Release film for rolling enhanced ultrathin lithium foil as well as preparation method and application of release film

Abstract

The invention discloses an enhanced ultrathin lithium foil calendering release film and a preparation method and application thereof, and relates to the technical field of release film preparation. The release film comprises a composite base material and a release layer arranged on the composite base material, wherein the composite base material comprises polyester fiber cloth and a polymer film; the thickness of the polyester fiber cloth is 20-50 [mu] m, the fiber diameter is 10-25 [mu] m, and the pore size is 0.1-1 [mu] m; and the thickness of the polymer film is 5-15 [mu] m. According to the composite base material disclosed by the invention, the polyester fiber cloth formed by weaving the fibers is adopted, and the polyester fiber cloth can provide excellent tear resistance by depending on interweaving point dispersed stress; the polymer film is compounded with the polyester fiber cloth to provide a carrier for the release agent, so that the release agent is prevented from permeating to the other side of the fiber cloth to cause non-uniform coating; the pores in the fiber cloth are utilized and are locally filled, so that the microstructure is finer, and a thinner lithium foil is obtained due to the fact that a larger membrane material is provided in the calendering process.

Description

Technical Field

[0001] This invention relates to the field of release film preparation technology, specifically to an enhanced ultrathin lithium foil calendering release film, its preparation method, and its application. Background Technology

[0002] During the initial charge and discharge cycle of lithium-ion batteries, a significant amount of electrolyte and lithium ions are consumed, resulting in irreversible capacity loss and lower coulombic efficiency, reduced energy density, and cycle life. Pre-lithiation technology offers an effective solution to this problem. This technology can significantly improve the initial coulombic efficiency of the anode, reduce lithium consumption during irreversible charging of the cathode, and increase battery energy density. Among these methods, rolled lithium foil composite anodes, as an effective pre-lithiation approach, are currently an important pathway for the industrial production of pre-lithiated batteries.

[0003] Lithium foil is generally produced using a calendering process. Lithium foil products have high requirements for surface smoothness, thickness uniformity, and thickness. The preparation of wide and thin lithium foil is currently a major challenge, placing high demands on both the manufacturing process and the performance of the release film. In particular, pre-physicochemical treatments typically require lithium foil thicknesses of 2μm to 5μm. This necessitates that the lithium metal possess good ductility on the release film to allow it to lay flat. Therefore, high requirements are placed on the strength and surface roughness of the release film. However, current PET release films cannot provide adequate support when preparing lithium foils within this thickness range, frequently resulting in cracks or wrinkles due to limitations in the material's inherent strength. Therefore, these issues need to be addressed.

[0004] Traditional release agent formulations can optimize the microstructure of materials, such as ultra-high molecular weight polyethylene and nano-silica anti-sticking agents, to improve the microscopic properties of the release layer surface. However, process control is difficult, especially regarding dispersion, resulting in low industrial production yields and hindering the stability of ultra-thin lithium foil calendering. Secondly, to accommodate the inherent limitations of added components (such as agglomeration), a thicker release layer (e.g., 2μm) is usually required to ensure surface roughness without exposing significant defects. However, thicker release layers tend to have higher silicone oil transfer rates and stronger adhesion to the lithium foil, which also negatively impacts the stability of continuous ultra-thin lithium foil production.

[0005] To address this issue, given current industrial capabilities, a template method can be employed. This involves using a plain-weave fabric with a stable structure as a support, which optimizes the surface structure and provides mechanical support. While many technologies currently use fabric as a release liner, they primarily utilize its porous nature, such as addressing resin film wetting. Existing technologies lack detailed studies of the fiber fabric's structure and specific structural designs to meet the crucial industrial application of ultra-thin lithium foil calendering. Therefore, developing specialized release films to address microstructural stability and enhance pressure resistance for stable calendering of ultra-thin lithium foil strips below 10μm is a pressing technical challenge. Summary of the Invention

[0006] The purpose of this invention is to at least solve one of the technical problems existing in the prior art, and to provide an enhanced ultrathin lithium foil calendering release film, its preparation method and application.

[0007] To address the following problems in existing technologies: 1. In the ultrathin lithium foil calendering process, when preparing thicknesses below 10μm, high strength requirements are placed on the release film substrate. It is necessary to ensure that the release film does not crack or wrinkle, affecting sample production. 2. Secondly, when the lithium foil is thin, it is required to spread quickly and evenly on the release film without slippage. This places high demands on the surface structure of the release film, ensuring that the lithium foil is uniformly locked onto the release film surface without slippage or defects. 3. Current industrial technologies struggle to construct consistent and stable micro / nano surface structures, easily leading to localized defects that render the ultrathin lithium foil unusable. This invention uses a composite substrate prepared by hot pressing polyester fiber cloth and a polymer film as the release film substrate. A release agent is coated onto the surface of the polymer film, and after curing, a release layer is formed, thus obtaining a reinforced release film for ultrathin lithium foil. On the one hand, compared with the prior art, the composite substrate of the present invention uses polyester fiber cloth instead of polyester film. Compared with polyester film, polyester fiber cloth is woven from fibers, which can provide excellent tear resistance by dispersing stress at the interlacing points. Furthermore, the present invention uses plain polyester fiber cloth, which is woven from interlaced fibers. It can provide excellent tear resistance by dispersing stress at the interlacing points. The fibers can bear greater stress, and the interlaced fibers can make the mechanical properties in both directions consistent, effectively inhibiting the damage to the film material and the spread of defects. Furthermore, the fibers in the plain polyester fiber cloth are tightly interlaced, and there is a stable and consistent micro-uneven structure on the surface. This structure can provide greater friction and more interfacial contact, allowing lithium metal to be laid flat on the film more effectively, realizing the calendering and forming of thinner lithium foil, and avoiding defects, which is beneficial to the peeling stability and quality improvement of lithium foil. On the other hand, the present invention uses a polymer film and polyester fiber cloth composite, which not only provides a carrier for the release agent and prevents the release agent from penetrating to the other side of the fiber cloth, causing uneven coating; but also fills some of the pores in the fiber cloth, making the microstructure more refined. During the calendering process, due to the elastic deformation of the release layer, the microstructure is transferred to the release surface, while the thickness of the release layer can be reduced, saving costs and improving the peeling effect of ultra-thin lithium foil.

[0008] The technical solution of the present invention is as follows: A first aspect of the present invention provides an enhanced ultrathin lithium foil calendering release film, the release film comprising a composite substrate and a release layer disposed on the composite substrate, the composite substrate comprising a polyester fiber cloth and a polymer film disposed on the polyester fiber cloth; The polyester fiber cloth is a cloth woven from polyester fibers. The thickness of the polyester fiber cloth is 20 μm to 50 μm, the diameter of the fibers in the polyester fiber cloth is 10 μm to 25 μm, and the pore size of the polyester fiber cloth is 0.1 μm to 1 μm. The thickness of the polymer film is 5 μm to 15 μm.

[0009] Optionally, the polyester fiber fabric is a plain weave fabric made of polyester fibers.

[0010] Optionally, the polymer film is made of at least one material selected from polypropylene, polyimide, polycarbonate, nylon and their modified products, and the melting temperature of the polymer film is 165℃~220℃.

[0011] Optionally, the thickness of the release layer is 0.5 μm to 1.5 μm.

[0012] Optionally, the composite substrate is prepared by hot pressing polyester fiber cloth and polymer film.

[0013] Optionally, the release layer is prepared from a release agent, which comprises the following raw materials in parts by weight: 100 parts of vinyl polysiloxane; 2 to 4 parts of hydrogen-containing polysiloxane; 3 to 5 parts of peel force modifier; 2 to 5 parts of anchoring agent; 1 to 2 parts of platinum catalyst; and 100 to 1000 parts of solvent.

[0014] Optionally, the viscosity of the vinyl polysiloxane is 100cp~5000cp, and the vinyl content is 10mmol / g~30mmol / g; The viscosity of the hydrogen-containing polysiloxane is 10cp~200cp, and the hydrogen content is 100mmol / g~500mmol / g; The peel force modifier is a hydrocarbon-modified MDQ type silicone resin; The anchoring agent is epoxypropyltriethoxysilane; The platinum-based catalyst is chloroplatinic acid; The solvent is 120# solvent oil.

[0015] A second aspect of the present invention provides a method for preparing the release film, comprising the following steps: Polyester fiber cloth and polymer film are hot-pressed to obtain a composite substrate; Vinyl polysiloxane, hydrogen-containing polysiloxane, peel force modifier, anchoring agent and platinum catalyst are added to solvent and mixed evenly to obtain release agent; The release agent is applied to the composite substrate, and the composite substrate coated with the release agent is dried to obtain the release film.

[0016] Optionally, the hot pressing temperature is 170℃~200℃, and the hot pressing roller is a rubber roller.

[0017] A third aspect of the present invention provides the application of the release film or the release film prepared by the preparation method in the preparation of ultrathin lithium strips, wherein the thickness of the ultrathin lithium strip is 2 μm to 5 μm.

[0018] This invention has at least one of the following beneficial effects: 1. Compared with the prior art, the composite substrate of the present invention uses polyester fiber cloth instead of polyester film. Compared with polyester film, polyester fiber cloth is made of woven fibers, which can provide excellent tear resistance by dispersing stress at the interlacing points.

[0019] 2. This invention uses a polymer film and polyester fiber cloth composite, which not only provides a carrier for the release agent and prevents the release agent from penetrating to the other side of the fiber cloth, causing uneven coating; but also fills some of the pores in the fiber cloth, making the microstructure more refined. During the calendering process, due to the elastic deformation of the release layer, the microstructure is transferred to the release surface, while the thickness of the release layer can be reduced, saving costs and improving the peeling effect of ultra-thin lithium foil. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the release film prepared in an embodiment of the present invention used for ultrathin lithium foil calendering. Detailed Implementation

[0021] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0022] An embodiment of the present invention provides a release film for an enhanced ultrathin lithium foil, the release film comprising a composite substrate and a release layer disposed on the composite substrate, the composite substrate comprising a polyester fiber cloth and a polymer film disposed on the polyester fiber cloth; The polyester fiber cloth is a cloth woven from polyester fibers. The thickness of the polyester fiber cloth is 20 μm to 50 μm, the diameter of the fibers in the polyester fiber cloth is 10 μm to 25 μm, and the pore size of the polyester fiber cloth is 0.1 μm to 1 μm. The thickness of the polymer film is 5 μm to 15 μm.

[0023] This invention utilizes a composite substrate made of polyester fiber cloth and polymer film prepared by hot pressing as the substrate for the release film. A release agent is coated onto the surface of the polymer film, and after curing, a release layer is formed, thus obtaining a reinforced release film for ultra-thin lithium foil. On one hand, compared to existing technologies, the composite substrate of this invention uses polyester fiber cloth instead of polyester film. Compared to polyester film, polyester fiber cloth is woven from fibers, and its stress dispersion at the interlacing points provides excellent tear resistance. On the other hand, the composite of polymer film and polyester fiber cloth in this invention not only provides a carrier for the release agent, preventing it from penetrating to the other side of the fiber cloth and causing uneven coating, but also fills some of the pores in the fiber cloth, resulting in a finer microstructure. During calendering, the elastic deformation of the release layer transfers the microstructure to the release surface, while simultaneously reducing the release layer thickness, saving costs, and improving the peeling effect of ultra-thin lithium foil. Therefore, the release film prepared by this invention can be used for the stable peeling and production of 2 μm~5 μm ultra-thin lithium foil, with a smooth surface.

[0024] In some embodiments, the thickness of the polyester fiber cloth is 25 μm to 50 μm, the fiber diameter in the polyester fiber cloth is 12 μm to 25 μm, and the pore size of the polyester fiber cloth is 0.2 μm to 1 μm; the thickness of the polymer film is 7 μm to 13 μm. Preferably, the thickness of the polyester fiber cloth is 25 μm to 45 μm, the fiber diameter in the polyester fiber cloth is 13 μm to 25 μm, and the pore size of the polyester fiber cloth is 0.3 μm to 1 μm; the thickness of the polymer film is 8 μm to 12 μm. More preferably, the thickness is 30 μm to 45 μm, the fiber diameter in the polyester fiber cloth is 15 μm to 25 μm, the pore size of the polyester fiber cloth is 0.4 μm to 1 μm; and the thickness of the polymer film is 9 μm to 11 μm.

[0025] In some embodiments, the polyester fiber fabric is a plain weave fabric made of polyester fibers.

[0026] Polyester plain weave fabric is woven from interlaced fibers, providing excellent tear resistance by dispersing stress at the interlacing points. Secondly, the fibers can withstand significant stress, and the interlacing ensures consistent mechanical properties in both directions, effectively inhibiting membrane damage and defect propagation. Furthermore, the tight interlacing of fibers in the polyester plain weave fabric creates a stable and consistent micro-uneven surface structure. This structure provides greater friction and more interfacial contact, allowing lithium metal to be more effectively laid flat on the membrane, enabling the calendering of thinner lithium foils, avoiding defects, and improving the peel stability and quality of the lithium foil.

[0027] In some embodiments, the polymer film is prepared from at least one material selected from polypropylene, polyimide, polycarbonate, nylon and their modified products, and the melting temperature of the polymer film is 165°C to 220°C.

[0028] The melting temperature of polymer materials is between 165℃ and 220℃ to prevent the film from shrinking during the curing process of the release agent, and also to avoid the polyester fiber cloth from softening and deforming during processing.

[0029] In some embodiments, the thickness of the release layer is 0.5 μm to 1.5 μm. Preferably, it is 0.5 μm to 1.2 μm; more preferably, it is 0.5 μm to 1.0 μm. In some embodiments, the composite substrate is prepared by hot pressing polyester fiber cloth and polymer film.

[0030] In some embodiments, the release layer is prepared from a release agent, which comprises the following raw materials in parts by weight: 100 parts vinyl polysiloxane; 2 to 4 parts hydrogen-containing polysiloxane; 3 to 5 parts peel force modifier; 2 to 5 parts anchoring agent; 1 to 2 parts platinum catalyst; and 100 to 1000 parts solvent. Preferably, the release agent comprises the following raw materials in parts by weight: 100 parts vinyl polysiloxane; 2.5 to 3.5 parts hydrogen-containing polysiloxane; 3.5 to 4.5 parts peel force modifier; 2.5 to 4.5 parts anchoring agent; 1.2 to 1.8 parts platinum catalyst; and 200 to 900 parts solvent. More preferably, the release agent comprises the following raw materials in parts by weight: 100 parts of vinyl polysiloxane; 2.8 to 3.2 parts of hydrogen-containing polysiloxane; 3.8 to 4.2 parts of peel force modifier; 3 to 4 parts of anchoring agent; 1.3 to 1.7 parts of platinum catalyst; and 300 to 800 parts of solvent.

[0031] In some embodiments, the viscosity of the vinyl polysiloxane is 100 cp to 4000 cp, and the vinyl content is 10 mmol / g to 30 mmol / g; preferably, the viscosity of the vinyl polysiloxane is 100 cp to 3000 cp, and the vinyl content is 15 mmol / g to 30 mmol / g; more preferably, the viscosity of the vinyl polysiloxane is 100 cp to 1000 cp, and the vinyl content is 20 mmol / g to 25 mmol / g.

[0032] In some embodiments, the viscosity of the hydrogen-containing polysiloxane is 10 cp to 200 cp, and the hydrogen content is 100 mmol / g to 500 mmol / g; preferably, the viscosity of the hydrogen-containing polysiloxane is 30 cp to 180 cp, and the hydrogen content is 200 mmol / g to 500 mmol / g; more preferably, the viscosity of the hydrogen-containing polysiloxane is 50 cp to 150 cp, and the hydrogen content is 200 mmol / g to 400 mmol / g.

[0033] In some embodiments, the peel force modifier is a hydrocarbon-modified MDQ type silicone resin.

[0034] In some embodiments, the anchoring agent is glycidyltriethoxysilane.

[0035] In some embodiments, the platinum-based catalyst is chloroplatinic acid.

[0036] In some embodiments, the solvent is 120# solvent oil.

[0037] Another embodiment of the present invention provides a method for preparing the release film, comprising the following steps: Polyester fiber cloth and polymer film are hot-pressed to obtain a composite substrate; Vinyl polysiloxane, hydrogen-containing polysiloxane, peel force modifier, anchoring agent and platinum catalyst are added to solvent and mixed evenly to obtain release agent; The release agent is applied to the composite substrate, and the composite substrate coated with the release agent is dried to obtain the release film.

[0038] The preparation method of the present invention is simple and practical. It only requires hot pressing polyester fiber cloth and polymer film to form a composite substrate, and then coating the composite substrate with a release agent.

[0039] In some embodiments, the hot pressing temperature is 170°C to 200°C, and the hot pressing roller is a rubber roller. Preferably, the hot pressing temperature is 180°C to 200°C; more preferably, the hot pressing temperature is 185°C to 195°C. Another embodiment of the present invention provides the application of the release film or the release film prepared by the preparation method in the preparation of ultrathin lithium strips.

[0040] The release film prepared by this invention can be used for the production of ultra-thin lithium foil, especially to achieve stable peeling and production of 2μm~5μm ultra-thin lithium foil. The surface of the ultra-thin lithium foil is flat and the film material will not break.

[0041] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited to the following specific embodiments.

[0042] In the following examples and comparative examples, the viscosity of vinyl polysiloxane is 500 cps and the vinyl content is 25 mmol / g; the viscosity of hydrogen-containing polysiloxane is 100 cps and the hydrogen content is 300 mmol / g; the peel force modifier is specifically hydrocarbon-modified MDQ type silicone resin; the anchoring agent is specifically epoxypropyltriethoxysilane; the platinum catalyst is specifically chloroplatinic acid; and the solvent is specifically 120# solvent oil.

[0043] In the following examples and comparative examples, the parts of raw materials added refer to parts by weight.

[0044] Example 1 A method for preparing an enhanced ultrathin lithium foil calendering release film includes the following steps: 1) Select a 30 μm thick PET polyester fiber plain weave fabric with a fiber diameter of 15 μm and a pore size of 0.5 μm; and a 10 μm polypropylene film; 2) The polypropylene film and polyester fiber plain weave fabric are rolled together at a rolling temperature of 190 ℃ to obtain a composite substrate, which is then cooled and rolled up for later use. 3) Add 100 parts of vinyl polysiloxane, 3 parts of hydrogen-containing polysiloxane, 4 parts of peel force modifier, 5 parts of anchoring agent, and 1 part of platinum catalyst to 500 parts of solvent and stir evenly to obtain release agent. 4) Apply the release agent to the composite substrate in a micro-grooving device and dry and cure it in a continuous oven; 5) After the solvent has evaporated and cured, a release film with a dry film thickness of 0.8 μm is obtained.

[0045] like Figure 1 As shown, release film was used for lithium metal twin-roll calendering, with release film on the top and bottom and lithium foil in the middle, and the calendering effect was observed.

[0046] Example 2 A method for preparing an enhanced ultrathin lithium foil calendering release film includes the following steps: 1) Select a 30 μm thick PET polyester fiber plain weave fabric with a fiber diameter of 10 μm and a pore size of 0.2 μm; and a 5 μm polypropylene film; 2) The polypropylene film and polyester fiber plain weave fabric are rolled together at a rolling temperature of 190 ℃ to obtain a composite substrate, which is then cooled and rolled up for later use. 3) Add 100 parts of vinyl polysiloxane, 3 parts of hydrogen-containing polysiloxane, 4 parts of peel force modifier, 5 parts of anchoring agent, and 1 part of platinum catalyst to 500 parts of solvent and stir evenly to obtain release agent. 4) Apply the release agent to the composite substrate in a micro-grooving device and dry and cure it in a continuous oven; 5) After the solvent has evaporated and cured, a release film with a dry film thickness of 0.5 μm is obtained.

[0047] like Figure 1 As shown, release film was used for lithium metal twin-roll calendering, with release film on the top and bottom and lithium foil in the middle, and the calendering effect was observed.

[0048] Example 3 A method for preparing an enhanced ultrathin lithium foil calendering release film includes the following steps: 1) Select a PET polyester fiber plain weave fabric with a thickness of 45 μm, a fiber diameter of 25 μm, and a pore size of 1 μm; and a 15 μm polypropylene film; 2) The polypropylene film and polyester fiber plain weave fabric are rolled together at a rolling temperature of 190 ℃ to obtain a composite substrate, which is then cooled and rolled up for later use. 3) Add 100 parts of vinyl polysiloxane, 3 parts of hydrogen-containing polysiloxane, 4 parts of peel force modifier, 5 parts of anchoring agent, and 1 part of platinum catalyst to 500 parts of solvent and stir evenly to obtain release agent; 4) Apply the release agent to the composite substrate in a micro-grooving device and dry and cure it in a continuous oven; 5) After the solvent has evaporated and cured, a release film with a dry film thickness of 1 μm is obtained.

[0049] like Figure 1 As shown, release film was used for lithium metal twin-roll calendering, with release film on the top and bottom and lithium foil in the middle, and the calendering effect was observed.

[0050] Comparative Example 1 A method for preparing a release film includes the following steps: 1) A 50 μm thick polyester film was selected as the substrate; 2) Add 100 parts of vinyl polysiloxane, 3 parts of hydrogen-containing polysiloxane, 4 parts of peel force modifier, 5 parts of anchoring agent, and 1 part of platinum catalyst to 500 parts of solvent and stir evenly to obtain release agent; 3) Apply the release agent onto the film in a micro-grooving device and dry and cure it in a continuous oven; 4) After the solvent has evaporated and cured, a release film with a dry film thickness of 1 μm is obtained.

[0051] Release films were used in lithium metal twin-roll calendering, with release films on the top and bottom and lithium foil in the middle. The calendering effect was observed.

[0052] Comparative Example 2 A method for preparing a release film includes the following steps: 1) A 50 μm thick polypropylene film was selected as the substrate; 2) Add 100 parts of vinyl polysiloxane, 3 parts of hydrogen-containing polysiloxane, 4 parts of peel force modifier, 5 parts of anchoring agent, and 1 part of platinum catalyst to 500 parts of solvent and stir evenly to obtain release agent; 3) Apply the release agent onto the film in a micro-grooving device and dry and cure it in a continuous oven; 4) After the solvent has evaporated and cured, a release film with a dry film thickness of 1 μm is obtained.

[0053] Release films were used in lithium metal twin-roll calendering, with release films on the top and bottom and lithium foil in the middle. The calendering effect was observed.

[0054] Comparative Example 3 A method for preparing a release film includes the following steps: 1) Select a 30 μm thick plain weave polyester fiber fabric with a fiber diameter of 10 μm and a pore size of 0.2 μm; and a 25 μm polypropylene film; 2) The polypropylene film and polyester fiber plain weave fabric are rolled together at a rolling temperature of 190 ℃ to obtain a composite substrate, which is then cooled and rolled up for later use. 3) Add 100 parts of vinyl polysiloxane, 3 parts of hydrogen-containing polysiloxane, 4 parts of peel force modifier, 5 parts of anchoring agent, and 1 part of platinum catalyst to 500 parts of solvent and stir evenly to obtain release agent; 4) Apply the release agent onto the film in a microgrooving device and dry and cure it in a continuous oven; 5) After the coating solvent has evaporated and cured, a release film with a dry film thickness of 1 μm is obtained.

[0055] Release films were used in lithium metal twin-roll calendering, with release films on the top and bottom and lithium foil in the middle. The calendering effect was observed.

[0056] Comparative Example 4 A method for preparing a release film includes the following steps: 1) Select a 30 μm thick plain weave polyester fiber fabric with a fiber diameter of 15 μm and a pore size of 0.5 μm; and a 10 μm polypropylene film; 2) Roll-press the polypropylene film with the polyester fiber plain weave fabric at a rolling temperature of 170 ℃, then cool and roll it up for later use. 3) Add 100 parts of vinyl polysiloxane, 3 parts of hydrogen-containing polysiloxane, 4 parts of peel force modifier, 5 parts of anchoring agent, and 1 part of platinum catalyst to 500 parts of solvent and stir evenly to obtain release agent; 4) Apply the release agent onto the film in a microgrooving device and dry and cure it in a continuous oven; 5) After the solvent has evaporated and cured, a release film with a dry film thickness of 0.8 μm is obtained.

[0057] Release films were used in lithium metal twin-roll calendering, with release films on the top and bottom and lithium foil in the middle. The calendering effect was observed.

[0058] Comparative Example 5 A method for preparing a release film includes the following steps: 1) Select a 30 μm thick plain weave polyester fiber fabric with a fiber diameter of 15 μm and a pore size of 0.5 μm; and a 10 μm polypropylene film; 2) Roll-press the polypropylene film with the polyester fiber plain weave fabric at a rolling temperature of 190 ℃, then cool and roll it up for later use. 3) Add 100 parts of vinyl polysiloxane, 3 parts of hydrogen-containing polysiloxane, 4 parts of peel strength modifier, 5 parts of anchoring agent, and 1 part of platinum catalyst to 500 parts of solvent and stir until homogeneous; 4) Apply the release agent onto the film in a microgrooving device and dry and cure it in a continuous oven; 5) After the solvent has evaporated and cured, a release film with a dry film thickness of 3 μm is obtained.

[0059] Release films were used in lithium metal twin-roll calendering, with release films on the top and bottom and lithium foil in the middle. The calendering effect was observed.

[0060] Comparative Example 6 The difference from Example 1 is that the phrase "selecting 30 μm thick, 15 μm fiber diameter, and 0.5 μm pore size PET polyester fiber plain weave fabric" in Example 1 is changed to "selecting 30 μm thick, 15 μm fiber diameter, and 0.5 μm pore size PET polyester fiber twill weave fabric". Then, the PET polyester fiber twill weave fabric is rolled with a 10 μm polypropylene film to form a composite substrate. Everything else is the same as in Example 1.

[0061] Comparative Example 7 The difference from Example 1 is that the phrase "selecting 30 μm thick, 15 μm fiber diameter, and 0.5 μm pore size PET polyester fiber plain weave fabric" in Example 1 is changed to "50 μm thick polyester film". Then, the 50 μm thick polyester film and a 10 μm polypropylene film are rolled together to form a composite substrate. Everything else is the same as in Example 1.

[0062] The effects of release films used in the above embodiments and comparative examples for lithium metal twin-roll calendering were measured, specifically by calendering thickness, surface condition, peelability, and stable production. The results are shown in Table 1. Table 1 As can be seen from the above examples and comparative examples, Examples 1 to 3 of the present invention can achieve stable production of ultra-thin lithium foil products with a thickness of less than 10 μm. In contrast, the polyester film used in Comparative Example 1 and the polypropylene film used in Comparative Example 2 cracked under high stress during calendering, with the gaps continuing to spread. The substrates designed in Examples 1 to 3 of the present invention, however, possess excellent tear resistance due to stress dispersion at interlacing points, and can withstand greater stress, ensuring no damage occurs during production. Secondly, it is also necessary to ensure that the microstructure of the polyester fiber plain weave fabric can be transferred to the interface between the ultra-thin lithium foil and the release layer, which requires the polymer film to possess a microstructure. In Comparative Example 3, when the polymer film is relatively thick (25 μm), the microstructure of the polyester fiber plain weave fabric is difficult to transfer to the surface of the polymer film, making it difficult to form a nanoscale microstructure. This prevents the lithium metal from extending and spreading in the narrow gaps during calendering, thus making it difficult to obtain a flat and uniform ultra-thin lithium foil. In Comparative Example 4, when low-temperature molding (rolling temperature 170 ℃) was used, the material's viscous deformation was low, insufficient to transfer the microstructure to the film material, resulting in a relatively smooth surface, but making it difficult to uniformly form the ultrathin lithium foil. In Comparative Example 5, the release layer was too thick (3 μm), covering the surface microstructure, and the excessive deformation of the release layer caused deeper bonding with the lithium foil interface, making it difficult to peel off. Although Comparative Examples 6 and 7 also used composite substrates, they used PET polyester fiber twill fabric and polyester film, respectively. The PET polyester fiber twill fabric had a problem with its calendering direction not being consistent with that of the lithium metal, affecting its elongation behavior and causing poor surface smoothness. The composite substrate formed by the polyester film and polypropylene film material would crack under strong stress during the calendering process.

[0063] Therefore, this invention uses a composite substrate formed from polyester fiber plain weave fabric and a polymer film. By controlling the thickness of the polymer film and the molding temperature, it can achieve stable peeling and production of ultra-thin lithium foil ranging from 2 μm to 5 μm with a smooth surface. The micro / nano surface structure constructed using the template method in this invention does not require formulation adjustments, which is beneficial for achieving surface structure consistency and stability, and also helps reduce defects.

[0064] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An enhanced ultra-thin lithium foil calendering release film, characterized in that, the release film comprises a composite substrate and a release layer disposed on the composite substrate, the composite substrate comprises a polyester fiber cloth and a polymer film disposed on the polyester fiber cloth; the polyester fiber cloth is a cloth woven with polyester fibers, the thickness of the polyester fiber cloth is 20 μm~50 μm, the fiber diameter in the polyester fiber cloth is 10 μm~25 μm, and the pore size of the polyester fiber cloth is 0.1 μm~1 μm; the thickness of the polymer film is 5 μm~15 μm.

2. The release film according to claim 1, wherein The polyester fiber cloth is a plain cloth woven with polyester fibers.

3. The release film according to claim 1, wherein The polymer film is prepared from at least one material selected from the group consisting of polypropylene, polyimide, polycarbonate, nylon and modified products thereof, and the melting temperature of the polymer film is 165℃~220℃.

4. The release film of claim 1, wherein The thickness of the release layer is 0.5 μm~1.5 μm.

5. The release film according to claim 1, wherein The composite substrate is prepared by hot pressing the polyester fiber cloth and the polymer film.

6. The release film according to claim 1, wherein The release layer is prepared from a release agent, and the release agent comprises the following raw materials by weight: 100 parts of vinyl polysiloxane; 2 parts~4 parts of hydrogen-containing polysiloxane; 3 parts~5 parts of release force adjuster; 2 parts~5 parts of anchoring agent; 1 part~2 parts of platinum catalyst; 100 parts~1000 parts of solvent.

7. The release film according to claim 6, characterized in that, the viscosity of the vinyl polysiloxane is 100 cp~5000 cp, and the content of vinyl is 10 mmol / g~30 mmol / g; the viscosity of the hydrogen-containing polysiloxane is 10 cp~200 cp, and the hydrogen content is 100 mmol / g~500 mmol / g; the release force adjuster is a hydrocarbon-modified MDQ type silicone resin; the anchoring agent is an epoxy propyl triethoxysilane; the platinum catalyst is chloroplatinic acid; the solvent is 120# solvent oil.

8. The method of producing the release film according to any one of claims 1 to 7, characterized by, comprising the following steps: hot pressing the polyester fiber cloth and the polymer film to obtain a composite substrate; mixing the vinyl polysiloxane, the hydrogen-containing polysiloxane, the release force adjuster, the anchoring agent and the platinum catalyst in the solvent to obtain a release agent; coating the release agent on the composite substrate, and drying the composite substrate coated with the release agent to obtain the release film.

9. The preparation method according to claim 8, characterized in that, The temperature of the hot pressing is 170℃~200℃, and the pressure roller of the hot pressing is a rubber roller.

10. Use of the release film according to any one of claims 1 to 7 or the release film produced according to the production method of any one of claims 8 to 9 for producing an ultrathin lithium ribbon, characterized in that, The thickness of the ultra-thin lithium strip is 2 μm~5 μm.

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