An on-line microwave annealing method and apparatus for composite current collectors

Abstract

This invention relates to an online microwave annealing method and apparatus for composite current collectors. The online microwave annealing method for composite current collectors includes pre-treating the composite current collector with a femtosecond laser to remove edge burrs; and continuously passing the pre-treated composite current collector through a microwave resonant cavity protected by an inert atmosphere at a preset linear velocity to complete the annealing process by utilizing the skin effect of microwaves on metals.

Description

Technical Field

[0001] This invention relates to the field of electronics, and more particularly to an online microwave annealing method and apparatus for composite current collectors. Background Technology

[0002] Composite current collectors are functional thin films composed of multiple layers of materials, typically employing a "metal-polymer-metal" structure. The polymer material serves as the intermediate layer, with metal layers (such as copper or aluminum) deposited on both sides. They are primarily used to replace traditional metal foils (such as copper or aluminum foil) as positive and negative electrode current collectors. Specifically, composite aluminum foil (hereinafter referred to as MA) is used for the positive electrode current collector, and composite copper foil (hereinafter referred to as MC) is used for the negative electrode current collector. Compared to traditional current collectors, composite current collectors offer advantages such as improved safety, reduced mass, increased energy density, and lower cost.

[0003] Taking composite copper foil as an example, after the composite copper foil is produced, its microstructure and properties are not stable, and it has a series of inherent defects. Key subsequent processes such as annealing are usually used to eliminate these defects and control the material properties.

[0004] Conventional annealing methods include self-annealing, low-temperature oven annealing (batch processing), and continuous hot air / infrared radiation annealing (online). However, these methods all have various problems. Self-annealing has a long cycle time and is easily affected by the environment; low-temperature oven annealing causes thermal shrinkage of the substrate. If the tension of the copper foil roll is uneven, the shrinkage at the edges and the middle is inconsistent, which can easily lead to wrinkling and cracking of the electrode sheets. In severe cases, it can even damage the inner ring, causing the entire roll to be scrapped; continuous hot air / infrared radiation annealing usually uses a faster production line to improve efficiency, but annealing requires a certain holding time (dwell time). If the dwell time is shortened to match the line speed, it will lead to insufficient annealing, and if the heating zone is extended, the equipment investment will be huge.

[0005] The above content is only used to help understand the technical solution of the present invention and does not represent an admission that the above content is prior art. Summary of the Invention

[0006] The main objective of this invention is to provide an online microwave annealing method and apparatus for composite current collectors, aiming to solve the technical problems of conventional annealing methods for composite copper foils, such as long self-annealing time, oven annealing causing thermal shrinkage and wrinkling of the substrate, and low efficiency of continuous annealing.

[0007] To achieve the above objectives, the present invention provides an online microwave annealing method for composite current collectors, the online microwave annealing method for composite current collectors comprising: The composite current collector is pretreated with a femtosecond laser to remove edge burrs; The pretreated composite current collector is continuously passed through a microwave resonant cavity protected by an inert atmosphere at a preset linear velocity, and the annealing process is completed by utilizing the skin effect of microwaves on metals.

[0008] Preferably, in the online microwave annealing method for the composite current collector, the metal layer is a copper layer or an aluminum layer; and / or, The thickness of the metal layer is ; and / or The preset linear velocity is 1 m / min to 15 m / min; and / or, The frequency of microwaves is 2.25 GHz to 2.65 GHz.

[0009] Preferably, in the online microwave annealing method for the composite current collector, the edge smoothness of the pretreated composite current collector is ≤1μm, the edge curvature radius is 50μm~80μm, and the edge roughness is ≤0.4μm; and / or, The preprocessing steps include: The edge of the composite current collector is cut using a femtosecond laser cutting device, wherein the laser pulse width is <500fs.

[0010] Preferably, in the online microwave annealing method for the composite current collector, the annealing process further includes: The electromagnetic field distribution within the microwave resonant cavity is continuously altered by rotating metal blades; and / or, The temperature of the metal layer of the composite current collector is monitored. If the metal layer of the composite current collector is not within its recrystallization temperature range, the temperature of the metal layer of the composite current collector is compensated by controlling the microwave power or auxiliary heating or cooling devices.

[0011] Preferably, in the online microwave annealing method for the composite current collector, the step of continuously passing the pretreated composite current collector through a microwave resonant cavity protected by an inert atmosphere at a preset linear velocity further includes: During the transmission process of the composite current collector, the composite current collector is in an equipotential state; An inert protective gas is introduced into the microwave resonant cavity to reduce the oxygen concentration inside the cavity to below 50 ppm.

[0012] To achieve the above objectives, the present invention also provides an online microwave annealing apparatus used in the above-described online microwave annealing method, the online microwave annealing apparatus comprising: A pretreatment device is used to pretreat the composite current collector using a femtosecond laser to remove edge burrs; A microwave processing device is located downstream of the pretreatment device along the transmission direction of the composite current collector. The microwave processing device has a microwave resonant cavity for selectively annealing the pretreated composite current collector. A temperature control device, located in the microwave processing device, is used to regulate the temperature of the metal layer of the composite current collector; A transmission device for transmitting composite current collectors along a preset transmission direction.

[0013] Preferably, in the online microwave annealing apparatus, the microwave processing device includes: The microwave resonant cavity; A microwave source system, installed in the microwave resonant cavity, for generating microwaves and transmitting them to the microwave resonant cavity; and, A mode stirrer is rotatably disposed within the microwave resonant cavity.

[0014] Preferably, in the online microwave annealing apparatus, the pretreatment module includes a femtosecond laser, a beam transmission system, a position adjustment mechanism, and a dust removal system; The femtosecond laser is mounted on the position adjustment mechanism and aligned with the first reflector of the beam transmission system. The pulse width of the femtosecond laser is less than 500 fs, and the wavelength is in the infrared or near-infrared band. The femtosecond laser is used to emit laser light. The beam transmission system includes a reflector and a focusing lens fixed to the position adjustment structure. The reflector is used to redirect the laser beam and then focus it to the edge of the composite current collector through the focusing lens. The position adjustment mechanism is used to adjust the position of the femtosecond laser and the beam transmission system; The dust extraction port of the dust removal system is located close to the focal point of the laser and is spaced apart from the femtosecond laser and the beam transmission system.

[0015] Preferably, the online microwave annealing apparatus further includes an atmosphere transition device, the atmosphere transition device comprising: An inlet airlock is located at the entrance of the microwave resonant cavity; An outlet airlock is provided at the outlet of the microwave resonant cavity; and, An air curtain nozzle is located inside the inlet air lock and the outlet air lock and within the microwave resonant cavity, for continuously spraying inert gas to form an air curtain; The inlet airlock and the outlet airlock are used to prevent outside air from entering the microwave resonant cavity and to prevent internal inert gas from flowing out of the microwave resonant cavity.

[0016] Preferably, the online microwave annealing apparatus further includes an atmosphere protection device, which includes a gas source, a gas supply pipeline, an air inlet, an exhaust outlet, and an oxygen analyzer. The oxygen analyzer is connected to the microwave resonant cavity and is used to measure the oxygen concentration in the microwave resonant cavity and control the increase of the air inlet / exhaust flow rate according to the oxygen concentration. The air inlet is located on the side wall or bottom of the microwave resonant cavity, the exhaust port is located on the top of the microwave resonant cavity, and the air source is connected to the air inlet through the air supply pipeline.

[0017] The present invention has at least the following beneficial effects: This invention pre-treats the composite current collector using a femtosecond laser to remove edge burrs; the pre-treated composite current collector is then continuously passed through a microwave resonant cavity protected by an inert atmosphere at a preset linear velocity to perform annealing by utilizing the skin effect of microwaves on metals. This allows for selective heating of the metal layer by leveraging the difference in microwave absorption between metals and polymer materials through the skin effect.

[0018] Furthermore, especially when microwaves in the 2.25GHz–2.65GHz frequency range are applied to the composite current collector, the microwave energy is concentrated and rapidly absorbed within the surface of the metal layer (copper, aluminum, etc.) due to the metal layer's excellent conductivity. Meanwhile, the polymer substrate (polypropylene, polyethylene, polyimide, etc.) in the composite current collector, being a dielectric, has extremely weak absorption capacity for this frequency band and absorbs almost no microwave energy. This allows the microwave energy to be precisely applied to the metal layer of the composite current collector, rapidly heating it to its recrystallization temperature (approximately 150℃–200℃ for copper and 110℃–180℃ for aluminum), completing the recrystallization annealing. The polymer substrate absorbs only a small amount of heat through thermal conduction from the metal layer, maintaining a temperature consistently below its thermal decomposition temperature (typically ≥250℃). This effectively prevents substrate degradation, yellowing, delamination, or deformation, perfectly meeting the annealing requirements of "metal-polymer" heterogeneous composite current collectors. Attached Figure Description

[0019] Figure 1 A flowchart of one embodiment of the online microwave annealing method for composite current collectors provided by the present invention; Figure 2 A schematic diagram of an embodiment of the online microwave annealing apparatus provided by the present invention; Figure 3 for Figure 2 Schematic diagram of the pretreatment unit; Figure 4 for Figure 2 A cross-sectional view of an embodiment of a microwave processing apparatus.

[0020] 1-Pretreatment device, 11-Femtosecond laser, 12-Beam transmission system, 13-Position adjustment mechanism, 14-Dust removal system, 2-Microwave processing device, 21-Microwave resonant cavity, 211-Feed port, 22-Mode stirrer, 3-Temperature control device, 4-Transmission device, 5-Atmosphere protection device, 51-Oxygen analyzer, 52-Gas supply pipeline, 53-Gas inlet, 6-Atmosphere transition device, 61-Inlet gas lock, 62-Outlet gas lock, 63-Air curtain nozzle.

[0021] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0022] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The present invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0023] In this embodiment of the invention, the term "and / or" describes the relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The character " / " generally indicates that the preceding and following associated objects have an "or" relationship.

[0024] It should be noted that the terms "first," "second," etc., in the specification, claims, and drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0025] In this embodiment of the invention, the term "multiple" refers to two or more, and other quantifiers are similar.

[0026] In this invention, unless otherwise stated, directional terms such as "upper," "lower," "top," and "bottom" are generally used in relation to the direction shown in the accompanying drawings, or in relation to the vertical, perpendicular, or gravitational direction of the component itself; similarly, for ease of understanding and description, "inner" and "outer" refer to the inner and outer contours of each component itself, but the above directional terms are not intended to limit this invention.

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details are presented in the embodiments of the present invention to facilitate a better understanding of the invention. However, the technical solutions claimed in the present invention can be implemented even without these technical details and various variations and modifications based on the following embodiments. The division of the following embodiments is for ease of description and should not constitute any limitation on the specific implementation of the present invention. The various embodiments can be combined with and referenced by each other without contradiction.

[0028] Figure 1 The diagram illustrates an online microwave annealing method for a composite current collector provided by the present invention.

[0029] In step S1000, the composite current collector is pretreated with a femtosecond laser to remove edge burrs.

[0030] It should be noted that burrs at the edges of the metal layer in a composite current collector can cause electric field concentration, resulting in point discharge and abnormal film burning. This invention utilizes the "cold processing" characteristics of femtosecond lasers to precisely remove edge burrs, micro-protrusions, and residual metal debris, while avoiding thermal damage to the polymer substrate. This provides a low-defect, high-insulation, and point discharge-resistant foundation for subsequent microwave annealing.

[0031] More specifically, a femtosecond laser cutting device is used to cut the edge of the composite current collector, where the laser pulse width is <500 fs. In some embodiments, the laser pulse width is typically 100 fs to 300 fs. This allows for material removal through the Coulomb explosion effect. The laser pulse duration is extremely short, and energy is rapidly transferred between photons and electrons in the material, preventing heat from diffusing into the polymer substrate (heat-affected zone HEL <1 μm), thus avoiding substrate melting, deformation, or thermal decomposition. For the metal layer (copper / aluminum, etc.) on the surface of the composite current collector, the laser photon energy directly breaks the chemical bonds between metal atoms, peeling off micron-sized burrs and protruding metal debris from the substrate surface through a micro-explosion effect, rather than melting and recasting. The laser is focused on the edge of the current collector, and by precisely controlling the ablation depth, the sharp metal edges (prone to point discharge) are processed into smooth arc transitions, reducing the risk of electric field concentration and avoiding delamination between the metal layer and the polymer layer.

[0032] By setting the laser pulse width to <500 fs (femtosecond level), the heat-affected zone is small, effectively removing burrs and protrusions generated during electroplating or deposition. Eliminating edge spikes avoids the sharp-point discharge effect in the subsequent microwave field, preventing the polymer substrate from being broken down (arson). It should be noted that the shorter the laser pulse width, the smaller the heat-affected zone, thus avoiding damage to the polymer substrate.

[0033] The laser wavelength is in the infrared or near-infrared band (e.g., 780nm, 1064nm, 1550nm), so the infrared or near-infrared light has high absorption efficiency in the metal layer and low penetration into the polymer substrate, reducing damage to the substrate.

[0034] The present invention pre-treats the composite current collector, resulting in an edge smoothness ≤1μm, an edge curvature radius ≥50μm, and an edge roughness ≤0.4μm. Preferably, the edge curvature radius is 50μm~80μm.

[0035] To verify the effect of the pretreatment of this invention, the following analysis focuses on three aspects: characterizing tip discharge, edge size, and process stability.

[0036] Table 1 Comparison of tip discharge before and after pretreatment Table 2 Comparison of edge dimensions before and after preprocessing Table 3 Comparison of process stability before and after pretreatment It should be noted that the electric field concentration factor in Table 1 refers to the ratio of the electric field strength at the tip to the average electric field strength. Before pretreatment, the local electric field is amplified hundreds of times, easily reaching the breakdown threshold of air or dielectric. After pretreatment, the electric field concentration factor is ≤10, reducing the electric field concentration effect by more than 90%, fundamentally eliminating the physical conditions for tip discharge. The critical breakdown field strength in Table 1 is the minimum electric field strength that causes ionization discharge of gas or polymer dielectric within the cavity. The local field strength after pretreatment in this invention... Slightly higher than the air breakdown threshold, this, combined with an inert atmosphere (which increases the breakdown threshold by 3-5 times), completely avoids discharge.

[0037] Before pretreatment, the burr height h is typically 5μm to 20μm. Table 2 shows that after pretreatment, the burrs are completely removed, and the edge smoothness is ≤1μm. The edge radius of curvature is the minimum radius of curvature of the edge profile. After pretreatment, the edge is smoothed and blunted. The edge roughness mentioned in this invention is the arithmetic mean deviation of the edge profile. Table 3 shows the production data for 100 rolls (5000 meters per roll) of composite current collectors. The burn-film defect rate is the number of substrate breakdowns (pinholes, ablation) caused by tip discharge per kilometer of composite current collector. Tables 1 to 3 show that the pretreatment of the composite current collector by this invention can effectively eliminate edge burrs, avoid tip discharge effects in the subsequent microwave field, and prevent the polymer substrate from being broken down.

[0038] In step S2000, the pretreated composite current collector is continuously passed through a microwave resonant cavity protected by an inert atmosphere at a preset linear velocity, and the annealing process is completed by utilizing the skin effect of microwaves on metals.

[0039] More specifically, the annealing process also includes monitoring the temperature of the metal layer of the composite current collector. If the metal layer of the composite current collector is not within its recrystallization temperature range, the temperature of the metal layer of the composite current collector is compensated by controlling the microwave power or an auxiliary heating or cooling device.

[0040] In some embodiments, the preset linear velocity is 1 m / min to 15 m / min. In some embodiments, the thickness of the metal layer is... Of course, the thickness of the metal layer also depends on the specific material.

[0041] In some embodiments, the metal layer is a copper layer or an aluminum layer; the frequency of the microwave is 2.25 GHz to 2.65 GHz.

[0042] This invention utilizes the difference in microwave absorption between metals and polymers to achieve selective heating of the metal layer through the skin effect. Thus, the difference in microwave absorption between metals and polymers can be used to achieve selective heating of the metal layer through the skin effect.

[0043] Especially when microwaves in the 2.25GHz–2.65GHz frequency range are applied to composite current collectors, the microwave energy is concentrated and rapidly absorbed within the surface of the metal layer (copper, aluminum, etc.) due to its good conductor properties. Meanwhile, the polymer substrate (polypropylene, polyethylene, polyimide, etc.) in the composite current collector acts as a dielectric, exhibiting extremely weak absorption of microwaves in this frequency band, absorbing almost no microwave energy. This allows the microwave energy to precisely target the metal layer of the composite current collector, rapidly heating it to its recrystallization temperature (approximately 150℃–180℃ for copper and 110℃–180℃ for aluminum), completing the recrystallization annealing. The polymer substrate absorbs only a small amount of heat through thermal conduction from the metal layer, maintaining a temperature consistently below its thermal decomposition temperature (typically ≥250℃). This effectively prevents substrate degradation, yellowing, delamination, or deformation, perfectly meeting the annealing requirements of "metal-polymer" heterogeneous composite current collectors.

[0044] It should be noted that the frequency of microwaves is determined based on the linear velocity and the thickness of the metal layer.

[0045] Excessive microwave frequency can lead to uneven heating and annealing of the metal layer, resulting in overheating of the metal layer surface and potential damage to the polymer substrate. Conversely, insufficient microwave frequency results in poor annealing. Therefore, this invention selects a microwave frequency of 2.25 GHz to 2.65 GHz for optimal performance. This utilizes the skin effect of microwaves on the metal layer, allowing the metal layer of the composite current collector to reach its recrystallization temperature while maintaining the polymer substrate at a low temperature.

[0046] Furthermore, taking copper as the metal layer as an example, while the copper layer reaches the recrystallization temperature, the substrate temperature remains at a low level. This greatly reduces the risk of thermal shrinkage, melting, or even decomposition of the polymer film, thus solving the core contradiction of annealing composite copper foil.

[0047] Furthermore, during microwave heating, uniform heating can be achieved by disrupting the electromagnetic field distribution within the microwave resonant cavity through stirring. This can be achieved by using the rotation of a stirrer. Further, the annealing process includes continuously altering the electromagnetic field distribution within the microwave resonant cavity by rotating metal blades, changing the boundary conditions of the electromagnetic field within the microwave resonant cavity 21, breaking the fixed standing wave mode, and making the time-averaged field strength distribution within the microwave resonant cavity 21 more uniform. This effectively eliminates localized overheating or cold spots caused by standing waves, ensuring the uniformity of the composite current collector annealing.

[0048] Simultaneously, it is necessary to monitor the temperature of the metal layer of the composite current collector in real time; based on the monitoring results, determine whether the metal layer of the composite current collector is within its recrystallization temperature range; if the determination result is negative, control the temperature compensation of the metal layer of the composite current collector. More specifically, the annealing process also includes: monitoring the temperature of the metal layer of the composite current collector; if it is detected that the metal layer of the composite current collector is not within its recrystallization temperature range, compensating the temperature of the metal layer of the composite current collector by controlling the microwave power or auxiliary heating or cooling device.

[0049] For example, when the temperature of the metal layer is detected to be outside its recrystallization temperature range and too low, the microwave power is increased to raise the temperature of the metal layer; when the temperature of the metal layer is detected to be outside its recrystallization temperature range and too high, the microwave power is decreased to lower the temperature of the metal layer. When adjusting the microwave power cannot meet the temperature control accuracy requirements (i.e., it cannot bring the temperature of the metal layer back to its recrystallization temperature range), an auxiliary cooling device or an auxiliary heating device is activated for compensation; when the temperature of the metal layer is detected to be outside its recrystallization temperature range and too high, the auxiliary cooling device is activated; when the temperature of the metal layer is detected to be outside its recrystallization temperature range and too low, the auxiliary heating device is activated.

[0050] It is worth noting that the composite current collector is in an equipotential state during the transmission process, which can prevent electrostatic accumulation or discharge breakdown caused by potential difference. The "equipotential state" mentioned in this application means that during the transmission process, any part of the composite current collector maintains a potential difference of less than 0.1V between itself and all transmission rollers, cavity walls and grounding system.

[0051] During the annealing process of the microwave resonant cavity, an inert protective gas is introduced into the cavity to reduce the oxygen concentration to below 50 ppm, thus creating an inert atmosphere. To ensure the effectiveness of the annealing process, the oxygen concentration in the microwave resonant cavity is typically reduced to below 50 ppm before the composite current collector enters the cavity.

[0052] The online microwave annealing method for composite current collectors provided by this invention allows for instantaneous microwave heating, significantly reducing the annealing time from several hours in a traditional oven to just minutes or even seconds. This eliminates the insufficient time for excessive diffusion or reaction between copper atoms and substrate atoms at the interface, which helps maintain a clear layered structure. Furthermore, the annealing process is completed in an extremely short time, and even if the atmosphere protection is not absolutely perfect, the contact time between the copper layer and residual oxygen is greatly shortened, thereby effectively inhibiting oxidation and discoloration. Microwave energy acts directly on the material, reducing heat loss from intermediate media such as the heating furnace and air, resulting in high energy utilization efficiency. Simultaneously, the rapid heating eliminates the need for lengthy heating and cooling processes, significantly improving production efficiency and reducing energy costs per unit product.

[0053] After annealing, the composite current collector is cooled to a safe temperature under an inert atmosphere and then wound up as needed.

[0054] Figure 2 The diagram illustrates the online microwave annealing apparatus for the composite current collector provided by this invention. Figure 3 and Figure 4 It indicates Figure 2 A schematic diagram of the middle section structure. Please refer to [link / reference]. Figures 2 to 4 The online microwave annealing apparatus includes a pretreatment device 1, a microwave processing device 2, a temperature control device 3, a transmission device 4, an atmosphere transition device 6, and an atmosphere protection device 5.

[0055] The pretreatment device 1 is used to pre-treat the composite current collector using a femtosecond laser to remove edge burrs. The laser pulse width in the pretreatment device 1 is <500 fs. In some embodiments, the laser pulse width is typically 100 fs to 300 fs. This allows material removal through the Coulomb explosion effect. The laser pulse duration is extremely short, and energy is rapidly transferred between photons and electrons in the material, preventing heat from diffusing into the polymer substrate (heat-affected zone HEL < 1 μm), thus avoiding substrate melting, deformation, or thermal decomposition. For the metal layer (copper / aluminum, etc.) on the surface of the composite current collector, the laser photon energy directly breaks the chemical bonds between metal atoms, peeling off micron-sized burrs and protruding metal debris from the substrate surface through a micro-explosion effect, rather than melting and recasting. The laser is focused on the edge of the current collector, and by precisely controlling the ablation depth, sharp metal edges (prone to tip discharge) are processed into smooth arc transitions, reducing the risk of electric field concentration and preventing delamination between the metal layer and the polymer layer.

[0056] More specifically, the pretreatment device 1 is installed upstream of the microwave processing device 2 along the transmission direction of the composite current collector. The inlet distance between the pretreatment device 1 and the microwave processing device 2 is 10cm to 50cm. The pretreatment device 1 is used for edge finishing of the material to prevent tip discharge.

[0057] In some embodiments, the pretreatment device 1 includes a femtosecond laser 11, a beam transmission system 12, a position adjustment mechanism 13, and a dust removal system 14. The femtosecond laser 11 is mounted on the position adjustment mechanism 13 and aligned with the first reflector of the beam transmission system 12, thus ensuring initial stability of the optical path. The femtosecond laser 11 has a pulse width of <500 fs and a wavelength in the infrared or near-infrared band, and is used to emit laser light. In some embodiments, the femtosecond laser 11 may be, but is not limited to, a fiber femtosecond laser 11, with an output power of 50W to 500W, and features adjustable pulse energy and stable frequency characteristics, suitable for long-term operation on continuous production lines.

[0058] The beam transmission system 12 includes a reflector and a focusing lens fixed to the position adjustment structure. The reflector is used to focus the laser beam onto the edge of the composite current collector after the laser beam is redirected by the focusing lens. This ensures that the beam spot is uniform and the energy density is stable, and avoids uneven local processing caused by beam spot deviation.

[0059] The position adjustment mechanism 13 is used to adjust the positions of the femtosecond laser 11 and the beam transmission system 12. In some embodiments, the position adjustment mechanism 13 is an XYZ three-axis fine-tuning platform. For example, the X-axis can be adjusted to adapt to composite current collectors of different widths, ensuring that the laser focus point is always aligned with the edge; the Y-axis can be adjusted to compensate for positional offset during the transmission of the current collector, ensuring that the laser continuously acts on the edge during continuous film transmission; and the Z-axis can be adjusted to precisely control the distance between the focus point and the surface of the current collector, adapting to metal layers of different thicknesses.

[0060] The dust removal system 14 has its suction port located close to the laser's focal point and spaced apart from the femtosecond laser 11 and the beam transmission system 12. In some embodiments, the dust removal system 14 is a negative pressure dust collection device. The suction port of the dust removal system 14 can be located close to the laser's focal point (distance ≤ 5cm), positioned below / to the side of the current collector edge, maintaining a safe distance of ≥ 10cm from the femtosecond laser 11 and the beam transmission system 12. This avoids airflow disturbance to the optical path or contamination of the optical lenses, and allows for real-time suction of metal chips and polymer debris generated during laser processing, preventing debris from adhering to the current collector surface or optical components, thus ensuring processing cleanliness.

[0061] When pre-processing is performed using pre-processing device 1, the unwinding device unwinds the material, and the femtosecond laser 11 emits an ultrashort pulse laser with a pulse width of <500 fs. The beam transmission system 12 focuses the laser onto the edge of the current collector for edge finishing. At this time, the position adjustment mechanism 13 automatically adjusts the laser position according to the width of the composite current collector. The laser beam scans synchronously along the film-moving direction of the composite current collector, removing micron-level burrs, protrusions, and metal residues at the edge through the Coulomb explosion effect. Simultaneously, the dust removal system 14 performs negative pressure dust collection on the processing area to thoroughly remove residual debris.

[0062] The microwave processing device 2 is located downstream of the pretreatment device 1 along the transmission direction of the composite current collector. The microwave processing device 2 has a microwave resonant cavity 21 for selectively annealing the pretreated composite current collector.

[0063] The microwave processing device 2 includes a microwave resonant cavity 21, a microwave source system, and a mode stirrer 22. The microwave resonant cavity 21 can be, but is not limited to, rectangular or cylindrical, depending on the layout requirements of different production lines. The microwave resonant cavity 21 can be made of stainless steel, which provides high temperature resistance and corrosion resistance, allowing it to withstand the scouring of circulating cooling water and contact with inert atmospheres (nitrogen, argon) for extended periods. It also possesses good electromagnetic shielding properties, effectively reflecting microwave energy and preventing microwave penetration and leakage. Furthermore, its surface is easy to polish, ensuring a smooth inner wall.

[0064] The microwave resonant cavity 21 adopts a double-layer stainless steel structure. A flow channel is provided between the inner and outer layers to form a closed flow channel for circulating cooling water. The flow channel can be, but is not limited to, a spiral or parallel flow channel.

[0065] The inner wall of the microwave resonant cavity 21 is smooth, and the corners are transitioned with large rounded arcs to avoid sharp edges causing electric field concentration. The length of the microwave resonant cavity 21 can be determined according to the film-laying speed and the required annealing time. In this embodiment, it is 2-5 meters. The microwave resonant cavity 21 is a sealed structure. In some embodiments, the microwave resonant cavity 21 is provided with an openable maintenance door. A conductive rubber sealing strip is used between the door body and the microwave resonant cavity 21, which has both electromagnetic shielding and airtight functions. The inlet and outlet of the composite current collector are provided with a choke groove structure to prevent microwave leakage.

[0066] The microwave source system is used to supply and transmit microwave energy. Installed in the microwave resonant cavity 21, the microwave source system generates microwaves and transmits them to the microwave resonant cavity 21. Specifically, the microwave source system includes a magnetron, a waveguide, and a tuner. The magnetron is the source of the microwaves, and multiple magnetron arrays can be set (e.g., typically 2 to 8, adjusted according to the cavity length and annealing power requirements). The power of a single magnetron can be set to 1kW to 6kW, and the total power can be continuously adjusted within the range of 2kW to 48kW, specifically according to the annealing requirements of composite current collectors of different thicknesses and materials.

[0067] In addition, multiple feed ports 211 are provided on the wall of the microwave resonant cavity 21, and the positions of the multiple feed ports 211 are staggered to achieve multi-mode excitation.

[0068] The waveguide connects to the magnetron and transmits the microwaves generated by the magnetron to the feed port 211 of the microwave resonant cavity 21, ensuring efficient microwave energy transfer. The tuner, which can be, but is not limited to, a three-pin or EH tuner, is installed between the waveguide and the microwave resonant cavity 21. Typically, the tuner is driven by a stepper motor. The tuner is used to achieve microwave impedance matching, reduce microwave reflection loss, and ensure efficient coupling of microwave energy into the microwave resonant cavity 21, thus ensuring energy transfer efficiency.

[0069] In actual operation, the magnetron generates microwaves in the range of 2.25 GHz to 2.65 GHz. The tuner adjusts the matching state in real time based on the feedback of the reflected power to ensure that the reflected power is less than 5%. The multi-feed port 211 design enables the formation of a multi-mode superposition field in the microwave resonant cavity 21, improving uniformity.

[0070] A mode stirrer 22 is rotatably disposed within the microwave resonant cavity 21. By rotating, the mode stirrer 22 alters the boundary conditions of the electromagnetic field within the microwave resonant cavity 21, breaking the fixed standing wave mode and making the time-averaged field strength distribution within the microwave resonant cavity 21 more uniform. This effectively eliminates localized overheating or cold spots caused by standing waves, ensuring the uniformity of the composite current collector annealing. The mode stirrer 22 includes stirring blades and a drive motor connected to the stirring blades. The stirring blades may be, but are not limited to, metal blades. The shape of the stirring blades may be fan-shaped or polygonal, with no specific limitation. The stirring blades may be mounted on the top or side wall of the microwave resonant cavity 21. The drive motor may be, but is not limited to, a speed-regulating motor, extending into the cavity through a magnetohydrodynamic sealed shaft. The rotation frequency of the stirrer is adjustable from 1Hz to 10Hz.

[0071] It should be noted that in the microwave processing device 2, all corners of the inner walls (including between side walls and between the side wall and the top / bottom) adopt a large arc transition to eliminate 90° sharp corners; the connection between the waveguide, feed port 211 and microwave resonant cavity 21 adopts a horn-shaped gradual structure to avoid abrupt step changes. The contact surface between the door frame of the inspection door and the microwave resonant cavity 21 adopts an embedded conductive sealing structure, and the inner edge of the door is rounded.

[0072] Temperature control device 3 is located in microwave processing device 2 and is used to regulate the temperature of the metal layer of the composite current collector. Specifically, temperature control device 3 includes a temperature monitoring device, an auxiliary heating device, and an auxiliary cooling device. The temperature monitoring device is installed in microwave resonant cavity 21 and is used to monitor the temperature of the metal layer of the composite current collector in real time, continuously, and without interference, providing an accurate and reliable data source for subsequent temperature regulation, and avoiding interference from contact temperature measurement on the transmission of the composite current collector and high-temperature loss of the temperature sensing element.

[0073] In some embodiments, the temperature monitoring device includes an infrared monitor, an observation window, and a purging device. The infrared monitor includes multiple probes arranged along the direction of the composite current collector and mounted on the observation window. The observation window is located on the side wall of the microwave resonant cavity 21. The observation window is made of quartz glass, making it transparent to the infrared band. An infrared anti-reflection film can also be coated on the surface of the observation window. The anti-reflection film's wavelength matches the operating wavelength of the infrared monitor, significantly improving infrared light transmittance, reducing temperature signal attenuation, and ensuring the accuracy of temperature data. The observation window is sealed and flush with the inner wall of the microwave resonant cavity 21 to avoid sharp edges that could lead to electric field concentration, while also providing microwave shielding to prevent microwave leakage from the cavity. The purging device is used to spray inert gas onto the inner surface of the observation window to prevent metal vapor condensation and contamination.

[0074] By using an infrared monitor to monitor the copper foil temperature in real time, and by introducing independent auxiliary heating and cooling devices, the copper foil temperature can be precisely controlled when microwave power is inconvenient to adjust, preventing overheating damage to the substrate. When the temperature monitoring device detects that the temperature of the metal layer of the composite current collector deviates from its recrystallization temperature range, the microwave processing device 2 will adjust the microwave power; when the microwave power adjustment response is not timely or the control accuracy is insufficient, supplementary heating or cooling can be performed through an auxiliary heating device or an auxiliary cooling device.

[0075] An auxiliary heating device serves as a supplementary heat source when microwave power adjustment cannot meet the requirements for precise temperature control. The auxiliary heating device may include, but is not limited to, an infrared radiation heater, a reflector, and a light-shielding plate. The infrared radiation heater is installed on the inner wall of the microwave resonant cavity 21 and is located above or below the composite current collector. The reflector is used to concentrate and reflect the heat radiation emitted by the infrared radiation heater onto the metal layer surface of the composite current collector, reducing the scattering of heat radiation to the surroundings of the cavity, improving heat utilization efficiency, and preventing the inner wall of the cavity from heating up due to the absorption of heat radiation. In this embodiment, the light-shielding plate has an adjustable angle, which facilitates control of the heating area.

[0076] An auxiliary cooling device is used as a supplementary cold source when microwave power adjustment cannot meet the requirements for precise temperature control. The auxiliary cooling device includes a cooling roller disposed at the outlet of the microwave resonant cavity 21, and coolant is circulated within the cooling roller. In some embodiments, a gas cooling nozzle is provided inside the microwave resonant cavity 21 or at its outlet for spraying room temperature or low temperature inert gas.

[0077] The auxiliary cooling device adopts a multi-stage cooling design. The gas cooling nozzle at the end of the heating zone inside the microwave resonant cavity 21 is the first stage of cooling, which achieves initial cooling of the metal layer and suppresses temperature overshoot. The gas cooling nozzle and cooling roller at the outlet of the microwave resonant cavity 21 is the second stage of cooling, which achieves deep cooling of the metal layer and rapidly reduces the temperature of the metal layer to a safe range (≤80℃). The cooling range of the two stages increases progressively, avoiding stress concentration caused by single-stage rapid cooling, and preventing the substrate from generating internal stress due to sudden temperature changes.

[0078] The transmission device 4 is used to transmit the composite current collector along a preset transmission direction. For example, it sequentially transmits the composite current collector from the pretreatment device 1 to the microwave processing device 2. The transmission device 4 includes multiple conductive rollers, which are drivenly connected to transmit the composite current collector. In some embodiments, the transmission device 4 also includes conductive slip rings mounted at the ends of the conductive rollers and grounded via wires.

[0079] All conductive rollers are connected to a common grounding point via grounding wires. Adjacent conductive rollers are connected by equipotential bonding wires to ensure consistent potential. The composite current collector makes conductive contact with the roller surface of the conductive roller. This allows static electricity to be dissipated in a timely manner, eliminating the accumulation of static electricity caused by high-speed film movement and preventing electrostatic breakdown of the film due to the potential difference between the roller shaft and the foil.

[0080] The atmosphere transition device 6 includes an inlet gas lock 61, an outlet gas lock 62, and an air curtain nozzle 63. The inlet gas lock 61 is located at the entrance of the microwave resonant cavity 21. The outlet gas lock 62 is located at the exit of the microwave resonant cavity 21. The air curtain nozzle 63 is located inside the inlet gas lock 61 and the outlet gas lock 62 and within the microwave resonant cavity 21, and is used to continuously spray inert gas to form an air curtain. The inlet gas lock 61 and the outlet gas lock 62 are used to prevent outside air from entering the microwave resonant cavity 21 and to prevent the internal inert gas from flowing out of the microwave resonant cavity 21.

[0081] In some embodiments, the inlet airlock 61 may include two sealing rollers arranged side by side and an inflation chamber. The two sealing rollers are respectively in close contact with the upper and lower surfaces of the composite current collector to form a line contact seal. This achieves both mechanical isolation of the gas inside and outside the microwave resonant cavity 21 and avoids hard contact scratching the foil surface. In some embodiments, the roller surface of the sealing rollers may be smoothed to a surface roughness Ra≤0.8μm to reduce the frictional resistance with the composite current collector and prevent the composite current collector from shifting or being stretched during film flow. The inflation chamber is located outside the two sealing rollers and is used to provide an inert gas source to the air curtain nozzle 63.

[0082] The inert gas source buffer and the inflation chamber are made of stainless steel with an optimized internal flow channel design to ensure that the inert gas is evenly distributed to all areas of the air curtain nozzle 63, ensuring that the air curtain thickness and pressure are uniform. The inflation chamber is seamlessly connected to the gas supply pipeline 52 of the atmosphere protection module, which can realize precise adjustment of gas pressure and flow.

[0083] The inflation chamber is a closed cavity structure to form a gas pressure stabilizing buffer chamber, which smooths out the fluctuating gas source pressure and keeps the gas pressure output to the air curtain nozzle 63 constant, ensuring the continuity and sealing of the air curtain and preventing outside air from seeping into the microwave resonant cavity 21 from the air curtain gap due to pressure fluctuations.

[0084] The atmosphere protection device 5 includes a gas source, a gas supply pipeline 52, an air inlet 53, an exhaust outlet, and an oxygen analyzer 51. The oxygen analyzer 51 is connected to the microwave resonant cavity 21 and is used to measure the oxygen concentration within the microwave resonant cavity 21, and control the increase of the air intake / exhaust flow rate based on the oxygen concentration. The air inlet 53 is located on the side wall or bottom of the microwave resonant cavity 21, and the exhaust outlet is located on the top of the microwave resonant cavity 21. The gas source is connected to the air inlet 53 through the gas supply pipeline 52. The gas source is an inert gas source, which can be, but is not limited to, a nitrogen source. More specifically, the gas source is a liquid nitrogen storage tank or a nitrogen generator with a purity >99.99%. When the oxygen analyzer 51 detects a value greater than a first preset value, it increases the air intake flow rate of the inert gas within the microwave resonant cavity 21. In some embodiments, the first preset value can be set to 50 ppm.

[0085] In addition, in some embodiments, the atmosphere protection device 5 also includes a pressure sensor, which detects the pressure inside the microwave resonant cavity 21. When the pressure inside the microwave resonant cavity 21 is greater than a second preset value, the exhaust port is opened.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. An online microwave annealing method for composite current collectors, characterized in that, include: The composite current collector is pretreated with a femtosecond laser to remove edge burrs; The pretreated composite current collector is continuously passed through a microwave resonant cavity protected by an inert atmosphere at a preset linear velocity, and the annealing process is completed by utilizing the skin effect of microwaves on metals.

2. The online microwave annealing method for composite current collectors as described in claim 1, characterized in that, The metal layer is a copper layer or an aluminum layer; and / or, The thickness of the metal layer is ; and / or The preset linear velocity is 1 m / min to 15 m / min; and / or, The frequency of microwaves is 2.25 GHz to 2.65 GHz.

3. The online microwave annealing method for composite current collectors as described in claim 1, characterized in that, The pretreated composite current collector has an edge smoothness ≤1μm, an edge curvature radius of 50μm~80μm, and an edge roughness ≤0.4μm; And / or, The preprocessing steps include: The edge of the composite current collector is cut using a femtosecond laser cutting device, wherein the laser pulse width is <500fs.

4. The online microwave annealing method for composite current collectors as described in claim 1, characterized in that, The annealing process also includes: The electromagnetic field distribution within the microwave resonant cavity is continuously altered by rotating metal blades; and / or, The temperature of the metal layer of the composite current collector is monitored. If the metal layer of the composite current collector is not within its recrystallization temperature range, the temperature of the metal layer of the composite current collector is compensated by controlling the microwave power or auxiliary heating or cooling devices.

5. The online microwave annealing method for the composite current collector as described in claim 1, characterized in that, The step of continuously passing the pretreated composite current collector through a microwave resonant cavity protected by an inert atmosphere at a preset linear velocity further includes: During the transmission process of the composite current collector, the composite current collector is in an equipotential state; An inert protective gas is introduced into the microwave resonant cavity to reduce the oxygen concentration inside the cavity to below 50 ppm.

6. An online microwave annealing apparatus used in the online microwave annealing method as described in claims 1 to 5, characterized in that, include: A pretreatment device is used to pretreat the composite current collector using a femtosecond laser to remove edge burrs; A microwave processing device is located downstream of the pretreatment device along the transmission direction of the composite current collector, and is used to selectively anneal the pretreated composite current collector. A temperature control device, located in the microwave processing device, is used to regulate the temperature of the metal layer of the composite current collector; A transmission device for transmitting composite current collectors along a preset transmission direction.

7. The online microwave annealing apparatus as described in claim 6, characterized in that, The microwave processing device includes: The microwave resonant cavity; A microwave source system, installed in the microwave resonant cavity, for generating microwaves and transmitting them to the microwave resonant cavity; and, A mode stirrer is rotatably disposed within the microwave resonant cavity.

8. The online microwave annealing apparatus as described in claim 6, characterized in that, The preprocessing module includes a femtosecond laser, a beam transmission system, a position adjustment mechanism, and a dust removal system; The femtosecond laser is mounted on the position adjustment mechanism and aligned with the first reflector of the beam transmission system. The pulse width of the femtosecond laser is less than 500 fs, and the wavelength is in the infrared or near-infrared band. The femtosecond laser is used to emit laser light. The beam transmission system includes a reflector and a focusing lens fixed to the position adjustment structure. The reflector is used to redirect the laser beam and then focus it to the edge of the composite current collector through the focusing lens. The position adjustment mechanism is used to adjust the position of the femtosecond laser and the beam transmission system; The dust extraction port of the dust removal system is located close to the focal point of the laser and is spaced apart from the femtosecond laser and the beam transmission system.

9. The online microwave annealing apparatus as described in claim 6, characterized in that, It also includes an atmosphere transition device, the atmosphere transition device comprising: An inlet airlock is located at the entrance of the microwave resonant cavity; An outlet airlock is provided at the outlet of the microwave resonant cavity; and, An air curtain nozzle is located inside the inlet air lock and the outlet air lock and within the microwave resonant cavity, for continuously spraying inert gas to form an air curtain; The inlet airlock and the outlet airlock are used to prevent outside air from entering the microwave resonant cavity and to prevent internal inert gas from flowing out of the microwave resonant cavity.

10. The online microwave annealing apparatus as described in claim 6, characterized in that, It also includes an atmosphere protection device, which includes a gas source, a gas supply pipeline, an air inlet, an exhaust outlet, and an oxygen analyzer. The oxygen analyzer is connected to the microwave resonant cavity and is used to measure the oxygen concentration in the microwave resonant cavity and control the increase of the air inlet / exhaust flow based on the oxygen concentration. The air inlet is located on the side wall or bottom of the microwave resonant cavity, the exhaust port is located on the top of the microwave resonant cavity, and the air source is connected to the air inlet through the air supply pipeline.

Images