Composite separator

Abstract

The utility model provides a kind of composite diaphragm, the composite diaphragm includes base film and paper-based cellulose film fixed on the surface of base film, the paper-based cellulose film is provided with multiple through holes.The quality area density of paper-based cellulose film is reduced by the mode for being provided with multiple through holes in paper-based cellulose film in the application, the contact area of paper-based cellulose film and environmental moisture is reduced, space is also left so that electrolyte stays, maintains and enhances its absorption capacity to electrolyte.The composite diaphragm provided in the application combines base film and paper-based cellulose provided with multiple through holes, both retains the characteristics of base film, and also combines the liquid absorption capacity and high temperature resistance advantage of paper-based cellulose film, and also reduces the affinity of paper-based cellulose film to water by using multiple through holes provided in paper-based cellulose film, to further realize better electrolyte retention, accelerate the infiltration speed of electrolyte, and improve the overall performance of battery.

Description

Technical Field

[0001] This utility model relates to the field of battery technology, and more specifically, to a composite separator. Background Technology

[0002] The separator is a key component of the battery. Existing separators have weak electrolyte wetting ability, especially in large-capacity batteries where wetting is difficult. The weak electrolyte absorption capacity of the separator will affect the transport of lithium ions between the positive and negative electrodes, affecting the battery capacity and cycle performance, and thus affecting the overall performance of the battery.

[0003] In view of the above, this application is hereby submitted. Utility Model Content

[0004] Paper-based cellulose membranes possess advantages such as strong liquid absorption capacity and high temperature resistance, along with uniform pore distribution and environmentally friendly raw materials, making them a promising candidate for battery separators. However, while absorbing electrolyte, paper-based cellulose membranes also exhibit a high affinity for moisture, which can lead to moisture mixing into the electrolyte, triggering side reactions and affecting battery stability.

[0005] The main objective of this invention is to provide a composite separator to solve the problem in the prior art where paper-based cellulose membranes have a high affinity for water while absorbing electrolyte, leading to water mixing into the electrolyte, which in turn triggers side reactions and affects battery stability.

[0006] To address the aforementioned problems, according to one aspect of the present invention, a composite diaphragm is provided, comprising a base membrane and a paper-based cellulose membrane fixed to the surface of the base membrane, wherein the paper-based cellulose membrane is provided with a plurality of through holes.

[0007] Furthermore, the porosity of paper-based cellulose is 30%-80%.

[0008] Furthermore, the through-hole can be circular, elliptical, or square.

[0009] Furthermore, the through holes are circular with a diameter of 0.5-2 mm, and the average spacing between adjacent through holes is 2-8 mm.

[0010] Furthermore, the thickness of the paper-based cellulose membrane is 10-30 μm.

[0011] Furthermore, the thickness of the paper-based cellulose membrane is 15-23 μm.

[0012] Furthermore, the thickness of the base film is 3-10 μm.

[0013] Furthermore, the base membrane is a polyolefin membrane or an aramid membrane.

[0014] Furthermore, an adhesive layer is provided between the base film and the paper-based cellulose film.

[0015] Furthermore, the areal density of the adhesive layer is 0.5-1.0 g / m³. 2 .

[0016] By applying the technical solution of this utility model, this application reduces the surface density of the paper-based cellulose membrane by setting multiple through-holes, thereby reducing the contact area between the paper-based cellulose membrane and environmental moisture, while still leaving space for the electrolyte to remain, maintaining and enhancing its absorption capacity for electrolyte. The composite separator provided by this application combines a base membrane and a paper-based cellulose membrane with multiple through-holes, retaining the characteristics of the base membrane while incorporating the liquid absorption capacity and high-temperature resistance advantages of the paper-based cellulose membrane. At the same time, the multiple through-holes in the paper-based cellulose membrane reduce its affinity for water, thereby achieving better electrolyte retention, accelerating the electrolyte wetting speed, and improving the overall performance of the battery. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an undue limitation of the present invention. In the drawings:

[0018] Figure 1 A schematic diagram of the structure of a composite diaphragm according to some embodiments of the present invention is shown;

[0019] Figure 2 The diagram shows a schematic representation of the structure of the paper-based cellulose membrane in some embodiments of this example.

[0020] The above figures include the following reference numerals:

[0021] 101. Base membrane; 102. Paper-based cellulose membrane; 103. Adhesive layer; 104. Through-hole. Detailed Implementation

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0023] The existing base membrane 101 used as a separator has poor electrolyte wetting ability, especially in large-capacity batteries where wetting is difficult, affecting the battery's initial charge / discharge efficiency, internal resistance, cycle life, rate performance, and safety. While the paper-based cellulose membrane 102 has excellent liquid absorption capacity and high-temperature resistance, and uniform pore distribution, it also exhibits a high affinity for water while absorbing electrolyte, causing water to mix into the electrolyte and triggering side reactions, thus affecting battery stability. To alleviate the aforementioned problems, this application provides a composite separator.

[0024] In one typical embodiment of this application, a composite membrane is provided, which includes a base membrane 101 and a paper-based cellulose membrane 102 fixed to the surface of the base membrane 101, and the paper-based cellulose membrane 102 is provided with a plurality of through holes 104.

[0025] This application reduces the surface density of the paper-based cellulose membrane 102 by providing multiple through-holes 104 on its surface, thereby reducing the contact area between the paper-based cellulose membrane 102 and ambient moisture. Simultaneously, it leaves space for electrolyte retention, maintaining and enhancing its electrolyte absorption capacity. The composite separator provided in this application combines a base membrane 101 with a paper-based cellulose membrane 102 having multiple through-holes 104. It retains the characteristics of the base membrane 101 while incorporating the liquid absorption capacity and high-temperature resistance of the paper-based cellulose membrane 102. Furthermore, the multiple through-holes 104 in the paper-based cellulose membrane 102 reduce its affinity for water, thus achieving better electrolyte retention, accelerating electrolyte wetting speed, and improving the overall performance of the battery.

[0026] In some embodiments of this application, the porosity of the paper-based cellulose membrane 102 is 30%-80% to better enhance the electrolyte absorption capacity of the composite membrane while reducing the contact area with environmental moisture, thereby further improving the stability of the battery.

[0027] Specifically, the porosity of the paper-based cellulose membrane is a range of 30%, 35%, 40%, 42%, 45%, 50%, 52%, 55%, 58%, 60%, 65%, 70%, 72%, 75%, 80%, or any combination of two values.

[0028] In some embodiments of this application, the shape of the through-holes 104 in the paper-based cellulose membrane 102 is not limited, and includes, but is not limited to, circular, elliptical, square, or irregular shapes. Irregular shapes refer to shapes other than circular, elliptical, and square.

[0029] In some embodiments of this application, the through hole 104 is circular with a diameter of 0.5-2 mm, and the average hole spacing between adjacent through holes 104 is 2 mm-8 mm, so as to further increase the electrolyte retention of the composite separator while reducing its affinity for water, thereby further improving the overall performance of the battery.

[0030] Specifically, the diameter of the circular through hole 104 is 0.5mm, 0.8mm, 1.0mm, 1.2mm, 1.5mm, 1.8mm, 2.0mm, or any combination of two such values. The spacing between adjacent through holes 104 is 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 6mm, 7mm, 8mm, or any combination of two such values.

[0031] In this application, the hole spacing between adjacent circular through holes 104 refers to the distance between the centers of adjacent circular holes.

[0032] If the through hole 104 is a shape other than a circle, the hole spacing between adjacent through holes 104 refers to the distance between the geometric centers of the through holes.

[0033] In some embodiments of this application, the thickness of the paper-based cellulose membrane 102 is 10-30 μm to improve the electrolyte retention of the paper-based cellulose membrane 102. Specifically, the thickness of the paper-based cellulose membrane 102 is 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm, 21 μm, 22 μm, 23 μm, 25 μm, 27 μm, 30 μm, or any range of two values.

[0034] In some embodiments of this application, when the thickness of the paper-based cellulose membrane 102 is 15-23 μm, it is more conducive to the composite membrane maintaining a better electrolyte retention capacity.

[0035] In some embodiments of this application, the thickness of the base film 101 is 3-10 μm, which is beneficial to further improve the strength of the base film 101, especially when the thickness of the base film 101 is 5-7 μm, it is even more beneficial to improve the strength of the base film 101.

[0036] Specifically, the thickness of the base film 101 is 3μm, 4μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 8μm, 9μm, 10μm or any range of two values.

[0037] In this application, the base film 101 is a commonly used base film 101 in the art, including but not limited to polyolefin film or aramid film.

[0038] In some embodiments of this application, an adhesive layer is provided between the base film 101 and the paper-based cellulose film 102 to facilitate the adhesion between the base film 101 and the paper-based cellulose film 102, and further improve the connection strength between the base film 101 and the paper-based cellulose film 102.

[0039] In some embodiments of this application, the areal density of the adhesive layer is 0.5-1.0 g / m³. 2 This facilitates the transfer of lithium ions while simultaneously increasing the adhesion strength between the base film 101 and the paper-based cellulose film 102. Specifically, the adhesive layer has a mass density of 0.5 g / m³. 2 0.6g / m 2 0.7g / m 2 0.8g / m 2 0.9g / m 2 1.0g / m 2 Or a range of values ​​consisting of any two numerical values.

[0040] The specific type of adhesive used in the adhesive layer 103 is not limited; it can be either a water-based adhesive or a non-water-washable adhesive. Water-based adhesives include, but are not limited to, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), and acrylate latex (AE); non-water-based adhesives include, but are not limited to, polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), and acrylonitrile (PAN).

[0041] The preparation method of the above-mentioned composite membrane is not limited, and any method commonly used in the field is acceptable.

[0042] In some embodiments of this application, the method for preparing the composite diaphragm includes the following steps: coating an adhesive slurry on the surface of a base membrane 101, and attaching a perforated paper-based cellulose membrane 102 to the adhesive slurry, followed by heat treatment to remove the solvent from the adhesive slurry and obtain the composite diaphragm.

[0043] Specifically, the adhesive slurry includes an adhesive and a solvent, the solvent including but not limited to one or more of N-methylpyrrolidone (NMP), water, dimethylamide (DMAc), dimethylformamide (DMF).

[0044] In some specific embodiments, the solid content of the adhesive slurry is 3-10 wt% to facilitate a suitable coating viscosity. Specifically, the solid content of the adhesive slurry is 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, or any combination of two values.

[0045] In some specific embodiments, the heat treatment method is high-temperature drying, with a drying temperature of 80-95°C and a drying time of 10-20 minutes. Specifically, the drying temperature is a range of 80°C, 82°C, 85°C, 88°C, 90°C, 95°C, or any two of these values; the drying time is a range of 10 minutes, 12 minutes, 15 minutes, 18 minutes, 20 minutes, or any two of these values, to ensure that the solvent in the adhesive slurry is removed.

[0046] The composite separator provided in this application combines a base membrane 101 and a perforated (with through holes 104) paper-based cellulose membrane 102. This retains the basic characteristics of the base membrane 101 while also incorporating the advantages of the perforated paper-based cellulose membrane 102, such as strong liquid absorption capacity and high temperature resistance. This results in better electrolyte retention and faster electrolyte wetting speed, thereby improving the overall performance of the battery.

[0047] In another typical embodiment of this application, a battery is also provided, wherein the separator used in the battery is the composite separator provided in the first typical embodiment of this application.

[0048] The battery provided in this application uses the aforementioned composite separator, which retains the characteristics of the base membrane 101 and integrates the liquid absorption capacity and high temperature resistance of the paper-based cellulose membrane 102. At the same time, it utilizes the multiple through-holes 104 provided in the paper-based cellulose membrane 102 to reduce the affinity of the paper-based cellulose membrane 102 for water, thereby achieving a better electrolyte retention capacity, accelerating the electrolyte wetting speed, and thus improving the overall performance of the battery.

[0049] The beneficial effects of this application will be further illustrated below with reference to embodiments and comparative examples.

[0050] Example 1

[0051] This embodiment provides a composite diaphragm, such as Figure 1 and Figure 2 As shown, the composite membrane includes a polyethylene membrane base 101 and a paper-based cellulose membrane 102 fixed on the polyethylene membrane base 101. The paper-based cellulose membrane 102 is provided with through holes 104, which are circular holes with a diameter of 1 mm and a distance of 5 mm between adjacent circular holes.

[0052] In this embodiment, the polyethylene-based film 101 and the paper-based cellulose film 102 are bonded and fixed together by an adhesive layer 103. The adhesive in the adhesive layer 103 is polyvinyl alcohol, and its surface density is 0.7 g / m³. 2 .

[0053] In this embodiment, the polyethylene film has a thickness of 5 μm, the paper-based cellulose film 102 has a thickness of 20 μm, and the paper-based cellulose film 102 was purchased from Xianhe Paper Industry Co., Ltd.

[0054] The composite diaphragm provided in this embodiment is prepared according to the following steps:

[0055] (1) Disperse polyvinyl alcohol (product model PVA 17-88) in water to prepare a polyvinyl alcohol slurry with a solid content of 5wt%;

[0056] (2) Polyvinyl alcohol slurry is coated onto polyethylene base film 101, with a coating density of 0.7 g / m³. 2 The paper-based cellulose membrane 102, which has been perforated to have through holes 104, is transferred onto a polyvinyl alcohol slurry and dried at 90°C for 15 minutes to obtain the composite membrane.

[0057] Example 2

[0058] The difference between this embodiment and Embodiment 1 is that the diameter of the circular holes on the paper-based cellulose membrane 102 is 2 mm, and the distance between adjacent circular holes is 8 mm.

[0059] Example 3

[0060] The difference between this embodiment and Embodiment 1 is that the diameter of the circular holes on the paper-based cellulose membrane 102 is 0.5 mm, and the distance between adjacent circular holes is 2 mm.

[0061] Comparative Example 1

[0062] The difference between this comparative example and Example 1 is that the paper-based cellulose membrane 102 does not have through holes 104.

[0063] Comparative Example 2

[0064] This comparative example provides a diaphragm, which is the polyethylene-based membrane 101 in Example 1.

[0065] Test case

[0066] The diaphragms provided in the above embodiments and comparative examples were tested for air permeability, electrolyte wetting performance, and shrinkage rate, respectively. The results are shown in Table 1 below.

[0067] Among them, (1) the test method for air permeability is: using a GURLEY 4110N standard air permeability meter for testing. The specific test method includes: at 60% humidity and 25℃ temperature, the diaphragms provided in the examples and comparative examples are cut into 100mm×100mm samples respectively, and the samples are clamped in the air permeability holes of the instrument for testing, with an air permeability of 100mL.

[0068] (2) The test method for electrolyte wetting performance is as follows: at 60% humidity and 25℃, the diaphragm is cut into a strip sample with a length of 200mm and a width of 25mm. It is dropped from a height of 0.2m into a beaker containing electrolyte, with the lower 3mm of the diaphragm immersed in the electrolyte. After standing for 30min, the height of the highest point of the electrolyte wetting of the diaphragm and the electrolyte surface is measured with a ruler. The specific composition of the electrolyte is that the mass ratio of EC / EMC / DMC is 1:1:1, and 1mol LiPF6. EC refers to ethylene carbonate, EMC refers to ethyl methyl carbonate, and DMC refers to dimethyl carbonate.

[0069] (3) The test method for heat shrinkage rate is as follows: cut the diaphragm into diaphragm samples with a length of 1000 mm and a width of 75 mm, place the diaphragm samples in a high-temperature drying oven, and heat-treat them at 105℃ for 1 hour. Take out the heat-treated diaphragm samples and test the change in length of the diaphragm before and after heat treatment. Heat shrinkage rate = (diaphragm length before heat treatment - diaphragm length after heat treatment) / diaphragm length before heat treatment.

[0070] Table 1

[0071]

[0072] Experimental Example 2

[0073] The separators provided in the above embodiments and comparative examples were assembled into 15Ah cylindrical batteries for testing. The positive electrode active material was lithium iron phosphate, and the negative electrode active material was graphite. The battery liquid retention, battery capacity, and 500-cycle cycle retention rate were tested, and the test results are shown in Table 2 below.

[0074] Among them, (1) the test method for battery liquid retention is as follows: after the battery is injected with liquid and fully soaked, the injection port is sealed under vacuum, and the weight is measured to obtain the battery mass after liquid injection. The battery liquid retention is obtained by subtracting the battery weight before liquid injection from the battery mass after liquid injection.

[0075] (2) The battery capacity test method is as follows: the battery is fully charged to 3.65V at room temperature, and then discharged to 2.5V with a current of 0.33C, and the battery capacity is measured.

[0076] (3) The test method for 500-cycle retention rate is as follows: At room temperature, the battery is charged to 3.65V with a current of 0.5C and then discharged to 2.5V with a current of 1C. After 500 cycles of charge and discharge, the capacity after 500 cycles is measured. 500-cycle retention rate = capacity after 500 cycles / initial capacity.

[0077] Table 2

[0078]

[0079]

[0080] As can be seen from the above description, the embodiments of this utility model achieve the following technical effects:

[0081] By applying the technical solution of this utility model, this application reduces the surface density of the paper-based cellulose membrane 102 by setting multiple through-holes 104 on its surface, thereby reducing the contact area between the paper-based cellulose membrane 102 and environmental moisture, while also leaving space for the electrolyte to remain, maintaining and enhancing its absorption capacity for electrolyte. The composite separator provided by this application combines the base membrane 101 and the paper-based cellulose membrane 102 with multiple through-holes 104, retaining the characteristics of the base membrane 101 while incorporating the liquid absorption capacity and high-temperature resistance advantages of the paper-based cellulose membrane 102. At the same time, the multiple through-holes 104 in the paper-based cellulose membrane 102 reduce its affinity for water, thereby achieving better electrolyte retention, accelerating the electrolyte wetting speed, and improving the overall performance of the battery.

[0082] The above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model. Various modifications and variations can be made to this utility model by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A composite diaphragm, characterized in that, The composite membrane includes a base membrane (101) and a paper-based cellulose membrane (102) fixed to the surface of the base membrane (101), and the paper-based cellulose membrane is provided with a plurality of through holes (104).

2. The composite diaphragm according to claim 1, characterized in that, The porosity of the paper-based cellulose membrane (102) is 30%-80%.

3. The composite diaphragm according to claim 1, characterized in that, The through hole (104) is circular, elliptical, or square in shape.

4. The composite diaphragm according to claim 1, characterized in that, The through hole (104) is circular with a diameter of 0.5-2mm, and the average hole spacing between adjacent through holes is 2-8mm.

5. The composite diaphragm according to claim 1, characterized in that, The thickness of the paper-based cellulose membrane (102) is 10-30 μm.

6. The composite diaphragm according to claim 1, characterized in that, The thickness of the paper-based cellulose membrane (102) is 15-23 μm.

7. The composite diaphragm according to claim 1, characterized in that, The thickness of the base film (101) is 3-10 μm.

8. The composite diaphragm according to any one of claims 1 to 7, characterized in that, The base film (101) is a polyolefin film or an aramid film.

9. The composite diaphragm according to any one of claims 1 to 7, characterized in that, An adhesive layer (103) is provided between the base film (101) and the paper-based cellulose film (102).

10. The composite diaphragm according to claim 9, characterized in that, The areal density of the adhesive layer (103) is 0.5-1.0 g / m³. 2 .

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