Battery diaphragm and battery

Abstract

The invention belongs to the technical field of diaphragm preparation, and particularly relates to a battery diaphragm and a battery. According to the invention, the heat shrinkage rate A of the base film lasting for 1 hour at the heat shrinkage test temperature of 105 DEG C is controlled to be greater than or equal to-3% and less than or equal to-0.05%, the shrinkage is less in the baking process, the problems of hemming, warping and the like of the diaphragm due to heat shrinkage can be solved, the safety problem caused by short circuit of a positive electrode and a negative electrode due to hemming and warping of the diaphragm is avoided, and the yield of the battery production process is also improved.

Description

Technical Field

[0001] The invention belongs to the technical field of diaphragm preparation, and in particular relates to a battery diaphragm and a battery. Background Art

[0002] The diaphragm is a layer of isolation film that prevents the positive and negative electrodes from directly contacting each other. At present, the lithium-ion battery diaphragm is mainly composed of a base film layer, a ceramic layer and a rubber coating layer. In the manufacturing process of the battery cell, especially in the baking stage, the diaphragm curling problem is obvious, thereby exposing the positive and negative electrodes, causing the positive and negative electrodes to short-circuit, which seriously affects the safety performance of the battery. Summary of the invention

[0003] Therefore, the technical problem to be solved by the present invention is to overcome the problem that the battery separator in the prior art causes curling due to thermal shrinkage, resulting in contact between the positive and negative poles of the battery, affecting safety, etc., thereby providing a battery separator and a battery.

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

[0005] The present invention provides a battery separator, comprising a base film, wherein the base film has a transverse heat shrinkage rate A that satisfies -3%≤A%≤-0.05% when the heat shrinkage test temperature is 105°C.

[0006] Furthermore, the thickness D1 of the base film and the transverse heat shrinkage rate A satisfy: 1 ​​μm≤|A×D1|≤56 μm.

[0007] Furthermore, the D1 satisfies: 2μm≤D1≤20μm.

[0008] Furthermore, the battery separator includes the base film and a ceramic layer disposed on at least one surface of the base film; the thickness D2 of the ceramic layer located on one side of the base film and the lateral heat shrinkage rate A satisfy: 0.05 μm≤|A×D2|≤10 μm.

[0009] Furthermore, the D2 satisfies: 0.5 μm≤D2≤4 μm.

[0010] Furthermore, the battery separator includes the base film and a ceramic layer arranged on one surface of the base film; when the base film is tested at a heat shrinkage temperature of 105°C, the transverse heat shrinkage rate A satisfies: -0.3%≤A%≤-0.1%.

[0011] Furthermore, the battery separator includes the base film and ceramic layers arranged on both side surfaces of the base film; when the base film is tested at a heat shrinkage temperature of 105°C, the transverse heat shrinkage rate A satisfies: -2.8%≤A%≤-0.05%.

[0012] The invention provides a method for preparing a battery separator, comprising preparing a base film, wherein the preparation process of the base film comprises melting and extruding powder to obtain a sheet; longitudinally stretching and once transversely stretching the sheet, extracting, and heat-setting.

[0013] Furthermore, the longitudinal stretching has a stretching ratio of ≤15 and a stretching temperature of 40-120°C; and / or,

[0014] The stretching ratio of the first transverse stretching is 10-25 times, and the stretching temperature is 110-130° C.; and / or,

[0015] The stretching ratio of the heat setting is ≤1.5, and the temperature is 100-130°C.

[0016] The present invention provides a battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and the above-mentioned battery separator.

[0017] The above technical solution has the following beneficial effects:

[0018] 1. The battery diaphragm provided by the present invention comprises a base film. The present invention controls the thermal shrinkage rate A of the base film at a thermal shrinkage test temperature of 105°C for 1 hour to satisfy: -3%≤A≤-0.05%. It shrinks less during the baking process, can solve the problems of curling and warping of the diaphragm due to thermal shrinkage, avoid the safety problems caused by short circuit of the positive and negative electrodes due to curling and warping of the diaphragm, and also improve the yield of the battery production process.

[0019] 2. The battery separator provided by the present invention can avoid excessive redundancy of the battery separator, ensure the space utilization of the battery, and prevent the separator from wrinkling easily, so as to avoid the phenomenon that the lithium ions at the corresponding position cannot be evenly embedded in the negative electrode after being embedded and extracted from the positive electrode, thereby preventing lithium deposition in the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 It is a structural schematic diagram of a battery separator of the present invention;

[0022] Figure 2 Schematic diagram of the structure of the battery separator of the present invention having a single-sided ceramic layer;

[0023] Figure 3 Schematic diagram of the structure of the battery separator of the present invention having a double-sided ceramic layer;

[0024] Reference numerals:

[0025] 1-base film; 2-ceramic layer; 3-glue layer. DETAILED DESCRIPTION

[0026] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0027] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0028] In the present invention, when referring to a numerical range, unless otherwise specified, the numerical range is deemed to be continuous and includes the minimum and maximum values ​​of the range, and every value between the minimum and maximum values.

[0029] In order to solve the problems of curling and warping of battery separators during the baking process, the present invention provides a battery separator, including a base film; the base film has a transverse heat shrinkage rate A of -3% ≤ A% ≤ -0.05% after the heat shrinkage test temperature is 105°C for 1 hour. The base film has a small heat shrinkage force during the baking process, which reduces the uneven force on the battery separator, thereby alleviating the curling and warping of the battery separator due to heat shrinkage in the baking section, reducing the short circuit of the positive and negative electrodes caused by the curling and warping of the battery separator, affecting the safety of the battery, and also improving the yield of the battery production process. The present invention controls the heat shrinkage rate A of the base film to meet: -3% ≤ A% ≤ -0.05%, reduces the shrinkage force of the base film when heated, thereby alleviating the uneven force on the battery separator, thereby reducing the problems of curling and warping of the battery separator. It should be explained that the heat shrinkage rate A% ≤ -0.05% of the base film indicates that the base film expands when heated. The transverse heat shrinkage rate A of the base film is a negative value. When the absolute value of the transverse heat shrinkage rate A is too large, the base film expands too much due to heat, resulting in excessive redundancy of the battery separator, affecting the space utilization of the battery, and the separator is prone to wrinkling. The lithium ions at the corresponding position cannot enter the negative electrode after being inserted and removed from the positive electrode, resulting in lithium deposition in the battery. When A is a negative value and the absolute value of A is too small, the battery separator is unevenly stressed, resulting in curling and warping of the battery separator.

[0030] In some embodiments of the present invention, the thickness D1 of the base film and the transverse heat shrinkage rate A satisfy: 1μm≤|A×D1|≤56μm. If the absolute value of D1×A is too large, on the one hand, it is easy to cause lithium deposition problems in the battery, and on the other hand, the battery separator is too redundant, affecting the space utilization of the battery. If the absolute value of D1×A is too small, the insulation performance of the battery separator is insufficient, and the base film curls and warps, and the risk of exposing the positive and negative pole pieces increases, which is easy to cause short circuits. A structure of a battery separator is shown in FIG. Figure 1 , the battery separator includes a base film 1.

[0031] In some embodiments of the present invention, the D1 satisfies: 2 μm≤D1≤20 μm.

[0032] If the thickness D1 of the base film is too thick, problems such as curling and warping of the base film will increase, the redundancy of the battery separator will increase, and the space utilization rate of the battery will be affected. If the thickness of the base film is too thin, the insulation performance of the battery separator will be affected.

[0033] The present invention also provides a battery separator, comprising a base film and a ceramic layer arranged on at least one side of the base film; the thickness D2 of the ceramic layer and the lateral heat shrinkage rate A satisfy: 0.05μm≤|A×D2|≤10μm.

[0034] A ceramic layer is provided on the surface of the base film to improve the thermal shrinkage and wettability of the battery separator. If the absolute value of D2×A is too small, on the one hand, the battery separator is prone to curling and warping, increasing the risk of exposing the positive and negative pole pieces and causing a short circuit; on the other hand, it will affect the thermal shrinkage and wettability of the battery separator. The ceramic layer affects the thermal shrinkage of the battery separator. If the absolute value of D2×A is too small, it will affect the performance of the ceramic layer, thereby affecting the wettability of the electrolyte. When the absolute value of D2×A is too large, the battery is prone to lithium precipitation problems, which reduces the battery space utilization and affects the battery energy density.

[0035] In some embodiments of the present invention, 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 wetting performance of the diaphragm to the electrolyte will be affected; if D2 is too large, the battery space utilization rate will be reduced and the battery energy density will be affected.

[0036] In some embodiments of the present invention, the battery separator includes the base film and a ceramic layer arranged on one side of the base film; the battery separator is tested at a heat shrinkage temperature of 105°C, and the transverse heat shrinkage rate A satisfies: -0.3% ≤ A% ≤ -0.1%. The structural schematic diagram of the ceramic layer arranged on one side of the base film is shown in Figure 2When the battery separator includes a base film and a ceramic layer disposed on one side of the base film, the base film shrinks when heated during the baking process, and the single-sided ceramic layer causes uneven force on both sides of the battery separator. The present invention further controls the lateral heat shrinkage rate A of the base film to meet: -0.3% ≤ A% ≤ -0.1%, thereby reducing the heat shrinkage force, preventing the base film from shrinking, and improving curling, warping and other problems. Figure 2 As shown, it includes a base film 1 and a ceramic layer 2 located on one side of the base film, and the surface of the ceramic layer 2 is coated with a glue layer 3.

[0037] In some embodiments of the present invention, the battery separator includes the base film and a ceramic layer arranged on the surfaces of both sides of the base film; when the thermal shrinkage test temperature of the battery separator is 105°C, the lateral thermal shrinkage rate A satisfies: -2.8% ≤ A% ≤ -0.05%. The present invention has ceramic layers on both sides of the base film. During the baking process, the forces on both sides of the battery separator are relatively uniform, and the lateral thermal shrinkage rate of the battery separator is controlled to meet -2.8% to -0.05%, which can reduce thermal shrinkage force and curling and warping, improve battery safety performance, and avoid problems such as battery lithium deposition. In the present invention, the material of the ceramic layer is a material known in the art. For example, at least one of alumina, boehmite, etc. The structure of the battery separator having a double-sided ceramic layer is shown in Figure 3 , including a base film 1 and a ceramic layer 2 located on both sides of the base film, and the surface of the ceramic layer 2 is coated with a glue layer 3.

[0038] Furthermore, the material of the base film includes polyolefins, such as polyethylene, and the molecular weight of the polyethylene is 500,000-2.5 million; optionally, the molecular weight of the polyethylene is 800,000-1.8 million or 2.1 million-2.5 million.

[0039] In some embodiments of the present invention, the battery separator further comprises a coating layer, and the coating layer is disposed on a surface of one side of the base film and / or the ceramic layer. In the present invention, the coating layer is made of a material known in the art, such as at least one of polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), etc.

[0040] The present invention also provides a method for preparing the above-mentioned battery separator, including preparing a base film, wherein the preparation process of the base film includes melting and extruding a polymer powder to obtain a sheet; longitudinally stretching and once transversely stretching the sheet, extracting, and heat-setting.

[0041] In some embodiments of the present invention, the stretching ratio of the longitudinal stretching is ≤15, and the stretching temperature is 40-120°C;

[0042] The stretching ratio of the first transverse stretching is 10-25 times, and the stretching temperature is 110-130°C.

[0043] In some embodiments of the present invention, the stretching ratio of the heat setting is ≤1.5, and the temperature is 100-130°C.

[0044] The present invention adjusts the temperature and stretching ratio of longitudinal stretching, one-time transverse stretching and heat setting, and can prepare a base film with a heat shrinkage rate of less than -0.05% at 105°C / 1h, reduce the shrinkage force of the base film in the baking process, solve the problems of uneven force on the base film, prone to curling and warping, which exposes the positive and negative pole pieces, causes short circuits, affects the safety performance of the battery, and improves the yield of the battery production process.

[0045] In some embodiments of the present invention, the extraction liquid used in the extraction process includes dichloromethane.

[0046] In some embodiments of the present invention, the ceramic slurry is coated on at least one surface of the base film by gravure coating, and the base film is dried and rolled up to obtain a diaphragm coated with a ceramic layer.

[0047] Optionally, the adhesive slurry is coated on at least one surface of the ceramic layer and / or the base film, and then rolled up after drying to obtain a battery separator.

[0048] The present invention also provides a battery, comprising the above-mentioned battery separator. The battery also comprises a positive electrode sheet and a negative electrode sheet and an electrolyte, the battery separator is arranged between the positive electrode sheet and the negative electrode sheet, the part with active material on the positive electrode sheet and the negative electrode sheet constitutes the main body of the electrode sheet, and the part without active material on the positive electrode sheet and the negative electrode sheet respectively forms a pole ear part, the separator serves as an insulating layer to prevent the short circuit inside the battery cell caused by the contact between the positive electrode sheet and the negative electrode sheet, and the separator serves as a semi-permeable layer to prevent the passage of larger molecules and allow the passage of small-volume charged ions.

[0049] Examples 1-5

[0050] Examples 1-5 respectively provide a base film, the base film is a polyethylene film (PE), the thickness D1 of the base film and the transverse heat shrinkage rate A at a heat shrinkage test temperature of 105° C. are shown in Table 1.

[0051] Embodiment 1-5 also provides a battery, including a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet, wherein the separator is from the base film of embodiment 1-5. The battery preparation process includes:

[0052] Positive electrode sheet: The positive electrode active material, conductive agent and binder are mixed, and a solvent is added to make a slurry. The slurry is coated on the positive electrode collector and dried to obtain the positive electrode sheet.

[0053] Negative electrode sheet: The negative electrode active material, conductive agent and binder are mixed, and a solvent is added to make a slurry. The slurry is coated on the negative electrode collector and dried to obtain the negative electrode sheet.

[0054] The positive electrode sheet, separator and negative electrode sheet are stacked, injected with electrolyte and assembled to obtain a battery.

[0055] Comparative Example 1-2

[0056] Comparative Examples 1-2 provide a base film, which is basically the same as Example 1 except that D1 and A are different, as shown in Table 1. Comparative Examples 1-2 also provide a battery preparation process, which is the same as Example 1.

[0057] Test Example 1

[0058] This test example provides the performance of the base film and battery of Examples 1-5 and Comparative Examples 1-2, as follows:

[0059] The judgment criteria for curling: vacuum baking at 105℃ for 5h; check whether the diaphragm curls over the negative electrode sheet, causing negative electrode foil leakage; if it causes negative electrode foil leakage, it is judged to be curled; if it does not cause negative electrode foil leakage, it is judged to be not curled.

[0060] The test method for heat shrinkage rate A is as follows: fix one end of the diaphragm on one side of the tooling, and after the other end is weighted with 110g, fix the diaphragm on the other side and remove the weight; at this time, test the dimension L1 of the diaphragm in the TD direction; then put the diaphragm into the oven at 105℃ / 5h and take it out, and test the dimension L2 of the diaphragm in the TD direction; the heat shrinkage rate of the diaphragm is calculated using the following formula.

[0061]

[0062] The test method for lithium deposition is as follows: set the working environment to 25℃, charge the battery to the upper limit voltage at a constant current and constant voltage of 2C on the LAND charging and discharging system, and the cut-off current is less than or equal to 0.05C; then discharge to the lower limit voltage at a 2C rate; repeat the above steps 100 times, where the upper and lower limits of the working voltage are different based on the different positive electrode materials used in the battery: LiFePO4: 2.5V~3.65V; lithium iron manganese phosphate: 2.5V~4.25V; ternary: 2.8V~4.25V. Disassemble the battery, select 30 negative electrode sheets, calculate the ratio of the area occupied by the lithium deposition area on each negative electrode sheet to the area of ​​the negative electrode sheet, and calculate the average ratio based on the ratios corresponding to the 30 electrode sheets. If the average ratio is greater than 0.5%, it is determined to be lithium deposition, otherwise, it is determined to be no lithium deposition.

[0063] Table 1

[0064]

[0065]

[0066] From the above results, it can be seen that the thermal shrinkage rate of the base film in Comparative Example 1 is too small, and the base film expands greatly during the baking process, resulting in problems such as lithium deposition in the battery. The base film in Comparative Example 2 shrinks during the baking process, causing the base film to curl, resulting in negative electrode foil leakage, affecting battery safety.

[0067] Examples 6-10

[0068] Examples 6-10 respectively provide a battery separator, including a base film and a ceramic layer. The thermal shrinkage rate A of the base film and the thickness D2 of the ceramic layer located on one side of the base film are different, see Table 2.

[0069] Embodiment 6-10 also provides a battery, which is the same as Embodiment 1 except that the battery separator is different. The separators in the batteries of Embodiment 6-10 are from Embodiment 6-10 respectively.

[0070] Comparative Examples 3-4

[0071] Comparative Examples 3-4 provide a separator, which is basically the same as Example 6 except that D2 and A are different, see Table 1. Comparative Examples 3-4 also provide a battery preparation process, which is the same as Example 6.

[0072] Test Example 2

[0073] This test example provides the performance of the base films and batteries of Examples 6-10 and Comparative Examples 3-4.

[0074] The test methods for curling, lithium deposition and thermal shrinkage are the same as those in Test Example 1.

[0075] Table 2

[0076] Example A D2 |A×D2| With or without curling Whether there is lithium deposition Example 6 -3 4 12 none none Example 7 -0.05 0.5 0.025 none none Example 8 -1.5 2.2 3.3 none none Example 9 -2.8 3.6 10 none none Example 10 -0.08 0.63 0.05 none none Comparative Example 3 -4 4.5 18 none have Comparative Example 4 0.2 0.2 0.04 have none

[0077] From the above results, it can be seen that the thermal shrinkage rate of the base film in the battery separator of Comparative Example 3 is too small, and the base film expands greatly during the baking process, resulting in problems such as lithium deposition in the battery. The base film in Comparative Example 4 shrinks during the baking process, causing the base film to curl, resulting in negative electrode foil leakage, affecting battery safety.

[0078] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A battery separator, characterized in that: The invention comprises a base film, wherein when the heat shrinkage test temperature of the base film is 105° C., the transverse heat shrinkage rate A of the base film satisfies: -3%≤A%≤-0.05%.

2. The battery separator according to claim 1, characterized in that: The thickness D1 of the base film and the transverse heat shrinkage rate A satisfy: 1 ​​μm≤|A×D1|≤56 μm.

3. The battery separator according to claim 2, characterized in that: The D1 satisfies: 2μm≤D1≤20μm.

4. The battery separator according to claim 1, characterized in that: The battery separator includes the base film and a ceramic layer disposed on at least one surface of the base film; the thickness D2 of the ceramic layer located on one side of the base film and the lateral heat shrinkage rate A satisfy: 0.05 μm≤|A×D2|≤10 μm.

5. The battery separator according to claim 4, characterized in that: The D2 satisfies: 0.5 μm≤D2≤4 μm.

6. The battery separator according to claim 4, characterized in that: The battery separator includes the base film and a ceramic layer arranged on one surface of the base film; when the base film is tested at a heat shrinkage temperature of 105° C., the transverse heat shrinkage rate A satisfies: -0.3%≤A%≤-0.1%.

7. The battery separator according to claim 4, characterized in that: The battery separator includes the base film and ceramic layers arranged on both side surfaces of the base film; when the base film is tested at a heat shrinkage temperature of 105° C., the transverse heat shrinkage rate A satisfies: -2.8%≤A%≤-0.05%.

8. A method for preparing a battery separator, characterized in that: The method comprises preparing a base film, wherein the preparation process of the base film comprises: melting and extruding powder to obtain a sheet; longitudinally stretching and once transversely stretching the sheet, extracting and heat-setting.

9. The preparation method according to claim 8, characterized in that: The longitudinal stretching has a stretching ratio of ≤15 and a stretching temperature of 40-120°C; and / or, The stretching ratio of the first transverse stretching is 10-25 times, and the stretching temperature is 110-130° C.; and / or, The stretching ratio of the heat setting is ≤1.5, and the temperature is 100-130°C.

10. A battery, characterized in that: It comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a battery separator as claimed in any one of claims 1 to 7.

Images