Glued diaphragm as well as preparation method and application thereof

Abstract

The invention discloses a glued diaphragm as well as a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. The preparation method of the glued diaphragm comprises the following steps: S1, heating a dispersing agent to be completely molten, mixing the molten dispersing agent with polymethyl methacrylate powder, and carrying out blending grinding to form a uniform blending system; s2, cooling and curing the blended and ground material, and crushing and screening the material to obtain a coating material; s3, uniformly mixing the coating material, a binder and water, adding a wetting agent, and uniformly dispersing to obtain slurry; and S4, coating the double surfaces of a base membrane with the slurry, and drying to obtain the glued diaphragm. After cold pressing of the lithium ion battery prepared from the glued diaphragm, the binding power and hardness of a roll core are enhanced, the cracking rate and the short-circuit rate of the first-layer diaphragm are both reduced, the appearance of the battery core is smooth, the assembly quality of the battery core is improved, the thickness meets the design standard, the pole piece interface is good, and the electrochemical performance of the battery core is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly relates to a coated separator and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have been widely used in electric vehicles, mobile communication devices, and renewable energy fields due to their advantages such as high energy density, long cycle life, and environmental friendliness. During the production process of lithium-ion batteries, the separator forms an ionic conductive channel between the positive and negative electrodes of the battery while blocking the charge transfer between the two electrodes, and is an indispensable part to ensure the normal operation of the battery. The performance of the separator directly affects the capacity, cycle performance, and safety of the battery.

[0003] The traditional polypropylene (PP) separator made by the dry method has the advantages of low cost and simple preparation, and is suitable for large-scale production, but it also has obvious deficiencies. The transverse tensile strength of the PP separator is relatively low, and it is easy to be damaged during the encapsulation process, thus causing a short circuit; when used in large-size soft-pack lithium-ion battery cells, the hardness of the battery cells is insufficient, and it is easy to be deformed by external forces, which will affect the assembly quality of the battery cells in the module; the easy wrinkling of the PP separator may lead to lithium deposition and black spots on the electrode sheet; in addition, the poor polarity of the PP separator may affect the infiltration of the electrolyte, thereby affecting the electrochemical performance of the battery. To solve these problems, many researchers are carrying out surface functional modification through coating technology to improve the performance of the PP separator.

[0004] Commonly used inorganic compounds for coating mainly include Al2O3, MoS2, SiO2, MXene, MnO2, etc., but the interlayer force between the inorganic compound and the separator is relatively weak, and the coating layer is easy to be unevenly distributed and fall off. Commonly used organic compounds for coating mainly include PVDF, aramid, etc. However, PVDF materials usually need to be processed by hot pressing and dissolved in organic solvents, which will have an adverse impact on production efficiency and environmental protection. In addition, the price of aramid is relatively high, which is also not conducive to reducing the cost of enterprises. Summary of the Invention

[0005] The purpose of the present invention is to provide a coated separator that can improve the assembly quality of battery cells; another purpose of the present invention is to provide a preparation method of a coated separator that can improve the assembly quality of battery cells.

[0006] The present invention discloses a preparation method of a coated separator, which includes the following steps:

[0007] S1: Heat the dispersant until it is completely melted, mix the melted dispersant with polymethyl methacrylate powder, and perform co-blending and grinding to form a uniform co-blending system;

[0008] S2: Cool and solidify the blended and ground material, and crush and screen it to obtain the coating material;

[0009] S3: Mix the coating material, binder, and water evenly, add a wetting agent, and disperse them evenly into a slurry;

[0010] S4: Coat the slurry on both sides of the base film and dry it to obtain the coated separator.

[0011] The function of the dispersant is to ensure good dispersibility of the polymethyl methacrylate powder and maintain the stability of the prepared slurry. As the dispersant, polymer dispersants such as polyvinylpyrrolidone, polyethylene glycol, and polycarboxylate dispersants can be used.

[0012] The binder is an aqueous binder, and polyvinyl alcohol, sodium carboxymethyl cellulose, polyacrylic acid and its salts, polyacrylamide, etc. can be used.

[0013] As the material of the base film, conventional PP or PE materials can be used.

[0014] The use of the wetting agent is mainly to improve the wettability of the slurry to the separator substrate, ensure a uniform and dense coating, and improve production efficiency and coating quality. As the wetting agent, non-ionic surfactants, anionic surfactants, and silicone-based wetting agents can be used.

[0015] As the non-ionic surfactant, polyoxyethylene alkyl ether such as C12-C14 fatty alcohol polyoxyethylene ether can be selected; polyoxyethylene alkylphenol ether such as nonylphenol polyoxyethylene ether can be selected. As the anionic surfactant, sulfonates such as sodium dodecylbenzenesulfonate can be selected; sulfate esters such as sodium lauryl sulfate can be selected. As the silicone-based wetting agent, polyether-modified silicone oil, polyether-modified polysiloxane, etc.

[0016] Further, in the step S1, the dispersant includes polyethylene glycol; the molecular weight of the polyethylene glycol is 4000-6000.

[0017] When polyethylene glycol with this molecular weight is used for blending and grinding, the temperature is 60-80 °C, and the grinding time is 5-10 min.

[0018] Further, in the step S1, the mass ratio of the polyethylene glycol to the polymethyl methacrylate powder is 9:1-7:3 for blending and grinding.

[0019] Further, in the step S1, the Tg of the polymethyl methacrylate powder ≤ 25 °C; the particle size D50 of the polymethyl methacrylate powder particles is 895-905 μm.

[0020] Further, in the step S3, the binder includes polyacrylic acid; the mass ratio of the coating material to the polyacrylic acid is 4-9:1.

[0021] Further, in the step S3, the wetting agent includes polyether-modified polysiloxane; the addition amount of the polyether-modified polysiloxane in the slurry is 0.2-1.5 wt%.

[0022] Further, in the step S4, the coating surface density of the coated separator is 0.5-1.0 g / m²; after drying, the average thickness of the coating layer is 0.8-1.2 μm.

[0023] The present invention also discloses a coated separator obtained by the preparation method described above.

[0024] The present invention also discloses a preparation method of a lithium-ion battery. The positive electrode sheet, the separator and the negative electrode sheet are stacked, cold-pressed, the electrode tabs are welded, then they are put into a packaging material, electrolyte is injected, and after formation and grading, the lithium-ion battery is manufactured.

[0025] Further, the cold-pressing and encapsulating operation is to keep the pressure at 4 T for 4 s at normal temperature.

[0026] In the coated separator provided by the present invention, the molecular structure of polymethyl methacrylate is rich in high-polarity functional groups such as ester groups, endowing the surface of the separator with significant polarity and high surface energy characteristics. It improves the wetting rate of the coated separator to the electrolyte and the liquid retention capacity, and this improvement promotes the formation of a SEI film with a three-dimensional stable structure at the electrode / electrolyte interface. It effectively improves the utilization rate of active lithium ions, enabling more carriers to participate in the electrode reaction process.

[0027] After the lithium-ion battery prepared with the coated separator is cold-pressed, the bonding force and hardness of the wound core are strengthened, the cracking rate and short-circuit rate of the first-layer separator are both reduced, the appearance of the battery core is flat, the thickness meets the design standard, the interface of the electrode sheet is good, and the assembly quality of the battery core is improved.

[0028] The soft-pack battery core prepared with the coated separator is superior to the battery core assembled with the PP separator in terms of reference capacity, high-rate performance, high-temperature discharge capacity and cycle life. Description of the Drawings

[0029] Figure 1 It is the SEM image of the coated separator obtained in Example 1 of the present invention;

[0030] Figure 2 It is the SEM image of the separator in Comparative Example 1 of the present invention;

[0031] Figure 3 It is the cell state diagram of the lithium-ion battery assembled in Example 2 of the present invention;

[0032] Figure 4 It is the cell state diagram of the lithium-ion battery assembled in Example 3 of the present invention;

[0033] Figure 5 It is the cell state diagram of the lithium-ion battery assembled in Example 4 of the present invention;

[0034] Figure 6 It is the cell state diagram of the lithium-ion battery assembled in Comparative Example 2 of the present invention;

[0035] Figure 7 It is the front and back appearance diagrams of the lithium-ion battery assembled in Example 2 of the present invention;

[0036] Figure 8 It is the front and back appearance diagrams of the lithium-ion battery assembled in Comparative Example 3 of the present invention;

[0037] Figure 9 It is the disassembled electrode sheet interface diagram of the fully charged cell of the lithium-ion battery assembled in Example 2 of the present invention;

[0038] Figure 10 It is the disassembled electrode sheet interface diagram of the fully charged cell of the lithium-ion battery assembled in Comparative Example 3 of the present invention;

[0039] Figure 11 It is the comparison diagram of the cycle performance at 25 °C of the lithium-ion batteries assembled in Example 2 and Comparative Example 3 of the present invention;

[0040] Figure 12 It is the comparison diagram of the cycle performance at 55 °C of the lithium-ion batteries assembled in Example 2 and Comparative Example 3 of the present invention. Detailed Embodiments

[0041] To make the technical solutions of the present invention clearer, the following further describes the present invention in detail with reference to the accompanying drawings and specific embodiments.

[0042] Example 1

[0043] Prepare the coated separator:

[0044] Place polyethylene glycol with a molecular weight of 5000 in a melting device, heat it to 60 °C and keep it at a constant temperature until the polyethylene glycol is completely melted. Subsequently, add polymethyl methacrylate (PMMA) powder with a glass transition temperature (Tg) of less than 25 °C to the melted polyethylene glycol step by step according to a mass ratio of 85:10, and carry out co-blending and grinding through a grinding device to ensure the formation of a uniform co-blending system. After the co-blended material is cooled and solidified, further crush the solidified material with a crushing device, and control the particle size range to be 895 - 905 μm through a screening device to obtain the coating material.

[0045] The prepared coating material and polyacrylic acid were added to deionized water in a mass ratio of 1:9 in sequence. A mechanical stirring device was used to stir for 30 minutes under the condition of 1500 r / min to ensure that the system was completely dissolved to form a uniform dispersion system. Subsequently, polyether-modified polysiloxane with a mass fraction of 1 wt% was added, and a high-speed dispersion device was used to continue dispersing for 3 hours under the condition of 3000 - 5000 r / min to prepare an aqueous PMMA dispersion system with a solid content of 10 wt%.

[0046] The above-prepared aqueous PMMA dispersion system was uniformly coated on both sides of a 14-μm-thick dry PP base film through a precision coating device at a linear speed of 80 m / min. During the coating process, a constant pressure and constant speed control technology was adopted to ensure the uniformity of the coating. After the coating was completed, the base film was placed in a hot air drying device and dried at 100 °C to remove the solvent, forming a PMMA adhesive layer with a double-sided symmetric structure. In the finally prepared coated separator, the average thickness of each adhesive layer was 1 μm, and the corresponding areal density was 0.7 g / m². The morphology of the coated separator was observed by scanning electron microscopy, and the results were as Figure 1 shown. On the surface of the separator treated with the PMMA aqueous polymer slurry coating, a uniform particle layer was locally covered, and the D50 particle size of PMMA was about 900 nm. Although the PMMA coating filled some of the original pores, the surface of the modified separator still maintained a certain porous structure, which helped to reduce the risk of cell pore blockage, thus ensuring the safe operation of the battery and extending its life. Overall, the presence of the coating changed the surface characteristics of the separator, but still retained enough pore structure to ensure the transport of lithium ions.

[0047] Comparative Example 1

[0048] For the PP separator, the morphology of the coated separator was observed by scanning electron microscopy, and the results were as Figure 2 shown. The surface of the uncoated PP separator was relatively smooth, with an obvious pore structure, and a porous network structure was distributed on the surface, which was caused by the characteristics of its dry processing technology.

[0049] Separator performance test:

[0050] Refer to GB / T 36363—2018 "Polyolefin Separators for Lithium-Ion Batteries" to test items such as thickness, air permeability, tensile strength, puncture strength, and thermal shrinkage rate. The test results are shown in Table 1.

[0051] Table 1 Separator test results of Comparative Example 1 and Example 1

[0052]

[0053] As shown in Table 1, although the coating process increased the air permeability index, the increase was still controlled within a reasonable range, indicating that the microporous structure of the base film was not completely blocked by PMMA particles, and the partial coverage characteristics of the coating had little effect on the gas permeability of the system. Analyzing from the characteristics of the porous structure, the porosity of the modified separator reached 50.8%, showing a significant increase compared with the PP separator. This structural optimization can not only enhance the infiltration and adsorption ability of the electrolyte, but also provide a better channel network for ion transport. In the mechanical property evaluation, the composite separator showed unique mechanical response characteristics: the transverse tensile strength remained stable, while the longitudinal tensile strength and puncture strength were effectively improved. This phenomenon confirmed that a composite interface with a synergistic effect was formed between the PMMA coating layer and the matrix material, and this structural strengthening mechanism significantly improved the ability of the separator to resist complex loads such as lamination stress and mechanical extrusion during battery assembly, thereby reducing the risk of battery failure caused by mechanical damage. The thermal stability test revealed that after heat treatment at 130 °C / 30 min, the longitudinal thermal shrinkage rate of the coated separator decreased significantly from 3.5% of the base material to 1%, and the thermal decomposition temperature range of the PMMA material itself at 200 - 250 °C played a key role in maintaining the high-temperature structural stability. By constructing this thermally stable composite structure, the risk of short circuit caused by separator shrinkage between electrodes can be effectively prevented, thereby significantly improving the thermal safety performance of the battery system.

[0054] Assembled into a lithium-ion battery:

[0055] The positive electrode system uses lithium iron phosphate as the active material, supplemented with conductive graphite and polyvinylidene fluoride binder, and is composed according to the mass ratio of 96:1.5:2.5. The slurry system selects N-methylpyrrolidone as the solvent. The negative electrode system consists of graphite as the main active material, combined with a conductive agent, polyacrylic acid binder and sodium carboxymethyl cellulose dispersant, and its mass ratio is 96.5:0.5:2.5:0.5. The solvent system uses deionized water. The electrode slurries prepared by mechanical stirring are respectively coated on 12 μm aluminum foil and 4.5 μm as the positive and negative current collectors. Commercial dry-process PP separators and 1 mol / L LiPF6 electrolyte are commercially available products.

[0056] Table 2 Design parameters of the assembled lithium-ion battery

[0057]

[0058] Example 2

[0059] Assembled into a lithium-ion battery. The positive electrode sheet, the coated separator prepared in Example 1 and the negative electrode sheet were laminated, cold-pressed, the electrode tabs were welded, then put into the encapsulation material, the electrolyte was injected, and after formation and grading, the lithium-ion battery was obtained. The operating conditions for cold pressing were: under a pressure of 4T, the pressure was maintained for 4s.

[0060] Test the air permeability and porosity of the coated separator before and after cold pressing. The results are shown in Table 3. After cold pressing, the air permeability of the coated separator increased by 17 s, while its porosity remained basically unchanged. This indicates that the coating layer has little effect on the ion transport performance.

[0061] Table 3 Comparison of Physical Properties of Coated Separators before and after Cold Pressing

[0062]

[0063] Example 3

[0064] The difference from Example 2 is that the operating conditions for cold pressing are: under a pressure of 2 T, hold the pressure for 4 s.

[0065] Example 4

[0066] The difference from Example 2 is that the operating conditions for cold pressing are: under a pressure of 6 T, hold the pressure for 4 s.

[0067] Comparative Example 2

[0068] The difference from Example 2 is that there is no cold pressing operation.

[0069] Comparative Example 3

[0070] The difference from Example 2 is that the separator of Comparative Example 1 is used for assembly.

[0071] The relatively low glass transition temperature of PMMA in the glue layer of the coated separator in this patent endows it with unique thermodynamic properties, enabling the coated separator to achieve core winding forming through the cold pressing process at room temperature. Compared with the traditional high-temperature hot pressing process, this property can reduce the manufacturing cost and improve the process efficiency. In addition, the cold pressing of the coated separator strengthens the bonding force and hardness of the core winding. The improvement of the bonding force ensures the firm combination of the electrode sheet and the separator, reduces the risk of re-introduction of foreign matters during the manufacturing process, and thus effectively reduces the incidence of short circuits and the appearance defects of the battery cells.

[0072] During the assembly process of lithium-ion batteries, the lamination technology is involved, and the control of pressure is particularly important. If the encapsulation pressure is too small, the adhesion force will be too small, and there will be gaps between the separator and the electrode sheet. Such macroscopic defects will lead to uneven distribution of internal resistance, resulting in local overcharging or over-discharging, affecting the consistency and cycle stability of the battery; overpressure blocking pores will increase the air permeability, affect the ion transport efficiency of the separator, and may also cause separation between the foil and the coating, resulting in the problem of coating adhesion on the separator. Therefore, it is necessary to optimize the cold pressing process window for pressure.

[0073] Such as Figures 3 - 6As shown, under different core pressures (increasing from 0 T to 6 T) and the same pressure-holding time (4 s), cold pressing and subsequent baking were carried out, and the hardness performance of the battery cells varied. The battery cells baked directly without cold pressing showed softening; when baked under the condition of 2 T / 4 s, the top of the battery cell maintained good hardness, while the bottom was softer; while when baked under the conditions of 4 T / 4 s and 6 T / 4 s, the battery cells maintained hardness. Therefore, after comprehensive consideration, 4 T / 4 s was selected as the optimal condition for cold pressing the battery cells.

[0074] Performance test of lithium-ion batteries:

[0075] 10,000 lithium-ion batteries were produced respectively using the methods of Example 2 and Comparative Example 3 for assembly, and tested, and the defective assembly situations were counted. The results are shown in Table 4.

[0076] Table 4 Defective assembly results of lithium-ion batteries assembled in Example 2 and Comparative Example 3

[0077]

[0078] As shown in Table 4, after assembling into lithium-ion batteries using Example 2, the cracking rate of the first-layer separator, the short-circuit rate before welding, and the encapsulation short-circuit rate were all greatly reduced compared with Comparative Example 3. The use of the coated separator strengthened the bonding force and hardness of the battery cell. The improvement of the bonding force ensured a firm combination between the electrode sheet and the separator during cold pressing, reduced the looseness phenomenon, and lowered the risk of re-introducing foreign matters during the manufacturing process, thus effectively reducing the incidence of short circuits. The short-circuit rate before welding decreased from 5.37% of the PP separator to 0.02%; the looseness state was likely to cause the separator to be damaged and lead to encapsulation short circuits, and the encapsulation short-circuit rate also decreased from 0.49% to 0%. The increase in hardness also facilitated the operation of the manipulator.

[0079] As Figures 7 - 8 shown, compared with Comparative Example 3, the application of the coated separator in Example 2 improved the appearance quality of the battery cell. Large-size soft-pack battery cells were prone to local bulging and deformation, especially after multiple charge and discharge cycles, and the repeated expansion of the negative electrode sheet made the appearance even worse. This kind of phenomenon not only deteriorated the appearance of the battery cell, but also might have an adverse impact on subsequent assembly and market sales. In the technical solution using the coated separator, after cold pressing treatment, the glue dots still maintained a certain height, which provided the necessary space for the rebound of the electrode sheet. At the same time, due to the higher hardness of the battery cell, its surface remained flatter. Such characteristics made the battery cell show better applicability and convenience during subsequent module packaging and transportation.

[0080] 30 fully charged battery cells assembled in Example 2 and Comparative Example 3 were taken for disassembly and analysis, and the results are as Figures 9 - 10As shown in the figure. There are still striped wrinkles in the separator in Comparative Example 3, and there are small black spots in the wrinkled area of the separator of some electrode sheets. After full charge, the interface of the electrode sheet in Example 2 is good, there is no purple spot and no lithium deposition, and no separator wrinkling phenomenon occurs.

[0081] Two cells of the lithium-ion batteries assembled with Example 2 and Comparative Example 3 were taken to test their electrical properties.

[0082] The specific operations are as follows:

[0083] The reference capacity test was carried out under the conditions of 0.33C charge and 1C discharge. The average value of the reference capacity of Comparative Example 3 was 51.8Ah, and the average value of the reference capacity of Example 2 was 52.5Ah. The reference capacity of the cell using the coated separator could be increased by 1.4%. The cells were charged at a constant current density of nC (multiple charge n = 0.33, 0.5, 1; multiple discharge n = 0.5) to 3.65V, then charged at a constant voltage of 3.65V until cutoff at 0.02C, and then discharged at a constant current density of nC (multiple charge n = 0.5; multiple discharge n = 0.5, 1, 1.5) to 2.5V. The results are shown in Table 5.

[0084] Table 5 Electrical performance test data of lithium-ion batteries

[0085]

[0086] As can be seen from Table 5, with the increase of the charge-discharge rate, the constant-current charge ratio and discharge capacity ratio of the lithium-ion batteries assembled with the two separators both show a decreasing trend. Because the increase of the current density will increase the concentration polarization and ohmic polarization in the battery, reduce the transmission speed of sodium ions, and the charge-discharge process of the battery cannot be fully carried out, resulting in the loss of battery capacity. In addition, during multiple charging, there is no obvious difference in the low-rate charging performance of Example 2 and Comparative Example 3 at 0.5C and below. The 1C multiple charging performance of Example 2 is better than that of Comparative Example 3, and the constant-current ratio increases by about 0.7%. During multiple discharging, there is no obvious difference in the 0.5 multiple discharging performance of Example 2 and Comparative Example 3. The 1C and 1.5C multiple discharging performances of Example 2 are better than those of Comparative Example 3, and the discharge capacity ratio increases by about 1%. The small difference in temperature rise at the same charge-discharge rate indicates that at high-rate charge-discharge, the PMMA-coated separator can reduce the polarization phenomenon of the battery and show a good performance improvement effect. The 1C discharge test was carried out at 55 °C, and the capacitance at 25 °C was used as the standard capacitance of the battery. The discharge capacitance of the cell in Example 2 increased slightly by about 1% - 2% compared with that in Comparative Example 3; there was no obvious difference in the results of other low-temperature performance and storage test data short-term performance test items.

[0087] As Figures 11 - 12As shown, when the battery is cycled at room temperature of 25°C to 500 cycles, the capacity retention rate of the battery cell of Example 2 is approximately 5% higher than that of Comparative Example 3. When the battery is cycled at a high temperature of 55°C, the difference in the initial capacity retention rate is small. After that, the capacity retention rates of the two types of batteries gradually show a difference. After 500 cycles, the cyclic capacity retention rate of Example 2 is 3.2% higher than that of Comparative Example 3. The long-term cyclic charge and discharge experiment shows that the PMMA-coated separator can effectively extend the cycle life of the battery.

[0088] The above-described embodiments only represent several implementation manners of the present invention, and the description thereof is relatively specific and detailed. However, it should not be construed as a limitation to the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the appended claims.

Claims

1. A method for preparing a coated separator, characterized in that, It includes the following steps: S1: Heat the dispersant until it is completely melted, mix the melted dispersant with polymethyl methacrylate powder, and conduct co-blending and grinding to form a uniform co-blending system; S2: Cool and solidify the material after co-blending and grinding, and crush and screen it to obtain the coating material; S3: Mix the coating material, binder and water evenly, add a wetting agent, and disperse evenly into a slurry; S4: Coat the slurry on both sides of the base film and dry it to obtain a coated separator.

2. The preparation method of a glue-coated diaphragm according to claim 1, wherein, In the step S1, the dispersant includes polyethylene glycol; the molecular weight of the polyethylene glycol is 4000-6000.

3. The preparation method of a glue-coated diaphragm according to claim 2, characterized in that, In the step S1, the mass ratio of the polyethylene glycol to the polymethyl methacrylate powder is 9:1-7:3 for co-blending and grinding.

4. The preparation method of a coated separator according to claim 1, characterized in that, In the step S1, the Tg of the polymethyl methacrylate powder ≤ 25 °C; the particle size D50 of the polymethyl methacrylate powder particles is 895-905 μm.

5. The preparation method of a coated separator according to claim 1, characterized in that, In the step S3, the binder includes polyacrylic acid; the mass ratio of the coating material to the polyacrylic acid is 4-9:

1.

6. The preparation method of a coated diaphragm according to claim 1, characterized in that, In the step S3, the wetting agent includes polyether-modified polysiloxane; the addition amount of the polyether-modified polysiloxane in the slurry is 0.2-1.5 wt%.

7. The preparation method of a coated separator according to claim 1, characterized in that, In the step S4, the coating surface density of the coated separator is 0.5-1.0 g / m²; after drying, the average thickness of the coating layer is 0.8-1.2 μm.

8. A glue-coated separator, characterized in that, It is obtained by the preparation method described in any one of claims 1-7.

9. A method for preparing a lithium-ion battery, characterized in that, Stack the positive electrode sheet, separator and negative electrode sheet, cold press, weld the electrode tabs, then put them into the encapsulation material, inject the electrolyte, and after formation and grading, a lithium-ion battery is obtained.

10. A method for preparing a lithium-ion battery according to claim 9, wherein, The operation of the cold pressing is to hold the pressure at 4 T for 4 s at room temperature.

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