A method for preparing a composite current collector conductive film layer by roll plating

Abstract

This invention discloses a roll-to-roll coating method for preparing a composite current collector conductive film. A flexible base film is passed through multiple working areas of a vacuum roll-to-roll coating apparatus, where vacuum coating processes are performed on both the front and back sides to prepare a conductive film layer. The vacuum coating process includes preparing a dense seed film layer on the flexible base film via magnetron sputtering and preparing a thickening film layer on the seed film layer via evaporation coating, thereby forming a conductive film layer on the flexible base film. Cooling media are circulated within both the magnetron sputtering and evaporation coating rollers to cool the flexible base film during magnetron sputtering and evaporation coating. A bias voltage is applied to ensure close contact between the flexible base film and the surfaces of the magnetron sputtering and evaporation coating rollers as it passes through them, achieving better cooling. An auxiliary electric field is provided downstream of the flexible base film as it passes through the magnetron sputtering and evaporation coating rollers, assisting in the removal of the flexible base film from the rollers.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery manufacturing technology, and particularly relates to a roll-coating method for preparing a composite current collector conductive film. Background Technology

[0002] In lithium-ion batteries, copper and aluminum foil are typically used as current collectors. Due to limitations in industrialization technology, 6μm and 8μm are the bottlenecks for the thickness of copper and aluminum foil current collectors, respectively, restricting the improvement of lithium-ion battery energy density. In recent years, composite current collectors, using flexible polymer films such as PET and PP as substrates and depositing a layer of copper or aluminum metal film on each side, have attracted increasing attention in the industry. These composite current collectors offer advantages such as light weight and thinness, potentially raising the energy density of lithium-ion batteries to new heights. In composite current collectors, the thickness of the metal film layer generally needs to reach at least 1μm to meet conductivity requirements.

[0003] To obtain high-quality metal films, the industry currently generally uses vacuum evaporation roll-to-roll coating technology. However, to achieve a thicker film, it is often necessary to increase the evaporation power or reduce the base film travel speed to increase the film thickness, or to accumulate the target film thickness by performing multiple roll-to-roll coating cycles on the same base film. In the former case, due to the limited heat resistance of flexible films, especially some ultra-thin flexible films that are more sensitive to coating operating temperatures, the flexible films are prone to thermal deformation and thermal damage during the preparation of metal films, which seriously affects product quality and makes production impossible. In the latter case, the base film needs to be removed between multiple coating cycles in the coating equipment. The equipment has to break the vacuum environment to reinstall the base film, which not only reduces production efficiency but also affects the coating quality, thus affecting the performance of the composite current collector. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a roll-to-roll coating method for preparing a composite current collector conductive film. This method uses a winding system to guide a flexible substrate film through multiple working areas of a vacuum roll-to-roll coating apparatus, performing vacuum coating processes on both the front and back surfaces of the flexible substrate film to prepare the conductive film layer. The vacuum coating process includes:

[0005] (1) In the magnetron sputtering working area, the flexible base film is sequentially wrapped around the magnetron front auxiliary roller, the magnetron coating roller and the magnetron rear auxiliary roller; while wrapping around the magnetron coating roller, a dense seed film layer is prepared on the flexible base film by magnetron sputtering coating.

[0006] (2) In the evaporation coating working area, the flexible base film is sequentially wrapped around the pre-evaporation auxiliary roller, the evaporation coating roller and the post-evaporation auxiliary roller; while wrapping around the evaporation coating roller, a thickened film layer is prepared on the seed film layer on the flexible base film through evaporation coating, thereby forming a conductive film layer on the flexible base film.

[0007] Both the seed film and the thickened film are composed of conductive materials.

[0008] Both the magnetron sputtering coating roller and the evaporation coating roller are filled with cooling media to cool the flexible base film during magnetron sputtering and evaporation coating.

[0009] Both the magnetron coating roller and the evaporation coating roller are biased. At least one of the auxiliary rollers—the magnetron post-auxiliary roller, the evaporation pre-auxiliary roller, and the evaporation post-auxiliary roller—is also biased, forming a biased auxiliary roller. The bias polarity of the magnetron coating roller and the evaporation coating roller is the same, resulting in a surface charge of the same polarity distributed on their surfaces. The biased auxiliary roller (i.e., the biased auxiliary roller among the magnetron post-auxiliary roller, the evaporation pre-auxiliary roller, and the evaporation post-auxiliary roller) has a bias polarity opposite to that of the magnetron coating roller and the evaporation coating roller. Because the flexible base film already has a conductive film layer in the seed film layer or thickening film layer stage on its surface when it passes through the magnetron sputtering auxiliary roller, the pre-evaporation auxiliary roller, and the post-evaporation auxiliary roller, the bias voltage on the bias auxiliary roller will cause the conductive film layer surface of the flexible base film in contact with the bias auxiliary roller to be distributed with a charge of opposite polarity to that distributed on the surfaces of the magnetron sputtering roller and the evaporation coating roller. Under the mutual attraction of the two opposite charges, the flexible base film is adsorbed when passing through the magnetron sputtering roller and the evaporation coating roller, and is closely attached to the surface of the magnetron sputtering roller and the evaporation coating roller, thus obtaining a better cooling effect. In a preferred embodiment, the magnetron sputtering auxiliary roller in the first magnetron sputtering working area of ​​the vacuum roll-to-roll coating equipment is at least a bias auxiliary roller. .

[0010] Auxiliary electric fields are provided downstream of the flexible base film passing through the magnetron coating roller and the evaporation coating roller. The polarity of the auxiliary electric fields is the same as the bias polarity of the magnetron coating roller and the evaporation coating roller. The auxiliary electric fields repel the charges of the same polarity on the magnetron coating roller and the evaporation coating roller, making the charge distribution density on the parts of the magnetron coating roller and the evaporation coating roller opposite to the auxiliary electric fields more sparse, thus weakening the adsorption of the flexible base film on the roller in this area. Under this effect, when the flexible base film needs to detach from the magnetron coating roller or the evaporation coating roller in this downstream area, the adsorption between the flexible base film and the magnetron coating roller or the evaporation coating roller is weakened, the adhesion is reduced, and the flexible base film is more easily detached from the roller surface. The auxiliary electric fields act as an auxiliary detachment mechanism. The auxiliary electric fields are gradually increasing in intensity, with the field strength gradually increasing along the direction of film movement of the flexible base film. The auxiliary electric field strength is lowest at the starting end of the downstream region. As it extends downstream, the electric field strength increases, leading to a stronger repulsion of like-polarity charges on the magnetron coating roller or evaporation coating roller. Consequently, the charge distribution density at this location becomes increasingly sparse, and the adsorption of the flexible base film at this location weakens. At the pre-designed separation point where the flexible base film separates from the magnetron coating roller or evaporation coating roller, the adsorption of the flexible base film by the magnetron coating roller or evaporation coating roller is weakest, resulting in separation of the flexible base film from the magnetron coating roller or evaporation coating roller at this point.

[0011] A bonding sensor is installed downstream of the magnetron coating roller and the evaporation coating roller to monitor the degree of bonding between the flexible base film and the magnetron coating roller or the evaporation coating roller online. The sensing signal detected by the bonding sensor, reflecting the degree of bonding, corresponds to the tension of the flexible base film downstream of the magnetron coating roller or the evaporation coating roller. When the sensing signal increases, it indicates that the tension is greater, meaning that the flexible base film is more tightly bonded to the magnetron coating roller or the evaporation coating roller, and the cooling effect is better. When the sensing signal decreases, it indicates that the tension is less, meaning that the bonding between the flexible base film and the magnetron coating roller or the evaporation coating roller is less, and the cooling effect is also weakened. The vacuum roll-to-roll coating equipment is equipped with a control module. The auxiliary electric field is generated by an auxiliary electric field generator, which includes multiple generating units arranged in a matrix. The control module can individually adjust each generating unit. The bonding sensor transmits the detected signal reflecting the degree of bonding to the control module. The control module then performs online feedback control on the magnitude and distribution of the auxiliary electric field based on the signal. Specifically, when the bonding sensor transmits the signal to the control module, the module determines the degree of bonding between the flexible base film and the magnetron coating roller or evaporation coating roller, and sends a control command to the auxiliary electric field generator. This causes the generator to produce an auxiliary electric field with appropriate magnitude and distribution in the downstream region of the magnetron coating roller or evaporation coating roller, effectively assisting the flexible base film in detaching from the roller surface. When the degree of bonding between the flexible base film and the magnetron coating roller or evaporation coating roller is too high or too low, the control module assesses the situation and sends an adjustment command to the auxiliary electric field generator. This adjusts the electric field intensity generated by certain generating units, increasing or decreasing the electric field intensity and changing the electric field distribution, allowing the auxiliary electric field to adapt to the situation while still maintaining an effective assisting effect on the flexible base film detaching from the roller surface. The control module can also perform online feedback regulation of the auxiliary electric field based on the cooling effect of the flexible base film on the magnetron coating roller or evaporation coating roller. By adjusting the electric field strength and distribution, the separation position between the flexible base film and the magnetron coating roller or evaporation coating roller can be adjusted online. When the control module determines that the flexible base film is insufficiently cooled, it sends a regulation command to the auxiliary electric field generator to reduce the electric field strength and change the electric field distribution, delaying the separation position between the flexible base film and the magnetron coating roller or evaporation coating roller by an appropriate range, thus enhancing the cooling effect of the flexible base film. When the control module determines that the flexible base film is excessively cooled, it sends a regulation command to the auxiliary electric field generator to increase the electric field strength and change the electric field distribution, advancing the separation position between the flexible base film and the magnetron coating roller or evaporation coating roller by an appropriate range, thus weakening the cooling effect of the flexible base film.

[0012] Multiple magnetron targets are arranged on the opposite side of the magnetron coating roller, and the magnetron sputtering coating in the magnetron sputtering working area is multi-target magnetron sputtering coating. The evaporation coating working area includes two or more evaporation coating rollers, and at least one evaporation boat is set below each evaporation coating roller. The arrangement of multiple evaporation coating rollers can achieve the preparation of thicker films, especially films larger than 1 μm, within a single vacuum coating process cycle under conventional or even faster film feeding speeds.

[0013] The control module can also perform online feedback control of the bias voltage of the magnetron coating roller, evaporation coating roller, and bias auxiliary roller based on sensor signals. Depending on specific process adjustments or when fluctuations occur during the vacuum coating process, the module can adjust the adhesion between the flexible base film and the surfaces of the magnetron coating roller and evaporation coating roller online to achieve the desired stable cooling effect. The bias voltage of each magnetron coating roller, evaporation coating roller, and bias auxiliary roller can be different. When the control module determines from the received sensor signals that the flexible base film needs increased or decreased cooling, it will send a control command to the bias voltage generator to increase or decrease the bias voltage of the magnetron coating roller and its adjacent bias auxiliary roller, or to increase or decrease the bias voltage of a specific evaporation coating roller and its adjacent bias auxiliary roller, thereby adjusting the adhesion between the flexible base film and the surface of that magnetron coating roller or evaporation coating roller online to achieve the desired stable cooling effect for the flexible base film.

[0014] By applying a bias voltage to at least one of the auxiliary rollers—the magnetron coating roller, the evaporation coating roller, the magnetron post-auxiliary roller, the evaporation pre-auxiliary roller, and the evaporation post-auxiliary roller—the magnetron coating roller and the evaporation coating roller have opposite charges to the conductive film surface on the flexible base film. This allows the flexible base film to adhere more tightly to the magnetron coating roller and the evaporation coating roller, resulting in better cooling of the flexible base film and overcoming problems such as thermal deformation or even thermal damage that easily occur when preparing thicker film layers. However, this bias voltage and cooling effect are not always better the higher they are. If the flexible base film is excessively cooled, on the one hand, the lower film formation temperature is not conducive to the formation of a good microstructure in the film layer; on the other hand, the lower surface temperature is also prone to condensation, affecting product quality. Therefore, this invention achieves a suitable, required, and stable cooling effect for the flexible base film by online feedback control of the bias voltage and auxiliary electric field of each roller. This allows the roll-to-roll vacuum coating process for preparing thicker film layers on the flexible base film to be carried out stably, resulting in high-quality flexible composite current collector thin film products.

[0015] The inventors discovered that when the bias voltage causes the flexible base film to adhere too tightly to the coating roller, and the flexible base film needs to be separated from the coating roller after passing through it, harmful phenomena can easily occur to the flexible film product: (1) When preparing a film layer on the reverse side of a flexible base film on which a film layer has already been prepared on the front side, in order to resist the large adsorption force between the flexible base film and the coating roller, it is necessary to increase the tension on the flexible base film. This can easily cause the film layer on the front side that is adsorbed and in contact with the roller surface to stick and tear, and fall off from the flexible base film; (2) When a large tension is applied to the flexible base film to make it detach from the roller, the flexible base film will be severely squeezed between the guide roller or auxiliary roller downstream of the coating roller, causing the newly prepared film layer to be squeezed in this way. Damage phenomena such as extrusion cracks and wrinkles occur; (3) The separation position between the flexible base film and the magnetron coating roller or evaporation coating roller is delayed too much than the planned separation position, causing an acute angle bend between the flexible base film after it is removed from the roller and the flexible base film held on the roller surface. This acute angle bend will produce an irreversible crease on the flexible base film. The crease will cause a height difference of micro-angle in the composite current collector. The thickness of the active material to be coated on the composite current collector is mostly less than 100 micrometers. Therefore, the existence of this height difference caused by the crease will cause uneven thickness of the active material coated near the crease, resulting in different expansion volumes of the active material, which will create hidden dangers for accidents such as electrode sheet breakage. When the bias voltage is insufficient, not only will the flexible base film not be able to obtain sufficient cooling from the coating roller, but the flexible base film will also separate from the magnetron coating roller or evaporation coating roller in advance, causing local film speed fluctuations in the winding system. This will bring uncertain fluctuation factors to the stability of the winding vacuum coating process, and thus affect the stability of the quality of the flexible thin film product. In the vacuum roll-to-roll coating process, bias voltage fluctuations caused by certain uncertainties can lead to abnormal increases or decreases in bias voltage, which can cause instability in the production process and affect the stability and consistency of the product. This invention addresses this problem by setting up an auxiliary electric field with gradually varying intensity to effectively assist the flexible base film in separating from the roller surface. Simultaneously, by online feedback control of the bias voltage and auxiliary electric field of each roller, the separation position between the flexible base film and the magnetron coating roller or evaporation coating roller can be adjusted online. These multifaceted technical effects not only ensure that the flexible base film receives suitable, necessary, and stable cooling, but also prevent damage to the film layer quality. More importantly, this comprehensive effect allows the roll-to-roll vacuum coating process to remain continuously and stably implemented without being affected by process fluctuations such as bias voltage fluctuations caused by certain uncertainties, resulting in highly consistent and high-quality flexible composite current collector thin film products.

[0016] When preparing a conductive film layer on the reverse side of a flexible base film through vacuum deposition, a thermally conductive electrically insulating layer is provided on the outer surface of the magnetron sputtering roller in the corresponding magnetron sputtering working area and the evaporation coating roller in the evaporation coating working area. The electrically insulating layer is composed of one of the following: aluminum oxide, aluminum nitride, silicon nitride, silicon oxide, zirconium oxide, or resin. The electrically insulating layer prevents the charge distributed on the conductive film layer surface on the front side of the flexible base film from neutralizing the charge on the magnetron sputtering roller and the evaporation coating roller during vacuum deposition on the reverse side, thus preventing adverse effects from the adsorption process between the flexible base film and the magnetron sputtering roller and the evaporation coating roller during vacuum deposition on the front side.

[0017] The conductive film layers prepared on the front and back sides of the flexible base film are composed of at least one of copper, aluminum, silver, nickel, molybdenum, titanium, niobium, iron, zinc, stainless steel, graphene, carbon nanotubes, Ketjen black, acetylene black, graphite powder and carbon fiber, respectively, and have a thickness in the range of 0.3 to 1.5 μm; among the conductive film layers, the thickness of the seed film layer is in the range of 20 to 150 nm.

[0018] The beneficial effects of this invention are:

[0019] (1) A seed film with good structure and density is first deposited on the surface of the flexible base film by magnetron sputtering with strong particle kinetic energy. Then, a thicker thickening film is deposited on the seed film by high speed through evaporation. The seed film with good structure is conducive to the thickening film particles deposited on it continuing to grow along the growth direction of the seed film structure, forming a better film structure.

[0020] (2) By using multi-target magnetron sputtering coating and arranging multiple evaporation modules including evaporation coating rollers and evaporation boats in the evaporation coating work area, and by using online controllable bias voltage to make the flexible base film fit more tightly with the coating rollers, the flexible base film can obtain a better and more stable cooling effect. This overcomes the problem that the flexible base film is prone to thermal deformation or even thermal damage when using higher coating power (including magnetron coating power and evaporation coating power). It enables the preparation of a thicker film layer in one vacuum coating process cycle without reducing the film feeding speed of the flexible base film.

[0021] (3) Setting an auxiliary electric field with gradually varying intensity effectively assists in the removal of the flexible base film from the roller surface, overcoming the problem that the flexible base film is easily damaged when it separates from the coating roller due to a large bias voltage. At the same time, by online feedback control of the bias voltage and auxiliary electric field of each roller, the production process of preparing a thick conductive film layer by winding vacuum coating can be carried out continuously and stably without being affected by process fluctuations such as bias voltage fluctuations caused by certain uncertain factors, so as to obtain flexible composite current collector thin film products with high consistency and high quality. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the roll-to-roll coating method for preparing the composite current collector conductive film layer according to the present invention.

[0023] Figure 2 This is a schematic diagram of the layout of the vacuum roll coating equipment involved in the roll coating method of the present invention.

[0024] The accompanying drawings are only used to illustrate the technical solution of the present invention, and the proportions of the parts in the drawings do not constitute a limitation on the present invention. Implementation

[0025] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0026] In the specification and claims of this invention, terms such as "first," "second," "front," and "back" are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate.

[0027] The term "correspondence" can refer to an association or binding relationship. The correspondence between A and B means that there is an association or binding relationship between A and B.

[0028] This invention provides a roll-to-roll coating method for preparing a composite current collector conductive film. The method involves using a winding system to guide a flexible substrate film through multiple working areas of a vacuum roll-to-roll coating apparatus, performing vacuum coating processes on both the front and back surfaces of the flexible substrate film to prepare the conductive film layer. This roll-to-roll coating method is as follows: Figure 1 As shown, it specifically includes:

[0029] (1) The flexible base film passes through the first magnetron sputtering working area and then passes through the magnetron front auxiliary roller, the magnetron coating roller and the magnetron rear auxiliary roller in sequence. When passing through the magnetron coating roller, a dense seed film layer is prepared on the front side of the flexible base film by magnetron sputtering.

[0030] (2) The flexible base film passes through the first evaporation coating working area and passes through the pre-evaporation auxiliary roller, the evaporation coating roller and the post-evaporation auxiliary roller in sequence. When passing through the evaporation coating roller, a thickened film layer is prepared on the seed film layer on the front side of the flexible base film through evaporation coating, thereby forming a conductive film layer on the front side of the flexible base film.

[0031] (3) The flexible base film passes through the second magnetron sputtering working area and a dense seed film layer is prepared on the reverse side of the flexible base film by magnetron sputtering.

[0032] (4) The flexible base film passes through the second evaporation coating working area and a thickened film layer is prepared on the seed film layer on the reverse side of the flexible base film through evaporation coating, thereby forming a conductive film layer on the reverse side of the flexible base film.

[0033] The thickened film layer and the seed film layer together constitute the conductive film layer of the composite current collector.

[0034] This roll-to-roll coating method uses... Figure 2 This is carried out in the vacuum roll-to-roll coating equipment shown. For example... Figure 2 As shown, the vacuum roll-to-roll coating equipment includes a first magnetron sputtering working area 3, a first evaporation coating working area 8, a second magnetron sputtering working area 15, and a second evaporation coating working area 37. Multiple magnetron targets 7 and 19 are arranged on opposite sides of the magnetron coating rollers 5 and 17, respectively. The magnetron sputtering coating in the first magnetron sputtering working area 3 and the second magnetron sputtering working area 15 is multi-target magnetron sputtering coating. The first evaporation coating working area 8 and the second evaporation coating working area 37 respectively include evaporation coating rollers 10, 13 and 23, 27. Evaporation boats 20 and 21 are respectively arranged below evaporation coating rollers 10 and 13, and evaporation boats 25 and 29 are respectively arranged below evaporation coating rollers 23 and 27. The arrangement of multiple evaporation coating rollers allows for the preparation of thicker films within a single vacuum coating cycle under conventional or even faster film feeding speeds.

[0035] The flexible base film 2 from the unwinding roller 1 enters the first magnetron sputtering working area 3. In the first magnetron sputtering working area 3, the flexible base film 2 sequentially passes through the magnetron front auxiliary roller 4, the magnetron coating roller 5, and the magnetron rear auxiliary roller 6. When passing through the magnetron coating roller 5, a dense seed film layer is prepared on the front side of the flexible base film 2 by magnetron sputtering. Then the flexible base film 2 enters the first evaporation coating working area 8, sequentially passing through the evaporation front auxiliary roller 9, the evaporation coating roller 10, the evaporation rear auxiliary roller 11, the evaporation front auxiliary roller 12, the evaporation coating roller 13, and the evaporation rear auxiliary roller 14. When passing through the evaporation coating rollers 10 and 13, a thickened film layer is prepared on the seed film layer on the front side of the flexible base film by evaporation coating, thereby forming a conductive film layer on the front side of the flexible base film. Then, the flexible base film 2 passes through the second magnetron sputtering working area 15, sequentially winding around the magnetron front auxiliary roller 16, the magnetron coating roller 17, and the magnetron rear auxiliary roller 18, forming a dense seed film layer on the reverse side of the flexible base film through magnetron sputtering. Next, the flexible base film passes through the second evaporation coating working area 37, sequentially winding around the evaporation front auxiliary roller 22, the evaporation coating roller 23, the evaporation coating roller 24, the evaporation front auxiliary roller 26, the evaporation coating roller 27, and the evaporation coating roller 28. While winding around the evaporation coating rollers 23 and 27, a thickened film layer is formed on the seed film layer on the reverse side of the flexible base film through evaporation coating, thereby forming a conductive film layer on the reverse side of the flexible base film. Finally, the flexible base film, with conductive film layers on both sides, is wound up by the take-up roller 36.

[0036] The flexible base film is flipped over as it passes through the guide rollers in the first evaporation coating working area 8 and the second magnetron sputtering working area 15. This allows conductive film layers to be prepared on both sides of the flexible base film within one process cycle of the vacuum winding coating equipment. This avoids the situation where the flexible base film roll, which requires film layers to be prepared on both sides, is exposed to the atmosphere between two process cycles, thus ensuring the quality of the thin film product.

[0037] Cooling medium is circulated inside the magnetron sputtering coating rollers 5 and 17 and the evaporation coating rollers 10, 13, 23 and 27 to cool the flexible base film during magnetron sputtering coating and evaporation coating.

[0038] Magnetron coating rollers 5 and 17, as well as evaporation coating rollers 10, 13, 23, and 27, are all biased. Magnetron auxiliary rollers 6 and 18 are also biased and serve as bias auxiliary rollers.

[0039] The magnetron coating roller and the evaporation coating roller have the same bias polarity, resulting in a surface charge of the same polarity on their surfaces. The bias auxiliary rollers (i.e., magnetron back auxiliary rollers 6 and 18) have a bias polarity opposite to that of the magnetron coating roller and the evaporation coating roller. When the flexible base film passes over the bias auxiliary rollers, the bias voltage on the rollers causes the already existing conductive film layer on the flexible base film to have a charge of opposite polarity to that distributed on the surfaces of the magnetron coating roller and the evaporation coating roller. Under the mutual attraction of these two oppositely polarized charges, the flexible base film is adsorbed as it passes over the magnetron coating roller and the evaporation coating roller, resulting in close contact with their surfaces and a better cooling effect.

[0040] Auxiliary electric fields are provided downstream of the flexible base film passing through the magnetron coating roller and the evaporation coating roller. The polarity of the auxiliary electric fields is the same as the bias polarity of the magnetron coating roller and the evaporation coating roller. The auxiliary electric fields repel the charges of the same polarity on the magnetron coating roller and the evaporation coating roller, making the charge distribution density on the parts of the magnetron coating roller and the evaporation coating roller opposite to the auxiliary electric fields more sparse, thus weakening the adsorption of the flexible base film on the roller in this area. Under this effect, when the flexible base film needs to detach from the magnetron coating roller or the evaporation coating roller in this downstream area, the adsorption between the flexible base film and the magnetron coating roller or the evaporation coating roller is weakened, the adhesion is reduced, and the flexible base film is more easily detached from the roller surface. The auxiliary electric fields act as an auxiliary detachment mechanism. The auxiliary electric fields are gradually increasing in intensity, with the field strength gradually increasing along the direction of film movement of the flexible base film. The auxiliary electric field strength is lowest at the starting end of the downstream region. As it extends downstream, the electric field strength increases, leading to a stronger repulsion of like-polarity charges on the magnetron coating roller or evaporation coating roller. Consequently, the charge distribution density at this location becomes increasingly sparse, and the adsorption of the flexible base film at this location weakens. At the pre-designed separation point where the flexible base film separates from the magnetron coating roller or evaporation coating roller, the adsorption of the flexible base film by the magnetron coating roller or evaporation coating roller is weakest, resulting in separation of the flexible base film from the magnetron coating roller or evaporation coating roller at this point.

[0041] A bonding sensor is installed downstream of the magnetron coating roller and the evaporation coating roller to monitor the degree of bonding between the flexible base film and the magnetron coating roller or the evaporation coating roller online. The sensing signal detected by the bonding sensor, reflecting the degree of bonding, corresponds to the tension of the flexible base film downstream of the magnetron coating roller or the evaporation coating roller. When the sensing signal increases, it indicates that the tension is greater, meaning that the flexible base film is more tightly bonded to the magnetron coating roller or the evaporation coating roller, and the cooling effect is better; when the sensing signal decreases, it indicates that the tension is less, meaning that the bonding between the flexible base film and the magnetron coating roller or the evaporation coating roller is less, and the cooling effect is also weakened. The vacuum roll coating equipment is equipped with a control module. The auxiliary electric field is generated by auxiliary electric field generating devices 30, 31, 32, 33, 34, and 35, which include multiple generating units arranged in a matrix. The control module can individually adjust each generating unit. The bonding sensor transmits the detected signal reflecting the degree of bonding to the control module. The control module then performs online feedback control on the magnitude and distribution of the auxiliary electric field based on the signal. Specifically, when the bonding sensor transmits the signal to the control module, the module determines the degree of bonding between the flexible base film and the magnetron coating roller or evaporation coating roller, and sends a control command to the auxiliary electric field generator. This causes the generator to produce an auxiliary electric field with appropriate magnitude and distribution in the downstream region of the magnetron coating roller or evaporation coating roller, effectively assisting the flexible base film in detaching from the roller surface. When the degree of bonding between the flexible base film and the magnetron coating roller or evaporation coating roller is too high or too low, the control module assesses the situation and sends an adjustment command to the auxiliary electric field generator. This adjusts the electric field intensity generated by certain generating units, increasing or decreasing the electric field intensity and changing the electric field distribution, allowing the auxiliary electric field to adapt to the situation while still maintaining an effective assisting effect on the flexible base film detaching from the roller surface. The control module can also perform online feedback regulation of the auxiliary electric field based on the cooling effect of the flexible base film on the magnetron coating roller or evaporation coating roller. By adjusting the electric field strength and distribution, the separation position between the flexible base film and the magnetron coating roller or evaporation coating roller can be adjusted online. When the control module determines that the flexible base film is insufficiently cooled, it sends a regulation command to the auxiliary electric field generator to reduce the electric field strength and change the electric field distribution, delaying the separation position between the flexible base film and the magnetron coating roller or evaporation coating roller by an appropriate range, thus enhancing the cooling effect of the flexible base film. When the control module determines that the flexible base film is excessively cooled, it sends a regulation command to the auxiliary electric field generator to increase the electric field strength and change the electric field distribution, advancing the separation position between the flexible base film and the magnetron coating roller or evaporation coating roller by an appropriate range, thus weakening the cooling effect of the flexible base film.

[0042] The control module can also perform online feedback regulation of the bias voltage on the magnetron coating rollers 5 and 17, the magnetron auxiliary rollers 6 and 18, and the evaporation coating rollers 10, 13, 23, and 27 based on sensor signals. According to specific process adjustments or when fluctuations occur during the vacuum coating process, the module can adjust the adhesion between the flexible base film and the surfaces of the magnetron coating rollers and evaporation coating rollers online to obtain the required stable cooling effect. The bias voltage of each magnetron coating roller, magnetron auxiliary roller, and evaporation coating roller can be different. When the control module determines that the flexible base film needs to increase or decrease the cooling effect based on the received sensor signals, it will send a regulation command to the bias voltage generator to increase or decrease the bias voltage of the magnetron coating roller and the adjacent magnetron auxiliary roller, or to increase or decrease the bias voltage of a certain evaporation coating roller and the adjacent magnetron auxiliary roller, thereby adjusting the adhesion between the flexible base film and the surface of the magnetron coating roller or evaporation coating roller online to achieve the required stable cooling effect for the flexible base film.

[0043] By applying bias voltages to the magnetron coating roller, the magnetron auxiliary roller, and the evaporation coating roller, the magnetron coating roller and the evaporation coating roller have opposite charges to the conductive film surface on the flexible base film. This allows the flexible base film to adhere more tightly to the magnetron coating roller and the evaporation coating roller, resulting in better cooling of the flexible base film and overcoming problems such as thermal deformation or even thermal damage that easily occur when preparing thicker film layers. However, higher bias voltages and cooling effects are not always better. If the flexible base film is excessively cooled, on the one hand, the lower film formation temperature is not conducive to the formation of a good microstructure; on the other hand, the lower surface temperature is also prone to condensation, affecting product quality. Therefore, this invention achieves suitable, required, and stable cooling effects for the flexible base film by online feedback control of the bias voltage and auxiliary electric field of each roller. This allows for the stable implementation of the roll-to-roll vacuum coating process for preparing thicker film layers on the flexible base film, resulting in high-quality flexible composite current collector thin film products.

[0044] When preparing a conductive film layer on the reverse side of a flexible base film through vacuum deposition, thermally conductive electrically insulating layers 40, 39, and 38 are respectively provided on the outer surface of the magnetron sputtering roller 17 in the second magnetron sputtering working area and the evaporation coating rollers 23 and 27 in the second evaporation coating working area. The electrically insulating layers are composed of one of the following: aluminum oxide, aluminum nitride, silicon nitride, silicon oxide, zirconium oxide, or resin. The electrically insulating layers prevent the charges distributed on the conductive film layer surface on the front side of the flexible base film from neutralizing the charges on the magnetron coating roller and evaporation coating roller used for vacuum deposition on the reverse side, thus preventing adverse effects from the adsorption process between the flexible base film and the magnetron coating roller and evaporation coating roller during vacuum deposition on the front side.

[0045] The conductive film layers prepared on the front and back sides of the flexible base film are composed of at least one of copper, aluminum, silver, nickel, molybdenum, titanium, niobium, iron, zinc, stainless steel, graphene, carbon nanotubes, Ketjen black, acetylene black, graphite powder and carbon fiber, respectively, and have a thickness in the range of 0.3 to 1.5 μm; among the conductive film layers, the thickness of the seed film layer is in the range of 20 to 150 nm.

Claims

1. A method for preparing a composite current collector conductive film layer by roll coating, characterized in that, A flexible substrate film is wound through multiple working areas of a vacuum winding coating equipment using a winding system, and a vacuum coating process is performed on both the front and back sides of the flexible substrate film to prepare a conductive film layer; the vacuum coating process includes: (1) In the magnetron sputtering working area, the flexible base film is sequentially wrapped around the magnetron front auxiliary roller, the magnetron coating roller and the magnetron rear auxiliary roller; while wrapping around the magnetron coating roller, a dense seed film layer is prepared on the flexible base film by magnetron sputtering coating. (2) In the evaporation coating working area, the flexible base film is sequentially wrapped around the pre-evaporation auxiliary roller, the evaporation coating roller and the post-evaporation auxiliary roller; while wrapping around the evaporation coating roller, a thickened film layer is prepared on the seed film layer on the flexible base film through evaporation coating, thereby forming a conductive film layer on the flexible base film. Both the magnetron sputtering coating roller and the evaporation coating roller are filled with cooling medium to cool the flexible base film during magnetron sputtering and evaporation coating. Both the magnetron coating roller and the evaporation coating roller are biased. At least one of the auxiliary rollers, including the magnetron post-auxiliary roller, the evaporation pre-auxiliary roller, and the evaporation post-auxiliary roller, is also biased, becoming a biased auxiliary roller. This bias makes the flexible base film fit tightly against the surfaces of the magnetron coating roller and the evaporation coating roller when it passes around them, so as to obtain a better cooling effect. An auxiliary electric field is provided in the downstream region of the flexible base film as it passes through the magnetron coating roller and the evaporation coating roller. When the flexible base film needs to detach from the magnetron coating roller or the evaporation coating roller in this downstream region, the auxiliary electric field plays an auxiliary role in detaching the film from the roller. The auxiliary electric field is a gradually increasing electric field, and the intensity of the electric field gradually increases along the direction of the flexible base film. A bonding sensor is installed downstream of the magnetron coating roller and the evaporation coating roller. The bonding sensor monitors the degree of bonding between the flexible base film and the magnetron coating roller or the evaporation coating roller. The vacuum winding coating equipment is equipped with a control module. The bonding sensor transmits the sensing signal reflecting the degree of bonding to the control module. The control module performs online feedback control on the magnitude and distribution of the electric field strength of the auxiliary electric field based on the sensing signal. When the sensing signal increases, it indicates a tighter bond between the flexible base film and the magnetron coating roller or evaporation coating roller, resulting in better cooling. Conversely, when the sensing signal decreases, it indicates a reduced bond between the flexible base film and the magnetron coating roller or evaporation coating roller, leading to a weaker cooling effect. The control module adjusts the auxiliary electric field online based on the assessment of the cooling effect of the flexible base film on the magnetron coating roller or evaporation coating roller. This adjustment of the electric field strength and distribution allows for online adjustment of the separation position between the flexible base film and the magnetron coating roller or evaporation coating roller. When the control module determines that the flexible base film is cooling... When the cooling is insufficient, the control module sends a control command to the auxiliary electric field generator to reduce the electric field strength and change the electric field distribution, so that the separation position between the flexible base film and the magnetron coating roller or evaporation coating roller is delayed within an appropriate range compared to the original separation position, thereby enhancing the cooling effect of the flexible base film. When the control module determines that the flexible base film is overcooled, the control module sends a control command to the auxiliary electric field generator to increase the electric field strength and change the electric field distribution, so that the separation position between the flexible base film and the magnetron coating roller or evaporation coating roller is advanced within an appropriate range compared to the original separation position, thereby weakening the cooling effect of the flexible base film.

2. The method for preparing a composite current collector conductive film layer by roll coating according to claim 1, characterized in that, The bias polarity of the magnetron coating roller and the evaporation coating roller is the same, while the bias polarity of the bias auxiliary roller is opposite to that of the magnetron coating roller and the evaporation coating roller.

3. The method for preparing a composite current collector conductive film layer by roll coating according to claim 2, characterized in that, The polarity of the auxiliary electric field is the same as the bias polarity of the magnetron coating roller and the evaporation coating roller.

4. The method for preparing a composite current collector conductive film layer by roll coating according to claim 1, characterized in that, The control module performs online feedback regulation of the bias of the magnetron coating roller, the evaporation coating roller and the bias auxiliary roller based on the sensor signals.

5. The method for preparing a composite current collector conductive film layer by roll coating according to claim 1, characterized in that, Multiple magnetron targets are arranged on the opposite side of the magnetron coating roller, and the magnetron sputtering coating in the magnetron sputtering working area is multi-target magnetron sputtering coating.

6. The method for preparing a composite current collector conductive film layer by roll coating according to claim 1, characterized in that, The evaporation coating work area includes two or more evaporation coating rollers, and at least one evaporation boat is set below each evaporation coating roller.

7. The method for preparing a composite current collector conductive film layer by roll coating according to claim 1, characterized in that, The conductive film layers prepared on the front and back sides of the flexible base film are composed of at least one of copper, aluminum, silver, nickel, molybdenum, titanium, niobium, iron, zinc, stainless steel, graphene, carbon nanotubes, Ketjen black, acetylene black, graphite powder and carbon fiber, respectively, and have a thickness in the range of 0.3 to 1.5 μm; among the conductive film layers, the thickness of the seed film layer is in the range of 20 to 150 nm.

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