Battery separator and battery

Abstract

A battery separator, characterized in that the battery separator comprises a base film, and the base film has a transverse thermal shrinkage A at a thermal shrinkage test temperature of 105 °C, satisfying: -3%≤A%≤-0.05%.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of separator manufacturing technology and, in particular, to a battery separator and a battery or accumulator. STATE OF THE ART

[0002] A separator is an insulating membrane that prevents direct contact between the positive and negative electrodes. The separator for a lithium-ion battery primarily includes a base film layer, a ceramic layer, and an adhesive layer. During battery cell manufacturing, especially during the heating or baking process, the problem of separator curling is significant. This exposes the positive and negative electrode plates, leading to short circuits between the positive and negative electrode plates and severely compromising the battery's safety performance. SUMMARY

[0003] The technical problem to be solved by the present application is therefore to overcome problems in the prior art, such as separator curling due to thermal shrinkage, which leads to contact between the positive and negative electrode plates and compromises safety. The present application therefore provides a battery separator and a battery.

[0004] To this end, the present application provides the following technical solutions.

[0005] The present application provides a battery separator comprising a base film, the base film having a transverse thermal shrinkage A at a thermal shrinkage test temperature of 105 °C, satisfying: -3%≤A%≤-0.05%.

[0006] A thickness D1 of the base film and the transverse thermal shrinkage A also satisfy: 1µm≤|A×D1|≤56µm.

[0007] D1 also satisfies: 2µm≤D1≤20µm.

[0008] The battery separator further comprises the base film and a ceramic layer disposed on at least one side surface of the base film; and a thickness D2 of the ceramic layer on one side of the base film and the transverse thermal shrinkage A satisfy: 0.05µm≤|A×D2|≤10µm.

[0009] The D2 also meets: 0.5µm≤D2≤4µm.

[0010] The battery separator further includes the base film and the ceramic layer disposed on a side surface of the base film; and the transverse thermal shrinkage A of the base film at the thermal shrinkage test temperature of 105 °C satisfies: -0.3%≤A%≤-0.1%.

[0011] The battery separator further includes the base film and the ceramic layers arranged on both side surfaces of the base film; and the transverse thermal shrinkage A of the base film at the thermal shrinkage test temperature of 105 °C satisfies: -2.8%≤A%≤-0.05%.

[0012] The present application provides a method for manufacturing a battery separator, comprising preparing a base film, wherein a manufacturing process of the base film comprises obtaining a sheet by melting and extruding a powder material, performing longitudinal stretching and one-time transverse stretching of the sheet, followed by extraction and heat setting.

[0013] A stretch ratio of the longitudinal stretching is also ≤15, and a stretching temperature is 40 to 120 °C; and / or a stretching ratio of the single transverse stretching is 10 to 25, and the stretching temperature is 110 to 130 °C; and / or a stretch ratio of heat setting is ≤1.5, and a temperature is 100 to 130 °C.

[0014] The present application provides a battery comprising a positive electrode plate, a negative electrode plate, an electrolyte and the above-mentioned battery separator.

[0015] The above technical solutions have the following beneficial effects: 1. The battery separator provided by the present application comprises a base film. In the present application, the thermal shrinkage A of the base film is controlled at a thermal shrinkage test temperature of 105°C for 1 h to satisfy the following: -3%≤A≤-0.05%, which results in less shrinkage during the baking process, can solve problems such as separator curling and warping due to thermal shrinkage, can avoid safety problems caused by short circuits between positive and negative electrodes due to separator curling and warping, and also improves the yield in the battery production process. 2. The battery separator provided by the present application can avoid excessive overfilling of the battery separator, ensure space utilization of the battery, and prevent the wrinkling problem of the separator, thereby avoiding the phenomenon that lithium ions cannot be uniformly inserted into the negative electrode after deintercalation from the corresponding position of the positive electrode, thus preventing lithium plating in the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] To better illustrate the technical solutions in the specific embodiments or prior art of the present application, a brief introduction to the drawings is provided, which are to be used in the description of the specific embodiments or prior art. It is understood that the drawings described below represent some embodiments of the present application. Those skilled in the art may obtain additional drawings based on these drawings without any creative effort. Fig. 1 is a structural diagram of a battery separator according to the present application. Fig. 2 is a structural diagram of the battery separator having a ceramic layer disposed on a side surface of the battery separator of the present application. Fig.3 is a structural diagram of the battery separator having ceramic layers arranged on both side surfaces of the battery separator of the present application. Reference numbers:

[0017] 1 - base film; 2 - ceramic layer; 3 - adhesive layer. DETAILED DESCRIPTION

[0018] The following embodiments are provided to facilitate further understanding of the present application and are not limited to the best modes described. They do not limit the content and scope of the present application. Any product that is the same as or similar to the present application, obtained by anyone under the inspiration of the present application or by combining features of the present application with features of other prior art, falls within the scope of the present application.

[0019] Experimental steps or conditions not specifically specified in the embodiments can be performed based on operations or conditions according to conventional experimental steps described in the literature in this sector. Reagents or instruments without manufacturer's specifications are conventional reagent products that can be purchased on the market.

[0020] In this application, with respect to numerical ranges, unless otherwise stated, the numerical ranges are considered to be continuous and include the minimum and maximum values ​​as well as any value between the minimum and maximum values.

[0021] To solve problems such as curling and warping of the battery separator during the baking process, the present application provides a battery separator comprising a base film. The base film has a transverse thermal shrinkage A at a thermal shrinkage test temperature of 105°C for 1 h, which satisfies the following: -3%≤A%≤-0.05%. This base film has a small thermal shrinkage force during the baking process, thereby reducing uneven mechanical stress on the battery separator, alleviating problems such as curling and warping of the battery separator during the baking process due to thermal shrinkage, reducing short circuits between positive and negative electrodes caused by curling and warping of the separator, which impair battery safety, and also improving the yield in the battery production process.In the present application, the thermal shrinkage A of the base film is controlled to satisfy the following: -3%≤A%≤-0.05%, which reduces the shrinkage force of the base film when heated, alleviating uneven mechanical stress on the battery separator and reducing problems such as curling and warping. It should be explained that A%≤-0.05% indicates expansion of the base film when heated. If the transverse thermal shrinkage A of the base film is a negative value and its absolute value is too large, the base film will expand excessively when heated, resulting in excessive overfilling of the battery separator, impairing the space utilization of the battery, and making the separator prone to wrinkling. This causes lithium ions from corresponding positions of the positive electrode to fail to reach the negative electrode after deintercalation, resulting in lithium plating in the battery.If A is a negative value and its absolute value is too small, the battery separator will show uneven mechanical stress, which will lead to problems such as curling and warping of the battery separator.

[0022] In some embodiments of the present invention, a thickness D1 of the base film and the transverse thermal shrinkage A satisfy: 1µm≤|A×D1|≤56µm. If the absolute value of D1×A is too large, it may cause lithium plating problems and excessive overfilling of the battery separator, thereby impairing the space utilization of the battery. If the absolute value of D1×A is too small, it indicates that the insulating performance of the battery separator is insufficient, and the base film is prone to curling and warping, increasing the risk of exposure of the positive and negative electrode plates, which can easily lead to short circuits. A structural diagram of the battery separator is shown in Fig.1, comprising a base film 1.

[0023] According to some embodiments of the present application, D1 satisfies: 2µm≤D1≤20µm.

[0024] If the thickness D1 of the base film is too thick, problems such as curling and warping increase, the battery separator becomes overcrowded, and the battery's space utilization is compromised. If the base film thickness is too thin, the battery separator's insulation performance is compromised.

[0025] The present application also provides a battery separator comprising a base film and a ceramic layer disposed on at least one side surface of the base film; wherein the thickness D2 of the ceramic layer and the transverse thermal shrinkage A satisfy: 0.05µm≤|A×D2|≤10µm.

[0026] The presence of a ceramic layer on the surface of the base film can improve the thermal shrinkage performance of the battery separator and its electrolyte wettability. If the absolute value of D2×A is too small, the battery separator is prone to curling and warping, increasing the risk of exposing positive and negative electrode flaps and causing short circuits. Furthermore, the thermal shrinkage performance of the battery separator and its electrolyte wettability are impaired. The ceramic layer impairs the thermal shrinkage of the battery separator. If the absolute value of D2×A is too small, the performance of the ceramic layer is impaired, thereby impairing electrolyte wettability.If the absolute value of D2×A is too large, the battery is prone to lithium plating problems, the space utilization of the battery is reduced, and the energy density of the battery is affected.

[0027] According to some embodiments of the present application, D2 satisfies: 0.5 µm≤D2≤4 µm. If the thickness D2 of the ceramic layer on one side of the base film is too small, the wettability of the separator with the electrolyte will be impaired; if D2 is too large, the space utilization of the battery will be reduced and the energy density of the battery will be impaired.

[0028] In some embodiments of the present application, the battery separator comprises the base film and a ceramic layer disposed on one side surface of the base film; and the transverse thermal shrinkage A of the battery separator at the thermal shrinkage test temperature of 105°C satisfies: -0.3%≤A%≤-0.1%. The structural diagram of the battery separator with a ceramic layer on one side of the base film is shown in Fig.2. When the battery separator comprises a base film and a ceramic layer on one side of the base film, thermal shrinkage occurs in the base film upon heating during the baking process, and the single-sided ceramic layer (or the ceramic layer on one side of the base film) leads to uneven mechanical stress on both sides of the battery separator. In the present application, the transverse thermal shrinkage A of the base film is further controlled to satisfy the following: -0.3%≤A%≤-0.1%, thereby reducing thermal shrinkage force, preventing shrinkage of the base film, and improving curling and warping problems. As shown in Fig. 2, the battery separator includes a base film 1 and a ceramic layer 2 on a side surface of the base film, with an adhesive layer 3 laminated on the ceramic layer 2.

[0029] In some embodiments of the present application, the battery separator comprises the base film and ceramic layers arranged on both side surfaces of the base film; and the transverse thermal shrinkage A of the battery separator at the thermal shrinkage test temperature of 105°C satisfies: -2.8%≤A%≤-0.05%. In the present application, the ceramic layers are respectively provided on both side surfaces of the base film. During the baking process, the mechanical stresses on both sides of the battery separator are relatively uniform. Controlling the transverse thermal shrinkage of the battery separator to satisfy -2.8% to -0.05% can reduce the thermal shrinkage force as well as curling and warping, improve battery safety performance, and avoid battery problems such as lithium plating.In the present application, the material for the ceramic layer is known in the art, such as at least one of alumina, boehmite, etc. The structure of the battery separator having ceramic layers on both its side surfaces is shown in . Fig. 3, including a base film 1 and ceramic layers 2 on both side surfaces of the base film, with adhesive layers 3 laminated on both ceramic layers 2.

[0030] The material for the base film also includes polyolefin, such as polyethylene having a molecular weight of 500,000 to 2,500,000; the molecular weight of polyethylene may be 800,000 to 1,800,000 or 2,100,000 to 2,500,000.

[0031] In some embodiments of the present application, the battery separator also comprises an adhesive layer disposed on a side surface of the base film and / or the ceramic layer. In the present application, the material for the adhesive layer is known in the art, such as at least one of polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), etc.

[0032] The present application also provides a manufacturing method for the above battery separator, comprising preparing a base film, wherein the base film manufacturing process includes obtaining a sheet by melting and extruding polymer powder; performing longitudinal stretching and one-time transverse stretching of the sheet, followed by extraction and heat setting.

[0033] In some embodiments of the present application, the stretch ratio of the longitudinal stretching is ≤15, and the stretching temperature is 40 to 120 °C; the stretching ratio of the single transverse stretching is 10 to 25, and the stretching temperature is 110 to 130 °C.

[0034] In some embodiments of the present application, the stretch ratio of heat setting is ≤1.5, and the temperature is 100 to 130 °C.

[0035] In the present application, by adjusting the temperature and stretching ratios of longitudinal stretching, one-time transverse stretching, and heat setting, a base film with thermal shrinkage below -0.05% at 105 °C / 1 h can be obtained, thereby reducing the shrinkage force of the base film during the baking process, solving problems such as curling and warping due to uneven mechanical stress of the base film, which would cause exposure of positive and negative electrodes and short circuits, thereby affecting battery safety performance, and thus improving the yield in battery production.

[0036] In some embodiments of the present application, the extraction liquid used in the extraction process includes dichloromethane.

[0037] In some embodiments of the present application, the manufacturing method includes coating at least one side surface of the base film with ceramic slurry using gravure coating, drying, and winding to obtain the ceramic layer-coated separator.

[0038] The manufacturing process optionally includes coating at least one side surface of the ceramic layer and / or the base film with the adhesive slurry, drying and winding to obtain the battery separator.

[0039] The present application also provides a battery comprising the above battery separator. The battery also includes a positive electrode plate, a negative electrode plate, and an electrolyte, with the battery separator disposed between the positive and negative electrode plates. The portions of the positive and negative electrode plates containing active materials constitute the main body of the electrode plates, while the portions of the positive and negative electrode plates without active materials form electrode tabs. The separator serves as an insulating layer to prevent short circuits within the battery cell caused by contact between the positive and negative electrode plates and also serves as a semipermeable layer to block large molecules while allowing small charged ions to pass through. Embodiments 1 to 5

[0040] Embodiments 1 to 5 each provide a base film made of polyethylene (PE) with thickness D1 and transverse thermal shrinkage A at thermal shrinkage test temperatures of 105 °C as shown in Table 1.

[0041] Embodiments 1 to 5 also provide a battery comprising a positive electrode plate, a negative electrode plate, and a separator between them, wherein the separator includes the base films of Embodiments 1 to 5. The manufacturing process of the battery includes: Positive electrode plate: A positive active material, a conductive agent, and a binder are mixed, a solvent is added to prepare a slurry, the slurry is coated on a positive current collector, and it is dried to obtain the positive electrode plate. Negative electrode plate: A negative active material, a conductive agent, and a binder are mixed, a solvent is added to prepare a slurry, the slurry is coated on a negative current collector, and it is dried to obtain the negative electrode plate.

[0042] The above positive electrode plate, separator, negative electrode plate are stacked, electrolyte is injected, and assembly is carried out to obtain the battery. Comparative examples 1 to 2

[0043] Comparative Examples 1 to 2 each provide a base film similar to Embodiment 1, except for different values ​​for D1 and A shown in Table 1. Comparative Examples 1 to 2 also provide a battery manufacturing process identical to Embodiment 1. Test example 1

[0044] This test example provides performance data for the base films and batteries of Embodiments 1 to 5 and Comparative Examples 1 to 2 specifically as follows: Curling determination criteria: Vacuum baking at 105 °C for 5 h; check whether the separator curl extends beyond the negative electrode plate, causing exposure of the negative electrodes; if exposure of the negative electrode occurs, it is determined as curling; if no exposure of the negative electrode occurs, it is determined as no curling.

[0045] Thermal Shrinkage Test Method A: One end of the separator is fixed to one side of the fixture, a 110 g weight is attached to the other end of the separator, the separator is fixed to the other side of the fixture, and then the weight is removed; the dimension L1 of the separator is measured in a TD direction; then the separator is placed in an oven at 105 °C for 5 h, removed, and the dimension L2 in the TD direction is measured; the thermal shrinkage of the separator is calculated using the following formula: thermal shrinkage A%=(L1−L2)L1×100%

[0046] Lithium plating test procedure: The working environment is set to 25°C, the battery is charged on a LAND charge / discharge system at a rate of 2C with constant current and constant voltage to the upper voltage limit, with a cut-off current ≤0.05C; then discharged at a rate of 2C to the lower voltage limit; these steps are repeated 100 times, varying the upper and lower working voltage limits based on the positive electrode material used: LiFePO4: 2.5V~3.65V; Manganese phosphate lithium carbonate (LMFP): 2.5V~4.25V; Nickel-based cathodes (NMC / NCA): 2.8 V~4.25 V. The battery is disassembled, 30 negative electrode plates are selected, the ratio of an area of ​​lithium plating to an area of ​​the negative electrode plate is calculated for each negative electrode plate, and the average ratio is calculated based on the ratio for each of the 30 negative electrode plates.If this average ratio exceeds 0.5%, it is determined as lithium plating; if not, it is determined as no lithium plating. Table 1 A D1 |A×D1| Curls: YES or NO Lithium plating: YES or NO Embodiment 1 -3 20 60 NO NO Embodiment 2 -0,05 2 0,1 NO NO Embodiment 3 -1,5 11 16,5 NO NO Embodiment 4 -2,8 19,6 55 NO NO Embodiment 5 -0,06 16,7 1 NO NO Comparison example 1 -4 22 88 NO YES Comparison example 2 0,2 1 0,2 YES NO

[0047] From the above results, it can be seen that the base film in Comparative Example 1 has too small a thermal shrinkage, resulting in excessive expansion during baking and causing lithium plating problems. The base film in Comparative Example 2 exhibits shrinkage during baking, causing curling and exposure of the negative electrode, thereby compromising battery safety. Embodiments 6 to 10

[0048] Embodiments 6 to 10 each provide a battery separator comprising a base film and a ceramic layer, with different thermal shrinkages A and different thicknesses D2 of the ceramic layer on one side of the base film, shown in Table 2.

[0049] Embodiments 6 to 10 also provide batteries similar to those of Embodiment 1, except for different separators. The separators in the batteries of Embodiments 6 to 10 come from Embodiments 6 to 10, respectively. Comparative examples 3 to 4

[0050] Comparative Examples 3 to 4 each provide a separator similar to Embodiment 6, except for different values ​​for D2 and A shown in Table 1. Comparative Examples 3 to 4 also provide a battery manufacturing process identical to Embodiment 6. Test example 2

[0051] This test example provides performance data for the base films and batteries of Embodiments 6 to 10 and Comparative Examples 3 to 4.

[0052] The test procedures for crimping, lithium plating, and thermal shrinkage are the same as in Test Example 1. Table 2 Example A D2 |A×D2| Curls: YES or NO Lithium plating: YES or NO Embodiment 6 -3 4 12 NO NO Embodiment 7 -0,05 0,5 0,025 NO NO Embodiment 8 -1,5 2,2 3,3 NO NO Embodiment 9 -2,8 3,6 10 NO NO Embodiment 10 -0,08 0,63 0,05 NO NO Comparison example 3 -4 4,5 18 NO YES Comparison example 4 0,2 0,2 0,04 YES NO

[0053] From the above results, it can be seen that the base film of the battery separator in Comparative Example 3 exhibits too small thermal shrinkage, resulting in excessive expansion of the base film during baking, which leads to lithium plating problems on the battery. The base film in Comparative Example 4 exhibits shrinkage during baking, causing curling of the base film and exposure of the negative electrode, thereby compromising battery safety.

[0054] Obviously, the above embodiments are merely examples for clarity and not limitations of implementation. Other forms of modification or variation may be made by ordinary technicians in this field based on the above description. It is neither necessary nor possible to list all implementations here. The obvious modifications or variations derived therefrom remain within the scope of the present invention.

Claims

[1] Battery separator, characterized by that the battery separator comprises a base film and the base film has a transverse thermal shrinkage A at a thermal shrinkage test temperature of 105 °C, satisfying the following: -3%≤A%≤-0.05%. [2] Battery separator according to claim 1, characterized by that a thickness D1 of the base film and the transverse thermal shrinkage A satisfy the following: 1 µm≤|A×D1 |≤56µm. [3] Battery separator according to claim 2, characterized by that D1 satisfies the following: 2µm≤D1≤20µm. [4] Battery separator according to one of claims 1 to 3, characterized by that the battery separator comprises the base film and a ceramic layer arranged on at least one side surface of the base film; and wherein a thickness D2 of the ceramic layer on one side of the base film and the transverse thermal shrinkage A satisfy the following: 0.05µm≤|A×D2|≤10µm. [5] Battery separator according to claim 4, characterized by that D2 satisfies the following: 0.5µm≤D2≤4µm. [6] Battery separator according to claim 4 or 5, characterized by that the battery separator comprises the base film and the ceramic layer disposed on a side surface of the base film; and the transverse thermal shrinkage A of the base film at the thermal shrinkage test temperature of 105 °C satisfies: -0.3%≤A%≤-0.1%. [7] Battery separator according to one of claims 4 to 6, characterized by that the battery separator comprises the base film and the ceramic layers arranged on both side surfaces of the base film; and the transverse thermal shrinkage A of the base film at the thermal shrinkage test temperature of 105 °C satisfies the following: -2.8%≤A%≤-0.05%. [8] Battery separator according to one of claims 1 to 7, characterized bythat the battery separator is manufactured by a method and the method comprises manufacturing a base film, wherein a manufacturing process of the base film comprises obtaining a sheet by melting and extruding a powder material, performing longitudinal stretching and one-time transverse stretching of the sheet, followed by extraction and heat setting. [9] Battery separator according to claim 8, characterized by that a stretching ratio of longitudinal stretching is ≤15, and a stretching temperature is 40 to 120 °C. [10] Battery separator according to claim 8 or 9, characterized by that a stretching ratio of the one-time transverse stretching is 10 to 25, and the stretching temperature is 110 to 130 °C. [11] Battery separator according to one of claims 8 to 10, characterized by that a stretch ratio of heat setting is ≤1.5, and a temperature is 100 to 130 °C. [12] Battery separator according to one of claims 8 to 11, characterized by that the powder material is a polymer powder. [13] Battery separator according to one of claims 1 to 12, characterized by that the base film comprises polyolefin, for example polyethylene having a molecular weight of 500,000 to 2,500,000; wherein the molecular weight of polyethylene is optionally 800,000 to 1,800,000 or 2,100,000 to 2,500,000. [14] Battery separator according to one of claims 4 to 13, characterized by that the battery separator comprises an adhesive layer arranged on the side surface of the base film and / or a side surface of the ceramic layer. [15] Battery separator according to claim 14, characterized by that the material for the adhesive layer is at least one of polyvinylidene fluoride (PVDF) and polymethyl methacrylate (PMMA). [16] Battery, characterized bythat the battery comprises a positive electrode plate, a negative electrode plate, an electrolyte and the battery separator according to one of claims 1 to 15.

Images