.5 using a 5% hydrochloric acid solution to obtain the rare earth activation solution. The preparation method of modified graphene oxide includes the following steps: A1. The mass ratio of graphene oxide powder, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, and deionized water was controlled at 1:3:2:300. Graphene oxide powder was added to deionized water and ultrasonically treated for 35 min at a frequency of 35 kHz and a power of 300 W to obtain a suspension. 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide were added to the suspension at a speed of 550 rpm. The mixture was stirred at room temperature and a speed of 550 rpm for 1.5 h. After the reaction was completed, an activated suspension was obtained. A2. Control the mass ratio of furfurylamine and activated suspension to 5:100. Under nitrogen protection, furfurylamine is added to the activated suspension and stirred for 8 hours at room temperature and 550 rpm. After the reaction is completed, the mixture is centrifuged at 10000 rpm for 5 minutes. The precipitate is washed 4 times each with deionized water and anhydrous ethanol and then dried at 60℃ for 12 hours to obtain modified graphene oxide. A method for preparing a buffer layer solution containing modified graphene oxide includes the following steps: The mass ratio of modified graphene oxide, bismaleimide, γ-mercaptopropyltrimethoxysilane and anhydrous DMF was controlled at 1:5.5:1.5:100. The modified graphene oxide and anhydrous DMF were mixed evenly, and bismaleimide and γ-mercaptopropyltrimethoxysilane were added. The mixture was stirred at room temperature and 650 rpm for 1.5 h to obtain a buffer layer solution containing modified graphene oxide. The preparation method of thiolized carbon nanotubes includes the following steps: B1. Control the mass ratio of multi-walled carbon nanotubes, sodium dodecylbenzenesulfonate and deionized water to 1:1.2:300. Mix multi-walled carbon nanotubes and deionized water, add sodium dodecylbenzenesulfonate, and sonicate for 50 min at a frequency of 35 kHz and a power of 350 W to obtain a carbon nanotube suspension. B2. The mass ratio of cysteine, hydrogen peroxide, and carbon nanotube suspension was controlled at 3:6:100. Cysteine ​​was added to the carbon nanotube suspension and stirred for 20 min at room temperature and 450 rpm. The temperature was raised to 80℃, and 30% hydrogen peroxide was added. The mixture was stirred for 3 h at 80℃ and 600 rpm. After the reaction was completed, the mixture was centrifuged at 10000 rpm for 5 min. The precipitate was washed 5 times each with deionized water and anhydrous ethanol and then dried at 70℃ for 12 h to obtain thiolized carbon nanotubes. A method for preparing a composite electrolyte containing thiolated carbon nanotubes includes the following steps: C1. Control the mass ratio of thiolized carbon nanotubes, alkyl glycosides and deionized water to 1:1.2:300. Mix the thiolized carbon nanotubes and deionized water, add the alkyl glycosides, and sonicate for 30 min at a frequency of 35 kHz and a power of 300 W to obtain nano-slurry. C2. Control the mass ratio of methanesulfonic acid, tin methanesulfonate and deionized water to 10:32:64. Mix methanesulfonic acid and deionized water, add tin methanesulfonate, and stir for 30 minutes at room temperature and 500 rpm to obtain MSA base solution. C3. Control the mass ratio of nano-slurry, MSA base solution and ascorbic acid to 3:100:0.2. Add nano-slurry to MSA base solution at 600 rpm. Stir for 30 min at room temperature and 600 rpm. Then add ascorbic acid and continue stirring for 20 min to obtain composite electrolyte containing thiolized carbon nanotubes. A method for preparing highly flexible tin-plated round copper wire includes the following preparation steps: S1. Immerse the round copper wire in an alkaline degreasing solution at 55℃ for 2 minutes; then clean it with deionized water; then activate the washed round copper wire in an 8% sulfuric acid solution for 20 seconds; finally clean it again with deionized water to obtain pretreated copper wire. Immerse the pretreated copper wire in a rare earth activation solution at 40℃ for 50 seconds, then remove it and dry it with hot air at 55℃ for 15 seconds until there are no obvious droplets on the surface to obtain a copper substrate. S2. The copper substrate is immersed in a buffer layer solution containing modified graphene oxide for 60 seconds and then taken out. It is then heat-treated at 100℃ for 20 minutes to form a buffer interface layer with a thickness of 0.5μm, thus obtaining the modified copper wire. S3. Using modified copper wire as the cathode and a high-purity tin plate with a polypropylene anode bag as the anode, the electrodeposition is carried out in a composite electrolyte containing thiolized carbon nanotubes. Pulse electrodeposition is performed at a temperature of 35℃, a duty cycle of 45%, a current density of 4A / dm², and a pulse frequency of 200Hz for 8 minutes to form a composite tin layer with a thickness of 6μm. The temperature is then increased to 100℃ at a heating rate of 4℃ / min and held for 8 minutes, then increased to 125℃ and held for 8 minutes, and then increased to 135℃ and held for 3 minutes. Finally, the temperature is cooled to room temperature to obtain a highly flexible tin-plated round copper wire.

[0057] To verify the comprehensive performance of the high-flexibility tin-plated round copper wires prepared in Examples 1-3 of this invention and their preparation methods, the inventors have set up Comparative Examples 1-5, as follows: Comparative Example 1 The difference between this comparative example and Example 1 is that, in preparing the buffer layer solution containing modified graphene oxide, the modified graphene oxide is replaced by graphene oxide powder in equal mass, while the remaining steps and raw materials are the same as in Example 1. A method for preparing a buffer layer solution containing graphene oxide includes the following steps: The mass ratio of graphene oxide powder, bismaleimide, γ-mercaptopropyltrimethoxysilane, and anhydrous DMF was controlled at 1:4.5:1:90. The graphene oxide powder and anhydrous DMF were mixed evenly, and then bismaleimide and γ-mercaptopropyltrimethoxysilane were added. The mixture was stirred for 2 hours at room temperature and 550 rpm to obtain a buffer layer solution containing graphene oxide.

[0058] Comparative Example 2 The difference between this comparative example and Example 1 is that in the original step C1, the thiolized carbon nanotubes were replaced with multi-walled carbon nanotubes of equal mass, while the remaining steps and raw materials were the same as in Example 1. Specifically: C1. Controlling the mass ratio of multi-walled carbon nanotubes, alkyl glycosides and deionized water to 1:0.8:280, the multi-walled carbon nanotubes and deionized water were mixed, and the alkyl glycosides were added. The mixture was ultrasonically treated for 40 minutes at a frequency of 25 kHz and a power of 200 W to obtain a nano-slurry.

[0059] Comparative Example 3 The difference between this comparative example and Example 1 is that lanthanum chloride hexahydrate and cerium chloride hexahydrate are not added to the rare earth activation solution, while the remaining steps and raw materials are the same as in Example 1. The method for preparing the activation solution includes the following steps: The mass ratio of ammonium citrate, glycine, and deionized water was controlled at 8.26:3.54:100. Ammonium citrate and glycine were added to deionized water and stirred for 25 minutes at room temperature and 350 rpm. The pH of the system was adjusted to 3.5 using a 5% hydrochloric acid solution to obtain the activated solution. A method for preparing highly flexible tin-plated round copper wire includes the following preparation steps: S1. Immerse the round copper wire in an alkaline degreasing solution at 45℃ for 3 minutes; then clean it with deionized water; then activate the washed round copper wire in a 5% sulfuric acid solution for 30 seconds; finally clean it again with deionized water to obtain pretreated copper wire. Immerse the pretreated copper wire in the activation solution at 30℃ for 60 seconds, then remove it and dry it with hot air at 45℃ for 25 seconds until there are no obvious droplets on the surface to obtain the copper substrate. S2. Immerse the copper substrate in a buffer layer solution containing modified graphene oxide for 50 seconds, then remove it and heat-treat it at 90℃ for 30 minutes to form a buffer interface layer with a thickness of 0.2μm, thus obtaining the modified copper wire. S3. Using modified copper wire as the cathode and a high-purity tin plate with a polypropylene anode bag as the anode, the electrodeposition is carried out in a composite electrolyte containing thiolized carbon nanotubes. Pulse electrodeposition is performed at a temperature of 25℃, a duty cycle of 35%, a current density of 3A / dm², and a pulse frequency of 150Hz for 10 minutes to form a composite tin layer with a thickness of 4μm. The temperature is then increased to 90℃ at a heating rate of 3℃ / min and held for 12 minutes, then increased to 115℃ and held for 12 minutes, then increased to 130℃ and held for 5 minutes, and then cooled to room temperature to obtain a highly flexible tin-plated round copper wire.

[0060] Comparative Example 4 The difference between this comparative example and Example 1 is that, in preparing the buffer layer solution containing modified graphene oxide, the modified graphene oxide is replaced by an equal mass of activated graphene oxide, which is obtained by post-treatment of the activated suspension. The remaining steps and raw materials are the same as in Example 1. A method for preparing activated graphene oxide includes the following steps: The mass ratio of graphene oxide powder, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, and deionized water was controlled at 1:2.5:1.5:280. Graphene oxide powder was added to deionized water and ultrasonically treated for 45 min at a frequency of 25 kHz and a power of 200 W to obtain a suspension. 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide were added to the suspension at a speed of 450 rpm. The mixture was stirred and reacted at room temperature and a speed of 450 rpm for 2 h. After the reaction was completed, an activated suspension was obtained. The suspension was centrifuged at a speed of 8000 rpm for 10 min. The precipitate was washed three times each with deionized water and anhydrous ethanol and then dried at 50 °C for 16 h to obtain activated graphene oxide. A method for preparing a buffer layer solution containing activated graphene oxide includes the following steps: The mass ratio of activated graphene oxide, bismaleimide, γ-mercaptopropyltrimethoxysilane, and anhydrous DMF was controlled at 1:4.5:1:90. The activated graphene oxide and anhydrous DMF were mixed evenly, and bismaleimide and γ-mercaptopropyltrimethoxysilane were added. The mixture was stirred for 2 hours at room temperature and 550 rpm to obtain a buffer layer solution containing activated graphene oxide.

[0061] Comparative Example 5 The difference between this comparative example and Example 1 is that in the original step S3, isothermal annealing is used instead of gradient annealing, while the remaining steps and raw materials are the same as in Example 1. A method for preparing highly flexible tin-plated round copper wire includes the following preparation steps: S1. Immerse the round copper wire in an alkaline degreasing solution at 45℃ for 3 minutes; then clean it with deionized water; then activate the washed round copper wire in a 5% sulfuric acid solution for 30 seconds; finally clean it again with deionized water to obtain pretreated copper wire. Immerse the pretreated copper wire in a rare earth activation solution at 30℃ for 60 seconds, then remove it and dry it with hot air at 45℃ for 25 seconds until there are no obvious liquid droplets on the surface to obtain a copper substrate. S2. Immerse the copper substrate in a buffer layer solution containing modified graphene oxide for 50 seconds, then remove it and heat-treat it at 90℃ for 30 minutes to form a buffer interface layer with a thickness of 0.2μm, thus obtaining the modified copper wire. S3. Using modified copper wire as the cathode and a high-purity tin plate with a polypropylene anode bag as the anode, the electrodeposition was carried out in a composite electrolyte containing thiolized carbon nanotubes. Pulse electrodeposition was performed for 10 min at a temperature of 25℃, a duty cycle of 35%, a current density of 3A / dm², and a pulse frequency of 150 Hz to form a composite tin layer with a thickness of 4 μm. The temperature was then raised to 130℃ at a heating rate of 3℃ / min and held for 29 min. After cooling to room temperature, a highly flexible tin-plated round copper wire was obtained.

[0062] Performance testing The comprehensive performance of the high-flexibility tin-plated round copper wires prepared in Examples 1-3 and Comparative Examples 1-5 of this invention was tested respectively.

[0063] 1. Tensile strength and elongation at break The test was conducted according to standard GB / T 4909.3-2009, "Test Methods for Bare Wires - Part 3: Tensile Test". High-flexibility tin-plated round copper wire specimens prepared in Examples 1-3 and Comparative Examples 1-5, each 500 mm in length, were used. Both ends of the specimen were clamped in upper and lower fixtures, ensuring the specimen axis coincided with the tensile centerline to avoid uneven loading. The initial gauge length between the fixtures was set to 200 mm, and a gauge length mark was made in the middle of the specimen. The ambient temperature was controlled at 23±2℃. A preload of 1 N was applied before the test to eliminate the effect of specimen relaxation. Then, continuous tensile testing was performed at a beam moving speed of 100 mm / min until the specimen broke. The maximum breaking force and the change in gauge length after breakage were recorded. Each group of samples was tested in parallel five times, and the average value was taken.

[0064] Tensile strength is calculated using the formula: σb=F max / A0, where F max The maximum breaking force is given by A0, which is the original metal cross-sectional area of ​​the conductor. The elongation at break is calculated using the formula: δ = (L1 - L0) / L0 × 100%, where L0 is the original gauge length and L1 is the gauge length after breakage.

[0065] 2. Coating adhesion test The tests were conducted according to standard GB / T 4909.11-2009, "Test Methods for Bare Wires - Part 11: Plating Adhesion Test". High-flexibility tin-plated round copper wire samples prepared in Examples 1-3 and Comparative Examples 1-5, each 250 mm in length, were tested at room temperature. The samples were spirally wound around a smooth test rod of a specified diameter to allow the plating to undergo adhesion testing. After winding, the plating condition on the outer periphery of the wound area was observed using a 10× magnifying glass. If the plating surface showed no cracks, peeling, flaking, or exposed copper, the sample was deemed to have acceptable adhesion; if any of these defects were present, the sample was deemed unacceptable.

[0066] 3. Interface bonding strength The scratch test was conducted using high-flexibility tin-plated round copper wire samples prepared in Examples 1-3 and Comparative Examples 1-5, each 50 mm in length. These samples were fixed on a scratch test bench, and a diamond indenter was used to scratch along the wire's axial direction. The scratch length was set to 5 mm, and the loading method was a gradually increasing load: an initial load of 0.5 N, an ending load of 20 N, a loading rate of 10 N / min, and a scratching rate of 5 mm / min. The critical load at which significant cracking or peeling of the plating or interface occurred was recorded as the interfacial bonding strength. The average value of five parallel tests was taken as the final result.

[0067] 4. Volume resistivity The tests were conducted in accordance with GB / T 3048.2-2007 "Test Methods for Electrical Properties of Wires and Cables - Part 2: Test for Resistivity of Metallic Materials". High-flexibility tin-plated round copper wire samples, each 1000 mm in length, prepared according to Examples 1-3 and Comparative Examples 1-5, were used. The resistance R of the samples was measured using the four-terminal method at 20±1℃. 20 Simultaneously, the effective length L of the sample and the cross-sectional area A of the metal conductor were measured.

[0068] Volume resistivity is calculated using the formula: ρ 20 =R 20 ×A / L, where R 20 The resistance value is given at 20℃, where A is the cross-sectional area of ​​the conductor metal and L is the measurement length.

[0069] 5. Rate of change of resistance The tests were conducted according to the standard GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test". High-flexibility tin-plated round copper wire samples with a length of 500 mm prepared in Examples 1-3 and Comparative Examples 1-5 were taken respectively. First, the initial resistance value R0 was measured at 20±1℃. Then, the samples were placed in a salt spray test chamber and sprayed with a 5% NaCl solution at 35℃ for 96 hours. After the test, the samples were rinsed with deionized water to remove salt spray deposits, dried at room temperature for 2 hours, and the resistance value R1 was measured again.

[0070] The rate of change of resistance is calculated using the formula: ΔR = (R1 - R0) / R0 × 100%, where R0 is the resistance value before the salt spray test and R1 is the resistance value after the salt spray test.

[0071] The specific test results are shown in Table 1.

[0072] Table 1: Performance parameters of the high-flexibility tin-plated round copper wires prepared in Examples 1-3 and Comparative Examples 1-5

[0073] As shown in Table 1, the high-flexibility tin-plated round copper wires prepared in Examples 1-3 of this invention are significantly better than those in Comparative Examples 1-5 in terms of tensile strength, elongation at break, coating adhesion, interfacial bonding strength, resistance change rate after salt spray test, and volume resistivity.

[0074] As can be seen from the data shown in Example 1 and Comparative Example 1, the use of graphene oxide powder to replace modified graphene oxide in Comparative Example 1 resulted in a decrease in the structural stability and interface reinforcement effect of the buffer interface layer, which in turn reduced the tensile strength, elongation at break and interface bonding strength of the tin-plated round copper wire, and increased the resistivity change rate and volume resistivity after the salt spray test.

[0075] As can be seen from the data shown in Example 1 and Comparative Example 2, the use of multi-walled carbon nanotubes instead of thiolized carbon nanotubes in Comparative Example 2 resulted in a weakening of the bonding ability between carbon nanotubes and the tin-based plating layer and the interface layer, and a decrease in the dispersion stability in the composite tin layer. Consequently, the tensile strength, elongation at break and interface bonding strength of the resulting tin-plated round copper wire decreased, and the resistivity change rate and volume resistivity increased after the salt spray test.

[0076] As can be seen from the data shown in Example 1 and Comparative Example 3, Comparative Example 3 used an activation solution that did not contain lanthanum chloride hexahydrate and cerium chloride hexahydrate, which resulted in a weakening of the activation effect on the copper substrate surface and a deterioration of the deposition and bonding state of the subsequent buffer interface layer and composite tin layer. As a result, the tensile strength, elongation at break and interface bonding strength of the obtained tin-plated round copper wire decreased, and the resistivity change rate and volume resistivity increased after the salt spray test.

[0077] As shown by the data from Example 1 and Comparative Example 4, the use of activated graphene oxide instead of modified graphene oxide in Comparative Example 4 resulted in insufficient interfacial synergy between graphene oxide and bismaleimide, γ-mercaptopropyltrimethoxysilane and the copper matrix, and a decrease in the reinforcing effect of the buffer interface layer. Consequently, the tensile strength, elongation at break and interfacial bonding strength of the obtained tin-plated round copper wire decreased, and the resistivity change rate and volume resistivity increased after the salt spray test.

[0078] As can be seen from the data shown in Example 1 and Comparative Example 5, the use of constant temperature annealing instead of gradient annealing in Comparative Example 5 resulted in insufficient stress release in the composite tin layer, poor optimization of the coating structure, and weakened interfacial bonding. Consequently, the tensile strength, elongation at break, and interfacial bonding strength of the obtained tin-plated round copper wire decreased, and the resistivity change rate and volume resistivity increased after the salt spray test.

[0079] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A highly flexible tin-plated round copper wire, characterized in that, From the inside out, it includes: copper substrate, buffer interface layer and composite tin layer; The copper substrate is a round copper wire activated by a rare earth activating solution; the buffer interface layer is formed by impregnating the surface of the copper substrate with a buffer layer solution containing modified graphene oxide and then heat-treating it; the composite tin layer is formed by electrodeposition on the surface of the buffer interface layer with a composite electrolyte containing thiolated carbon nanotubes.

2. The high-flexibility tin-plated round copper wire according to claim 1, characterized in that, The preparation method of the rare earth activation solution includes the following steps: Ammonium citrate and glycine were added to deionized water and stirred until homogeneous. The mixture was then heated to 45-55°C, and lanthanum chloride hexahydrate and cerium chloride hexahydrate were added. The mixture was stirred until homogeneous, and the pH of the system was adjusted to 3.5-4.5 to obtain the rare earth activation solution.

3. The high-flexibility tin-plated round copper wire according to claim 2, characterized in that, The mass ratio of ammonium citrate, glycine, lanthanum chloride hexahydrate, cerium chloride hexahydrate, and deionized water is 7:3-4:0.9-1.1:0.9-1.1:

100.

4. The high-flexibility tin-plated round copper wire according to claim 1, characterized in that, The method for preparing the modified graphene oxide includes the following steps: A1. Add graphene oxide powder to deionized water and sonicate to obtain a suspension. Under stirring, add 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to the suspension and stir to react. After the reaction is completed, an activated suspension is obtained. A2. Under nitrogen protection, furfurylamine was added to the activated suspension and stirred to react. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain modified graphene oxide.

5. The high-flexibility tin-plated round copper wire according to claim 1, characterized in that, The method for preparing the buffer layer solution containing modified graphene oxide includes the following steps: Modified graphene oxide and anhydrous DMF were mixed evenly, and bismaleimide and γ-mercaptopropyltrimethoxysilane were added and stirred evenly to obtain a buffer layer solution containing modified graphene oxide.

6. The high-flexibility tin-plated round copper wire according to claim 5, characterized in that, The mass ratio of the modified graphene oxide, bismaleimide, γ-mercaptopropyltrimethoxysilane and anhydrous DMF is 1:4.5-5.5:1-1.5:90-100.

7. The high-flexibility tin-plated round copper wire according to claim 1, characterized in that, The method for preparing the thiolized carbon nanotubes includes the following steps: B1. Mix multi-walled carbon nanotubes and deionized water, add sodium dodecylbenzenesulfonate, and sonicate to obtain a carbon nanotube suspension. B2. Add cysteine ​​to the carbon nanotube suspension, stir evenly, heat to 70-80℃, add hydrogen peroxide, stir to react, and after the reaction is completed, centrifuge, wash and dry to obtain thiolized carbon nanotubes.

8. The high-flexibility tin-plated round copper wire according to claim 1, characterized in that, The preparation method of the composite electrolyte containing thiolated carbon nanotubes includes the following steps: C1. Thiolized carbon nanotubes and deionized water are mixed, alkyl glycosides are added, and the mixture is ultrasonically treated to obtain a nano slurry. C2. Mix methanesulfonic acid and deionized water, add tin methanesulfonate, and stir until homogeneous to obtain MSA base solution; C3. Under stirring, the nano-slurry is added to the MSA base solution. After stirring evenly, ascorbic acid is added and stirring is continued to be evenly mixed to obtain a composite electrolyte containing thiolized carbon nanotubes.

9. A method for preparing a highly flexible tin-plated round copper wire according to any one of claims 1-8, characterized in that, The preparation steps include the following: S1. After pretreatment, the round copper wire is immersed in rare earth activation solution for impregnation treatment, and then dried with hot air to obtain a copper matrix. S2. After immersing the copper substrate in a buffer layer solution containing modified graphene oxide, remove it and perform heat treatment to form a buffer interface layer, thus obtaining modified copper wire. S3. Using modified copper wire as the cathode and a high-purity tin plate with a polypropylene anode bag as the anode, the copper wire is placed in a composite electrolyte containing thiolated carbon nanotubes for electrodeposition treatment to form a composite tin layer. Then, it is subjected to gradient annealing to obtain a highly flexible tin-plated round copper wire.

10. The method for preparing high-flexibility tin-plated round copper wire according to claim 9, characterized in that, The electrodeposition process in step S3 refers to: using pulsed electrodeposition, electrodepositing for 8-10 minutes under the conditions of temperature 25-35℃, duty cycle 35-45%, current density 3-4A / dm², and pulse frequency 150-200Hz.

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