A method for improving edge lifting of a negative electrode current collector copper foil for a lithium ion secondary battery

Abstract

The present application relates to the technical field of lithium ion secondary battery material, and particularly relates to a method for improving edge warping of negative electrode current collector copper foil for lithium ion secondary battery. The method comprises the following steps: electroplating liquid improvement, adding small molecule polyether with a molecular weight of 300-1000 as a walking agent in the copper foil electroplating liquid; online stress release, performing online heating treatment at 80-120 DEG C on the copper foil after passivation and before winding; real-time detection and feedback adjustment, real-time detection of the warping height of the edge of the copper foil and automatic adjustment of the heating temperature. The present application narrows the size difference between the smooth surface and the rough surface to below 0.16 microns, reduces the internal stress by 80%, stably controls the dynamic warping height to below 5 mm, and obtains the copper foil with a thickness of 4-10 microns, a yellow print defect rate of less than or equal to 2%, a tearing edge rate of less than or equal to 1%, and a copper foil finished product rate of greater than or equal to 90%, effectively solves the problem of edge warping of the copper foil, and significantly improves the production qualified rate and the battery performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion secondary battery materials technology, and in particular to a method for improving the edge curling of copper foil in the negative electrode current collector of lithium-ion secondary batteries. Background Technology

[0002] The core performance characteristics of lithium-ion secondary batteries, such as energy density, cycle life, and safety, are directly related to the performance of the copper foil in the negative electrode current collector. As a key carrier for the negative electrode active material, the negative electrode current collector must simultaneously meet three core requirements: high conductivity, excellent mechanical properties, and good chemical stability.

[0003] Currently, the industry commonly uses electrolytic copper foil as the negative electrode current collector, with a thickness mostly concentrated between 4-10 micrometers, in an attempt to achieve a balance between battery lightweighting and processing feasibility. However, copper foil in this thickness range has always faced the technical challenge of edge curling in production and application, becoming a key bottleneck restricting battery process stability, product yield, and end-use performance.

[0004] Edge curling of rolled copper foil can trigger a series of cascading technical problems: First, during the foil-making process, curling leads to incomplete acid and water extraction, causing residual liquid to react chemically and form brown oxide precipitates, resulting in yellowing defects and causing the copper foil to be downgraded or scrapped. Simultaneously, residual anti-oxidation solution reduces the adhesion between the copper foil and the negative electrode active material. Second, during the winding and slitting stages, curling easily leads to edge tearing, resulting in reduced yield and production accidents. Furthermore, curling also reduces slitting accuracy and widens width tolerances, creating safety hazards during cell assembly. Finally, during battery manufacturing, curling can cause uneven coating thickness, wrinkles or even strip breakage during rolling, and poor welding of the electrode tabs, severely affecting the battery's rate performance, cycle stability, and safety, and in severe cases, even causing thermal runaway.

[0005] To address these issues, various technical solutions have been proposed within the industry. Some studies attempt to improve copper foil performance by optimizing electroplating additives. For example, Chinese patent application CN102965698A discloses a low-warpage electrolytic copper foil production process, the core of which involves continuously adding low-molecular-weight collagen as an additive to a copper sulfate solution, while simultaneously adjusting the copper acid concentration and temperature of the electrolyte to produce low-stress, low-warpage electrolytic copper foil. However, this primarily focuses on the impact of collagen on overall stress, failing to deeply analyze and resolve the fundamental internal cause of warpage—the difference in grain structure between the smooth and rough surfaces of the copper foil (fine grains on the smooth surface, large grains on the rough surface). Other solutions attempt to release stress through physical means. For example, Chinese patent application CN212925089U discloses an online heating device for reducing the warpage of electrolytic copper foil. This device uses a housing with a heating plate placed before the winding roller to uniformly heat the electrolytic copper foil to release its stress. However, this is a single-stage process adjustment and does not involve optimizing the source of copper foil deposition—the grain structure. Therefore, it cannot fundamentally eliminate the root cause of internal stress, resulting in limited improvement. Furthermore, some solutions comprehensively improve copper foil performance by adding composite additives in stages. For example, patent application CN115287715A discloses a production process for dual-bright copper foil for medium-tensile strength lithium batteries. This process aims to improve tensile strength, reduce roughness, and prevent warping of ultra-thin copper foil through the combined use of pre- and post-processing additives. However, its warping control index (not greater than 8mm) is relatively lenient, and its complex additive system does not precisely control the warping microstructure of the asymmetric structure of the smooth / rough surface.

[0006] However, the aforementioned existing technologies generally suffer from the following shortcomings: First, there is insufficient understanding of the root causes of edge warping, and most solutions only address the symptoms, failing to eliminate internal stress at the microscopic level; second, most are isolated optimizations of single aspects, such as adjusting additives or adding heating devices only; and third, the improvement effects are limited and the stability is poor, making it difficult to meet the increasingly stringent requirements of lithium-ion battery manufacturing. Therefore, there is an urgent need for a systematic method that can fundamentally solve the problem of copper foil edge warping and achieve stable, efficient, and industrially applicable solutions. Summary of the Invention

[0007] In view of the shortcomings of the prior art described above, the present invention provides a method for improving the edge curling of copper foil for negative electrode current collectors in lithium-ion secondary batteries. It is particularly suitable for electrolytic copper foil with a thickness of 4 to 10 micrometers and can be widely used in the preparation process of negative electrode current collectors for power lithium-ion batteries (e.g., for new energy vehicles), energy storage lithium-ion batteries (e.g., for grid energy storage and home energy storage), and consumer lithium-ion batteries (e.g., for mobile phones and computers).

[0008] The first aspect of this invention provides a method for improving the edge curling of copper foil in a negative electrode current collector for lithium-ion secondary batteries, comprising the following steps:

[0009] (A) Electroplating solution improvement: Add a position agent to the copper foil electroplating solution, wherein the position agent is a small molecule polyether with a molecular weight of 300~1000;

[0010] (B) Online stress relief: After passivation and before winding in the copper foil forming machine, the copper foil is subjected to online heating treatment at a temperature of 80~120℃;

[0011] (C) Real-time detection and feedback adjustment: Before the copper foil is wound up, the warping height of the copper foil edge is detected in real time, and the heating temperature of the online heating step is automatically adjusted according to the detection results.

[0012] The second aspect of the present invention provides a copper foil for a negative electrode current collector for a lithium-ion secondary battery, which is prepared by the above-described method for improving the edge curling of the copper foil for a negative electrode current collector for a lithium-ion secondary battery.

[0013] A third aspect of the present invention provides a system for improving edge warping of copper foil in a negative electrode current collector for lithium-ion secondary batteries, for implementing the above-described method, comprising:

[0014] Electrolysis unit, used for electrodeposition to form copper foil;

[0015] An online stress relief unit, located downstream of the electrolysis unit, includes an online drying oven for online heating treatment of copper foil;

[0016] A real-time detection and feedback adjustment unit, located downstream of the online stress relief unit, includes a warping detection device and a control system. The warping detection device is used to collect warping height data of the copper foil edge in real time. The control system is communicatively connected to the warping detection device and the online oven, and is used to receive the warping height data and automatically adjust the heating temperature of the online oven according to a preset value.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] 1. This invention utilizes small-molecule polyethers (molecular weight 300-1000) to regulate the grain structure from the source, reducing the grain size difference between smooth and rough surfaces from 0.47μm in traditional processes to below 0.16μm, and decreasing the internal stress difference from 210MPa to ≤48MPa. Combined with online heating treatment at 80~120℃, the internal stress reduction rate reaches 80%, and the dynamic warpage height is stably controlled below 5mm (as low as 2.7mm) from 8.6mm, a reduction of over 54%, fundamentally solving the problem of copper foil edge warpage. Precise optimization has been achieved for copper foils of different thicknesses: the grain size difference for 4~6μm thin copper foil is ≤0.15μm (0.14μm in Example 1, 0.13μm in Example 2), and the internal stress difference for 7~10μm thick copper foil is ≤40MPa (38MPa in Example 3), solving the problem of insufficient specificity in general formulations.

[0019] 2. The copper foil prepared by this invention reduces the yellowing defect rate from 8.2% in traditional processes to 1.2% (a reduction of 85.4%), the edge tearing rate from 8.5% to 0.8% (a reduction of 90.6%), the coating uniformity error from 8.3% to 2.5%, and the roll breakage rate from 1.2% to 0.3%. The copper foil yield rate increases from 80.3% to over 91.2% (up to 92.5%), the production line utilization rate increases to over 85%, and the production efficiency increases by 15%. Lithium-ion batteries prepared using the copper foil of this invention have a warpage height ≤5mm (2.7~3.6mm), resulting in a tight fit between the tabs and the copper foil. This avoids tab folding and welding defects caused by warpage, reduces the risk of sudden increases in battery internal resistance and thermal runaway, and significantly improves the cycle stability and safety of the battery.

[0020] 3. This invention forms a three-in-one synergistic system of source control, process adjustment, and real-time correction. Through real-time detection and feedback adjustment (warning value 3mm), it ensures stable and controllable warpage height. All indicators of this synergistic solution are significantly superior to single-stage optimization solutions (additive improvement only, online heating only, real-time detection and adjustment only), demonstrating the necessity of the synergistic effect of the three steps. The method of this invention can be adapted to existing production lines, with a single-line modification cost of ≤200,000 RMB and an investment payback period of ≤6 months. It is applicable to copper foil of all specifications from 4 to 10 μm, meeting the needs of power, energy storage, and consumer batteries, and is both environmentally friendly and economical. This invention reduces copper foil scrap and raw material waste by lowering the yellowing defect rate and tearing rate, while also reducing the emission of pollutants such as pickling waste liquid and copper foil debris, meeting the requirements of green production. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the copper foil warping phenomenon described in the present invention. The arrows in the diagram indicate the warping direction, illustrating the characteristic of the copper foil warping from the smooth side to the rough side.

[0022] Figure 2SEM comparison images of the smooth and rough grain structures of copper foil prepared by traditional processes, with the left image showing the smooth surface with fine grain structure and the right image showing the rough surface with large grain structure.

[0023] Figure 3 This is a schematic diagram of the installation of the online drying oven and edge warping detection device described in this invention.

[0024] Figure label:

[0025] A - Smooth surface of copper foil; B - Rough surface of copper foil; 1 - Electrolytic cell; 2 - Cathode roller; 3 - Copper foil; 4 - Peeling roller; 5 - Transition roller; 6 - Passivation tank; 7 - Passivation liquid roller; 8 - Lower passivation squeezing roller; 9 - Upper passivation squeezing roller; 10 - Oven fan; 11 - Online oven; 12 - Transition roller; 13 - Copper foil trimming roller; 14 - Edge warping detection device; 15 - Transition roller; 16 - Rewinding roller and copper foil roll. Detailed Implementation

[0026] The following specific embodiments further illustrate a method for improving the edge curling of copper foil in the negative electrode current collector of lithium-ion secondary batteries.

[0027] In this invention, copper foil edge curling refers to the directional warping phenomenon that occurs in the edge region (within a range of 5-100mm from the edge) of electrolytic copper foil used in lithium-ion secondary batteries along the width direction (perpendicular to the copper foil winding direction) during the foil forming, winding, slitting, and battery manufacturing processes. Macroscopically, it exhibits the characteristic of warping from smooth to rough surfaces (e.g., ...). Figure 1 (As shown). Warpage height is primarily measured by the vertical distance between the highest point of the copper foil edge and the reference plane. Essentially, it's due to the imbalance of internal stress caused by the difference in microstructure between the smooth and rough surfaces of the copper foil. Specifically, the smooth surface, influenced by the fine-grained template on the titanium roller surface, initially deposits small copper grains (approximately 0.4~0.5μm) with high grain orientation consistency; while the rough surface, under the action of traditional macromolecular polyether (molecular weight 5000~6000) dispersing agents, forms an unevenly thick hindrance layer, causing the grains to gradually grow (approximately 0.8~0.9μm), resulting in an asymmetric structure of fine grains on the smooth surface and large grains on the rough surface (e.g., ...). Figure 2 As shown in the figure, this generates a difference in internal stress, which in turn causes warping.

[0028] Existing solutions for copper foil edge curling have the following drawbacks: First, there is insufficient understanding of the root causes of curling, and physical suppression methods such as adjusting winding tension and increasing squeeze roller pressure are often used, which are only temporary solutions and result in a high curling rebound rate. Second, additive optimization is not designed to address the uniformity of grain growth. Traditional macromolecular polyether molecules are too long and disperse unevenly in the electrolyte, exacerbating the grain size difference between smooth and rough surfaces. Third, there is a lack of real-time feedback and adjustment mechanisms, relying mainly on manual inspection, which makes it impossible to adjust process parameters in a timely manner. Fourth, optimization of individual links lacks collaborative design and has not formed a complete technical solution of source control, process adjustment, and real-time correction.

[0029] To solve the above-mentioned technical problems, the first aspect of the present invention provides a method for improving the edge curling of copper foil for negative electrode current collectors in lithium-ion secondary batteries, comprising the following steps:

[0030] (A) Electroplating solution improvement: Add a position agent to the copper foil electroplating solution, wherein the position agent is a small molecule polyether with a molecular weight of 300~1000;

[0031] (B) Online stress relief: After passivation and before winding in the copper foil forming machine, the copper foil is subjected to online heating treatment at a temperature of 80~120℃;

[0032] (C) Real-time detection and feedback adjustment: Before the copper foil is wound up, the warping height of the copper foil edge is detected in real time, and the heating temperature of the online heating step is automatically adjusted according to the detection results.

[0033] This invention systematically studied the microscopic mechanism of copper foil edge warping using scanning electron microscopy, X-ray diffraction, and electron backscattering diffraction. The core mechanism by which small-molecule polyethers replace traditional large-molecule polyethers lies in the following: the smaller molecular size of small-molecule polyethers (radius of gyration approximately 0.5~1.0 nm) allows for more uniform dispersion in the electrolyte, resulting in a uniformly thick barrier layer that avoids localized accumulation caused by the chain length of large-molecule polyethers; the moderate inhibitory effect of small-molecule polyethers on copper atom deposition increases the nucleus density by approximately three times without excessively hindering grain growth, ultimately reducing the grain size difference between smooth and rough surfaces and lowering the internal stress difference.

[0034] To verify the effects of polyethers with different molecular weights, comparative experiments were conducted, and the results are shown in Table 1. Table 1 shows that small molecule polyethers with molecular weights of 300-1000 can achieve a grain size difference ≤0.3μm, an internal stress difference ≤80MPa, and a warpage height ≤3.4mm. The preferred molecular weight range is 300-800, which achieves even better results with an internal stress difference ≤55MPa and a warpage height ≤2.4mm. When the molecular weight is higher than 1000, the excessively long molecular chains easily lead to localized aggregation, causing the grain size difference to rise back to the critical value of 0.3μm, and the internal stress difference to exceed 80MPa.

[0035] Table 1. Effects of polyethers of different molecular weights on grain structure and warpage height

[0036]

[0037] Note: The test conditions were as follows: copper foil thickness 6μm, electroplating solution basic formula: copper ions 90g / L, sulfuric acid 110g / L, chloride ions 30mg / L, polyether addition 5mg / L, brightener addition 6.5mg / L, leveling agent addition 4mg / L, stabilizer addition 1.5mg / L, grain refiner addition 2mg / L, and dynamic warpage test method was used.

[0038] In some embodiments of the present invention, in step (A), the small molecule polyether is selected from at least one of polyethylene glycol (PEG), polypropylene glycol (PPG), or a copolymer of the two. Preferably, the molecular weight of the small molecule polyether is 300-800, and can be 300-400, 400-500, 500-600, 600-700, or 700-800. More preferably, it is PEG-400, PEG-600, or PPG-500. These small molecule polyethers have excellent stability in the electrolyte (no decomposition after 15 days of continuous use at 60°C, additive loss rate ≤10%), and no antagonistic effect with other additives.

[0039] In some embodiments of the present invention, the amount of the small molecule polyether added is 3~8 mg / L, specifically 3~4 mg / L, 4~5 mg / L, 5~6 mg / L, 6~7 mg / L, or 7~8 mg / L. To verify the effect of the amount of small molecule polyether (PEG-400) added on the edge-curling improvement effect, a comparative experiment was conducted, and the results are shown in Table 2. As can be seen from the experimental data in Table 2, when the addition amount is less than 3 mg / L, the crystal nucleus density is low (1.8 × 10⁻⁶). 6 pcs / cm 2 The grain size control effect was not significant, with a warpage height ≥4.3mm. When the addition amount exceeded 8mg / L, it excessively inhibited the copper deposition rate (reducing it from 2.1μm / min to below 1.5μm / min), reducing production efficiency, and the improvement in warpage height tended to saturate. The optimal addition amount was 5~8mg / L, which could achieve a crystal nucleus density ≥3.2×10⁻⁶. 6 pcs / cm 2 It exhibits excellent performance with grain size difference ≤0.14μm and warpage height ≤2.7mm.

[0040] Table 2. Effect of the amount of small molecule polyether (taking PEG-400 as an example) added on the effect of improving edge curling.

[0041]

[0042] Note: Test conditions: copper foil thickness 6μm, dynamic warpage test method.

[0043] In some embodiments of the present invention, the basic formulation of the copper foil electroplating solution is: 85-95 g / L copper ions, 100-120 g / L sulfuric acid, and 20-40 mg / L chloride ions. The concentration of chloride ions can be 20-25 mg / L, 25-30 mg / L, 30-35 mg / L, or 35-40 mg / L. Controlling the chloride ion concentration at 20-40 mg / L can improve the surface gloss of the copper foil and inhibit dendrite growth.

[0044] In some embodiments of the present invention, a synergistic agent is further added to the copper foil electroplating solution. The synergistic agent is selected according to the thickness of the target copper foil: when the copper foil thickness is 4~6 μm, the synergistic agent is a nitrogen-containing heterocyclic compound, and its addition amount is 0.5~1 mg / L; when the copper foil thickness is 7~10 μm, the synergistic agent is an organophosphonate, and its addition amount is 5~10 mg / L. The nitrogen-containing heterocyclic compound is an imidazole derivative, preferably 2-methylimidazole; the organophosphonate is hydroxyethylidene diphosphonic acid.

[0045] This invention achieves precise control through thickness-adaptive synergistic optimization, combined with the size effect of copper foil thickness. The core role of nitrogen-containing heterocyclic compounds (such as 2-methylimidazole) is to enhance crystal nucleus refinement, further reducing the grain size difference between smooth and rough surfaces; the core role of organophosphonates (such as HEDP) is to improve grain boundary bonding and reduce internal stress difference. To verify the synergistic effect of adding additives to copper foils of different thicknesses, comparative experiments were conducted, and the results are shown in Table 3. As shown in Table 3, after adding 2-methylimidazole to 4-6 μm thin copper foil, the grain size difference was further reduced from 0.16 μm to 0.13-0.14 μm, a reduction of 12.5%-18.75%, strengthening the suppression of edge warping at its source. After adding organophosphonates to 7-10 μm thick copper foil, the grain boundary bonding was improved, controlling the internal stress difference below 40 MPa, avoiding edge warping rebound caused by internal stress accumulation in thick foils (see Example 3, internal stress difference 38 MPa).

[0046] Table 3 Synergistic Effects of Additives for Copper Foil of Different Thicknesses

[0047]

[0048] Note: The test conditions were as follows: copper foil thickness of 4μm and 6μm, basic electroplating solution formulation of copper ions 90g / L, sulfuric acid 110g / L, chloride ions 30mg / L, PEG-400 addition of 5mg / L, brightener addition of 6.5mg / L, leveling agent addition of 4mg / L, stabilizer addition of 1.5mg / L, grain refiner addition of 2mg / L, and dynamic warpage test method was used.

[0049] In some embodiments of the present invention, the copper foil electroplating solution further contains 4-8 mg / L of brightener, 3-8 mg / L of leveling agent, 0.5-2 mg / L of stabilizer, and 1-3 mg / L of grain refiner. Preferably, the brightener is sodium polydisulfide dipropane sulfonate (SPS), used to improve the surface gloss of the copper foil (target gloss ≥ 100 GU); the leveling agent is collagen, used to optimize the surface smoothness of the copper foil (target surface roughness Ra ≤ 0.2 μm); the stabilizer is hydroxyethyl cellulose (HEC), which can be adsorbed around copper ions, reducing the probability of copper ions combining with hydroxide ions, inhibiting the formation of copper hydroxide precipitate, and extending the service life of the plating solution; the grain refiner is 2-mercaptobenzimidazole (MBI), which can form a dense adsorption film on the cathode surface, significantly refining the grains and inhibiting pinholes in the plating layer. The grain refiner and small molecule polyether have a synergistic effect, and under their combined action, the surface gloss of the copper foil can be further improved without affecting the uniformity of the grains.

[0050] In some embodiments of the present invention, the current density of the electrolysis process is controlled at 45~65 A / dm². 2 Preferably, it is 50~60 A / dm 2 Too low a current density will lead to a decrease in deposition rate and reduced production efficiency; too high a current density may result in coarse grains and increased internal stress. In some embodiments of the present invention, the electrolyte temperature in the electrolysis process is controlled at 48~55°C, preferably 50~53°C, and more preferably 52°C.

[0051] In some embodiments of the present invention, in step (B), the heat treatment is performed within 30 seconds after the copper foil is formed. If the heat treatment is delayed (e.g., cooled to room temperature and then reheated), the stress release effect will decrease by more than 40% (at 100°C, the stress release rate is 75% with immediate heating, but only 45% with delayed heating for 2 hours). In the present invention, the copper foil forming refers to the state of the copper foil after electrodeposition and peeling on the surface of the cathode roller. Since the time from peeling to entering the passivation tank is usually controlled at 10-15 seconds, and the passivation treatment time is about 5-8 seconds, the 30 seconds after forming actually corresponds to immediate heating after passivation, ensuring that the copper foil is subjected to heat treatment within a total time of no more than 30 seconds after peeling. The online heating temperature is adjusted according to the copper foil thickness: the online heating temperature for 4-6μm thin copper foil is 80-100°C (thin copper foil has slightly poor thermal stability and is easily deformed at high temperatures), and the online heating temperature for 7-10μm thick copper foil is 90-120°C (thick copper foil has greater internal stress and requires higher temperature for release). The copper foil passes through at a speed synchronized with the foil-making machine's winding speed.

[0052] The thermodynamic mechanism of online heating lies in the fact that heating temperatures of 80~120℃ can enhance the atomic mobility of copper foil (increasing the diffusion coefficient to 1×10⁻⁶). -12 m2 (At temperatures exceeding / s, which are 5 to 10 times higher than room temperature), grain boundary slip intensifies, and internal stress is gradually released through atomic rearrangement. The stress release rate is positively correlated with temperature: 60% at 80℃, 75% at 100℃, and 85% at 120℃. During the heating process, the copper foil tension needs to be controlled at 20~25 kgf (approximately 200~245 N). Excessive tension will cause the copper foil to stretch and deform, generating new stress, while insufficient tension will cause the copper foil to wrinkle, affecting the uniformity of stress release.

[0053] The results of the comparative experiment on the synergistic effect and the improvement effect of a single step are shown in Table 4. As can be seen from the data in Table 4, online heating and small molecule polyether modification have a significant synergistic effect. Modification with a single additive can reduce internal stress by 59.5%, and online heating alone can reduce internal stress by 35.2%. However, the synergistic effect of both can reduce internal stress by 80%, far exceeding the improvement effect of a single method, demonstrating the necessity of the synergistic effect of the three steps.

[0054] Table 4 Comparison of synergistic effects and improvement effects of single-step processes

[0055]

[0056] Note: The test conditions were as follows: copper foil thickness 6μm, electroplating solution basic formula: copper ions 90g / L, sulfuric acid 110g / L, chloride ions 30mg / L, polyether addition 5mg / L, brightener addition 6.5mg / L, leveling agent addition 4mg / L, hydroxyethyl cellulose (HEC) addition 1.5mg / L, grain refiner addition 2mg / L, online heating temperature 100℃, and dynamic warpage test method.

[0057] In some embodiments of the present invention, the online heating treatment is performed using a horizontal continuous oven, which includes: a shell having an inlet and an outlet for copper foil to pass through; and a heating assembly disposed within the shell, the heating assembly including infrared heating tubes and a hot air circulation system, the infrared heating tubes being evenly arranged on the upper and lower sides of the copper foil, and the hot air circulation system being used to ensure uniform temperature within the shell. In some specific embodiments of the present invention, the maximum adjustable spacing of the infrared heating tubes is 200mm (for easy foil passing). In some specific embodiments of the present invention, the hot air circulation system is provided by a centrifugal fan (air volume 1000m³ / h). 3 The oven consists of a baffle plate and a hot air deflector, with the preferred hot air velocity being 0.5~1.0 m / s. In some specific embodiments of the invention, elastic sealing curtains (e.g., made of silicone, 10 mm thick) are provided at the oven inlet and outlet to reduce the entry of cold air.

[0058] This invention employs a heating method combining infrared heating and hot air circulation. The heat radiated by the infrared heating tube can quickly penetrate the surface of the copper foil, achieving rapid temperature rise. The hot air circulation system uses forced convection to ensure uniform temperature distribution within the oven, preventing localized overheating. This combination guarantees both heating efficiency and temperature uniformity (≤±2℃) along the width and length of the copper foil, thereby ensuring uniform stress release across the entire copper foil. It should be noted that the combination of infrared heating and hot air circulation is a preferred embodiment of this invention. Those skilled in the art can employ other heating methods capable of achieving uniform heating according to actual needs; these equivalent substitutions all fall within the scope of protection of this invention.

[0059] In some specific embodiments of the present invention, the oven has a length of 1.0~1.5m and a width adapted to the maximum width of copper foil (1600mm). A 50mm thick insulation layer (rock wool) is used to reduce heat loss, and high-temperature resistant sealant (≥200℃) is used at the joints to prevent heat leakage. Three temperature sensors (inlet, middle, and outlet) are installed inside the oven, and closed-loop temperature control is achieved through a PLC controller. The internal temperature uniformity is ≤±2℃, and the temperature control accuracy is ±1℃.

[0060] During online heating, the operating tension of the copper foil needs to be controlled between 20 and 25 kgf (approximately 200 to 245 N). This tension range ensures that the copper foil moves smoothly within the oven without wrinkling, while also preventing the introduction of new tensile stress due to excessive tension. If the tension is below 20 kgf, the copper foil is prone to shaking or wrinkling under the influence of hot air, affecting the uniformity of stress release; if the tension is above 25 kgf, it may cause plastic deformation of the copper foil, generating new internal stress and negating the stress release effect of the heat treatment.

[0061] In some embodiments of the present invention, in step (C), the warp height data of the copper foil edge is collected in real time by a two-dimensional laser displacement sensor, and the controller compares the real-time warp height with a preset value. When the warp height exceeds the preset value, the heating temperature of the online heating step is automatically adjusted. The two-dimensional laser displacement sensor (such as Keyence IL-300) has a measurement range of 0~50mm, a measurement accuracy of ±1mm, and a sampling frequency of 100Hz. One sensor is set at each edge of the copper foil (two in total, arranged on the left and right sides respectively). The sensor is installed at a height of 5~50mm from the copper foil reference surface, and the installation angle is perpendicular to the copper foil surface. The average value of the copper foil warp height within one circumference of the cathode roller is calculated as the real-time warp degree. The PLC controller is communicatively connected to the two-dimensional laser sensor and the online oven, collects data in real time, and outputs adjustment signals. Preferably, the PLC controller is communicatively connected to the laser sensor and the temperature control valve of the online oven, collects data in real time, and outputs adjustment signals to realize the automatic adjustment of baking process parameters.

[0062] In some embodiments of the present invention, the preset values ​​include a warning value of 3mm and an alarm value of 10mm; when 3mm < real-time warp height ≤ 10mm, the oven temperature is adjusted; when the real-time warp height > 10mm, an alarm is issued. The warning value of 3mm is set based on the following: considering the requirements of subsequent processes (the maximum allowable warp height for coating and slitting processes), when the warp height exceeds 3mm, it begins to affect the coating uniformity and slitting accuracy, requiring intervention and adjustment. The alarm value of 10mm is set based on the following: when the warp height exceeds 10mm, it has seriously affected subsequent processes, requiring machine shutdown and manual intervention.

[0063] In some embodiments of the present invention, the feedback adjustment adopts a tiered adjustment strategy: when the real-time warpage height is ≤3mm, the current heating temperature is maintained; when 3mm < real-time warpage height ≤10mm, the oven temperature is adjusted (incrementing by 2~5℃, with a maximum not exceeding 120℃); when the real-time warpage height is >10mm, an alarm is issued, and an engineer confirms whether to stop the machine for inspection or adjust the winding tension. Through real-time detection and feedback adjustment, process parameters can be adjusted in a timely manner to address fluctuations in the production process (such as changes in raw material composition and ambient temperature), ensuring stable control of the warpage height.

[0064] Table 5 shows a comparison of the improvement effects of the synergistic solution with those of each individual step. As can be seen from the data in Table 5, the present invention achieves comprehensive optimization of key indicators such as warpage height, yellowing defect rate, tearing rate, coating uniformity error, and roll breakage rate through the synergistic effect of the three major steps. The copper foil yield is increased from 80.3% in the traditional solution to 91.2%, which is significantly better than the single-step optimization solution.

[0065] Table 5 Comparison of the improvement effects of the collaborative solution and each individual link

[0066]

[0067] Note: The test conditions were a copper foil thickness of 6 μm, dynamic warpage test method, and a sample size of 8000 m of copper foil. Electroplating solution composition for each scheme: the traditional scheme and the schemes with only online heating and only real-time detection and adjustment used the formulation of Comparative Example 1 (traditional macromolecular polyether PEG-6000); the schemes with only additive modification and additive modification (including thickness-adaptive additives) used a small molecule polyether formulation (PEG-400, basic formulation same as in Table 1); the synergistic scheme of this invention used the complete formulation of Example 2 (small molecule polyether PEG-600 + 2-methylimidazole).

[0068] The following is combined with Figure 3 The complete process flow of the method for improving the edge curling of copper foil in negative electrode current collectors for lithium-ion secondary batteries described in this invention is explained.

[0069] The production of copper foil begins in electrolytic cell 1. In electrolytic cell 1, electrolyte is deposited on the surface of rotating cathode roller 2 under the action of an electric field to form copper foil 3. After deposition, the copper foil 3 rotates with cathode roller 2, is peeled off from the surface of cathode roller 4 by peeling roller 4, and then guided into the post-processing process by transition roller 5.

[0070] The copper foil first enters the passivation tank 6 for anti-oxidation treatment. The passivation liquid is carried by the passivation liquid roller 7 to treat the surface of the copper foil. Then, it is squeezed by the lower passivation squeezing roller 8 and the upper passivation squeezing roller 9 to remove the residual passivation liquid on the surface.

[0071] After passivation, the copper foil enters the online drying oven 11. The online drying oven 11 is equipped with an oven fan 10 to achieve hot air circulation, and simultaneously works with an infrared heating tube to uniformly heat the copper foil. The online stress release in step (B) of this invention is achieved at this stage, accelerating the release of internal stress in the copper foil through heating treatment at 80~120℃. The copper foil's throughput speed is synchronized with the subsequent winding speed.

[0072] After being processed in the online drying oven, the copper foil enters the copper foil trimming roller 13 through the transition roller 12 for trimming, removing a 15-30mm wide area from the edge. This area may have acid seepage oxidation or uneven thickness, which may affect the accuracy of warpage detection.

[0073] After trimming, the copper foil enters the warping detection device 14, which uses a two-dimensional laser displacement sensor to detect the warping height of the copper foil edge in real time. The two-dimensional laser displacement sensor is fixedly installed using an aluminum profile bracket. During installation, a level is used for calibration to ensure that the horizontal deviation of the sensor installation is ≤±0.1° to guarantee measurement accuracy. The real-time detection and feedback adjustment in step (C) of this invention is realized in this stage. The detection data is transmitted to the control system (such as a PLC controller, not shown in the figure) in real time. The control system is communicatively connected to the temperature adjustment unit of the online oven 11. According to preset logic (such as a warning value of 3mm and an alarm value of 10mm), the control system outputs adjustment signals to the oven to control the heating temperature. When the warping height exceeds the preset value, the system automatically adjusts the heating temperature of the online oven 11 to form a closed-loop control.

[0074] Finally, the qualified copper foil is guided by the transition roller 15 and wound up by the winding roller and the copper foil roll 16.

[0075] Through the above complete process flow, this invention organically integrates the three steps of electroplating additive improvement, online stress release, and real-time detection and feedback adjustment into the same production line, forming a synergistic system of source control, process adjustment, and real-time correction, which fundamentally solves the problem of copper foil edge warping.

[0076] The second aspect of the present invention provides a copper foil for a negative electrode current collector for lithium-ion secondary batteries, which is prepared by the above-mentioned method for improving the edge warping of the copper foil for a negative electrode current collector for lithium-ion secondary batteries. The thickness of the copper foil is 4~10μm, and the edge warping height measured by the dynamic warping test method is ≤5mm, the yellowing defect rate is ≤2%, the tearing rate is ≤1%, and the copper foil yield is ≥90%.

[0077] In this invention, the dynamic warpage testing method is implemented as follows: A two-dimensional laser displacement sensor (e.g., Keyence IL-300) is installed above each of the left and right edges of the copper foil, before the winding station of the foil forming machine and after the edge-cutting roller. The sensor is installed 20-30 mm above the copper foil reference surface, with the installation angle perpendicular to the copper foil surface to ensure the measuring beam is incident perpendicularly. The sensor continuously collects warpage height data of the copper foil edges at a sampling frequency of 100 Hz. This sampling frequency can be adjusted according to production speed and detection requirements. The control system uses one revolution of the cathode roller (e.g., cathode roller diameter 2.5 m, circumference 7.85 m) as a calculation cycle, and takes the arithmetic mean of all warpage height data collected within this cycle as the real-time warpage of the copper foil. This testing method overcomes the limitations of traditional disc sampling methods, which can only detect static, localized areas, and can truly reflect the edge warpage of the rolled copper foil under actual operating conditions.

[0078] The dynamic warpage test method of this invention overcomes the detection blind spot of static qualification and dynamic edge warpage in the traditional disc sampling method. It can truly reflect the edge warpage behavior of rolled copper foil under actual operating conditions. The measured warpage height ≤ 5mm directly corresponds to the processing stability of subsequent coating and slitting processes.

[0079] A third aspect of the present invention provides a system for improving edge warping of copper foil in a negative electrode current collector for lithium-ion secondary batteries, for implementing the above-described method, comprising:

[0080] Electrolysis unit, used for electrodeposition to form copper foil 3;

[0081] An online stress relief unit, located downstream of the electrolysis unit, includes an online drying oven 11 for online heating treatment of copper foil;

[0082] A real-time detection and feedback adjustment unit is located downstream of the online stress relief unit and includes a warping detection device 14 and a control system. The warping detection device 14 is used to collect warping height data of the copper foil edge in real time. The control system is communicatively connected to the warping detection device 14 and the online oven 11 and is used to receive the warping height data and automatically adjust the heating temperature of the online oven 11 according to a preset value.

[0083] In some embodiments of the present invention, the system further includes a passivation treatment unit disposed between the electrolysis unit and the online stress relief unit, including a passivation tank 6 and passivation squeezing rollers (lower passivation squeezing roller 8 and upper passivation squeezing roller 9), for performing anti-oxidation treatment on the copper foil.

[0084] In some embodiments of the present invention, the system further includes an edge trimming unit disposed between the online stress relief unit and the real-time detection and feedback adjustment unit, including a copper foil edge trimming roller 13 for trimming the edge area of ​​the copper foil.

[0085] In some embodiments of the present invention, the system further includes a winding unit disposed downstream of the real-time detection and feedback adjustment unit, including a winding roller 16 for winding the finished copper foil.

[0086] In some embodiments of the present invention, the two-dimensional laser displacement sensor in the warping detection device 14 is fixedly installed by an aluminum profile bracket, with an installation horizontal deviation ≤ ±0.1°.

[0087] In some embodiments of the present invention, the online oven 11 is a horizontal continuous oven, including an infrared heating tube and a hot air circulation system, with internal temperature uniformity ≤ ±2℃ and temperature control accuracy ±1℃.

[0088] In some embodiments of the present invention, the control system includes a PLC controller which is communicatively connected to the temperature regulation unit of the online oven 11 for outputting heating temperature regulation signals.

[0089] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention.

[0090] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, this invention can be implemented using any prior art methods, apparatus, and materials similar to or equivalent to those described in the embodiments of this invention, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention.

[0091] Unless otherwise stated, the experimental methods, detection methods, and preparation methods disclosed in this invention all employ conventional techniques in analytical chemistry and related fields. Unless otherwise stated, all materials and equipment used in this invention are commercially available.

[0092] Example 1 (4μm thin copper foil, for power lithium-ion batteries)

[0093] This embodiment provides a method for improving the edge curling of 4μm thin copper foil, which is implemented on an integrated electrolytic copper foil production line. The production line includes processes such as copper melting, filtration, electrolytic foil production, passivation, online heating, and winding. Except for the parameters specifically noted in this embodiment, the other processes adopt the conventional process parameters for lithium battery copper foil production.

[0094] (1) Electroplating solution formula:

[0095] Basic components: Copper ions 90g / L, sulfuric acid 110g / L, chloride ions 30mg / L;

[0096] Additives: PEG-400 (molecular weight 400) added at 4 mg / L, sodium polydisulfide dipropane sulfonate (SPS) added at 6.5 mg / L, collagen added at 5 mg / L, hydroxyethyl cellulose (HEC) added at 0.8 mg / L, 2-mercaptobenzimidazole (MBI) added at 1.5 mg / L, and 2-methylimidazole (nitrogen-containing heterocyclic compound) added at 0.8 mg / L.

[0097] (2) Electrolysis process parameters:

[0098] Current density: 55 A / dm 2 ;

[0099] Electrolyte temperature: 52℃.

[0100] (3) Online oven parameters:

[0101] Oven temperature: 90℃;

[0102] Copper foil passing speed: 10m / min;

[0103] Oven structure: Horizontal continuous oven, 1.2m in length, using a combination of infrared heating and hot air circulation, with temperature uniformity ≤±1℃.

[0104] (4) Real-time detection and adjustment parameters:

[0105] Laser sensor: Two-dimensional laser displacement sensor, measurement accuracy ±1mm, sampling frequency 100Hz;

[0106] Preset values: Warning value 3mm, Alarm value 10mm;

[0107] Adjustment logic: When the real-time warpage is less than 3mm and less than or equal to 10mm, the oven temperature is adjusted in increments of 4℃, with a maximum of 120℃; when the real-time warpage is greater than 10mm, an audible and visual alarm is triggered.

[0108] (5) Implementation results:

[0109] Warpage height: 3.5mm (dynamic test method);

[0110] Grain size variation: 0.14 μm;

[0111] Internal stress difference: 45 MPa;

[0112] Yellow stamp defect rate: 1.0%;

[0113] Tearing rate: 0.7%;

[0114] Coating uniformity error: 2.3%;

[0115] Roller-pressed belt breakage rate: 0.2%;

[0116] Copper foil yield: 91.8%.

[0117] Example 2 (6μm thin copper foil, for energy storage or lithium-ion batteries)

[0118] This embodiment provides a method for improving edge curling of 6μm thin copper foil, including the following steps:

[0119] (1) Electroplating solution formula:

[0120] Basic components: Copper ions 90g / L, sulfuric acid 110g / L, chloride ions 30mg / L;

[0121] Additives: PEG-600 (molecular weight 600) added at 4 mg / L, sodium polydipropane sulfonate (SPS) added at 6.5 mg / L, collagen added at 5 mg / L, hydroxyethyl cellulose (HEC) added at 0.8 mg / L, 2-mercaptobenzimidazole (MBI) added at 1.5 mg / L, and 2-methylimidazole added at 0.6 mg / L;

[0122] (2) Electrolysis process parameters:

[0123] Current density: 58 A / dm 2 ;

[0124] Electrolyte temperature: 53℃.

[0125] (3) Online oven parameters:

[0126] Oven temperature: 100℃;

[0127] Copper foil throughput speed: 8.5 m / min;

[0128] Oven structure: Same as in Example 1;

[0129] (4) Real-time detection and adjustment parameters:

[0130] Laser sensor: Same as in Example 1;

[0131] Preset values: Warning value 3mm, Alarm value 10mm;

[0132] Adjustment logic: When 3mm < real-time warpage ≤ 10mm, adjust the oven temperature in increments of 3℃, with a maximum not exceeding 120℃.

[0133] (5) Implementation results:

[0134] Warpage height: 2.7mm (dynamic test method);

[0135] Internal stress difference: 48 MPa;

[0136] Grain size variation: 0.13 μm;

[0137] Yellow stamp defect rate: 1.1%;

[0138] Tearing rate: 0.6%;

[0139] Coating uniformity error: 2.1%;

[0140] Roller-pressed belt breakage rate: 0.2%;

[0141] Copper foil yield: 92.5%.

[0142] Example 3 (8μm thick copper foil, for consumer lithium-ion batteries)

[0143] This embodiment provides a method for improving edge curling of 8μm thick copper foil, including the following steps:

[0144] (1) Electroplating solution formula:

[0145] Basic components: Copper ions 90g / L, sulfuric acid 110g / L, chloride ions 30mg / L;

[0146] Additives: PEG-500 (molecular weight 500) added at 4 mg / L, sodium polydipropane sulfonate (SPS) added at 6.5 mg / L, collagen added at 5 mg / L, hydroxyethyl cellulose (HEC) added at 0.8 mg / L, 2-mercaptobenzimidazole (MBI) added at 1.5 mg / L, and hydroxyethylidene diphosphonic acid (HEDP, organophosphonate) added at 8 mg / L;

[0147] (2) Electrolysis process parameters:

[0148] Current density: 60 A / dm 2 ;

[0149] Electrolyte temperature: 50℃.

[0150] (3) Online oven parameters:

[0151] Oven temperature: 110℃;

[0152] Copper foil throughput speed: 8 m / min;

[0153] Oven structure: Same as in Example 1;

[0154] (4) Real-time detection and adjustment parameters:

[0155] Laser sensor: Same as in Example 1;

[0156] Preset values: Warning value 3mm, Alarm value 10mm;

[0157] Adjustment logic: When 3mm < real-time warpage ≤ 10mm, adjust the oven temperature in increments of 2℃, with a maximum not exceeding 120℃.

[0158] (5) Implementation results:

[0159] Warpage height: 3.6mm (dynamic test method);

[0160] Internal stress difference: 38 MPa;

[0161] Grain size variation: 0.16 μm;

[0162] Yellow stamp defect rate: 1.3%;

[0163] Tearing rate: 0.9%;

[0164] Coating uniformity error: 2.7%;

[0165] Roller-pressed belt breakage rate: 0.4%;

[0166] Copper foil yield: 90.7%.

[0167] Comparative Example 1 (Traditional method, 6μm copper foil)

[0168] The basic production line for this comparative example is the same as that in Example 2. The difference is that a traditional macromolecular polyether (PEG-6000) is used as the positioning agent, and there is no online drying oven or real-time detection and adjustment. Other production parameters (such as current density, electrolyte temperature, winding tension, etc.) are the same as in Example 2. The specific formula is as follows: basic components: copper ions 90g / L, sulfuric acid 110g / L, chloride ions 30mg / L; additives: PEG-6000 4mg / L, SPS 6.5mg / L, collagen 5mg / L, HEC 0.8mg / L, MBI 1.5mg / L, 2-methylimidazole 0.6mg / L.

[0169] Implementation results:

[0170] Warpage height: 6.6mm (dynamic test method);

[0171] Internal stress difference: 210 MPa;

[0172] Grain size variation: 0.47 μm;

[0173] Yellow stamp defect rate: 7.2%;

[0174] Tearing rate: 3.5%;

[0175] Coating uniformity error: 5.3%;

[0176] Roller-pressed belt breakage rate: 1.2%;

[0177] Copper foil yield: 80.3%.

[0178] Comparative Example 2 (Single-stage optimization, 6μm copper foil)

[0179] The basic production line for this comparative example is the same as that of Example 2. The difference lies in the use of the small molecule polyether additive formulation of this invention (completely identical to Example 2: PEG-600 4mg / L, SPS 6.5mg / L, collagen 5mg / L, HEC 0.8mg / L, MBI 1.5mg / L, 2-methylimidazole 0.6mg / L). Only the additive improvement step is retained, and there is no online oven stress release and real-time detection and adjustment system. Other production parameters (such as current density, electrolyte temperature, winding tension, etc.) are consistent with those of Example 2.

[0180] Implementation results:

[0181] Warpage height: 5.2mm (dynamic test method);

[0182] Internal stress difference: 85 MPa;

[0183] Grain size variation: 0.16 μm;

[0184] Yellow stamp defect rate: 3.8%;

[0185] Tearing rate: 2.7%;

[0186] Coating uniformity error: 4.1%;

[0187] Roller-pressed belt breakage rate: 0.9%;

[0188] Copper foil yield: 85.7%.

[0189] The implementation effects of the above embodiments and comparative examples are shown in Table 6 below.

[0190] Table 6 Summary of performance data for both examples and comparative examples

[0191]

[0192] As can be seen from the comparison of the embodiments and comparative examples, the synergistic technical solution of the present invention can significantly improve the problem of copper foil warping, while improving the copper foil production yield and battery performance. The warping height (2.7 mm) of Example 2 (synergistic solution) is reduced by 59.1% compared with Comparative Example 1 (conventional solution, 6.6 mm) and by 48.1% compared with Comparative Example 2 (single additive improvement, 5.2 mm); the yellowing defect rate is reduced from 7.2% to 1.1%, the tearing rate is reduced from 3.5% to 0.6%, and the copper foil yield is increased from 80.3% to 92.5%, which fully demonstrates the superiority of the synergistic effect of the three steps.

[0193] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for improving the edge curling of copper foil in the negative electrode current collector of lithium-ion secondary batteries, characterized in that, Includes the following steps: (A) Electroplating solution improvement: Add a position agent to the copper foil electroplating solution, wherein the position agent is a small molecule polyether with a molecular weight of 300~1000; (B) Online stress relief: After passivation and before winding in the copper foil forming machine, the copper foil is subjected to online heating treatment at a temperature of 80~120℃; (C) Real-time detection and feedback adjustment: Before the copper foil is wound up, the warping height of the copper foil edge is detected in real time, and the heating temperature of the online heating step is automatically adjusted according to the detection results.

2. The method for improving the edge curling of copper foil in the negative electrode current collector of lithium-ion secondary batteries as described in claim 1, characterized in that, Step (A) includes one or more of the following features: (a) The small molecule polyether is selected from at least one of polyethylene glycol, polypropylene glycol, or copolymers of the two; (b) The molecular weight of the small molecule polyether is 300~800; (c) The amount of the small molecule polyether added is 3~8 mg / L; (d) The basic formula of the copper foil electroplating solution is: copper ions 85~95g / L, sulfuric acid 100~120g / L, chloride ions 20~40mg / L; (e) The copper foil electroplating solution also contains a synergistic agent, which is selected according to the thickness of the target copper foil: when the copper foil thickness is 4~6μm, the synergistic agent is a nitrogen-containing heterocyclic compound, and its addition amount is 0.5~1mg / L; when the copper foil thickness is 7~10μm, the synergistic agent is an organophosphonate, and its addition amount is 5~10mg / L; (f) The copper foil electroplating solution also contains 4~8 mg / L of brightener, 3~8 mg / L of leveling agent, 0.5~2 mg / L of stabilizer, and 1~3 mg / L of grain refiner.

3. The method for improving the edge curling of copper foil in the negative electrode current collector of lithium-ion secondary batteries as described in claim 2, characterized in that, The nitrogen-containing heterocyclic compound is an imidazole derivative, preferably 2-methylimidazolium; the organophosphonate is hydroxyethylidene diphosphonic acid.

4. The method for improving the edge curling of copper foil in the negative electrode current collector for lithium-ion secondary batteries as described in claim 1, characterized in that, In step (B), the heat treatment is carried out within 30 seconds after the copper foil is formed; the online heating temperature is adjusted according to the thickness of the copper foil: the online heating temperature for 4~6μm copper foil is 80~100℃, and the online heating temperature for 7~10μm copper foil is 90~120℃.

5. The method for improving the edge curling of copper foil for negative electrode current collectors in lithium-ion secondary batteries as described in claim 4, characterized in that, The online heating treatment is carried out in a horizontal continuous oven, which includes: a shell with an inlet and an outlet for copper foil to pass through; and a heating assembly disposed inside the shell, which includes infrared heating tubes and a hot air circulation system. The infrared heating tubes are evenly arranged on the upper and lower sides of the copper foil, and the hot air circulation system is used to make the temperature inside the shell uniform.

6. The method for improving the edge curling of copper foil for negative electrode current collectors in lithium-ion secondary batteries as described in claim 5, characterized in that, The oven has a length of 1.0~1.5m, an internal temperature uniformity of ≤±2℃, and a temperature control accuracy of ±1℃.

7. The method for improving the edge curling of copper foil in the negative electrode current collector for lithium-ion secondary batteries as described in claim 1, characterized in that, In step (C), the warp height data of the copper foil edge is collected in real time by a two-dimensional laser displacement sensor, and the controller compares the real-time warp height with a preset value. When the warp height exceeds the preset value, the heating temperature of the online heating step is automatically adjusted.

8. The method for improving the edge curling of copper foil in the negative electrode current collector for lithium-ion secondary batteries as described in claim 7, characterized in that, The preset values ​​include a warning value of 3mm and an alarm value of 10mm; when 3mm < real-time warp height ≤ 10mm, the oven temperature is adjusted; when the real-time warp height > 10mm, an alarm is issued.

9. A copper foil for a negative electrode current collector in a lithium-ion secondary battery, characterized in that, It is prepared by the method described in any one of claims 1 to 8.

10. A system for improving edge curling of copper foil in a negative electrode current collector for lithium-ion secondary batteries, used to implement the method according to any one of claims 1 to 8, characterized in that, include: Electrolysis unit, used for electrodeposition to form copper foil (3); An online stress relief unit, located downstream of the electrolysis unit, includes an online oven (11) for online heating treatment of copper foil; The real-time detection and feedback adjustment unit is located downstream of the online stress relief unit and includes a warping detection device (14) and a control system. The warping detection device (14) is used to collect warping height data of the copper foil edge in real time. The control system is connected to the warping detection device (14) and the online oven (11) for receiving warping height data and automatically adjusting the heating temperature of the online oven (11) according to the preset value.

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