A coated separator, its preparation method and use

Abstract

The application provides a coated diaphragm and a preparation method and application thereof. The coated diaphragm comprises a base film and a concave-convex coating layer coated on at least one side of the base film. The concave-convex coating layer comprises alternating convex coating layers and concave coating layers. The convex coating layer comprises a plurality of parallel convex structure units, and the concave coating layer comprises a plurality of parallel concave structure units. The elastic modulus of the concave coating layer is higher than that of the convex coating layer. The convex coating layer can be compressed and elastically restored after absorbing electrolyte. The coated diaphragm can effectively exert the liquid storage advantage of the concave-convex structure of the coating layer. The convex coating layer has a certain elastic recovery rate. The compressed convex coating layer can restore the initial state after electrolyte injection, thereby avoiding the aggravation of C-corner stress, preventing lithium precipitation at the C-corner, improving the current stability at the C-corner position, and finally improving the overall cycle performance of the battery cell.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy batteries, in particular to a coated diaphragm and a preparation method and application thereof. BACKGROUND

[0002] As one of the four components of a battery, a diaphragm can prevent direct contact between the positive and negative electrodes, and allow the passage of ions, thereby playing an important role in the performance of the battery. It is well known that the capacity and cycle performance of a battery are closely related to the amount of electrolyte in the battery cell. After the diaphragm and the electrode sheet are hot-pressed, the larger the effective storage space between them, the more conducive to the cycle performance of the battery cell.

[0003] With the pursuit of the charge and discharge rate of the battery, under high-rate charge and discharge, the rapid consumption of electrolyte in the battery with increasing cycle number, the battery cell cannot quickly replenish the electrolyte, resulting in serious lithium precipitation, especially in the center of the battery cell, the purple stain phenomenon of lithium precipitation is more serious than that in the surrounding area, thus the cycle performance of the battery cell is significantly reduced. To solve this problem of the battery cell, patent number CN117438743A discloses a porous aramid coating layer including a high-density region and a low-density region that are intermingled and connected, which ensures the film breaking temperature and thermal shrinkage performance of the diaphragm, and the pits formed by the high-density region provide better flow and liquid storage channels for the electrolyte, improve the electrolyte absorption rate of the battery cell, and reduce the difficulty of liquid injection during the production of the battery cell. Patent number CN119812674A discloses a composite diaphragm including a plurality of parallel and alternating convex structures and concave structures, which improves the heat resistance and electrolyte storage capacity of the composite diaphragm, and is beneficial to the liquid injection efficiency of the battery cell, and can improve the cycle performance of the battery.

[0004] The coated diaphragm of patent number CN117438743A has poor supportability due to the low-density layer, and after the diaphragm and the electrode sheet are hot-pressed, the high-density and low-density regions are in contact with the electrode sheet, which greatly reduces the liquid storage performance in practical applications. When the height difference between the concave structure and the convex structure is small or the width of the concave structure is too small, the gap between the coated diaphragm and the electrode sheet is reduced, and the liquid storage performance is reduced. When the width of the concave structure is too large, the supportability of the convex structure is reduced, which also reduces the liquid storage space. At the same time, the concave-convex structure of the coated diaphragm is coated by a conventional micro-concave plate, and after the coated diaphragm and the electrode sheet are hot-pressed, the convex structure is severely compressed. In practical applications, the effective liquid storage space provided by the concave-convex structure design is reduced, and the high-rate cycle performance of the battery cell is poor.

[0005] Therefore, the present application is proposed. SUMMARY

[0006] The inventor has found, through research and analysis, that the prior art needs to be improved in the following aspects: when designing high and low density areas or concave-convex structures, the rigidity of the low density area or the convex structure is weak, and after the coated separator and the electrode sheet are hot-pressed, the low density area or the convex structure is prone to collapse, which seriously reduces the effective liquid storage space or even causes no effective storage space, the battery cannot be quickly replenished due to the consumption of electrolyte after high-rate charge-discharge cycling, the battery is prone to lithium precipitation, especially the central part of the battery, which seriously reduces the cycle performance of the battery.

[0007] In addition, after the coated separator and the electrode sheet are wound and hot-pressed, the flat bare battery is obtained, which includes two parts, one part is in contact with the hot press, referred to as the hot-pressed part, and the other part is not in contact with the hot press, i.e. the corner part of the battery, referred to as C corner in the following. The thickness of the hot-pressed part is reduced due to pressure, and the thickness of the hot-pressed part is thinner than that of the C corner part, and the thickness of the hot-pressed part is much thinner than that of the C corner of the battery, thereby deteriorating the stress of the C corner, intensifying the stress of the C corner, and even causing the C corner to wrinkle or break, which seriously reduces the cycle performance of the battery.

[0008] In order to achieve the above-mentioned purpose of the present application, the following technical solutions are adopted:

[0009] A coated separator includes a base film and a concave-convex coating layer coated on at least one side of the base film, the concave-convex coating layer includes alternating convex coating layers and concave coating layers, the convex coating layer includes a plurality of parallel convex structure units, and the concave coating layer includes a plurality of parallel concave structure units; the elastic modulus of the concave coating layer is higher than that of the convex coating layer; the convex coating layer can be compressed and elastically recovered after absorbing electrolyte after compression.

[0010] Further, the hot-pressing compression ratio of the convex coating layer is η1, and η1≤30%.

[0011] Further, the elastic recovery rate of the convex coating layer after absorbing electrolyte after compression is η2, and 95%≤η2≤105%.

[0012] Further, the elastic modulus of the concave coating layer is E1, the elastic modulus of the convex coating layer is E2, 10 GPa≤E1≤20 GPa, 5 GPa≤E2≤15 GPa, and E1-E2>4 Gpa.

[0013] Further, the thickness of the base film is 4-16 μm.

[0014] Further, the base film is one of a single-layer PP film, a single-layer PE film, a double-layer PE / PP composite film, and a double-layer PP / PP composite film.

[0015] Further, the height of a single concave structure unit is H1, and the height of a single convex structure unit is H2, satisfying 0.5 μm≤H1≤7.0 μm and 1.5 μm≤H2≤10 μm.

[0016] Further, the height difference between the height H2 of a single convex structure unit and the height H1 of a single concave structure unit is ΔH, satisfying ΔH-η1*H2≥1 μm.

[0017] Further, the width of a single concave structure unit is W1, and the width of a single convex structure unit is W2, satisfying 0.2 mm≤W1≤4.0 mm and 0.2 mm≤W2≤4.0 mm.

[0018] Further, the ratio W2 / W1 of the width W2 of a single convex structure unit to the width W1 of a single concave structure unit is N, and N≥0.5.

[0019] Further, the angle between the extension direction of a single concave structure unit, the extension direction of a single convex structure unit, and the MD direction of the separator is θ, and 25°≤θ≤90°; preferably 50°≤θ≤90°.

[0020] Further, the adhesion between the coated separator and the electrode sheet is F, F=0, or 2 N / m≤F≤8 N / m.

[0021] Further, the raw material of the convex coating layer comprises a first component, a second polymer, and a silane coupling agent, and the raw material of the concave coating layer comprises a first component, a second polymer, and a silane coupling agent.

[0022] The first component comprises first filler particles or / and first polymer particles.

[0023] Further, the first component comprises first filler particles, and the proportion of the first filler particles in the coating layer is 65wt%-95wt%.

[0024] Further, the first component comprises first filler particles and first polymer particles, the first filler particles account for 65wt% to 95wt% of the coating, and the first polymer particles account for 0wt% to 30wt% of the coating, and the first polymer particles are not 0wt%.

[0025] Further, the first component comprises first polymer particles, and the first polymer particles account for 90wt% to 95wt% of the coating.

[0026] Further, the first component comprises first filler particles, or the first component comprises first filler particles and first polymer particles.

[0027] Further, the second polymer accounts for 2wt% to 8wt% of the coating.

[0028] Further, the silane coupling agent accounts for 1wt% to 3wt% of the coating.

[0029] Further, the silane coupling agent is at least one of γ-aminopropyl triethoxysilane, γ-glycidoxypropyl trimethoxysilane, γ-methacryloxypropyl trimethoxysilane, vinyl trimethoxysilane, and vinyl triethoxysilane.

[0030] Further, the first filler particles are at least one of alumina, boehmite, silica, titanium dioxide, magnesium oxide, zirconium oxide, LATP, LLZO, and melamine cyanurate.

[0031] Further, the first filler particles have a particle size of 0.3μm to 0.8μm.

[0032] Further, the first polymer particles are at least one of polyvinylidene fluoride polymer, polymethyl methacrylate, polystyrene-acrylate copolymer, and polyacrylonitrile-acrylate copolymer.

[0033] Further, the first polymer particles are secondary agglomerate particles or / and primary particles, and preferably the first polymer particles are secondary agglomerate particles.

[0034] Further, the first polymer particles have a particle size of 3μm to 8μm.

[0035] Further, the second polymer comprises at least one of styrene-butadiene rubber, polyacrylate, polyacrylamide, polyacrylonitrile, and epoxy resin.

[0036] A preparation method of a coated separator, comprising the following steps:

[0037] Step S1, mixing the first component, the second polymer, the silane coupling agent, and water in a proportion to obtain a mixed slurry;

[0038] Step S2, first coating, the mixed slurry is coated on the base film, a strip-shaped mask plate with parallel and alternating exposure area width and non-exposure area is placed above the coated separator, ultraviolet light is transmitted through the exposure area of the mask plate to perform first exposure treatment on the coated separator, the mixed glue in the non-exposure area is washed away after exposure, and drying is performed to obtain a semi-finished coated separator with a convex structure.

[0039] Step S3, second coating, the mixed slurry is coated on the semi-finished coated separator, a strip-shaped mask plate with parallel and alternating exposure area width and non-exposure area is placed above the coated separator, the exposure area is adjusted to be aligned with the non-exposure area of the first exposure, ultraviolet light is transmitted through the exposure area of the mask plate to perform second exposure treatment on the coated separator, the mixed glue in the non-exposure area is washed away after exposure, and drying is performed to obtain a finished coated separator with a concave-convex structure.

[0040] Further, the height of the concave-convex structure in steps S2 and S3 is obtained by adjusting the coating speed ratio.

[0041] Further, the light intensity of the first exposure in step S2 is 8.0-12.0 mW / cm 2 , the light intensity of the second exposure in step S3 is 9.5-13.5 mW / cm 2 , and the light intensity of the second exposure is at least 1.5 mW / cm 2 higher than that of the first exposure.

[0042] The coated separator and the preparation method of the coated separator have applications in the preparation of secondary batteries and electric appliances.

[0043] Compared with the prior art, the present application has the following advantages:

[0044] 1. The surface of the coated separator is coated with a plurality of concave-convex structures arranged in parallel and alternately on at least one side, and the convex coating layer has a certain compression ratio. After the coated separator is hot-pressed with the electrode sheet, the convex coating layer will not be completely compressed, solving the problem of easy collapse of the convex structure in the prior art, preventing the collapse of the convex structure from causing a significant reduction in the effective liquid storage space or even no effective storage space, effectively utilizing the liquid storage advantage of the concave-convex structure of the coating layer, and the convex coating layer has a certain elastic recovery rate. The compressed convex coating layer can recover to the initial state after electrolyte injection, thereby avoiding the aggravation of C-angle stress, preventing lithium precipitation at the C-angle, improving the current stability at the C-angle position, and ultimately improving the overall cycle performance of the battery cell.

[0045] 2. The preparation method of the coated separator adopts a post-coating exposure manufacturing process, so that the concave-convex coating has strong rigidity, the convex coating has a certain compression ratio, after the coated separator is hot-pressed with the electrode sheet, the convex coating will not be completely compressed, effectively playing the liquid storage advantage of the concave-convex structure of the coating, at the same time, the convex coating has a certain elastic recovery rate, the compressed convex coating can recover to the initial state after electrolyte injection, solving the problem of C corner stress aggravation, thereby avoiding the problems of lithium precipitation and current instability at the C corner; in addition, the rigidity strength of the concave coating is higher than that of the convex coating when the concave-convex coating is designed, so that the convex coating is compressed during hot-pressing of the coated separator and the electrode sheet, which can avoid extrusion of the concave coating, deterioration of the compactness of the concave coating, and ion shuttling, thereby deteriorating the overall cycle performance of the battery.

[0046] 3. The preparation method of the coated separator adopts an ultraviolet exposure method when coating the concave-convex coating, and a silane coupling agent is added to the mixed solution used in the coating, the silane coupling agent is crosslinked under ultraviolet exposure, the crosslinking includes not only the crosslinking of the silane coupling agent, but also the crosslinking of the second polymer, i.e. the binder, the crosslinking of the second polymer is crosslinked by free radical polymerization under ultraviolet exposure, thereby improving the overall crosslinking degree of the coating, thereby improving the overall rigidity of the concave-convex coating structure, after the coated separator is hot-pressed with the electrode sheet, the concave-convex coating can still maintain a high concave-convex morphology, at the same time, the concave-convex coating has a high elastic recovery rate, the convex coating after hot-pressing can recover to the initial morphology after absorbing electrolyte, thereby improving the liquid storage performance of the battery, solving the problem of C corner stress aggravation, and thereby improving the overall performance of the battery.

[0047] 4. After the coated separator is prepared into a battery, the problem of lithium precipitation of the battery during high-rate charge and discharge cycles can be solved, especially the problem of lithium precipitation at the central part of the battery and the C corner part of the battery, thereby improving the overall cycle performance of the battery, and the beneficial effects are as follows: (1) the overall air permeability of the coated separator is low; (2) the overall heat resistance of the coated separator is high; (3) the electrolyte wettability of the coated separator is high; (4) the ion conductivity of the coated separator is high; (5) the cycle performance of the battery prepared from the coated separator is good under high-rate charge and discharge; (6) the battery prepared from the coated separator is not prone to lithium precipitation under high-rate charge and discharge; (7) the battery prepared from the coated separator is not prone to bulging. BRIEF DESCRIPTION OF DRAWINGS

[0048] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the description of the specific embodiments or the prior art. Obviously, the drawings described below are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0049] Figure 1A schematic diagram of a cross section of the coated separator along the MD direction of the present application;

[0050] Figure 2 A schematic diagram of a cross section of the bare cell.

[0051] Legend: 1 - concave coating layer, 2 - convex coating layer, 3 - base film, 4 - coated separator, 5 - negative electrode sheet, 6 - positive electrode sheet, 7 - cell hot-pressing part, 8 - C corner part of the cell. DETAILED DESCRIPTION

[0052] The technical solutions of the present application will be described clearly and completely in combination with the specific embodiments below, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, not all the embodiments, and are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0053] A coated separator, as shown in Figure 1 includes a base film and a concave-convex coating layer coated on at least one side of the base film, the concave-convex coating layer includes alternating convex coating layers and concave coating layers, the convex coating layer includes a plurality of parallel convex structure units, and the concave coating layer includes a plurality of parallel concave structure units; the elastic modulus of the concave coating layer is higher than that of the convex coating layer, or the crosslinking degree of the concave coating layer is higher than that of the convex coating layer; the convex coating layer can be compressed, and after compression, it can absorb electrolyte and elastically recover.

[0054] When the slurry coated on the concave structure unit and the convex structure unit is the same, the density difference between the concave structure unit and the convex structure unit is less than 0.1 g / cm 3 . Under the same coating slurry, the difference in crosslinking degree is only the difference brought by the crosslinking degree of the second polymer and the silane coupling agent, and does not affect the density of the whole coating layer. When the slurry coated on the concave structure unit and the convex structure unit is different, the density difference between the concave structure unit and the convex structure unit is determined according to the material of the slurry used.

[0055] The surface of the coated separator of the present application is coated with a plurality of concave-convex structures of concave-convex coating layer arranged alternately and parallel to each other, the convex coating layer has a certain compression ratio, and after the coated separator is hot-pressed with the electrode sheet, the convex coating layer will not be completely compressed, effectively exerting the liquid storage advantage of the concave-convex structure of the coating layer, the convex coating layer has a certain elastic recovery rate, and the compressed convex coating layer can recover to the original initial state after electrolyte injection, thereby avoiding the aggravation of the C corner stress, preventing lithium precipitation at the C corner, improving the current stability at the C corner position, and ultimately improving the overall cycle performance of the cell.

[0056] Preferably, the thermal compression ratio of the convex coating is η1, and η1≤30%, and η1 includes but is not limited to 30%, 25%, 20%, 15%, 10%, 5%, or η1 is less than or equal to one of the values 30%, 25%, 20%, 15%, 10%, 5%.

[0057] Preferably, the elastic recovery rate of the convex coating after absorbing the electrolyte after compression is η2, and 95%≤η2≤105%, and η2 includes but is not limited to 95%, 96%, 97%, 98%, 99%, 100%, 101%, 102%, 103%, 104%, 105%.

[0058] The convex coating of the present application has a certain elastic recovery rate. The compressed convex coating can recover to the original state after injecting electrolyte, thereby avoiding the aggravation of C corner stress, preventing lithium precipitation at the C corner, improving the current stability at the C corner position, and ultimately improving the overall cycle performance of the battery cell.

[0059] Preferably, the elastic modulus of the concave coating is E1, and the elastic modulus of the convex coating is E2, 10GPa≤E1≤20GPa, E1 includes but is not limited to 10GPa, 11GPa, 12GPa, 13GPa, 14GPa, 15GPa, 16GPa, 17GPa, 18GPa, 19GPa, 20GPa, 5GPa≤E2≤15GPa, E2 includes but is not limited to 5GPa, 6GPa, 7GPa, 8GPa, 9GPa, 10GPa, 11GPa, 12GPa, 13GPa, 14GPa, 15GPa, and E1-E2>4Gpa, (E1-E2) includes but is not limited to 4.1Gpa, 5Gpa, 6GPa, 7GPa, 8GPa, 9GPa, 10GPa, 11GPa, 12GPa, 13GPa, 14GPa, 15GPa.

[0060] Preferably, the crosslinking degree X1 of the concave coating is greater than the crosslinking degree X2 of the convex coating, and X1-X2>5%, preferably X1-X2>10%.

[0061] Preferably, the height of a single concave structure unit is H1, and the height of a single convex structure unit is H2, satisfying: 0.5μm≤H1≤7.0μm, 1.5μm≤H2≤10μm, H1 includes but is not limited to 0.5μm, 1.0μm, 2.0μm, 3.0μm, 4.0μm, 5.0μm, 6.0μm, 7.0μm, and H2 includes but is not limited to 1.5μm, 2.0μm, 3.0μm, 4.0μm, 5.0μm, 6.0μm, 7.0μm, 8.0μm, 9.0μm, 10.0μm.

[0062] Preferably, the height difference between the height H2 of the single convex structure unit and the height H1 of the single concave structure unit is ΔH, satisfying: ΔH-η1*H2≥1μm. The present application sets ΔH-η1*H2≥1μm, mainly considering that there is still a large height difference between the convex structure and the concave structure after being compressed, so as to ensure that there is still a large liquid storage space after the coated separator and the electrode sheet are hot-pressed, and to improve the poor cycle performance and lithium precipitation problem of the battery during high-rate cycling.

[0063] Preferably, the width of the single concave structure unit is W1, and the width of the single convex structure unit is W2, satisfying: 0.2mm≤W1≤4.0mm, 0.2mm≤W2≤4.0mm, W1 includes but is not limited to 0.2mm, 0.4mm, 0.5mm, 1.0mm, 1.2mm, 2.0mm, 3.0mm, 4.0mm, and W2 includes but is not limited to 0.2mm, 0.4mm, 0.5mm, 1.0mm, 1.2mm, 2.0mm, 3.0mm, 4.0mm.

[0064] Preferably, the ratio W2 / W1 of the width W2 of the single convex structure unit to the width W1 of the single concave structure unit is N, N≥0.5, N includes but is not limited to 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, or N is greater than or equal to one of the values 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5. The present application sets the width ratio W2 / W1 of the convex structure and the concave structure to be ≥0.5, mainly considering that if the ratio of the convex structure and the concave structure is too small, the supporting property of the convex structure becomes smaller at this time, the corresponding compression ratio increases, and finally leads to the reduction of the effective space after the coated separator and the electrode sheet are hot-pressed, and the cycle performance of the hard battery.

[0065] Preferably, the angle between the extension direction of the single concave structure unit and the extension direction of the single convex structure unit of the concave-convex coating and the MD direction (coating separator winding direction) of the separator is θ, 25°≤θ≤90°, θ includes but is not limited to 25°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85°, 90°; preferably 50°≤θ≤90°. As the angle between the concave-convex structure of the coated separator and the MD direction of the separator becomes larger and larger, the larger the angle is after the coated separator and the electrode sheet are hot-pressed, the shorter the distance of the peripheral electrolyte entering the central position of the battery through the concave structure channel is, so the climbing height of the electrolyte shows an upward trend, and the cycle performance of the battery is also improved accordingly, but the difference is not large; when the angle between the concave-convex structure and the MD direction of the separator is 0°, the electrolyte cannot enter the central position of the battery through the concave structure channel after the separator and the battery are wound, and the cycle performance of the battery is poor.

[0066] Preferably, the adhesion between the coated separator and the electrode sheet is F, F = 0, or 2 N / m ≤ F ≤ 8 N / m, F includes but is not limited to 0, 2 N / m, 3 N / m, 4 N / m, 5 N / m, 6 N / m, 7 N / m, 8 N / m. When the first component is the filler particles, there is no adhesion between the coated separator and the electrode sheet during hot pressing, because the filler particles do not function as an adhesive; when the first component is the first polymer particles or the first polymer particles and the filler particles, there is adhesion between the coated separator and the electrode sheet during hot pressing.

[0067] Preferably, the raw material of the convex coating layer comprises the first component, the second polymer and the silane coupling agent, and the raw material of the concave coating layer comprises the first component, the second polymer and the silane coupling agent; the first component comprises the first filler particles or / and the first polymer particles; the raw material of the convex coating layer and the raw material of the concave coating layer can be the same or different.

[0068] Preferably, the first component comprises the first filler particles, and the first filler particles account for 65wt%~95wt% of the coating layer.

[0069] Preferably, the first component comprises the first filler particles and the first polymer particles, the first filler particles account for 65wt%~95wt% of the coating layer, and the first polymer particles account for 0wt%~30wt% of the coating layer, excluding 0wt%.

[0070] Preferably, the first component comprises the first polymer particles, and the first polymer particles account for 90wt%~95wt% of the coating layer.

[0071] Preferably, the first component comprises the first filler particles, or the first component comprises the first filler particles and the first polymer particles.

[0072] Preferably, the first filler particles are at least one of alumina, boehmite, silica, titania, magnesia, zirconia, LATP (lithium aluminum titanium phosphate, chemical formula Li 1+x Al x Ti 2-x (PO4)3, 0≤x≤0.5), LLZO (lithium lanthanum zirconium oxide), melamine cyanurate.

[0073] Preferably, the particle size of the first filler particles is 0.3μm~0.8μm, including but not limited to 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm or a range between the values.

[0074] Preferably, the first polymer particles are at least one of polyvinylidene fluoride polymer, polymethyl methacrylate, polystyrene-acrylate copolymer, polyacrylonitrile-acrylate copolymer.

[0075] Preferably, the first polymer particles are secondary agglomerate particles or / and primary particles, preferably secondary agglomerate particles. At the same particle size, the ion channels provided by primary particles are less than those provided by secondary particles, so the primary particles have a greater impact on ion shuttling than the secondary particles, and the corresponding cycle performance is poorer than that of the secondary particles, so the secondary agglomerate particles are further preferred.

[0076] Preferably, the particle size of the first polymer particles is 3-8 μm, including but not limited to 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, or a range between the values.

[0077] Preferably, the second polymer includes at least one of styrene butadiene rubber, polyacrylate, polyacrylamide, polyacrylonitrile, and epoxy resin; and the second polymer accounts for 2-8 wt% of the coating.

[0078] Preferably, the amount of the silane coupling agent added accounts for 1-3% of the coating.

[0079] Preferably, the silane coupling agent is at least one of γ-aminopropyl triethoxysilane, γ-glycidoxypropyl trimethoxysilane, γ-methacryloyloxypropyl trimethoxysilane, vinyl trimethoxysilane, and vinyl triethoxysilane.

[0080] Preferably, the thickness of the base film is 4-16 μm, including but not limited to 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, and 16 μm.

[0081] Preferably, the base film is one of a single-layer PP film, a single-layer PE film, a double-layer PE / PP composite film, and a double-layer PP / PP composite film.

[0082] A preparation method of a coated separator, including the following steps:

[0083] Step S1, mixing the first component, the second polymer, the silane coupling agent, and water in proportion to obtain a mixed slurry;

[0084] Step S2, first coating, coating the mixed slurry on the base film, selecting a strip-shaped mask plate with mutually parallel and alternating exposed area widths (corresponding to convex structures) and non-exposed areas, placing the mask plate above the coated separator, and performing first exposure treatment on the coated separator by allowing ultraviolet light to pass through the exposed area of the mask plate, washing away the mixed glue solution in the non-exposed area after exposure, and drying to obtain a semi-finished coated separator with convex structures;

[0085] Step S3, second coating, the mixed slurry is coated on the semi-finished product coating separator, the strip-shaped exposure area (corresponding to the concave structure) width and the non-exposure area mask plate are selected to be parallel to each other and are placed above the coating separator, the exposure area is aligned with the non-exposure area of the first exposure, the coating separator is subjected to the second exposure treatment by the ultraviolet light passing through the exposure area of the mask plate, the non-exposure area mixed glue is washed away after exposure, and drying is performed, so that the finished product coating separator with the concave-convex structure is obtained.

[0086] In step S2, the convex structure is not washed away by water washing due to cross-linking and water evaporation curing, and the pre-coated non-exposure area is still slurry, so it can be washed away by water.

[0087] In step S3, the mixed slurry is coated on the convex structure area and the blank area (corresponding to the concave structure) exposed by water washing in step S2, the concave structure is not washed away by water washing due to cross-linking and water evaporation curing, and the surface of the convex structure is still uncross-linked slurry which can be washed away by water.

[0088] The application adopts the post-coating exposure mode, so that the concave-convex coating has a certain cross-linking degree, the cross-linking includes not only the cross-linking of the silane coupling agent but also the cross-linking of the second polymer, i.e., the binder, the cross-linking of the second polymer is cross-linked by free radical polymerization under ultraviolet exposure, thereby enhancing the overall rigidity of the concave-convex coating, the convex coating has a certain compression ratio, and after the coating separator is hot-pressed, the convex coating or the convex coating and the concave coating basically maintain the original morphology structure and can store electrolyte. In addition, the application sets a certain elastic recovery rate for the convex coating, after the coating separator is hot-pressed with the electrode sheet and then injected, the thickness of the convex coating can recover to 95% to 105% of the original thickness, so that the thickness of the hot-pressed part is basically consistent with the thickness of the C corner after injection, thereby solving the problem of stress aggravation of the C corner, improving the stress unevenness of the C corner, and finally avoiding the problems of lithium precipitation or unstable current of the C corner after the battery cycle.

[0089] The ultraviolet exposure has two effects, one is to generate free radicals for ammonium persulfate, and the other is to evaporate local moisture to form a coating that is not washed away.

[0090] Preferably, a wetting agent is also added in step S1, and the proportion of the wetting agent in the coating is 0.1wt% to 1wt%.

[0091] Preferably, the wetting agent includes at least one of alkyl sulfate, sulfonate, polyoxyethylene alkyl phenol ether, polyoxyethylene fatty alcohol ether, alkyl phenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and fatty acid polyoxyethylene ether.

[0092] Preferably, the height of the concave-convex structure in steps S2 and S3 is obtained by adjusting the coating speed ratio.

[0093] Preferably, the height of the concave-convex structure in steps S2 and S3 is obtained by adjusting the coating speed ratio.Preferably, the light intensity of the second exposure is higher than the light intensity of the first exposure, and the light intensity of the second exposure is at least 1.5 mW / cm higher than the light intensity of the first exposure 2 , so that the cross-linking degree of the concave coating is greater than the cross-linking degree of the convex coating, and the elastic modulus of the concave coating is greater than the elastic modulus of the convex coating, the light intensity affects the elastic modulus of the concave-convex layer, the stronger the light, the higher the elastic modulus; the cross-linking degree of the concave coating is greater than the cross-linking degree of the convex coating, and the elastic modulus of the concave coating is greater than the elastic modulus of the convex coating, which can avoid the bottom of the convex coating extruding the concave coating after the convex coating is hot-pressed, so that the density of the concave coating increases, the internal resistance of the battery cell is deteriorated, and the cycle performance is deteriorated.

[0094] Preferably, the light intensity of the first exposure in step S2 is 8.0-12.0 mW / cm 2 , including but not limited to 8.0 mW / cm 2 , 9.0 mW / cm 2 , 10.0 mW / cm 2 , 11.0 mW / cm 2 , and 12.0 mW / cm 2 .

[0095] Preferably, the light intensity of the second exposure in step S3 is 9.5-13.5 mW / cm 2 , including but not limited to 9.5 mW / cm 2 , 10.0 mW / cm 2 , 10.5 mW / cm 2 , 11.0 mW / cm 2 , 11.5 mW / cm 2 , 12.0 mW / cm 2 , 12.5 mW / cm 2 , 13.0 mW / cm 2 , and 13.5 mW / cm 2 .

[0096] The coated diaphragm, the preparation method of the coated diaphragm has the application in the preparation of secondary batteries and electric appliances.

[0097] Embodiment 1

[0098] A preparation method of a coated diaphragm, comprising the following steps:

[0099] a. Take 92 parts of alumina with a particle size of 0.4 μm (first filler particles), 5 parts of polyacrylamide (second polymer), 2.5 parts of vinyl triethoxysilane (silane coupling agent), and 0.5 parts of alkylphenol polyoxyethylene ether (wetting agent) and 100 parts of deionized water, mix uniformly, add 0.2 parts of ammonium persulfate (initiator) and stir uniformly to obtain a mixed slurry;

[0100] b. The first coating is performed using micro-gravure technology, the coating speed ratio is controlled, and the mixed slurry is coated on the PE-7 μm base film. The coated separator is placed on the carrier table of the exposure machine for the first exposure. A mask with a strip-shaped exposure area (corresponding to a convex structure) with a width of 0.2 mm and a non-exposure area with a width of 0.4 mm is placed above the coated separator. The mask is adjusted to have an angle of 60° with the MD direction of the separator. The power of the exposure machine is turned on. A light source with a wavelength of 360 nm is used. The light intensity is adjusted to 8.0 mW / cm 2 The coated separator is subjected to the first exposure treatment by allowing the ultraviolet light to pass through the exposure area of the mask. After exposure for 10 s, the non-exposure area of the mixed glue is washed away with deionized water, and the coated separator is dried to obtain a semi-finished product with a convex structure.

[0101] c. The second coating is performed on the semi-finished product using micro-gravure technology. The coating speed ratio is controlled, and the mixed slurry is coated on the semi-finished product. The coated separator is placed on the carrier table of the exposure machine for the second exposure. A mask with a strip-shaped exposure area (corresponding to a concave structure) with a width of 0.4 mm and a non-exposure area with a width of 0.2 mm is placed above the coated separator. The mask is adjusted to have an angle of 60° with the MD direction of the separator. At the same time, the exposure area is adjusted to be aligned with the non-exposure area of the first exposure. The power of the exposure machine is turned on. A light source with a wavelength of 360 nm is used. The light intensity is adjusted to 9.8 mW / cm 2 The coated separator is subjected to the second exposure treatment by allowing the ultraviolet light to pass through the exposure area of the mask. After exposure for 10 s, the non-exposure area of the mixed glue is washed away with deionized water, and the coated separator is dried to obtain a finished product with a convex-concave structure.

[0102] The height, width, compression ratio, elastic recovery rate, crosslinking degree, air permeability growth rate, thermal shrinkage, electrolyte immersion speed, ion conductivity of the finished product with a convex-concave structure, and the performance of the battery after the coated separator is prepared into a battery are tested. The test results are shown in Tables 1, 2 and 3.

[0103] Example 2

[0104] The difference between this example and Example 1 is that in step b, the light intensity is adjusted to 8.2 mW / cm 2 during the first exposure. The mask is replaced with a mask with an exposure area width of 1.2 mm and a non-exposure area width of 1.0 mm.

[0105] In step c, the light intensity is adjusted to 10.0 mW / cm 2 during the second exposure. The mask is replaced with a mask with an exposure area width of 1.0 mm and a non-exposure area width of 1.2 mm. The height of the convex-concave structure can be obtained by adjusting the speed ratio.

[0106] Other than Example 1.

[0107] Example 3

[0108] The difference between this example and Example 1 is that in the first exposure in step b, the light intensity is adjusted to 8.6 mW / cm 2 , and the mask is changed to one with an exposed area width of 3.0 mm and a non-exposed area width of 3.0 mm;

[0109] In the second exposure in step c, the light intensity is adjusted to 10.6 mW / cm 2 , and the mask is changed to one with an exposed area width of 3.0 mm and a non-exposed area width of 3.0 mm, and the height of the concave-convex structure can be obtained by adjusting the speed ratio;

[0110] Other than Example 1.

[0111] Example 4

[0112] The difference between this example and Example 1 is that in the first exposure in step b, the light intensity is adjusted to 8.4 mW / cm 2 , and the mask is changed to one with an exposed area width of 4.0 mm and a non-exposed area width of 4.0 mm;

[0113] In the second exposure in step c, the light intensity is adjusted to 10.4 mW / cm 2 , and the mask is changed to one with an exposed area width of 4.0 mm and a non-exposed area width of 4.0 mm, and the height of the concave-convex structure can be obtained by adjusting the speed ratio;

[0114] Other than Example 1.

[0115] Example 5

[0116] The difference between this example and Example 1 is that in the first exposure in step b, the light intensity is adjusted to 8.4 mW / cm 2 , and the mask is changed to one with an exposed area width of 3.0 mm and a non-exposed area width of 4.0 mm;

[0117] In the second exposure in step c, the light intensity is adjusted to 10.2 mW / cm 2 , and the mask is changed to one with an exposed area width of 4.0 mm and a non-exposed area width of 3.0 mm, and the height of the concave-convex structure can be obtained by adjusting the speed ratio;

[0118] Other than Example 1.

[0119] Example 6

[0120] The difference between this embodiment and embodiment 1 is that the light intensity is adjusted to 8.6 mW / cm 2 in the first exposure in step b, and the mask is replaced by a mask with an exposure area width of 1.0 mm and a non-exposure area width of 2.0 mm;

[0121] The light intensity is adjusted to 10.8 mW / cm 2 in the second exposure in step c, the mask is replaced by a mask with an exposure area width of 2.0 mm and a non-exposure area width of 1.0 mm, and the height of the concave-convex structure can be obtained by adjusting the speed ratio;

[0122] The rest is the same as embodiment 1.

[0123] Embodiment 7

[0124] The difference between this embodiment and embodiment 1 is that the light intensity is adjusted to 8.8 mW / cm 2 in the first exposure in step b, and the mask is replaced by a mask with an exposure area width of 0.8 mm and a non-exposure area width of 1.0 mm;

[0125] The light intensity is adjusted to 10.4 mW / cm 2 in the second exposure in step c, the mask is replaced by a mask with an exposure area width of 1.0 mm and a non-exposure area width of 0.8 mm, and the height of the concave-convex structure can be obtained by adjusting the speed ratio;

[0126] The rest is the same as embodiment 1.

[0127] Embodiment 8

[0128] The difference between this embodiment and embodiment 2 is that, in addition to the mask being at an angle of 85° to the MD direction of the diaphragm in steps b and c, the rest is the same as embodiment 2.

[0129] Embodiment 9:

[0130] The difference between this embodiment and embodiment 2 is that, in addition to the mask being at an angle of 30° to the MD direction of the diaphragm in steps b and c, the rest is the same as embodiment 2.

[0131] Embodiment 10

[0132] The difference between this embodiment and embodiment 1 is that 92 parts of alumina with a particle size of 0.4 μm in the mixed slurry in step a are replaced by 70 parts of alumina with a particle size of 0.4 μm and 22 parts of polyvinylidene fluoride polymer with a secondary particle size of 4.0 μm (first polymer particles);

[0133] The light intensity is adjusted to 9.0 mW / cm 2, the mask is replaced by a mask with an exposed area width of 2.0 mm and a non-exposed area width of 4.0 mm;

[0134] In the second exposure in step c, the light intensity is adjusted to 11.4 mW / cm 2 , the mask is replaced by a mask with an exposed area width of 4.0 mm and a non-exposed area width of 2.0 mm, and the height of the concave-convex structure can be obtained by adjusting the speed ratio;

[0135] The rest is the same as in Example 1.

[0136] Example 11:

[0137] The difference between this example and Example 10 is that in the first exposure in step b, the light intensity is adjusted to 9.6 mW / cm 2 , the mask is replaced by a mask with an exposed area width of 1.2 mm and a non-exposed area width of 2.0 mm;

[0138] In the second exposure in step c, the light intensity is adjusted to 11.8 mW / cm 2 , the mask is replaced by a mask with an exposed area width of 2.0 mm and a non-exposed area width of 1.2 mm, and the height of the concave-convex structure can be obtained by adjusting the speed ratio;

[0139] The rest is the same as in Example 10.

[0140] Example 12:

[0141] The difference between this example and Example 10 is that in the first exposure in step b, the light intensity is adjusted to 9.2 mW / cm 2 , the mask is replaced by a mask with an exposed area width of 1.5 mm and a non-exposed area width of 3.0 mm;

[0142] In the second exposure in step c, the light intensity is adjusted to 11.0 mW / cm 2 , the mask is replaced by a mask with an exposed area width of 3.0 mm and a non-exposed area width of 1.5 mm, and the height of the concave-convex structure can be obtained by adjusting the speed ratio;

[0143] The rest is the same as in Example 10.

[0144] Example 13:

[0145] The difference between this example and Example 10 is that in step a, the polyvinylidene fluoride polymer with a secondary particle size of 4.0 μm is replaced by a polymethyl methacrylate with a secondary particle size of 4.0 μm;

[0146] The rest is the same as in Example 10.

[0147] Example 14:

[0148] The difference between this example and Example 11 is that the polyvinylidene fluoride polymer having a secondary particle size of 4.0 μm in step a is replaced with polymethyl methacrylate having a primary particle size of 4.0 μm;

[0149] The other is the same as Example 11.

[0150] Example 15:

[0151] The difference between this example and Example 12 is that the polyvinylidene fluoride polymer having a secondary particle size of 4.0 μm in step a is replaced with polymethyl methacrylate having a primary particle size of 4.0 μm;

[0152] The other is the same as Example 12.

[0153] Example 16

[0154] The difference between this example and Example 1 is that the 92 parts of alumina having a particle size of 0.4 μm in the mixed slurry in step a is replaced with polyvinylidene fluoride polymer having a secondary particle size of 5.0 μm;

[0155] In the first exposure in step b, the light intensity is adjusted to 10.2 mW / cm 2 , and the mask is replaced with a mask having an exposed area width of 2.0 mm and a non-exposed area width of 3.5 mm;

[0156] In the second exposure in step c, the light intensity is adjusted to 12.8 mW / cm 2 , and the mask is replaced with a mask having an exposed area width of 3.5 mm and a non-exposed area width of 2.0 mm, and the height of the concave-convex structure can be obtained by adjusting the speed ratio;

[0157] The other is the same as Example 1.

[0158] Example 17

[0159] The difference between this example and Example 16 is that in the first exposure in step b, the light intensity is adjusted to 11.2 mW / cm 2 , and the mask is replaced with a mask having an exposed area width of 1.2 mm and a non-exposed area width of 2.0 mm;

[0160] In the second exposure in step c, the light intensity is adjusted to 13.0 mW / cm 2 , and the mask is replaced with a mask having an exposed area width of 2.0 mm and a non-exposed area width of 1.2 mm, and the height of the concave-convex structure can be obtained by adjusting the speed ratio;

[0161] The other is the same as Example 16.

[0162] Example 18

[0163] The difference between this example and Example 16 is that the polyvinylidene fluoride polymer with a secondary particle size of 5.0 μm in step a is replaced by polyacrylamide with a secondary particle size of 5.0 μm;

[0164] The rest is the same as Example 16.

[0165] Example 19

[0166] The difference between this example and Example 17 is that the polyvinylidene fluoride polymer with a secondary particle size of 5.0 μm in step a is replaced by polyacrylamide with a secondary particle size of 5.0 μm;

[0167] The rest is the same as Example 17.

[0168] Comparative Example 1

[0169] Using conventional coating method, 94.5 parts of alumina with a particle size of 0.4 μm, 5 parts of polyacrylamide, 0.5 parts of alkylphenol polyoxyethylene ether and 100 parts of deionized water are uniformly mixed, coated with a concave-convex structure micro-gravure, dried to obtain a coated separator with H1 = 2.0 μm, W1 = 4.0 mm, H2 = 5.0 μm, W2 = 4.0 mm, the concave-convex structure being 60° to the MD direction of the separator, the performance of the coated separator and the performance of the battery prepared therefrom are tested, and the test results are shown in Tables 1, 2 and 3.

[0170] Comparative Example 2

[0171] Using conventional coating method, 72.5 parts of alumina with a particle size of 0.4 μm and 22 parts of polyacrylamide with a secondary particle size of 4.0 μm, 5 parts of polyacrylamide, 0.5 parts of alkylphenol polyoxyethylene ether and 100 parts of deionized water are uniformly mixed, coated with a concave-convex structure micro-gravure, dried to obtain a coated separator with H1 = 4.0 μm, W1 = 4.0 mm, H2 = 10.0 μm, W2 = 2.0 mm, the concave-convex structure being 60° to the MD direction of the separator, the performance of the coated separator and the performance of the battery prepared therefrom are tested, and the test results are shown in Tables 1, 2 and 3.

[0172] Comparative Example 3

[0173] Using conventional coating method, 94.5 parts of polyvinylidene fluoride polymer with a secondary particle size of 5.0 μm, 5 parts of polyacrylamide, 0.5 parts of alkylphenol polyoxyethylene ether and 100 parts of deionized water are uniformly mixed, coated with a concave-convex structure micro-gravure, dried to obtain a coated separator with H1 = 6.0 μm, W1 = 2.0 mm, H2 = 10.0 μm, W2 = 1.2 mm, the concave-convex structure being 60° to the MD direction of the separator, the performance of the coated separator and the performance of the battery prepared therefrom are tested, and the test results are shown in Tables 1, 2 and 3.

[0174] Comparative Example 4

[0175] Using the mixed slurry of Example 2, the mixed slurry was coated on PE-7 μm base film by micro gravure coating technology, adjusting the coating speed ratio, and a full-coated coated separator with a thickness of 3.0 μm was obtained by general UV exposure, and the performance of the coated separator and the performance of the battery prepared therefrom were tested. The test results are shown in Tables 1, 2 and 3.

[0176] Comparative Example 5

[0177] Using the mixed slurry of Example 11, the mixed slurry was coated on PE-7 μm base film by micro gravure coating technology, adjusting the coating speed ratio, and a full-coated coated separator with a thickness of 5.5 μm was obtained by general UV exposure, and the performance of the coated separator and the performance of the battery prepared therefrom were tested. The test results are shown in Tables 1, 2 and 3.

[0178] Comparative Example 6

[0179] Using the mixed slurry of Example 17, the mixed slurry was coated on PE-7 μm base film by micro gravure coating technology, adjusting the coating speed ratio, and a full-coated coated separator with a thickness of 6.0 μm was obtained by general UV exposure, and the performance of the coated separator and the performance of the battery prepared therefrom were tested. The test results are shown in Tables 1, 2 and 3.

[0180] Comparative Example 7

[0181] The difference between this example and Example 4 is that the angle between the concave-convex structure and the MD direction of the separator in steps b and c is 0°.

[0182] The rest is the same as Example 4.

[0183] Test method:

[0184] I. Determination of various parameters and performance of coated separators

[0185] 1. Measurement method of concave-convex structure height of coated separator: place the coated coated separator on a two-dimensional image tester (JTVMA-3020), turn on the transmitted light, control the light intensity at 350 microcandela, use the transmission of light, the image of the convex structure is dark black, and the image of the concave structure is relatively light white compared with the image of the convex structure, mark the middle position of the dark black and light white, use SEM-CP technology, test the distance from the dark black middle position and the light white middle position to the base film, which is H2 and H1 respectively, test 10 groups in parallel, take the final average value, which is the convex structure height H2 and the concave structure height H1.

[0186] 2. The method for measuring the width of the convex structure of the coated separator: Place the coated separator on the two-dimensional image tester (JTVMA-3020), turn on the transmitted light, control the light intensity at 350 microcandela, use the light transmission, the image of the convex structure is dark, and the image of the concave structure is relatively light, take the middle of the intersection of the dark and light as the boundary, measure the width of the dark and light along the direction perpendicular to the convex and concave structure, which is W2 and W1 respectively, test 10 groups in parallel, take the final average value, and the width of the convex structure W2 and the width of the concave structure W1 can be obtained.

[0187] 3. The method for measuring the angle between the convex and concave structure of the coated separator and the MD direction of the separator: Place the coated separator on the two-dimensional image tester (JTVMA-3020), turn on the transmitted light, control the light intensity at 350 microcandela, the convex and concave structure is respectively represented as light and dark, take the winding direction of the coated separator as the MD direction, align the MD direction of the separator with the X axis of the two-dimensional image, measure the angle between the dark and light strip structure and the X axis, which is the angle θ between the convex and concave structure of the coated separator and the MD direction of the separator, test 10 groups in parallel, take the final average value, which is the angle θ between the convex and concave structure of the coated separator and the MD direction of the separator.

[0188] 4. The compression ratio test of the convex coating of the coated separator: use Mahr Millimar C1216 (test pressure 0.25N, test head size 12mm) to test the thickness of the coated separator and the base film respectively, which is h1 and h0, take the coated separator, the base film and the PET film, cut them into the size of 2cm*10cm, respectively align and paste the coated separator and the base film with the PET film, adjust the parameters of the hot press (5MPa, 60s, 85℃), then hot press, take out the coated separator and the base film after hot pressing, test the thickness of the coated separator and the base film after hot pressing, which is h1' and h0', then the compression ratio η1 of the convex coating = (h1-h0-(h1'-h0')) / (h1-h0).

[0189] 5. The elastic recovery rate test of the convex coating of the coated separator: use Mahr Millimar C1216 (test pressure 0.25N, test head size 12mm) to test the thickness of the coated separator and the base film respectively, which is h1 and h0, take the coated separator, the base film and the PET film, cut them into the size of 2cm*10cm, respectively align and paste the coated separator and the base film with the PET film, adjust the parameters of the hot press (5MPa, 60s, 85℃), then hot press, take out the coated separator and the base film after hot pressing, test the thickness of the coated separator and the base film after hot pressing, which is h1" and h0", then the elastic recovery rate η2 of the convex coating after absorbing electrolyte = (h1"-h0") / (h1-h0).

[0190] 6. Elastic modulus test of the coated separator: The elastic modulus of the coated separator was tested by FT-NMT04 in-situ nanoindenter. The conical indenter was used. The loading and unloading time was set to 5 s. The relationship between load and displacement was established. The final elastic modulus was calculated by Oliver principle. Ten points were tested in parallel. The final average values E1 and E2 were taken.

[0191] 7. Air permeability growth rate test of the coated separator: The air permeability refers to the time required for 100 ml of gas to pass through a separator of fixed area. The air permeability growth rate = (air permeability of the coated separator - air permeability of the base film) / air permeability of the base film * 100%.

[0192] 8. Heat shrinkage test of the coated separator: The coated separator was taken. A 100 mm*50 mm rectangular piece of the coated separator was taken along the MD direction. The lengths M1 and T1 in the MD and TD directions were tested. The piece was clamped with two A4 papers and placed in a 130°C oven for 30 min. The lengths M2 and T2 in the MD and TD directions of the coated separator were tested again. The heat shrinkage values of the coated separator in the MD and TD directions were (M1-M2) / M1 and (T1-T2) / T1, respectively.

[0193] 9. Adhesion test of the coated separator and the electrode sheet: The coated separator and the electrode sheet (the electrode sheet was a cathode sheet composed of 93.5 parts of lithium iron phosphate + 2.5 parts of conductive carbon black + 4 parts of PVDF with a melting point of 150°C) were cut into a size of 2 cm*10 cm. The coated surface of the electrode sheet was opposite to and overlapped with the coated surface of the separator. The hot press parameters (2 MPa, 60 s, 85°C) were adjusted for hot pressing. After hot pressing, the adhesion of the separator and the electrode sheet was tested by 180° peeling, wherein the peeling speed was 50 mm / min. Finally, the adhesion of the coated separator and the electrode sheet was obtained.

[0194] 10. Electrolyte wettability test of the coated separator: The coated separator and the positive electrode sheet were cut into 20 m*2 cm and 20 cm*2 cm, respectively. The coated surface of the coated separator was aligned and attached to the long edges of the positive electrode sheet. The hot press was used. The pressure, time and temperature were adjusted to 2 MPa, 60 s and 85°C. One end of the pressed coated separator and electrode sheet was immersed in electrolyte (EC:PC:DEC=2:3:4, 1.2 Mol / L LiPF6) for 5 mm. The climbing height of the electrolyte was measured for 10 min. The higher the height, the better the wettability of the coated separator and the electrode sheet after compounding.

[0195] Table 1. Test results of various parameters and angles of the coated separator

[0196]

[0197] Note: The embossed structure coating obtained by conventional microgravure coating in Comparative Examples 1-3 has unclear boundaries of the embossed structure, and the convex structure is prone to collapse, so the convex coating / convex coating elastic modulus values are not shown; Comparative Examples 4-6 are full-coated coatings without embossed structures, so the convex coating compression ratio, convex coating elastic recovery rate, and convex coating / convex coating elastic modulus values are not shown.

[0198] Table 2 Test results of various properties of coated separators

[0199]

[0200] II. Test of electrical properties of coated separators

[0201] 1. Test of ion conductivity of coated separators: (In an argon glove box, the separator was made into a 2016 button cell, and an appropriate amount of electrolyte (EC:PC:DEC=2:3:4, 1.2 Mol / L LiPF6) was added. The AC impedance test in the electrochemical workstation can be used to obtain σ=L / (Rb*A), where σ is the ion conductivity (mS / cm); L is the thickness of the separator (cm); Rb is the intrinsic resistance of the separator (Ω); and A is the effective area (cm 2 ).

[0202] 2. Test of battery capacity retention rate: After the coated separator, positive and negative electrodes, and electrolyte were prepared into a battery, the battery was charged at 5C to 3.6V, then charged at 3.6V to a current of 0.02C, and the charging was terminated. After 20 min of standing, the battery was discharged at 5C to 2.0V, and the discharge was terminated. After 20 min of standing, the first discharge capacity was recorded. The cycle was repeated 200 times, and the discharge capacity of the 200th cycle was recorded. The ratio of the discharge capacity of the 200th cycle to the first cycle was the capacity retention rate of the battery after 200 cycles. The positive electrode was composed of 92 parts of lithium iron phosphate, 6 parts of polyvinylidene fluoride, and 2 parts of acetylene black. The negative electrode was composed of 91 parts of artificial graphite, 5.0 parts of butadiene rubber, 3.0 parts of acetylene black, and 1 part of carboxymethyl cellulose. The electrolyte was EC:PC:DEC=2:3:4, 1.2 Mol / L LiPF6.

[0203] 3. Test of battery swelling coefficient: In the above test of battery capacity retention rate, the overall thickness of the battery before and after 200 cycles was tested, and the battery swelling coefficient was h2 / h1.

[0204] 4. Test of lithium precipitation in battery: In the above test of battery capacity retention rate, the battery was disassembled after 200 cycles, and the lithium precipitation around the battery, in the center of the battery, and at the C corner of the battery was observed.

[0205] Table 3 Test results of coated separators and electrode sheets made into batteries

[0206]

[0207] Note: The C corner does not include the electrolyte injection part, and the C corner refers to the C corner of the battery cell.

[0208] The prior art coated separator applied in the battery cell cannot solve the problem of lithium precipitation in the battery cell after high-rate charge-discharge cycling, especially in the central part of the battery cell and the C corner part of the battery cell. The convex coating layer has a certain elastic recovery rate. After the electrolyte is injected, the compressed convex coating layer can recover to the initial state, thereby avoiding the aggravation of the C corner stress, preventing lithium precipitation in the C corner, improving the current stability of the C corner position, and ultimately improving the overall cycle performance of the battery cell.

[0209] As shown in Tables 1-3, the coated finished separator in the examples has a concave-convex structure with parameters meeting the numerical range set by the present application, and the coated separator has good performance. At the same time, the coated separator is prepared into a battery cell, and as shown in Table 4, the battery cell has good performance. Figure 2

[0210] Compared with Examples 2 / 8 / 9, as the angle between the concave-convex structure of the coated separator and the MD direction of the separator becomes larger, the larger the angle after the coated separator and the electrode sheet are hot-pressed, the shorter the distance of the electrolyte outside the electrolyte from the concave structure channel to the central position of the battery cell, and therefore the climbing height of the electrolyte shows an upward trend, and the cycle performance of the battery cell also improves accordingly, but the difference is not large. Compared with Comparative Example 7, the angle between the concave-convex structure and the MD direction of the separator is 0°, and after the separator and the battery cell are wound, the electrolyte cannot enter the central position of the battery cell through the concave structure channel, and the cycle performance of the battery cell is poor. Therefore, the angle between the concave-convex structure and the MD direction of the separator is set to 25°-90°, and preferably 50°-90°.

[0211] The main components of the concave-convex structure of the coated separator in Examples 1-9, 10-15, and 16-19 are first filler particles (Examples 1-9), first filler particles + first polymer particles (Examples 10-15), and first polymer particles (Examples 16-19), respectively. Since the hardness of the first filler particles is stronger than that of the first polymer particles, the compression ratio of the coating corresponding to the first polymer particles also increases accordingly compared with the first filler particles. In particular, when the main component is only the first polymer particles, the compression ratio will be larger accordingly. In addition, after the first polymer absorbs the electrolyte, the space in the concave structure is occupied by the expansion of the first polymer. Therefore, the performance of the battery cell in Examples 16-19 is better than that in Examples 1-15, and there is slight lithium precipitation in the central part of the battery cell and the C corner. Therefore, the main component of the concave-convex structure in the present application can be further optimized to be the first filler particles or a combination of the first filler particles and the first polymer particles.

[0212] ​The present application sets ΔH-η1*H2≥1μm, mainly considering that the convex structure still has a large height difference with the concave structure after being compressed, so that the coated diaphragm still has a large liquid storage space after being hot-pressed with the electrode sheet, and the poor cycle performance and lithium precipitation problems of the battery during high-rate cycling are improved.

[0213] The present application sets the width ratio of the convex structure to the concave structure W2 / W1≥0.5, mainly considering that if the ratio of the convex structure to the concave structure is too small, the supportability of the convex structure becomes smaller, the corresponding compression ratio increases, and finally the effective space of the coated diaphragm after being hot-pressed with the electrode sheet is reduced, which deteriorates the cycle performance of the battery.

[0214] The present application adopts the post-coating exposure method to cross-link the second polymer, and the silane coupling agent is cross-linked under ultraviolet exposure to enhance the overall rigidity of the concave-convex coating. The convex coating has a certain compression ratio, and the coated diaphragm basically maintains the original morphology structure of the convex coating or the convex coating and the concave coating after being hot-pressed, which can store electrolyte. In addition, the present application sets a certain elastic recovery rate for the convex coating. After the coated diaphragm is hot-pressed with the electrode sheet, the thickness of the convex coating can be restored to 95% to 105% of the original thickness (since the test conditions of the compression ratio and the elastic recovery rate are different: the test compression ratio is in a dry state, that is, it is tested without soaking in electrolyte; the test elastic recovery rate is in a wet state, that is, it is tested after the diaphragm is soaked in electrolyte, including the elastic recovery rate of the polymer itself and the volume expansion rate caused by the swelling of the polymer, so the value of the elastic recovery rate η2 of the convex coating after absorbing electrolyte can be greater than 100%). Therefore, the thickness of the hot-pressed part is basically the same as the thickness of the C corner after being soaked, thereby solving the problem of stress aggravation of the C corner, improving the stress non-uniformity of the C corner, and finally avoiding the problems of lithium precipitation or unstable current of the C corner after the battery is cycled.

[0215] The elastic modulus of the concave coating is greater than that of the convex coating, which can avoid the bottom of the convex coating extruding the concave coating after being hot-pressed, so as to increase the density of the concave coating and deteriorate the internal resistance of the battery, thereby deteriorating the cycle performance. Therefore, in the present application, the elastic modulus of the concave coating E1 is greater than the elastic modulus of the convex coating E2, E1-E2>4Gpa, the cross-linking degree X1 of the concave coating is greater than the cross-linking degree X2 of the convex coating, X1-X2>5%, and further preferably X1-X2>10%. The light intensity of the second exposure is higher than that of the first exposure, and the light intensity of the second exposure is at least 1.5mW / cm 2 higher than that of the first exposure, so that the cross-linking degree of the concave coating is greater than that of the convex coating, and the elastic modulus of the concave coating is greater than that of the convex coating. The light intensity affects the elastic modulus of the concave-convex layer, and the stronger the light, the higher the elastic modulus.

[0216] In this invention, 5 MPa and 85°C are selected when testing the compression ratio and elastic recovery rate of the raised coating. This is mainly because excessive pressure or temperature can easily lead to an excessively high compression ratio, causing severe deformation of the raised coating. After the battery cell is injected with electrolyte, the raised coating cannot recover to its original height level. Therefore, the pressure and temperature conditions for the main application of the compression ratio and elastic recovery rate of the raised coating of this invention are less than 5 MPa and 85°C.

[0217] Comparative Examples 1-3 used conventional micro-gravure coating, resulting in a coated separator with a textured structure. The convex structure had a high compression ratio, leaving no effective liquid storage space after the coated separator was hot-pressed with the electrode sheet. Furthermore, the thickness of the hot-pressed portion differed significantly from the C-corner, exacerbating the stress at the C-corner. This led to poor cycle performance of the battery cell after high-rate charge-discharge cycles, and also caused lithium plating problems in the central part of the battery cell and at the C-corner. In addition, when using a micro-gravure roller to coat the textured structure, due to the fluidity of the slurry, the slurry in the convex structure easily flowed into the concave structure area due to gravity when the micro-gravure transferred the textured structure coating onto the base film. This made it difficult to coat coatings with a height difference greater than 2 μm in practical applications. Therefore, in this invention, the coating process involves first coating the convex layer, then curing the convex layer, followed by coating the concave layer, and then curing the concave layer again, ultimately obtaining the textured structure coated separator designed in this invention.

[0218] Comparative Examples 4-6 used a conventional full-coating process to coat the separator. After the coated separator and the electrode sheet were hot-pressed, there was no space for storing electrolyte or electrolyte transfer channels. When the coated separator was assembled into a battery, the battery had poor cycle performance and serious lithium plating.

[0219] In Comparative Example 7, the angle between the concave-convex structure and the MD direction of the separator is 0°. After the coated separator and electrode sheet are assembled into a cell, there is no effective channel for transporting electrolyte, resulting in poor cycle performance of the cell and lithium plating problems.

Claims

1. A coated separator, characterized by, The base film and the concave-convex coating layer coated on at least one side of the base film, the concave-convex coating layer comprising alternating convex coating layers and concave coating layers, the convex coating layer comprising a plurality of parallel convex structure units, and the concave coating layer comprising a plurality of parallel concave structure units; the elastic modulus of the concave coating layer is higher than that of the convex coating layer; The convex coating layer can be compressed, and can be elastically restored after absorbing electrolyte after compression; The hot-pressing compression ratio of the convex coating layer is η1, and η1≤30%; The elastic recovery rate of the convex coating layer after compression and absorption of electrolyte is η2, and 95%≤η2≤105%; The elastic modulus of the concave coating layer is E1, and the elastic modulus of the convex coating layer is E2, 10GPa≤E1≤20GPa, 5GPa≤E2≤15GPa, and E1-E2>4GPa; The height difference between the height H2 of a single convex structure unit and the height H1 of a single concave structure unit is ΔH, and ΔH-η1*H2≥1μm.

2. The coated separator of claim 1, wherein, At least one of the following technical features is included: (1) The thickness of the base film is 4-16μm; (2) The base film is one of a single-layer PP film, a single-layer PE film, a double-layer PE / PP composite film, and a double-layer PP / PP composite film.

3. The coated separator according to claim 1 or 2, characterized in that, At least one of the following technical features is included: (1) The height of a single concave structure unit is H1, and the height of a single convex structure unit is H2, satisfying 0.5μm≤H1≤7.0μm and 1.5μm≤H2≤10μm; (2) The width of a single concave structure unit is W1, and the width of a single convex structure unit is W2, satisfying 0.2mm≤W1≤4.0mm and 0.2mm≤W2≤4.0mm; (3) The ratio W2 / W1 of the width W2 of a single convex structure unit to the width W1 of a single concave structure unit is N, and N≥0.5; (4) The angle between the extension direction of a single concave structure unit, the extension direction of a single convex structure unit, and the MD direction of the diaphragm is θ, and 25°≤θ≤90°; (5) The adhesion of the coated diaphragm to an electrode sheet is F, F=0, or 2N / m≤F≤8N / m.

4. The coated separator of claim 1, wherein, The raw material of the convex coating layer comprises a first component, a second polymer, and a silane coupling agent, and the raw material of the concave coating layer comprises a first component, a second polymer, and a silane coupling agent; The first component comprises first filler particles or / and first polymer particles; The first filler particles are at least one of alumina, boehmite, silicon dioxide, titanium dioxide, magnesium oxide, zirconium oxide, LATP, LLZO, melamine cyanurate; The first polymer particles are at least one of polyvinylidene fluoride polymer, polymethyl methacrylate, polystyrene-acrylate copolymer, and polyacrylonitrile-acrylate copolymer; The second polymer includes at least one of butadiene-styrene rubber, polyacrylate, polyacrylamide, polyacrylonitrile, and epoxy resin.

5. The coated separator of claim 4, wherein, At least one of the following technical features is included: (1) The first component comprises first filler particles, and the first filler particles account for 65wt%-95wt% of the coating layer. (2) the first component contains first filler particles and first polymer particles, the first filler particles account for 65wt%-95wt% of the coating, and the first polymer particles account for 0wt%-30wt% of the coating, not including 0wt%; (3) the first component contains first polymer particles, and the first polymer particles account for 90wt%-95wt% of the coating; (4) the first component contains first filler particles, or the first component contains first filler particles and first polymer particles; (5) the second polymer accounts for 2wt%-8wt% of the coating; (6) the amount of silane coupling agent added accounts for 1wt%-3wt% of the coating; (7) the silane coupling agent is at least one of gamma-aminopropyl triethoxysilane, gamma-glycidyl ether propyl trimethoxysilane, gamma-methacryloyloxy propyl trimethoxysilane, vinyl trimethoxysilane, and vinyl triethoxysilane.

6. The coated separator of claim 5, wherein, At least one of the following technical features is included: (1) the particle size of the first filler particles is 0.3-0.8 microns; (2) the first polymer particles are secondary agglomerate particles or / and primary particles; (3) the particle size of the first polymer particles is 3-8 microns.

7. The method of claim 1 to 6, wherein: The following steps are included: Step S1, mixing the first component, the second polymer, the silane coupling agent, and water in proportion to obtain a mixed slurry; Step S2, first coating, coating the mixed slurry on the base film, selecting a strip-shaped mask plate with mutually parallel and alternating exposure area width and non-exposure area width, placing the mask plate above the coated separator, and making the coated separator undergo first exposure treatment by ultraviolet light passing through the exposure area of the mask plate, then washing away the mixed glue solution in the non-exposure area after exposure, drying, and obtaining a semi-finished coated separator with convex structures; Step S3, second coating, coating the mixed slurry on the semi-finished coated separator, selecting a strip-shaped mask plate with mutually parallel and alternating exposure area width and non-exposure area width, placing the mask plate above the coated separator, adjusting the exposure area to align with the non-exposure area of the first exposure, making the coated separator undergo second exposure treatment by ultraviolet light passing through the exposure area of the mask plate, the light intensity of the second exposure being higher than that of the first exposure, washing away the mixed glue solution in the non-exposure area after exposure, drying, and obtaining a finished coated separator with concave-convex structures; In step S1, the first component contains first filler particles or / and first polymer particles; The first filler particles are at least one of alumina, boehmite, silicon dioxide, titanium dioxide, magnesium oxide, zirconium oxide, LATP, LLZO, and melamine cyanurate; The first polymer particles are at least one of polyvinylidene fluoride polymer, polymethyl methacrylate, polystyrene-acrylate copolymer, and polyacrylonitrile-acrylate copolymer; The second polymer includes at least one of styrene-butadiene rubber, polyacrylate, polyacrylamide, polyacrylonitrile, and epoxy resin.

8. The method of claim 7, wherein the coating solution is applied to the porous membrane by a method selected from the group consisting of dip coating, spin coating, spray coating, and combinations thereof. The height of the concave-convex structure in steps S2 and S3 is obtained by adjusting the coating speed ratio.

9. The method of claim 7, wherein the coating solution is prepared by dissolving the polymeric compound in a solvent. The light intensity of the first exposure in step S2 is 8.0-12.0 mW / cm 2 The light intensity of the second exposure in step S3 is 9.5-13.5 mW / cm 2 The light intensity of the second exposure is at least 1.5 mW / cm 2 higher than the light intensity of the first exposure.

10. Use of the coated separator according to any one of claims 1 to 6 or the method of producing a coated separator according to any one of claims 7 to 9 in the production of a secondary battery, an electrical appliance.

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