A method for preparing mica insulating sheets without aluminum metal layers for lithium-ion batteries

Abstract

This invention provides a method for preparing a mica insulating sheet for lithium-ion batteries without an aluminum metal layer, relating to the technical field of electrical insulation materials and insulating component molding / manufacturing processes. The method includes: S1. providing a sheet-like mica substrate and preparing an organosilicon resin bonding system for impregnation; simultaneously preparing a ceramic barrier slurry for surface layering, wherein the ceramic barrier slurry includes silica sol, zirconium oxide sol, and titanium dioxide. This method for preparing a mica insulating sheet for lithium-ion batteries without an aluminum metal layer utilizes a ceramic barrier system constructed from Si sol + Zr sol + titanium dioxide, avoiding the existing technology's reliance on an aluminum reflective layer in the process path. This allows the lithium-ion battery insulating material to meet heat resistance and insulation requirements while achieving aluminum-free insulation, improving its application compatibility between cells and between cells and the casing.

Description

Technical Field

[0001] This invention relates to the technical field of forming / manufacturing processes for electrical insulating materials and insulating components, specifically a method for preparing mica insulating sheets for lithium-ion batteries without aluminum metal layers. Background Technology

[0002] In the application of insulation protection and thermal runaway isolation of lithium-ion batteries, existing solutions generally adopt mica sheets / mica plates as the core of the heat insulation material, or combine mica with other heat insulation materials to form multi-layer heat insulation sheets, and assemble them by means of adhesive bonding / edge sealing; at the same time, there are also technical routes that improve the heat insulation or protection effect by introducing structures such as reflective film layers into mica-based materials.

[0003] Current drawbacks: To achieve thermal insulation or protective performance, the aforementioned existing technologies often employ aluminum-containing structures or components. For example, the optional material for reflective films may contain aluminum, resulting in a common pathway for introducing aluminum into existing mica insulating and protective material systems for batteries. This not only makes it difficult to directly meet the demand for aluminum-free products, but also, under the long-term service environment of batteries, may introduce potential risks to interface consistency and reliability between aluminum-containing layers and other interlayer materials. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing mica insulating sheets for lithium-ion batteries without aluminum metal layers. By using a method of continuous ceramic layering and vacuum hot-pressure differential sealing and co-curing, the invention solves the problem that existing battery insulation protection relies on aluminum reflective layers and is prone to interlayer interface reliability issues.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a mica insulating sheet for lithium-ion batteries without an aluminum metal layer, comprising:

[0006] S1. Provide a sheet-like mica substrate, and formulate an organosilicon resin bonding system for impregnation; simultaneously formulate a ceramic barrier slurry for surface layering, the ceramic barrier slurry comprising silica sol, zirconium oxide sol and titanium dioxide, perform shear dispersion on the ceramic barrier slurry, and sequentially perform filtration and vacuum degassing treatment to obtain a coating slurry suitable for coating layering, the preparation method does not include the step of forming an aluminum metal layer, aluminum foil layer, aluminum plating layer or aluminum reflective layer;

[0007] S2. The sheet-like mica substrate is placed in the impregnation station, and the organosilicon resin bonding system is made to enter the mica pore structure under vacuum-pressure alternating impregnation conditions to obtain an impregnated preform. The impregnated preform is then dried in sections and pre-cured to obtain a resin-impregnated mica preform.

[0008] S3. The coating slurry is applied to at least one side surface of the resin-impregnated mica preform using a slot coating method, and cross-directional recoating is performed. The cross-directional recoating includes coating in two mutually perpendicular directions and overlapping coating at the coating boundary. Combined with leveling and sequential segmented gelation and segmented drying processes, the coating slurry forms a continuously covering ceramic precursor layer on the surface of the resin-impregnated mica preform, resulting in a film preform.

[0009] S4. The preform of the film layer is placed into a hot press mold for vacuum hot pressing co-curing. The hot press mold is provided with an annular limiting pressing step on the circumferential edge to form a sealing edge area. The circumferential edge area of ​​the preform of the film layer forms a pressing edge area under the limiting pressing action of the annular limiting pressing step, and co-curing is performed under the vacuum hot pressing co-curing conditions. The compression ratio of the pressing edge area relative to the main body area is 12%-20%, forming an integrated sealing edge area, and obtaining a mica insulating sheet without aluminum metal layer for use between battery cells or between battery cells and the shell.

[0010] Preferably, the organosilicon resin bonding system comprises methylphenyl silicone resin, crosslinking agent, catalyst and organic solvent, wherein, by mass, the methylphenyl silicone resin is 40-70 parts, the crosslinking agent is 1-10 parts, the catalyst is 0.01-0.20 parts, and the organic solvent is 20-50 parts.

[0011] Preferably, in the ceramic barrier slurry: the SiO2 solid content of the silica sol is 20wt%-40wt%; the ZrO2 solid content of the zirconia sol is 10wt%-30wt%; the titanium dioxide is rutile type with a median particle size of 200nm-350nm; the ceramic barrier slurry does not contain nano-aerogels and does not contain silane coupling agents.

[0012] Preferably, the shear dispersion rotation speed is 2000rpm-8000rpm and the time is 5min-30min, the filtration uses a filter medium with a pore size of 50μm-150μm, and the vacuum degassing is -0.08MPa-0.095MPa and the time is 5min-20min.

[0013] Preferably, the vacuum-pressure alternating impregnation includes a cycle consisting of a vacuum impregnation step and a pressure impregnation step. The cycle includes: first, evacuating the vacuum at a vacuum degree of -0.08MPa to -0.095MPa for 5min to 30min, and then impregnating the vacuum at a pressure of 0.2MPa to 0.8MPa for 5min to 30min; the cycle is repeated 1 to 3 times.

[0014] Preferably, the segmented drying includes two temperature stages: the first stage is drying at 80℃-100℃ for 10min-25min, and the second stage is drying at 100℃-120℃ for 10min-35min; the pre-curing is carried out at 120℃-160℃ for 10min-30min, so that the organosilicon resin bonding system reaches a semi-cured state that can be further cross-linked and cured in subsequent vacuum hot pressing co-curing, thus obtaining a resin-impregnated mica preform.

[0015] Preferably, the slit coating has a coating gap of 0.15mm-0.35mm, a wet film thickness of 50μm-150μm, a coating line speed of 2m / min-20m / min, and an apparent viscosity of 0.20Pa·s-1.20Pa·s at 25℃.

[0016] Preferably, the overlap width of the overlapping coating is 2mm-8mm, and the leveling is maintained for 1min-2min between adjacent coatings.

[0017] Preferably, the segmented gelation includes: performing a first-stage gelation at 25℃-35℃ for 2 min-8 min, followed by a second-stage gelation at 40℃-55℃ for 3 min-10 min, with a total holding time of 5 min-15 min; the segmented drying includes drying at 70℃-85℃ for 10 min-30 min and drying at 95℃-110℃ for 15 min-40 min, to complete the stepwise curing and shaping of the ceramic precursor layer.

[0018] Preferably, the vacuum degree of the vacuum hot pressing co-curing is not lower than -0.085MPa, the hot pressing temperature is 180℃-210℃, the hot pressing pressure is 4MPa-8MPa, and the holding time is 20min-60min; the step width of the annular limiting pressing step is 5mm-12mm, and the compression ratio of the pressing area relative to the main body area is 12%-20% by setting the step limiting gap.

[0019] This invention provides a method for preparing mica insulating sheets for lithium-ion batteries without an aluminum metal layer. It has the following beneficial effects:

[0020] This method for preparing mica insulating sheets for lithium-ion batteries without aluminum metal layers uses a ceramic barrier system constructed from Si sol, Zr sol, and titanium dioxide. This avoids the existing technology's reliance on aluminum reflective layers, enabling the lithium-ion battery insulation material to meet heat resistance and insulation requirements while achieving aluminum-free insulation, thus improving its compatibility in applications between cells and between cells and the casing.

[0021] This invention achieves continuous layering of ceramic layers through alternating vacuum-pressure impregnation, slit coating with cross-coating and overlapping, segmented gelation, and segmented drying. During the vacuum hot-pressing co-curing process, annular limiting edge pressing steps are used to form an edge pressing zone and control the compression ratio, thereby achieving integrated edge sealing and interlayer co-curing. This reduces the risks caused by interlayer interface defects and weak edge areas, and improves the interface consistency and reliability of the battery under long-term service conditions. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the internal process of the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] like Figure 1 As shown, this embodiment of the invention provides a method for preparing a mica insulating sheet for lithium-ion batteries without an aluminum metal layer, comprising:

[0025] Parameter selection criteria: To ensure the reliability of the interface between the continuous ceramic precursor layer and the sealing structure, the process parameters of this invention preferably satisfy the following linkage relationship: When the slit coating line speed increases in the range of 2m / min to 20m / min, the apparent viscosity of the coating slurry at 25℃ increases accordingly in the range of 0.20Pa·s to 1.20Pa·s, and the wet film thickness decreases accordingly in the range of 50μm to 150μm; when the wet film thickness increases, the coating line speed decreases accordingly, and the subsequent segmented drying time is extended accordingly, preferably extending the second stage drying time to reduce the risk of surface skinning, bubbles, and drying cracking.

[0026] The preferred segmented gelation of the ceramic precursor layer includes holding the first segment at 25℃~35℃ for 2min~8min, the second segment at 40℃~55℃ for 3min~10min, and segmented drying at 70℃~85℃ for 10min~30min and at 95℃~110℃ for 15min~40min, to achieve progressive network formation and devolatilization. When the compression ratio of the edge pressing zone is relatively high within the range of 12%~20%, the vacuum hot pressing pressure is relatively high within the range of 4MPa~8MPa or the holding time is relatively high within the range of 20min~60min to complete the compaction and degassing of the edge pressing zone. At the same time, the hot pressing temperature is not at the extreme end within the range of 180℃~210℃ to avoid excessive resin flow leading to edge structure instability. When the compression ratio is relatively low, the pressure or holding time is medium to low to balance the co-curing of the main area and edge shaping.

[0027] Methylphenyl silicone resin is used to form a heat-resistant bonding skeleton. Too low a resin ratio can lead to insufficient bonding to the mica matrix, while too high a ratio can increase the system viscosity, reducing porosity, impregnation, and coating leveling properties. In one embodiment, the silicone resin bonding system may consist of approximately 55 parts by weight of methylphenyl silicone resin, approximately 5 parts of crosslinking agent, approximately 0.05 parts of catalyst, and approximately 35 parts of organic solvent to balance impregnation and subsequent co-curing. The ceramic barrier slurry uses silica sol and zirconium oxide sol to form a ceramic precursor network. Too low a solids content may result in insufficient film-forming skeleton, while too high a solids content may increase viscosity and the risk of coating defects. In one embodiment, the SiO2 solids content of the silica sol may be approximately 30 wt%, and the ZrO2 solids content of the zirconium oxide sol may be approximately 20 wt% to obtain a precursor network suitable for slot coating and easy continuous layering. The titanium dioxide is selected from rutile type to provide non-metallic reflection or shielding enhancement and to synergistically form the barrier layer microstructure. Smaller particle size may increase the difficulty of agglomeration and dispersion, while larger particle size may reduce scattering efficiency and coverage uniformity. In one embodiment, the median particle size of rutile titanium dioxide can be selected to be about 300 nm to balance dispersion stability and reflection enhancement effect.

[0028] In the alternating vacuum-pressure impregnation process, the vacuum stage is used to remove gas from the mica pores, and the pressure stage is used to drive the resin into the pore structure. The number of cycles can be selected within the allowable range based on the mica thickness, pore structure, and resin viscosity. A cycle termination criterion can be used when the weight gain per unit area after two consecutive cycles is ≤3%, or when bubble precipitation significantly decreases and stabilizes during the vacuum stage. The process parameters for shear dispersion, filtration, and vacuum degassing can be adjusted within the specified range based on the viscosity stability of the coating slurry, bubble precipitation, and the risk of streaks or pinholes on the coating surface, to ensure the stability of the slot coating process and reduce delamination defects.

[0029] Example 1:

[0030] S1. Provide a sheet-like mica substrate, and formulate an organosilicon resin bonding system for impregnation; simultaneously formulate a ceramic barrier slurry for surface layering, the ceramic barrier slurry including silica sol, zirconium oxide sol and titanium dioxide, perform shear dispersion on the ceramic barrier slurry, and sequentially perform filtration and vacuum degassing treatment to obtain a coating slurry suitable for coating layering, the preparation method does not include the step of forming an aluminum metal layer, aluminum foil layer, aluminum plating layer or aluminum reflective layer.

[0031] The silicone resin bonding system comprises methylphenyl silicone resin, a crosslinking agent, a catalyst, and an organic solvent. By weight, the methylphenyl silicone resin is 55 parts, the crosslinking agent is 5 parts, the catalyst is 0.05 parts, and the organic solvent is 35 parts. In the ceramic barrier slurry: by weight, the silica sol is 60 parts, with a SiO2 solid content of 30 wt%; the zirconium oxide sol is 30 parts, with a ZrO2 solid content of 20 wt%; and the titanium dioxide is 10 parts, which is rutile type with a median particle size of 300 nm. The ceramic barrier slurry does not contain nano-aerogels or silane coupling agents. Shear dispersion was performed at 5000 rpm for 15 min. Filtration was conducted using a 100 μm pore size filter medium, and vacuum degassing was performed at -0.09 MPa for 10 min.

[0032] S2. Place the sheet-like mica substrate in the impregnation station, and allow the silicone resin bonding system to enter the mica pore structure under vacuum-pressure alternating impregnation conditions to obtain an impregnated preform. Dry the impregnated preform in sections and pre-cur it to obtain a resin-impregnated mica preform.

[0033] The vacuum-pressure alternating impregnation consists of a cycle consisting of a vacuum impregnation step and a pressure impregnation step. The cycle includes: first, evacuating at a vacuum degree of -0.09MPa for 15 minutes, and then impregnating at a pressure of 0.5MPa for 15 minutes; the cycle is repeated twice.

[0034] The segmented drying process includes two temperature stages: the first stage is drying at 90℃ for 20 minutes, and the second stage is drying at 110℃ for 25 minutes. The pre-curing process is carried out at 140℃ for 20 minutes, so that the silicone resin bonding system reaches a semi-cured state that can be further cross-linked and cured in the subsequent vacuum hot pressing co-curing, thus obtaining the resin-impregnated mica preform.

[0035] S3. Apply a slurry to at least one side of the resin-impregnated mica preform using a slot coating method, and perform cross-directional recoating. Cross-directional recoating includes coating in two mutually perpendicular directions and overlapping coating at the coating boundary. Combined with leveling and sequential segmented gelation and segmented drying processes, the slurry forms a continuous ceramic precursor layer on the surface of the resin-impregnated mica preform, resulting in a film preform.

[0036] The slot coating has a coating gap of 0.25 mm, a wet film thickness of 100 μm, a coating line speed of 10 m / min, and an apparent viscosity of 0.6 Pa·s at 25 °C. The overlap width of the lap coating is 5 mm, and a 1.5 min leveling period is allowed between adjacent coatings.

[0037] The segmented gelation process includes: holding at 30°C for 5 minutes for the first stage of gelation, followed by holding at 48°C for 6 minutes for the second stage of gelation, with a total holding time of 11 minutes; the segmented drying process includes drying at 80°C for 20 minutes and drying at 105°C for 25 minutes in sequence to complete the stepwise curing and shaping of the ceramic precursor layer.

[0038] S4. The preform of the film layer is placed into a hot press mold for vacuum hot pressing co-curing. The hot press mold is provided with an annular limiting pressing step on the circumferential edge to form a sealing area. The circumferential edge area of ​​the preform of the film layer forms a pressing area under the limiting pressing action of the annular limiting pressing step. Co-curing is carried out under vacuum hot pressing co-curing conditions. The compression ratio of the pressing area to the main body area is 15%, forming an integrated sealing area, and obtaining a mica insulating sheet without aluminum metal layer for use between cells or between cells and the shell.

[0039] The vacuum degree of vacuum hot pressing co-curing is -0.09MPa, the hot pressing temperature is 195℃, the hot pressing pressure is 6MPa, and the holding time is 35min; the step width of the annular limiting pressure step is 8mm, and the compression ratio of the pressure area relative to the main body area is 15% through the step limiting gap setting.

[0040] Performance tests were conducted on the mica insulating sheet without an aluminum metal layer obtained in Example 1. The sample size was 100mm × 100mm, the finished product thickness was 0.45mm, and the edge sealing width was 8mm. Five samples were taken for each test, and the average value was given. The electrical strength test was performed according to GB / T1408.1, using a flat electrode (electrode diameter 25mm), AC power frequency of 50Hz, and a voltage rise rate of 0.5kV / s. The breakdown voltage was measured to be 8.1kV, and the equivalent breakdown strength was 18.0kV / mm. Tests were conducted at points in the main body area and the edge sealing area. The breakdown strength in the edge sealing area was 19.1kV / mm, indicating that the edge sealing area was the first to break down. The thermal performance test was performed according to GB / T10294. The thermal conductivity was measured to be 0.22W / (m·K) at 25℃. Regarding interface reliability, the ceramic layer or mica substrate was subjected to a 180° peel test according to GB / T2790 standard, with a peel strength of 18N / 25mm. A thermal cycling test was also conducted, cycling between -40℃ and 85℃, with each end held at that temperature for 30 minutes and a transition time ≤10 minutes, for a total of 200 cycles. The peel strength retention rate was 89%, and the samples showed no peeling, delamination, or edge cracking. These results indicate that the insulating sheet obtained in this embodiment possesses both high electrical strength and stable edge insulation performance. The annular differential pressure edge-sealing co-curing structure effectively reduces the risk of breakdown caused by weak points at the edges, thus meeting the insulation protection requirements between cells or between the cell and the casing. The low thermal conductivity indicates that the ceramic barrier layer and the mica substrate work together to provide good thermal barrier capabilities, which helps to mitigate heat transfer. The high peel strength retention rate after thermal cycling and the absence of delamination or peeling indicate that the continuous layered coating and integrated edge-sealing structure have good interface consistency and long-term service reliability.

[0041] Example 2:

[0042] Based on Example 1, a combination of endpoint parameters with higher coating line speed, higher apparent viscosity of coating slurry, and lower wet film thickness was adopted, and the parameters of segmented gelation and segmented drying processes were adjusted accordingly to adapt to high-speed film formation. Except for the following explicit changes, the other raw materials, steps and process parameters are the same as in Example 1, and the preparation process does not include the steps of forming an aluminum metal layer, aluminum foil layer, aluminum coating or aluminum reflective layer.

[0043] S1. Prepare the ceramic barrier slurry and complete shear dispersion, filtration and vacuum degassing; by fine-tuning the amount of solvent or deionized water, make the apparent viscosity of the resulting coating slurry at 25℃ 1.20 Pa·s.

[0044] S2. The number of vacuum-pressure alternating impregnation cycles is fixed at 2 times. Then, the impregnated preform is dried in sections and pre-cured to obtain resin-impregnated mica preform.

[0045] S3. Apply the coating slurry to one side of the resin-impregnated mica preform using a slot coating method, and perform cross-directional recoating, one longitudinal and one transverse coat, followed by overlapping coating; the slot coating gap is 0.15 mm, the wet film thickness is 50 μm, the coating line speed is 20 m / min, the overlap width is 2 mm, and a 1 min leveling period is allowed between adjacent coatings; then, perform segmented gelation and segmented drying sequentially. The segmented gelation is performed by holding the first segment at 35°C for 2 min and the second segment at 55°C for 3 min, and the segmented drying is performed by drying the first segment at 85°C for 10 min and the second segment at 110°C for 15 min, so that the coating slurry forms a continuous ceramic precursor layer on the surface of the resin-impregnated mica preform, resulting in a film preform.

[0046] S4. The preform of the film layer is placed into a hot press mold with an annular limiting edge pressing step for vacuum hot pressing co-curing; the vacuum degree is -0.095MPa, the hot pressing temperature is 205℃, the hot pressing pressure is 8MPa, the holding time is 60min, and the step width is 12mm; the circumferential edge area of ​​the preform of the film layer forms a pressing area under the limiting edge pressing action of the annular limiting edge pressing step and co-cures. The compression ratio of the pressing area relative to the main body area is 20%, forming an integrated sealing area, and obtaining a mica insulating sheet without aluminum metal layer for use between battery cells or between battery cells and the shell.

[0047] Performance tests were conducted on the mica insulating sheet without an aluminum metal layer obtained in Example 2. The sample size was 100mm × 100mm, the finished product thickness was 0.40mm, and the width of the sealing area was 10mm. Five samples were taken for each test, and the average value was given. The electrical strength test was performed according to GB / T1408.1, using a flat electrode (electrode diameter 25mm), AC power frequency of 50Hz, and a voltage rise rate of 0.5kV / s. The breakdown voltage was measured to be 6.8kV, and the equivalent breakdown strength was 17.0kV / mm. Tests were conducted at points in the main body area and the sealing area. The breakdown strength of the sealing area was 19.0kV / mm, indicating that the sealing area was the primary site for breakdown. The thermal performance test was performed according to GB / T10294. The thermal conductivity was measured to be 0.24W / (m·K) at 25℃. Regarding interface reliability, a 180° peel test was performed on the ceramic layer or mica substrate, with a peel strength of 16 N / 25 mm. After thermal cycling, the peel strength retention rate was 88%, and the samples showed no warping, delamination, or edge cracks. These results demonstrate that even under high-speed coating and film deposition end-point processes, a continuously covered ceramic precursor layer can still be formed and stable insulation performance can be achieved, indicating that the process parameter linkage rules of this invention have good process adaptability and manufacturability. The breakdown strength in the edge sealing area is significantly higher than that in the main body area, which helps to suppress the risk of local breakdown caused by weak edge areas under high-speed preparation conditions, thereby improving the insulation safety margin in the edge area. The high peel strength retention rate and absence of appearance defects after thermal cycling indicate that the differential pressure edge-sealing co-curing structure can maintain good interface consistency and reliability under high-cycle preparation conditions.

[0048] Example 3:

[0049] Based on Example 1, a combination of endpoint parameters with lower coating line speed, lower apparent viscosity of coating slurry, and higher wet film thickness is adopted, and the parameters of segmented gelation and segmented drying processes are extended accordingly to adapt to the low-speed layering of thick film; except for the following explicit changes, the other raw materials, steps and process parameters are the same as in Example 1, and the preparation process does not include the steps of forming aluminum metal layer, aluminum foil layer, aluminum coating or aluminum reflective layer.

[0050] S1. Prepare the ceramic barrier slurry and complete shear dispersion, filtration and vacuum degassing; by finely adjusting the amount of solvent or deionized water, make the apparent viscosity of the resulting coating slurry at 25℃ 0.20 Pa·s.

[0051] S2. The number of vacuum-pressure alternating impregnation cycles is fixed at 2 times. Then, the impregnated preform is dried in sections and pre-cured to obtain resin-impregnated mica preform.

[0052] S3. A slit coating is applied to one side of the resin-impregnated mica preform using a slot coating method, followed by cross-directional recoating and overlapping coating. The slot coating has a spacing of 0.35 mm, a wet film thickness of 150 μm, a coating line speed of 2 m / min, and an overlap width of 8 mm. A 2-minute leveling period is allowed between adjacent coatings. Subsequently, segmented gelation and segmented drying are performed sequentially. The segmented gelation process involves holding the first segment at 25°C for 8 minutes and the second segment at 40°C for 10 minutes. The segmented drying process involves drying the first segment at 70°C for 30 minutes and the second segment at 95°C for 40 minutes. This allows the coating slurry to form a continuous ceramic precursor layer on the surface of the resin-impregnated mica preform, resulting in a preform.

[0053] S4. The preform of the film layer is placed into a hot press mold with an annular limiting edge step for vacuum hot pressing and co-curing; the vacuum degree is -0.085MPa, the hot pressing temperature is 180℃, the hot pressing pressure is 4MPa, the holding time is 20min, and the step width is 5mm; the circumferential edge area of ​​the preform of the film layer forms an edge pressing area under the limiting edge pressing action of the annular limiting edge step and is co-cured. The compression ratio of the edge pressing area to the main body area is 12%, forming an integrated edge sealing area, and obtaining a mica insulating sheet without aluminum metal layer for use between battery cells or between battery cells and the shell.

[0054] Performance tests were conducted on the mica insulating sheet without an aluminum metal layer obtained in Example 3. The sample size was 100mm × 100mm, the finished product thickness was 0.60mm, and the edge sealing width was 6mm. Five samples were taken for each test, and the average value was given. The electrical strength test was performed according to GB / T1408.1, using a flat electrode (electrode diameter 25mm), AC power frequency of 50Hz, and a voltage rise rate of 0.5kV / s. The breakdown voltage was measured to be 9.6kV, and the equivalent breakdown strength was 16.0kV / mm. Tests were conducted at points in the main body area and the edge sealing area. The breakdown strength in the edge sealing area was 16.5kV / mm, and no preferential breakdown occurred in the edge sealing area. The thermal performance test was performed according to GB / T10294. The thermal conductivity was measured to be 0.20W / (m·K) at 25℃. Regarding interface reliability, a 180° peel test was performed on the ceramic layer or mica substrate, with a peel strength of 20 N / 25 mm. After thermal cycling, the peel strength was retested, maintaining 90% of the required strength. The samples showed no peeling, delamination, or edge cracking. These results demonstrate that under the end-stage process conditions of low-speed thick film deposition, continuous layering and stable electrical insulation performance can still be achieved by extending the gelation and drying / setting processes. This indicates that the process window of this invention can cover the requirements of thick film preparation and maintain feasibility. Compared to thin-film end-stage processes, the thermal conductivity is further reduced, reflecting a more significant inhibitory effect of the thick film barrier layer on heat transfer, which is beneficial for improving the thermal protection capability of the battery system. The high peel strength retention rate and the absence of delamination or peeling after thermal cycling indicate that the interface bonding and edge sealing structure formed under thick film conditions also possess good long-term service reliability.

[0055] Example 4:

[0056] This embodiment is a comparative embodiment. To compare the role of titanium dioxide in the ceramic barrier system, samples were prepared under the same process conditions as in Example 1. The only difference is that titanium dioxide was not added to the ceramic barrier slurry. All other raw materials, steps and process parameters were the same as in Example 1, and the preparation process did not include the steps of forming an aluminum metal layer, aluminum foil layer, aluminum coating or aluminum reflective layer.

[0057] S1. Prepare the silicone resin bonding system for impregnation. When preparing the ceramic barrier slurry, only silica sol and zirconium oxide sol are used to form the slurry system, without adding titanium dioxide; the SiO2 solid content of the silica sol is 30wt%, and the ZrO2 solid content of the zirconium oxide sol is 20wt%. The slurry is subjected to shear dispersion, filtration, and vacuum degassing treatment. The shear dispersion speed is 5000rpm for 15min, the filtration pore size is 100μm, and the vacuum degassing degree is -0.09MPa for 10min; if necessary, the amount of solvent or deionized water is finely adjusted so that the apparent viscosity of the resulting coating slurry at 25℃ is 0.60Pa·s.

[0058] S2. Perform vacuum-pressure alternating impregnation, with a fixed number of cycles of 2, followed by segmented drying and pre-curing to obtain resin-impregnated mica preforms.

[0059] S3. A slit coating is used to form a layer on one side of the resin-impregnated mica preform. The slit coating has a coating gap of 0.25 mm, a wet film thickness of 100 μm, and a coating line speed of 10 m / min. Cross-directional recoating and overlapping coating are performed with an overlap width of 5 mm. A leveling period of 1.5 min is allowed between adjacent coatings. Then, segmented gelation and segmented drying are performed sequentially. The segmented gelation is performed at 30°C for 5 min for the first segment and at 48°C for 6 min for the second segment. The segmented drying is performed at 80°C for 20 min for the first segment and at 105°C for 25 min for the second segment, to obtain the film preform.

[0060] S4. The preform of the film layer is placed into a hot press mold with an annular limiting pressing step for vacuum hot pressing co-curing. The vacuum degree is -0.09MPa, the hot pressing temperature is 195℃, the hot pressing pressure is 6MPa, the holding time is 35min, and the step width is 8mm. The compression ratio of the pressing area to the main body area is 15%, forming an integrated sealing area, and a comparison sample of mica insulating sheet without aluminum metal layer is obtained for use between battery cells or between battery cells and the shell.

[0061] Performance tests were conducted on the mica insulating sheet without an aluminum metal layer obtained in Example 4. The sample size was 100mm × 100mm, the finished product thickness was 0.45mm, and the width of the sealing area was 8mm. Five samples were taken for each test, and the average value was given. The electrical strength test was performed according to GB / T1408.1, using a flat electrode (electrode diameter 25mm), AC power frequency of 50Hz, and a voltage rise rate of 0.5kV / s. The breakdown voltage was measured to be 7.6kV, and the equivalent breakdown strength was 16.9kV / mm. Tests were conducted at points in the main body area and the sealing area. The breakdown strength in the sealing area was 17.6kV / mm, indicating that the sealing area was the first to break down. The thermal performance test was performed according to GB / T10294. The thermal conductivity was measured to be 0.25W / (m·K) at 25℃. Regarding interface reliability, a 180° peel test was performed on the ceramic layer / mica substrate, with a peel strength of 15 N / 25 mm. A retest was conducted after thermal cycling, and the peel strength retention rate was 80%. No obvious peeling was observed on the sample appearance, but slight interlayer whitening was observed at the edges. These results indicate that under the same process conditions, removing titanium dioxide decreased the breakdown strength, interface peel strength, and thermal cycling retention rate of the samples, while increasing the thermal conductivity. This suggests that the ceramic precursor network formed by titanium dioxide, silica sol, and zirconium oxide sol has a synergistic effect, helping to improve the continuous coverage stability and interfacial bonding strength of the ceramic layer, and further enhancing insulation and thermal barrier properties. Therefore, compared to the system using only silica sol and zirconium oxide sol, the introduction of titanium dioxide can achieve better interface consistency and performance retention under long-term battery service conditions.

[0062] Example 5:

[0063] This embodiment is a comparative embodiment. To compare the interface reliability and electrical insulation risk of the aluminum reflective layer structure in battery insulation protection applications, samples were prepared under the same process conditions as in Embodiment 1. The only difference is that after obtaining the film preform in S3 of Embodiment 1, an aluminum reflective layer was laminated on the outer surface of the ceramic precursor layer. The aluminum reflective layer is an aluminum foil with a thickness of 10 μm. The aluminum reflective layer covers to 1 mm from the circumferential edge of the film preform and is bonded to the film preform before entering S4 for vacuum hot pressing co-curing. Except for the above differences, the other raw materials, steps and process parameters are the same as in Embodiment 1.

[0064] Performance tests were conducted on the aluminum-reflective composite insulating sheet obtained in Example 5. The sample size was 100mm × 100mm, the finished product thickness was 0.47mm, and the width of the sealing area was 8mm. Five samples were taken for each test, and the average value was given. The electrical strength test was performed according to GB / T1408.1, using a flat electrode (electrode diameter 25mm), AC power frequency of 50Hz, and a voltage rise rate of 0.5kV / s. The breakdown voltage was measured to be 7.2kV, and the equivalent breakdown strength was 15.3kV / mm. Tests were conducted at points in the main body area and the sealing area. The breakdown strength in the sealing area was 13.5kV / mm, and some samples showed preferential breakdown near the edge of the aluminum reflective layer. The thermal performance test was performed according to GB / T10294, and the thermal conductivity was measured to be 0.28W / (m·K) at 25℃. Regarding interface reliability, a 180° peel test was conducted on the composite layers, with a peel strength of 12 N / 25 mm. A retest was performed after thermal cycling, showing a peel strength retention rate of 58%. Localized warping and interlayer whitening were observed in the peripheral area of ​​the sample, and slight cracks appeared in the sealing area. These results indicate that, under the same main process conditions, the introduction of an aluminum reflective layer makes the sealing area and the area near the metal layer edge more prone to electric field concentration or interface defect sensitivity, thus increasing the risk of edge breakdown. Furthermore, the peel strength retention rate after thermal cycling is significantly reduced, and failure characteristics such as edge warping or cracking appear. In addition, the increased thermal conductivity is detrimental to thermal barrier requirements. Therefore, compared to structures containing aluminum reflective layers, this invention uses a continuous ceramic layering and differential pressure sealing co-curing to form an integrated sealing structure, which is more conducive to improving interface consistency and long-term service reliability without introducing an aluminum reflective layer.

[0065] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a mica insulating sheet for lithium-ion batteries without an aluminum metal layer, characterized in that, include: S1. Provide a sheet-like mica substrate, and formulate an organosilicon resin bonding system for impregnation; simultaneously formulate a ceramic barrier slurry for surface layering, the ceramic barrier slurry comprising silica sol, zirconium oxide sol and titanium dioxide, perform shear dispersion on the ceramic barrier slurry, and sequentially perform filtration and vacuum degassing treatment to obtain a coating slurry suitable for coating layering, the preparation method does not include the step of forming an aluminum metal layer, aluminum foil layer, aluminum plating layer or aluminum reflective layer; S2. The sheet-like mica substrate is placed in the impregnation station, and the organosilicon resin bonding system is made to enter the mica pore structure under vacuum-pressure alternating impregnation conditions to obtain an impregnated preform. The impregnated preform is then dried in sections and pre-cured to obtain a resin-impregnated mica preform. S3. The coating slurry is applied to at least one side surface of the resin-impregnated mica preform using a slot coating method, and cross-directional recoating is performed. The cross-directional recoating includes coating in two mutually perpendicular directions and overlapping coating at the coating boundary. Combined with leveling and sequential segmented gelation and segmented drying processes, the coating slurry forms a continuously covering ceramic precursor layer on the surface of the resin-impregnated mica preform, resulting in a film preform. S4. The preform of the film layer is placed into a hot press mold for vacuum hot pressing co-curing. The hot press mold is provided with an annular limiting pressing step on the circumferential edge to form a sealing edge area. The circumferential edge area of ​​the preform of the film layer forms a pressing edge area under the limiting pressing action of the annular limiting pressing step, and co-curing is performed under the vacuum hot pressing co-curing conditions. The compression ratio of the pressing edge area relative to the main body area is 12%-20%, forming an integrated sealing edge area, and obtaining a mica insulating sheet without aluminum metal layer for use between battery cells or between battery cells and the shell.

2. The method for preparing a mica insulating sheet for lithium-ion batteries without an aluminum metal layer according to claim 1, characterized in that: The organosilicon resin bonding system includes methylphenyl silicone resin, crosslinking agent, catalyst and organic solvent. By mass, the methylphenyl silicone resin is 40-70 parts, the crosslinking agent is 1-10 parts, the catalyst is 0.01-0.20 parts, and the organic solvent is 20-50 parts.

3. The method for preparing a mica insulating sheet for lithium-ion batteries without an aluminum metal layer according to claim 1, characterized in that: In the ceramic barrier slurry: the SiO2 solid content of the silica sol is 20wt%-40wt%; the ZrO2 solid content of the zirconia sol is 10wt%-30wt%; the titanium dioxide is rutile type with a median particle size of 200nm-350nm; the ceramic barrier slurry does not contain nano-aerogels or silane coupling agents.

4. The method for preparing a mica insulating sheet for lithium-ion batteries without an aluminum metal layer according to claim 1, characterized in that: The shear dispersion is performed at a speed of 2000 rpm to 8000 rpm for 5 min to 30 min. The filtration uses a filter medium with a pore size of 50 μm to 150 μm. The vacuum degassing is performed at a vacuum degree of -0.08 MPa to 0.095 MPa for 5 min to 20 min.

5. The method for preparing a mica insulating sheet for lithium-ion batteries without an aluminum metal layer according to claim 1, characterized in that: The vacuum-pressure alternating impregnation includes a cycle consisting of a vacuum impregnation step and a pressure impregnation step. The cycle includes: first, evacuating the vacuum at a vacuum degree of -0.08MPa to -0.095MPa for 5min to 30min, and then impregnating the vacuum at a pressure of 0.2MPa to 0.8MPa for 5min to 30min; the cycle is repeated 1 to 3 times.

6. The method for preparing a mica insulating sheet for lithium-ion batteries without an aluminum metal layer according to claim 1, characterized in that: The segmented drying includes two temperature stages: the first stage is drying at 80℃-100℃ for 10min-25min, and the second stage is drying at 100℃-120℃ for 10min-35min; the pre-curing is carried out at 120℃-160℃ for 10min-30min, so that the organosilicon resin bonding system reaches a semi-cured state that can be further cross-linked and cured in subsequent vacuum hot pressing co-curing, thus obtaining a resin-impregnated mica preform.

7. The method for preparing a mica insulating sheet for lithium-ion batteries without an aluminum metal layer according to claim 1, characterized in that: The slit coating has a coating gap of 0.15mm-0.35mm, a wet film thickness of 50μm-150μm, a coating line speed of 2m / min-20m / min, and an apparent viscosity of 0.20Pa·s-1.20Pa·s at 25℃.

8. The method for preparing a mica insulating sheet for lithium-ion batteries without an aluminum metal layer according to claim 1, characterized in that: The overlap width of the overlapping coating is 2mm-8mm, and leveling is maintained for 1min-2min between adjacent coatings.

9. A method for preparing a mica insulating sheet for lithium-ion batteries without an aluminum metal layer according to claim 1, characterized in that: The segmented gelation includes: performing the first stage of gelation at 25℃-35℃ for 2min-8min, followed by performing the second stage of gelation at 40℃-55℃ for 3min-10min, with a total holding time of 5min-15min; the segmented drying includes drying at 70℃-85℃ for 10min-30min and drying at 95℃-110℃ for 15min-40min, to complete the stepwise curing and shaping of the ceramic precursor layer.

10. A method for preparing a mica insulating sheet for lithium-ion batteries without an aluminum metal layer according to claim 1, characterized in that: The vacuum degree of the vacuum hot-press co-curing is not lower than -0.085MPa, the hot-pressing temperature is 180℃-210℃, the hot-pressing pressure is 4MPa-8MPa, and the holding time is 20min-60min; the step width of the annular limiting pressing step is 5mm-12mm, and the compression ratio of the pressing area relative to the main body area is 12%-20% by setting the step limiting gap.

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