A method for preparing a multilayered separator

Abstract

The present application relates to a kind of preparation methods of multilayer diaphragm, multilayer diaphragm is n layer diaphragm, n≥2, m layer diaphragm is layered to obtain r n layer diaphragm, r≥1, m≥r×n, m layer diaphragm is compounded by m single layer diaphragm, one surface of each single layer diaphragm is sticking roll surface, another surface is non-sticking roll surface, sticking roll surface is treated by corona or not, non-sticking roll surface is treated by corona or not, sticking roll surface not treated by corona is marked as A, sticking roll surface treated by corona is marked as A*, non-sticking roll surface not treated by corona is marked as B, non-sticking roll surface treated by corona is marked as B*;The opposite surface to be separated in m layer diaphragm is A and A, the opposite surface not to be separated is B* and B*, or B* and A*, or A* and A*.The preparation method of the present application can improve the production speed of dry method flow casting production line, and when layered composite diaphragm, no bubble will be generated between non-specified interface.

Description

Technical Field

[0001] This invention belongs to the field of battery separators and relates to a method for preparing a multilayer separator. Background Technology

[0002] In the production process of existing dry casting films, such as Figure 1 As shown, when the production line speed is high, due to air entrapment, the adhesion line 4 between the casting sheet and the casting roller 6 widens, and may even change from a straight line to a curve (e.g., Figure 5 As shown in the figure, this resulted in a significant decrease in product thickness, making it impossible to meet quality requirements and restricting the production speed of the production line.

[0003] To solve the above problems, such as Figure 1 , 4 As shown, existing technologies (such as patent CN208946495U, which discloses a film casting air knife device and film casting equipment) use an air knife 16 to blow air at the attachment line position 15 between the casting sheet and the casting roller 6, so that the casting sheet can be tightly attached to the casting roller 6 at the attachment line position 15. Although this method improves the condition of the attachment line position 15, the air leaving the attachment line position 15 will blow onto the melt curtain 1, causing the melt curtain 1 to shake, which also results in poor product thickness. Even if the angle of the air knife 16 is adjusted, although there is some improvement, the effect is not obvious. Therefore, it has not been widely used in the industry.

[0004] In addition, with the same total membrane thickness, products composed of multilayer (2-4) composite membranes have greater puncture strength than single-layer membrane products (including single-layer and multilayer co-extruded products) due to the misalignment of micropores between layers, higher micropore tortuosity, and relatively dispersed internal defects. For example, the strength of a double-layer 20μm (10+10μm) membrane is greater than that of a single-layer 20μm membrane. Therefore, in the production of lithium-ion batteries with higher safety requirements, such as energy storage and power batteries, products composed of multilayer composite dry-process lithium-ion battery membranes are often selected. The production process of the dry-process membrane is as follows: casting (1 layer of membrane) → lamination (2-4 layers of cast film are laminated into 1 group) → multi-station unwinding (2-8 groups of composite film) → online annealing → multilayer stretching (4-32 layers) → delamination (1, 2, 3, or 4 layers are delaminated according to thickness requirements) → slitting.

[0005] Because the compounding and stretching processes do not involve chemical reactions or the use of adhesives, and are purely physical processes, after stretching, the peeling force between the layers of the membrane (4-32 layers) is provided by intermolecular forces (hydrogen bonds and van der Waals forces). Because the intermolecular forces are relatively small, and the peeling forces between the layers are basically the same, it is easy to cause separation between non-designated interfaces and generate bubbles during the process of separating multilayer membranes.

[0006] The position where the bubbles are generated enters the battery, causing local thickness increase, making the battery deformed, uneven performance, and in severe cases, the position where the bubbles are generated is broken, causing short circuit or even explosion of the battery. Therefore, in the production process of the separator, the bubbles are treated as defects, resulting in a large number of unqualified products.

[0007] To improve this situation, as shown in Figure 1 、 2 In the production of 2-layer separator 9, the prior art mostly uses the method of non-sticking roll surface 2 with higher roughness of the casting film and non-sticking roll surface 2 corresponding to each other to increase the effective contact area between the non-designated interface 10, and then increase the peeling force between the non-designated interface 10; since the designated interface 11 is the relative sticking roll surface 3 and the sticking roll surface 3, the effective contact area is small, so the peeling force between the designated interface 11 is relatively small. However, since the roughness difference between the non-sticking roll surface 2 and the sticking roll surface 3 is not particularly significant, the peeling force between the non-designated interface 10 is not significantly higher than the peeling force between the designated interface 11, and a large number of bubbles will inevitably be generated at the non-designated interface 10 during peeling; in addition, when the number of layers of the target separator is greater than 2 (as shown in Figure 3 ), this method cannot be used. SUMMARY

[0008] The purpose of the present application is to solve the problems existing in the prior art and provide a preparation method of a multi-layer separator.

[0009] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0010] A preparation method of a multi-layer separator, the multi-layer separator is an n-layer separator, n≥2, m-layer separators are layered to obtain r n-layer separators, r≥1, m≥r×n, the m-layer separators are composed of m single-layer separators, one surface of each single-layer separator is a sticking roll surface, and the other surface is a non-sticking roll surface, the sticking roll surface is treated by corona or not treated by corona, the non-sticking roll surface is treated by corona or not treated by corona, the sticking roll surface not treated by corona is marked as A, the sticking roll surface treated by corona is marked as A*, the non-sticking roll surface not treated by corona is marked as B, and the non-sticking roll surface treated by corona is marked as B*.

[0011] The opposite surfaces to be separated in the m-layer separators are A and A, the opposite surfaces not to be separated are B* and B*, or B* and A*, or A* and A*.

[0012] One of the technical problems to be solved by the present application is that the prior art is prone to cause separation between non-specified interfaces (i.e. non-opposite faces to be separated) and produce bubbles during the process of separating the composite film into multiple layers of the separator; the present application solves the problem by increasing the peeling force between the non-specified interfaces, which is significantly higher than the peeling force between the specified interfaces (i.e. the opposite faces to be separated); specifically, the present application controls the specified interfaces to be the surfaces of the bonding rollers that have not been subjected to corona treatment, so that the peeling force between them is minimized; at the same time, the present application controls the non-specified interfaces to be the surfaces that have been subjected to corona treatment, so that the peeling force between them is significantly higher than the peeling force between the specified interfaces; during the layer separation, only the separation between the specified interfaces occurs, and the separation between the non-specified interfaces does not occur, thereby avoiding the production of bubbles between the non-specified interfaces.

[0013] Corona treatment (also known as electric spark treatment) is to apply high voltage and high frequency of 2-100 kV and 2-10 kHz to the discharge electrode to generate a large amount of plasma gas ozone, which directly or indirectly acts on the surface molecules of the high polymer material to produce polar groups such as carbonyl and nitrogen-containing groups on the surface molecular chain of the high polymer material, and the surface tension is significantly improved; the strong ion impact will cause the chemical bonds of the plastic molecules to break and degrade, increasing the surface roughness and surface area; the synergistic results of these actions lead to a significant improvement in the adhesion of the surface of the high polymer material, achieving the purpose of surface pretreatment of the high polymer material.

[0014] The reason why corona treatment improves the peeling force is that after the film surface is subjected to corona treatment, the roughness and surface area increase, and the corresponding surface energy also significantly improves; the increase in roughness and surface area increases the effective contact area when the two layers of the separator are attached to each other, and under the premise that the unit area peeling force remains unchanged, the overall peeling force will increase due to the increase in the contact area. Within a certain range, the greater the corona power, the greater the film surface roughness, and the greater the surface energy (the greater the dyne value).

[0015] As a preferred technical solution:

[0016] The preparation method of the multi-layer separator described above, the number of black spots on the film surface of the n layers of the separator is 0 per 1000 m 2 , and the bubble scrap rate is 0%.

[0017] The preparation method of the multi-layer separator described above, n=2, and the m layers of the separator have a periodic structure (i.e. a structure formed by periodically arranging the same unit), and each cycle unit is composed of two adjacent upper and lower single-layer separators; the upper surface of the upper single-layer separator is A, the lower surface of the upper single-layer separator is B*, the upper surface of the lower single-layer separator is B*, and the lower surface of the lower single-layer separator is A.

[0018] The preparation method of the multilayer separator as described above, when n=3, the m-layer separator has a periodic structure, each cycle unit is composed of single-layer separator I, single-layer separator II and single-layer separator III arranged from top to bottom in turn, the upper surface of the single-layer separator I is A, the lower surface of the single-layer separator I is B*, the upper surface of the single-layer separator II is A*, the lower surface of the single-layer separator II is B*, the upper surface of the single-layer separator III is B*, and the lower surface of the single-layer separator III is A.

[0019] The preparation method of the multilayer separator as described above, n=4, the m-layer separator has a periodic structure, each cycle unit is composed of single-layer separator I, single-layer separator II, single-layer separator III and single-layer separator IV arranged from top to bottom in turn, the upper surface of the single-layer separator I is A, the lower surface of the single-layer separator I is B*, the upper surface of the single-layer separator II is A*, the lower surface of the single-layer separator II is B*, the upper surface of the single-layer separator III is B*, the lower surface of the single-layer separator III is A*, the upper surface of the single-layer separator IV is B*, and the lower surface of the single-layer separator IV is A.

[0020] Alternatively, the upper surface of the single-layer separator I is A, the lower surface of the single-layer separator I is B*, the upper surface of the single-layer separator II is B*, the lower surface of the single-layer separator II is A*, the upper surface of the single-layer separator III is B*, the lower surface of the single-layer separator III is A*, the upper surface of the single-layer separator IV is B*, and the lower surface of the single-layer separator IV is A.

[0021] Alternatively, the upper surface of the single-layer separator I is A, the lower surface of the single-layer separator I is B*, the upper surface of the single-layer separator II is B*, the lower surface of the single-layer separator II is A*, the upper surface of the single-layer separator III is A*, the lower surface of the single-layer separator III is B*, the upper surface of the single-layer separator IV is B*, and the lower surface of the single-layer separator IV is A.

[0022] The preparation method of the multilayer separator as described above, the Darcy value of A* or B* is 40-41.

[0023] The preparation method of the multilayer separator as described above, the thickness of the single-layer separator is 10-25 μm; when the corona treatment is performed, the corona power is 2-3.2 kW, the number of corona core is 3-4, and the distance between the corona core and the single-layer separator is 5-9 mm.

[0024] The preparation method of the multilayer separator as described above, the overall process flow is: casting to form a single-layer separator, and performing corona treatment on a single surface or both surfaces of the single-layer separator → 2-4 single-layer separators are compounded into one group → 2-8 groups of multistation unwinding → online annealing → stretching → delamination → slitting.

[0025] The preparation method of the multilayer diaphragm as described above, when the single surface or the two surfaces of the single-layer diaphragm is subjected to the corona treatment, at least one corona treatment device is located at the attaching line position of the casting sheet and the casting roller; when the single-layer diaphragm is formed by casting, the production speed of the production line is 140-180 m / min.

[0026] The technical problem solved by the present application is that the attaching effect of the casting sheet and the casting roller is poor in the production process of the dry method casting film in the prior art, which restricts the production speed of the production line (only 100-120 m / min); the present application solves the problem by arranging one corona treatment device at the attaching line position of the casting sheet and the casting roller, because the spark of the corona can provide a force to the casting sheet at the attaching line position, expel the air between the casting sheet and the casting roller, and make the casting sheet closely attach to the casting roller without causing the melt curtain to shake, and the present application can increase the production speed of the dry method casting production line by 40-50% (from 100-120 m / min to 140-180 m / min).

[0027] The preparation method of the multilayer diaphragm as described above, after the corona treatment, the thickness 2δ value of the single-layer diaphragm is ≤0.15.

[0028] The preparation method of the multilayer diaphragm as described above, in the stretching process, the annealing temperature is 125-155℃, the annealing time is 5-25 min; the cold stretching temperature is 65-95℃, the cold stretching ratio is 1.05-1.25; the hot stretching temperature is 125-158℃, the hot stretching ratio is 1.3-2.7; the shrinkage ratio is 0.8-1.0; the high-temperature setting temperature is 140-160℃, and the high-temperature setting time is 3-17 min.

[0029] Beneficial effects:

[0030] (1) The preparation method of the multilayer diaphragm of the present application arranges one corona treatment device at the attaching line position of the casting sheet and the casting roller, so that the spark of the corona can provide a force to the casting sheet at the attaching line position, expel the air between the casting sheet and the casting roller, and make the casting sheet closely attach to the casting roller without causing the melt curtain to shake, thereby increasing the production speed of the dry method casting production line.

[0031] (2) The present application treats the single or double surface of the single-layer diaphragm by the corona treatment device, controls the peeling force between the specified interface and the non-specified interface, adjusts the darcy value, and only causes the separation between the specified interfaces when the layers are separated, and does not cause the separation between the non-specified interfaces, thereby avoiding the generation of bubbles between the non-specified interfaces.

[0032] (3) the present application can meet the demand that rough surface can correspond and roughness can be adjusted even when the diaphragm is divided into 2 / 3 / 4 layers under the premise of ensuring product quality, solves the problem of bubble generation and brings great benefits to the diaphragm production process. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 schematic diagram of the existing technology of the pasting roller surface and the non-pasting roller surface;

[0034] Figure 2 schematic diagram of the existing technology of the diaphragm divided into 2 layers;

[0035] Figure 3 schematic diagram of the existing technology of the diaphragm divided into 3 layers;

[0036] Figure 4 schematic diagram of the use of the air knife of the existing technology;

[0037] Figure 5 schematic diagram of the existing technology of the pasting line being a curve;

[0038] Figure 6 schematic diagram of the corona treatment of the present application;

[0039] Figure 7 schematic diagram of the diaphragm divided into 3 layers after the corona treatment of the present application;

[0040] Figure 8 schematic diagram of the diaphragm divided into 4 layers after the corona treatment of the present application;

[0041] Figure 9 schematic diagram of the diaphragm divided into 2 layers after the corona treatment of the present application;

[0042] wherein 1 is a melt curtain, 2 is a non-pasting roller surface, 3 is a pasting roller surface, 4 is a pasting line, 5 is a die head, 6 is a casting roller, 9 is a diaphragm divided into 2 layers, 10 is a non-specified interface, 11 is a specified interface, 12 is a diaphragm divided into 3 layers, 13 is a corona treatment device I, 14 is a diaphragm divided into 4 layers, 15 is a pasting line position, 16 is an air knife, and 17 is a corona treatment device II. DETAILED DESCRIPTION

[0043] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. In addition, it should be understood that those skilled in the art can make various modifications or changes to the present application after reading the content taught by the present application, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

[0044] The following is the test method of the performance in each embodiment:

[0045] Dyne value: first select an intermediate value, take dyne pen as the starting point, draw a line on the film surface with dyne pen quickly, if the dyne liquid drawn on the substrate surface is wetted within 2 seconds, the surface tension of the substrate is greater than or equal to the selected value, then a dyne pen with a larger dyne value needs to be selected for testing, and so on, until the dyne liquid drawn on the substrate can shrink into a ball (water bead) within 2 seconds, then the previous one is regarded as the dyne value of the substrate surface. If the test result of the first test is a ball, a dyne pen with a smaller dyne value is selected for testing until the dyne liquid can wet the substrate surface.

[0046] Thickness 2δ value: real-time monitoring is performed by an on-line thickness detector (Schenk brand) in the casting process, and 2δ value≤0.15 belongs to the quality requirement.

[0047] Film surface black point number: real-time detection is performed by an on-line defect detector in the casting process, and the number of film surface black points of each roll of multilayer separator (roll width 1.4m, length 2000m) is recorded in real time according to the defect detector.

[0048] Bubble scrap rate: real-time detection is performed by an on-line defect detector in the slitting process (each multilayer separator is divided into 7 small rolls), if the defect detector shows that bubbles appear on the non-specified interface of the small roll after slitting, the small roll is recorded as unqualified, and the proportion of the number of unqualified products to the total number of small rolls is the bubble scrap rate.

[0049] Example 1

[0050] A preparation method of a 3-layer separator, the steps are as follows:

[0051] (1) 6 single-layer separators are prepared by dry casting, the sticking roller surface of the single-layer separator is marked as A, and the non-sticking roller surface is marked as B. A corona treatment device is arranged at the sticking line position of the casting sheet and the casting roller to treat B by corona treatment, and B treated by corona treatment is marked as B*;

[0052] Among them, the production speed of the production line is 180m / min; the power of the corona treatment device is 2.5kW, the number of corona core is 4, and the distance between the corona core and the single-layer separator is 7mm;

[0053] After corona treatment, the thickness of the single-layer separator is 14μm, the thickness 2δ value is 0.13, and the dyne value of B* is 41;

[0054] (2) as Figure 6As shown, three single-layer separators are prepared by dry casting (the device includes a die 5, a casting roll 6, etc.), the roll-adhering surface 3 of the single-layer separator is marked as A, and the non-roll-adhering surface 2 is marked as B. A corona treatment device (marked as corona treatment device I 13) is arranged above A to perform corona treatment on A, and the corona-treated A is marked as A*. Another corona treatment device (marked as corona treatment device II 17) is arranged at the position 15 where the casting sheet adheres to the casting roll 6 to perform corona treatment on B, and the corona-treated B is marked as B*.

[0055] The production speed of the production line is 180 m / min; the power of the corona treatment device I 13 is 2.7 kW, the number of corona core is 4, and the distance between the corona core and the single-layer separator is 7 mm; the power of the corona treatment device II 17 is 2.5 kW, the number of corona core is 4, and the distance between the corona core and the single-layer separator is 7 mm.

[0056] After corona treatment, the thickness of the single-layer separator is 14 μm, the thickness 2δ value is 0.13, the dino value of A* is 41, and the dino value of B* is 41.

[0057] (3) After the three single-layer separators are compounded into one group, three groups of multi-station unwinding, online annealing and stretching are performed to obtain nine-layer separators, and the surfaces of the nine-layer separators are A, B*, A*, B*, B*, A, A, B*, A*, B*, B*, A, A, B*, A*, B*, B*, A from top to bottom, as shown in Figure 7 ;

[0058] In the stretching process, the annealing temperature is 140℃, the annealing time is 10 min, the cold stretching temperature is 85℃, the cold stretching ratio is 1.1, the hot stretching temperature is 150℃, the hot stretching ratio is 2.0, the shrinkage ratio is 0.95, the high-temperature setting temperature is 155℃, and the high-temperature setting time is 8 min.

[0059] (4) The third single-layer separator and the fourth single-layer separator in the nine-layer separator are separated, and the sixth single-layer separator and the seventh single-layer separator are separated to obtain three 3-layer separators 12 as shown in Figure 7 ;

[0060] The final 3-layer separator has 0 black spots per 1000 m 2 of film surface, and the bubble scrap rate is 0%.

[0061] Example 2

[0062] A method for preparing a 4-layer separator, the steps are as follows:

[0063] (1) 6 pieces of single-layer separators were prepared by dry casting, the side of the single-layer separator in contact with the casting roll was marked as A, and the side not in contact with the casting roll was marked as B. A corona treatment device was arranged at the position of the contact line between the casting sheet and the casting roll to corona treat B. The corona-treated B was marked as B*;

[0064] The production speed of the production line was 140 m / min; the power of the corona treatment device was 3 kW, the number of corona core was 3, and the distance between the corona core and the single-layer separator was 5 mm;

[0065] After corona treatment, the thickness of the single-layer separator was 25 μm, the thickness 2δ value was 0.14, and the darcy value of B* was 41;

[0066] (2) 6 pieces of single-layer separators were prepared by dry casting, the side of the single-layer separator in contact with the casting roll was marked as A, and the side not in contact with the casting roll was marked as B. A corona treatment device (marked as corona treatment device I) was arranged above A to corona treat A. The corona-treated A was marked as A*. Another corona treatment device (marked as corona treatment device II) was arranged at the position of the contact line between the casting sheet and the casting roll to corona treat B. The corona-treated B was marked as B*;

[0067] The production speed of the production line was 140 m / min; the power of the corona treatment device I was 3.2 kW, the number of corona core was 3, and the distance between the corona core and the single-layer separator was 5 mm; the power of the corona treatment device II was 3 kW, the number of corona core was 3, and the distance between the corona core and the single-layer separator was 5 mm;

[0068] After corona treatment, the thickness of the single-layer separator was 25 μm, the thickness 2δ value was 0.14, the darcy value of A* was 41, and the darcy value of B* was 41;

[0069] (3) After 4 single-layer separators were compounded into 1 group, 3 groups of multi-station unwinding, on-line annealing and stretching were performed to obtain 12-layer separators. The surface of the 12-layer separators was A, B*, A*, B*, B*, A*, B*, A, A, B*, A*, B*, B*, A*, B*, A, A, B*, A*, B*, B*, A*, B*, A from top to bottom, as shown in Figure 8 ;

[0070] In the stretching process, the annealing temperature was 155 ℃, the annealing time was 5 min, the cold stretching temperature was 95 ℃, the cold stretching ratio was 1.25, the hot stretching temperature was 125 ℃, the hot stretching ratio was 1.3, the shrinkage ratio was 1.0, the high-temperature setting temperature was 160 ℃, and the high-temperature setting time was 17 min;

[0071] (4) The 4th single-layer separator and the 5th single-layer separator were separated from the 12-layer separators, and the 8th single-layer separator and the 9th single-layer separator were separated to obtainFigure 8 After the 3 pieces of 4-layer separator 14 are shown, slitting is performed.

[0072] The final 4-layer separator has 0 black spots per 1000 m of film surface 2 , and the bubble scrap rate is 0%.

[0073] Example 3

[0074] A method for preparing a 4-layer separator, comprising the following steps:

[0075] (1) 6 pieces of single-layer separators are prepared by dry casting, the side in contact with the casting roll is denoted as A, and the other side is denoted as B. A corona treatment device is arranged at the position of the contact line between the casting sheet and the casting roll to treat B by corona treatment. The treated B is denoted as B*.

[0076] The production speed of the production line is 160 m / min. The power of the corona treatment device is 2.3 kW, the number of corona core is 4, and the distance between the corona core and the single-layer separator is 8 mm.

[0077] After corona treatment, the thickness of the single-layer separator is 12 μm, the thickness 2δ value is 0.09, and the darcy value of B* is 40.

[0078] (2) 6 pieces of single-layer separators are prepared by dry casting, the side in contact with the casting roll is denoted as A, and the other side is denoted as B. A corona treatment device (denoted as corona treatment device I) is arranged above A to treat A by corona treatment. The treated A is denoted as A*. Another corona treatment device (denoted as corona treatment device II) is arranged at the position of the contact line between the casting sheet and the casting roll to treat B by corona treatment. The treated B is denoted as B*.

[0079] The production speed of the production line is 160 m / min. The power of the corona treatment device I is 2.5 kW, the number of corona core is 4, and the distance between the corona core and the single-layer separator is 8 mm. The power of the corona treatment device II is 2.3 kW, the number of corona core is 4, and the distance between the corona core and the single-layer separator is 8 mm.

[0080] After corona treatment, the thickness of the single-layer separator is 12 μm, the thickness 2δ value is 0.09, the darcy value of A* is 40, and the darcy value of B* is 40.

[0081] (3) After 4 single-layer separators are compounded into 1 group, 3 groups of multi-station unwinding, online annealing, and stretching are performed to obtain 12-layer separators. The surface of the 12-layer separators is A, B*, B*, A*, B*, A*, B*, A, A, B*, B*, A*, B*, A*, B*, A, A, B*, B*, A*, B*, A*, B*, A, from top to bottom.

[0082] In the stretching process, the annealing temperature is 135 DEG C, the annealing time is 20 min, the cold stretching temperature is 85 DEG C, the cold stretching ratio is 1.15, the hot stretching temperature is 130 DEG C, the hot stretching ratio is 1.8, the shrinkage ratio is 0.95, the high-temperature setting temperature is 140 DEG C, and the high-temperature setting time is 3 min;

[0083] (4) After separating the 4th single-layer separator and the 5th single-layer separator and separating the 8th single-layer separator and the 9th single-layer separator from the 12-layer separator, 3 four-layer separators are obtained, and then slitting is performed.

[0084] The number of black spots on the surface of the finally prepared four-layer separator is 0 per 1000 m 2 , and the bubble scrap rate is 0%.

[0085] Example 4

[0086] A method for preparing a four-layer separator, comprising the following steps:

[0087] (1) Six single-layer separators are prepared by dry casting, the attached roll surface of the single-layer separator is denoted as A, and the non-attached roll surface is denoted as B; a corona treatment device is arranged at the attachment line position of the casting sheet and the casting roll to corona treat B; and the corona-treated B is denoted as B*;

[0088] In the method, the production speed of the production line is 150 m / min; the power of the corona treatment device is 2 kW, the number of corona core is 4, and the distance between the corona core and the single-layer separator is 9 mm;

[0089] After corona treatment, the thickness of the single-layer separator is 10 μm, the thickness 2δ value is 0.08, and the dyne value of B* is 40;

[0090] (2) Six single-layer separators are prepared by dry casting, the attached roll surface of the single-layer separator is denoted as A, and the non-attached roll surface is denoted as B; a corona treatment device (denoted as corona treatment device I) is arranged above A to corona treat A; and the corona-treated A is denoted as A*; another corona treatment device (denoted as corona treatment device II) is arranged at the attachment line position of the casting sheet and the casting roll to corona treat B; and the corona-treated B is denoted as B*;

[0091] In the method, the production speed of the production line is 150 m / min; the power of the corona treatment device I is 2.2 kW, the number of corona core is 4, and the distance between the corona core and the single-layer separator is 9 mm; the power of the corona treatment device II is 2 kW, the number of corona core is 4, and the distance between the corona core and the single-layer separator is 9 mm;

[0092] After corona treatment, the thickness of the single-layer separator is 10 μm, the thickness 2δ value is 0.08, the dyne value of A* is 40, and the dyne value of B* is 40;

[0093] (3) 4 single-layer separators are compounded into 1 group, 3 groups of multi-station unwinding, online annealing and stretching to obtain 12-layer separators, and the surfaces of the 12-layer separators are A, B*, B*, A*, A*, B*, B*, A, A, B*, B*, A*, A*, B*, B*, A, A, B*, B*, A*, A*, B*, B*, A from top to bottom;

[0094] In the stretching process, the annealing temperature is 125℃, the annealing time is 25min, the cold stretching temperature is 65℃, the cold stretching ratio is 1.05, the hot stretching temperature is 158℃, the hot stretching ratio is 2.7, the shrinkage ratio is 0.8, the high-temperature setting temperature is 150℃, and the high-temperature setting time is 10min;

[0095] (4) The 4th single-layer separator and the 5th single-layer separator in the 12-layer separator are separated, and the 8th single-layer separator and the 9th single-layer separator are separated, and then 3 4-layer separators are obtained and cut.

[0096] The number of black spots on the surface of the finally prepared 4-layer separator is 0 / 1000m 2 , and the bubble scrap rate is 0%.

[0097] Example 5

[0098] A method for preparing a 2-layer separator, comprising the following steps:

[0099] (1) 6 single-layer separators are prepared by dry casting, the sticking roller surface of the single-layer separator is marked as A, and the non-sticking roller surface is marked as B; a corona treatment device is arranged at the sticking line position of the casting piece and the casting roller to perform corona treatment on B, and the treated B is marked as B*;

[0100] The production speed of the production line is 160m / min; the power of the corona treatment device is 3kW, the number of corona core is 3, and the distance between the corona core and the single-layer separator is 7mm;

[0101] After corona treatment, the thickness of the single-layer separator is 16μm, the thickness 2δ value is 0.1, and the dyne value of B* is 41;

[0102] (2) 2 single-layer separators are compounded into 1 group, 3 groups of multi-station unwinding, online annealing and stretching to obtain 6-layer separators, and the surfaces of the 6-layer separators are A, B*, B*, A, A, B*, B*, A, A, B*, B*, A from top to bottom, as shown in Figure 9 ;

[0103] In the stretching process, the annealing temperature is 145℃, the annealing time is 15min, the cold stretching temperature is 80℃, the cold stretching ratio is 1.1, the hot stretching temperature is 145℃, the hot stretching ratio is 2.0, the shrinkage ratio is 0.9, the high-temperature setting temperature is 155℃, and the high-temperature setting time is 10min.

[0104] (4) Separating the second single-layer separator and the third single-layer separator in the 6-layer separator, and separating the fourth single-layer separator and the fifth single-layer separator to obtain three 2-layer separators 9 as shown in Figure 9 After that, slitting is performed.

[0105] The number of black spots on the surface of the finally prepared 2-layer separator is 0 per 1000m 2 , and the bubble scrap rate is 0%.

[0106] Comparative Example 1

[0107] A method for preparing a 2-layer separator, which is basically the same as Example 5, except that the roll surface and the non-roll surface are not subjected to corona treatment; the surface of the obtained 6-layer separator is A, B, B, A, A, B, B, A, A, B, B, A from top to bottom.

[0108] The thickness 2δ value of the single-layer separator is 0.32; the number of black spots on the surface of the finally prepared 2-layer separator is 0 per 1000m 2 , and the bubble scrap rate is 4.76% (after slitting, a total of 3x7=21 small rolls are obtained, of which 1 small roll has bubbles, and the remaining small rolls have no bubbles, so the bubble scrap rate=1 / 21=0.0476).

[0109] Comparing Comparative Example 1 and Example 5, the 2-layer separator in Comparative Example 1 is not subjected to corona treatment, and due to the faster production speed, air is rolled into the position of the attachment line, causing the attachment line to be unstable, and the thickness 2δ value of the finally prepared 2-layer separator is much larger than the quality control standard of 0.15; in addition, the dyne value (roughness) between the A and B surfaces is basically close, causing the interfacial peeling force between the specified interface and the non-specified interface to be close, and more bubbles are generated on the non-specified interface during layering.

[0110] Example 6

[0111] A method for preparing a 2-layer separator, which is basically the same as Example 5, except that the corona treatment device is arranged above the cast sheet away from the attachment line position of the casting roll and the casting roll.

[0112] After corona treatment, the thickness 2δ value of the single-layer separator is 0.32; the number of black spots on the surface of the finally prepared 2-layer separator is 0 per 1000m 2 , and the bubble scrap rate is 0%.

[0113] Comparing Example 6 and Example 5, the thickness of the 2-layer separator of Example 6 is worse because the production speed is faster, leading to air being rolled in at the position of the attachment line, causing the attachment line to be unstable, and the thickness 2δ value of the 2-layer separator finally prepared is much greater than the quality control standard 0.15.

Claims

1. A method for preparing a multilayer diaphragm, wherein the multilayer diaphragm is an n-layer diaphragm, n≥2, and an m-layer diaphragm is layered to obtain r n-layer diaphragms, r≥1, m≥r×n, the m-layer diaphragm is composed of m single-layer diaphragms, and one surface of each single-layer diaphragm is a roller-attached surface and the other surface is a non-roller-attached surface, characterized in that... The roller-attached surface may or may not be corona-treated, and the non-roller-attached surface may or may not be corona-treated. The roller-attached surface that has not been corona-treated is denoted as A, the roller-attached surface that has been corona-treated is denoted as A*, the non-roller-attached surface that has not been corona-treated is denoted as B, and the non-roller-attached surface that has been corona-treated is denoted as B*. In the m-layer membrane, the opposite faces to be separated are A and A, and the opposite faces not to be separated are B* and B*, or B* and A*, or A* and A*.

2. The method for preparing a multilayer diaphragm according to claim 1, characterized in that, The number of black spots on the surface of the n-layer membrane is 0 per 1000m. 2 The percentage of waste due to air bubbles was 0%.

3. The method for preparing a multilayer diaphragm according to claim 1, characterized in that, With n=2 and m layers of membranes, there is a periodic structure. Each circulation unit consists of two adjacent single-layer membranes, one above the other. The upper surface of the upper single-layer membrane is A, and the lower surface of the upper single-layer membrane is B*. The upper surface of the lower single-layer membrane is B*, and the lower surface of the lower single-layer membrane is A.

4. The method for preparing a multilayer diaphragm according to claim 1, characterized in that, When n=3, the m-layer diaphragm has a periodic structure. Each circulation unit consists of single-layer diaphragm I, single-layer diaphragm II and single-layer diaphragm III arranged from top to bottom. The upper surface of single-layer diaphragm I is A and the lower surface of single-layer diaphragm I is B*. The upper surface of single-layer diaphragm II is A* and the lower surface of single-layer diaphragm II is B*. The upper surface of single-layer diaphragm III is B* and the lower surface of single-layer diaphragm III is A.

5. The method for preparing a multilayer diaphragm according to claim 1, characterized in that, n=4, m-layer diaphragms have a periodic structure. Each circulation unit consists of single-layer diaphragm I, single-layer diaphragm II, single-layer diaphragm III and single-layer diaphragm IV arranged from top to bottom. The upper surface of single-layer diaphragm I is A, the lower surface of single-layer diaphragm I is B*, the upper surface of single-layer diaphragm II is A*, the lower surface of single-layer diaphragm II is B*, the upper surface of single-layer diaphragm III is B*, the lower surface of single-layer diaphragm III is A*, the upper surface of single-layer diaphragm IV is B*, and the lower surface of single-layer diaphragm IV is A. Alternatively, the upper surface of single-layer diaphragm I is A, the lower surface of single-layer diaphragm I is B*, the upper surface of single-layer diaphragm II is B*, the lower surface of single-layer diaphragm II is A*, the upper surface of single-layer diaphragm III is B*, the lower surface of single-layer diaphragm III is A*, the upper surface of single-layer diaphragm IV is B*, and the lower surface of single-layer diaphragm IV is A. Alternatively, the upper surface of single-layer diaphragm I is A, the lower surface of single-layer diaphragm I is B*, the upper surface of single-layer diaphragm II is B*, the lower surface of single-layer diaphragm II is A*, the upper surface of single-layer diaphragm III is A*, the lower surface of single-layer diaphragm III is B*, the upper surface of single-layer diaphragm IV is B*, and the lower surface of single-layer diaphragm IV is A.

6. The method for preparing a multilayer diaphragm according to claim 1, characterized in that, The dyne value of A* or B* is 40-41.

7. The method for preparing a multilayer diaphragm according to claim 6, characterized in that, The thickness of the single-layer diaphragm is 10-25μm; during corona treatment, the corona power is 2-3.2kW, the number of corona electrodes is 3-4, and the distance between the corona electrodes and the single-layer diaphragm is 5-9mm.

8. The method for preparing a multilayer diaphragm according to claim 1, characterized in that, The overall process flow is as follows: casting to form a single-layer diaphragm, and corona treatment on one or two surfaces of the single-layer diaphragm → 2-4 single-layer diaphragms are combined into one group → 2-8 groups of multi-station unwinding → online annealing → stretching → delamination → slitting.

9. The method for preparing a multilayer diaphragm according to claim 8, characterized in that, When corona treatment is applied to a single surface or two surfaces of a single-layer diaphragm, at least one corona treatment device is located at the attachment line between the casting sheet and the casting roller; when casting to form a single-layer diaphragm, the production speed of the production line is 140-180 m / min.

10. The method for preparing a multilayer diaphragm according to claim 9, characterized in that, After corona treatment, the thickness 2δ value of the single-layer diaphragm is ≤0.15.

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