Diaphragm, lithium ion battery and electric equipment

Abstract

For a blade battery, since electrolyte can only enter from the positions of an upper side plate and a lower side plate, the middle part of a battery cell is infiltrated slowly, in the process of charging and discharging with a small electrolyte injection amount or a large multiplying power, the middle part of the battery cell is extremely easy to cause local lithium precipitation due to electrolyte deficiency, and the safety and the overall performance of the battery cell are influenced. According to the diaphragm, the lithium ion battery and the electric equipment, in the length direction of the diaphragm, the air permeability of the middle of the diaphragm is smaller than that of the ends of the diaphragm, the smaller the air permeability of the diaphragm is, the higher the liquid absorption capacity and the higher the mass transfer capacity are, and by adopting the design, the liquid absorption capacity and the mass transfer capacity of the middle of the diaphragm are improved; the overall strength and safety of the diaphragm are improved.

Description

Technical Field

[0001] The utility model belongs to the technical field of lithium ion battery structure, and specifically relates to a diaphragm, a lithium ion battery and electrical equipment. Background Art

[0002] In VDA (square) or cylindrical cells, the pores and porosity of the diaphragm are evenly distributed. Since the electrolyte infiltration path is short, the even distribution of the diaphragm pores and porosity has little effect on the electrolyte infiltration during battery operation. In blade batteries, since the cells are long and the electrolyte can only enter from the left and right side plates in the length direction of the cells, the middle of the cells is infiltrated more slowly. During the process of low electrolyte injection or high rate charge and discharge, the middle of the cells is prone to local lithium precipitation due to lack of liquid, affecting the safety and overall performance of the cells.

[0003] In order to ensure the electrolyte infiltration in the middle of the battery cell, the conventional method is to increase the amount of liquid injection. This method increases the cost of the electrolyte and also has a significant impact on the energy density (GED) of the battery cell. The air permeability of the diaphragm reflects the liquid absorption capacity of the diaphragm. The smaller the air permeability, the stronger the liquid absorption capacity. Utility Model Content

[0004] In view of the technical problem of lack of liquid in the middle of the existing battery cell, the present application provides a diaphragm, an electrode and a lithium-ion battery.

[0005] In order to solve the above problems, this application provides the following technical solutions:

[0006] In a first aspect, the present application provides a diaphragm, wherein in a first direction, the air permeability of the middle portion of the diaphragm is less than the air permeability of the end portion of the diaphragm, and the air permeability of the diaphragm is t, satisfying: Among them, 5.18 -3 is the empirical constant of the diaphragm, ε is the porosity, d is the pore size, D is the thickness of the diaphragm, and the first direction is the length direction of the diaphragm.

[0007] In some embodiments, the porosity of the middle portion of the diaphragm is greater than the porosity of the ends of the diaphragm and / or the pore size of the middle portion of the diaphragm is greater than the pore size of the ends of the diaphragm.

[0008] In some embodiments, the porosity of the diaphragm is 0.3-0.5, and the pore size of the diaphragm is 25 mm-45 mm.

[0009] In some embodiments, a line passing through the midpoint of the diaphragm and perpendicular to the first direction is a center line, and the ends of the diaphragm include a first end and a second end; the first end and the second end are symmetrical with respect to the center line, and the middle of the diaphragm is symmetrical with respect to the center line.

[0010] In some embodiments, with the center line as a reference, the pore distribution of the membrane is symmetric with respect to the center line and / or the pore size distribution of the membrane is symmetric with respect to the center line.

[0011] In some embodiments, the length of the diaphragm in the first direction is L, and the length of the middle portion of the diaphragm in the first direction is L d , satisfying: L / 4≤L d ≤3L / 4.

[0012] In some embodiments, in the thickness direction of the diaphragm, the diaphragm includes multiple sub-layer diaphragms, and the porosity of at least some of the sub-layer diaphragms in the middle in the first direction is greater than the porosity of the end portions and / or the pore size of at least some of the sub-layer diaphragms in the middle in the first direction is greater than the pore size of the end portions.

[0013] In some embodiments, the diaphragm includes an intermediate sublayer diaphragm and an outer sublayer diaphragm, the porosity of the intermediate sublayer diaphragm in the middle in the first direction is greater than the porosity of the end portions and / or the pore size of the intermediate sublayer diaphragm in the middle in the first direction is greater than the pore size of the end portions.

[0014] In some embodiments, the middle sub-layer separator is a base film; and the outer sub-layer separator is a coated functional layer.

[0015] In a second aspect, the present application provides a lithium-ion battery, comprising the above-mentioned separator.

[0016] In some embodiments, the length direction of the separator corresponds to the length direction of the lithium-ion battery, and the lithium-ion battery is injected from left and right ends of the length direction.

[0017] In a third aspect, the present application provides an electrical device comprising the lithium-ion battery described in the second aspect.

[0018] The diaphragm provided in the present application has the following technical effects: in the length direction of the diaphragm, the air permeability of the middle part of the diaphragm is less than the air permeability of the end part of the diaphragm, the liquid absorption capacity and mass transfer capacity of the middle part of the diaphragm are optimized, and a smaller electrolyte injection amount can be used in the battery cell design, further reducing the battery cell manufacturing cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0020] The structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with this technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantive technical significance. Any structural modification, change in proportion or adjustment of size, without affecting the effects and purposes that can be achieved by the present invention, should still fall within the scope of the technical contents disclosed by the present invention.

[0021] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0022] Figure 1 This is a schematic diagram of the diaphragm structure in one embodiment of the utility model;

[0023] Figure 2 This is a schematic diagram of the diaphragm structure in one embodiment of the utility model;

[0024] Figure 3 This is a schematic diagram of the diaphragm structure in one embodiment of the utility model;

[0025] Figure 4 This is a schematic diagram of the diaphragm structure in one embodiment of the utility model;

[0026] Figure 5 It is a schematic diagram of a normal diaphragm structure in the prior art.

[0027] Description of the accompanying drawings: A1: first end of the diaphragm; A2: second end of the diaphragm; B: middle of the diaphragm; X: first direction. DETAILED DESCRIPTION

[0028] In order to make the technical problems, technical solutions and beneficial effects solved by the utility model more clear, the utility model is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the utility model and are not used to limit the utility model.

[0029] The utility model provides a diaphragm, in a first direction X, the air permeability of the middle part of the diaphragm is less than the air permeability of the end part of the diaphragm, the air permeability of the diaphragm is t, and satisfies: Among them, 5.18 -3 is the empirical constant of the membrane, ε is the porosity, d is the pore size, D is the thickness of the membrane, and the first direction X is the length direction of the membrane.

[0030] Specifically, the first direction X is the length direction of the separator, corresponding to the length direction of the battery.

[0031] Specifically, the air permeability t of the diaphragm is a measure of the permeability of the diaphragm. The air permeability specifically refers to the time required for a liquid to pass through a diaphragm of a specific area under a specific pressure. To a certain extent, it can reflect the liquid absorption capacity of the diaphragm. The larger the air permeability t of the diaphragm, the longer the time required for the electrolyte to pass through the diaphragm, the worse the permeability of the diaphragm, and the weaker the liquid absorption capacity of the diaphragm; the smaller the air permeability t of the diaphragm, the shorter the time required for the electrolyte to pass through the diaphragm, and the stronger the liquid absorption capacity of the diaphragm. When the thickness D of the diaphragm is constant, the air permeability t of the diaphragm is inversely proportional to the porosity ε and the pore size d. Therefore, the larger the porosity ε and the pore size d of the diaphragm, the smaller the air permeability t of the diaphragm, and the stronger the liquid absorption capacity of the diaphragm.

[0032] The diaphragm provided in the present application has the following technical effects: in the length direction of the diaphragm, the air permeability of the middle part of the diaphragm is less than the air permeability of the end part of the diaphragm, the liquid absorption capacity and mass transfer capacity of the diaphragm are optimized, and a smaller electrolyte injection amount can be used in the battery cell design, further reducing the battery cell manufacturing cost.

[0033] In some embodiments, the porosity of the middle portion B of the membrane is greater than the porosity of the ends of the membrane and / or the pore size of the middle portion B of the membrane is greater than the pore size of the ends of the membrane.

[0034] Specifically, the porosity of the diaphragm refers to the proportion of pores in the diaphragm material to the total volume of the diaphragm; the pore size of the diaphragm refers to the size of the pores on the diaphragm.

[0035] Specifically, the diaphragm end portion includes a first end portion A1 and a second end portion A2 that are opposite to each other in the first direction X.

[0036] It can be understood that the porosity of the middle portion B of the diaphragm is greater than the porosity of the end portion of the diaphragm and / or the pore size of the middle portion B of the diaphragm is greater than the pore size of the end portion of the diaphragm. Specifically, the porosity of the middle portion B of the diaphragm is greater than the porosity of the end portion of the diaphragm, and the pore size of the middle portion of the diaphragm is greater than the pore size of the end portion of the diaphragm. Figure 1 , the middle part of the diaphragm is designed with large porosity and large pore size, and the porosity and pore size of the middle part of the diaphragm are larger than the porosity and pore size of the end part of the diaphragm; or, the porosity of the middle part B of the diaphragm is larger than the porosity of the end part of the diaphragm, and the pore size of the middle part B of the diaphragm is not larger than the pore size of the end part of the diaphragm, which can be referred to Figure 3 and Figure 4 , the middle part of the diaphragm is designed with a large porosity, the porosity of the middle part of the diaphragm is greater than the porosity of the ends of the diaphragm, the pore size of the middle part and the ends of the diaphragm is the same or the pore size of the middle part of the diaphragm is smaller than the pore size of the ends of the diaphragm; or, the porosity of the middle part B of the diaphragm is not greater than the porosity of the ends of the diaphragm, and the pore size of the middle part B of the diaphragm is greater than the pore size of the ends of the diaphragm, which can be referred to Figure 2The middle part B of the diaphragm adopts a large pore size design, the pore size of the middle part B of the diaphragm is larger than the pore size of the end part of the diaphragm, and the porosity of the diaphragm remains unchanged. The porosity of the middle part B of the diaphragm is larger than the porosity of the end part of the diaphragm and / or the pore size of the middle part B of the diaphragm is larger than the pore size of the end part of the diaphragm, which can improve the liquid absorption capacity of the middle part B of the diaphragm and improve the mass transfer capacity.

[0037] It is understandable that the material of the diaphragm can be, but is not limited to, polyethylene film (PE film), polypropylene film (PP film), polyvinylidene fluoride film and non-woven fabric, etc. At the same time, the diaphragm can have different coating layers, such as alumina coating, boehmite coating, PVDF coating, polymethyl methacrylate, polyvinylidene fluoride, polyacrylonitrile, etc., without limitation.

[0038] In some embodiments, the porosity of the membrane is 0.3-0.5; the pore size of the membrane is 25 nm-45 nm.

[0039] Specifically, the porosity of the diaphragm is 0.35-0.5, and can be, but not limited to, 0.3, 0.35, 0.38, 0.4, 0.42, 0.45, 0.47, and 0.5; the greater the porosity of the diaphragm, the stronger the liquid absorption and liquid retention capacity of the diaphragm. In order to ensure the liquid absorption capacity of the diaphragm, the porosity of the diaphragm cannot be less than 0.35; the smaller the porosity of the diaphragm, the better the mass transfer characteristics of the diaphragm, which ensures the electrochemical performance of the battery, so the porosity of the diaphragm cannot be greater than 0.5. Therefore, the porosity of the diaphragm is 0.3-0.5, which not only ensures the mass transfer characteristics of the diaphragm, but also improves the liquid absorption capacity of the diaphragm, and enhances the safety performance and electrochemical performance of the battery.

[0040] Specifically, the pore size of the diaphragm is 25nm to 45nm, and can be, but not limited to, 25nm, 27nm, 30nm, 33nm, 35nm, 38nm, 40nm, and 45mm; the larger the pore size of the diaphragm, the stronger the liquid absorption capacity of the diaphragm, the stronger the ion penetration capacity, and the better the electrochemical performance of the battery, so the pore size of the diaphragm should be greater than 25nm; the smaller the pore size of the diaphragm, the more effectively it can isolate the positive and negative electrodes, prevent short circuits and electrochemical reactions inside the battery, and the higher the safety performance of the battery, so the pore size of the diaphragm should be less than 45nm. The pore size of the diaphragm is 25nm to 45nm, which not only ensures the safety performance of the battery, but also enhances the liquid absorption capacity of the diaphragm.

[0041] In some preferred embodiments, the porosity of the middle portion of the diaphragm is 0.4-0.5, and the pore size of the middle portion of the diaphragm is 35 mm-45 mm; the porosity of the ends of the diaphragm is 0.3-0.4, and the pore size of the ends of the diaphragm is 25 nm-35 nm.

[0042] Furthermore, the porosity and pore size in the middle and end portions of the diaphragm are within this range, which is beneficial to improving the strength and safety performance of the diaphragm and enhancing the liquid absorption capacity of the diaphragm.

[0043] In some embodiments, a line passing through the midpoint of the diaphragm and perpendicular to the first direction is the center line, and the ends of the diaphragm include a first end A1 and a second end A2; the first end A1 and the second end A2 are symmetrical relative to the center line, and the middle part B of the diaphragm is symmetrical relative to the center line.

[0044] In some embodiments, with the midline as a reference, the pore distribution of the membrane is symmetric with respect to the midline and / or the pore size distribution of the membrane is symmetric with respect to the midline.

[0045] Specifically, the pore distribution of the diaphragm is symmetrical relative to the midline and / or the pore size distribution of the diaphragm is symmetrical relative to the midline, which can make the liquid absorption capacity and strength on the left and right sides of the midline of the diaphragm the same, thereby better improving the liquid absorption capacity of the diaphragm and achieving better results.

[0046] In some embodiments, the length of the diaphragm in the first direction is L, and the length of the middle portion of the diaphragm in the first direction is L d , satisfying: L / 4≤L d ≤3L / 4.

[0047] Specifically, the length L of the middle portion B of the diaphragm in the first direction X is d , satisfying: L / 4≤L d ≤3L / 4, specifically but not limited to L / 4, 3L / 8, L / 2, 5L / 8, 3L / 4; the length L of the middle part B of the diaphragm in the first direction X d The longer it is, the larger the area of ​​the middle part B of the diaphragm with strong liquid absorption ability will be, and the stronger the ion penetration ability will be. Therefore, it is necessary to ensure that the length L of the middle part B of the diaphragm in the first direction X is d Greater than L / 4; length L of the middle portion B of the diaphragm in the first direction X d The shorter the length L, the smaller the area occupied by the middle part B of the diaphragm on the diaphragm, and the better the mechanical strength and mass transfer characteristics of the diaphragm. Therefore, the length L of the middle part B of the diaphragm in the first direction X should be ensured. d Less than 3L / 4. Therefore, the length L of the middle portion B of the diaphragm in the first direction X is d , satisfying: L / 4≤L d ≤3L / 4, which not only ensures the mechanical strength of the diaphragm but also improves the liquid absorption capacity of the diaphragm, thereby improving the safety and electrochemical performance of the battery.

[0048] In some embodiments, in the thickness direction of the diaphragm, the diaphragm includes multiple sub-layer diaphragms, and the porosity of at least some of the sub-layer diaphragms in the middle of the first direction X is greater than the porosity at the end and / or the pore size of at least some of the sub-layer diaphragms in the middle of the first direction X is greater than the pore size at the end.

[0049] Specifically, the diaphragm includes multiple sub-layer diaphragms, which means that in the thickness direction of the diaphragm, the diaphragm is formed by a composite of multiple layers of materials; the porosity of at least some of the sub-layer diaphragms in the middle of the first direction X is greater than the porosity at the end and / or the pore size of at least some of the sub-layer diaphragms in the middle of the first direction X is greater than the pore size at the end, which means that the porosity of any sub-layer diaphragms or a combination of them in the middle of the first direction X is greater than the porosity at the end and / or the pore size of at least some of the sub-layer diaphragms in the middle of the first direction X is greater than the pore size at the end, and at least one sub-layer diaphragm has uneven pores and different pore size designs, which can enhance the liquid absorption capacity of the diaphragm and achieve the technical effect of the present invention.

[0050] In some embodiments, the diaphragm includes a middle sublayer diaphragm and an outer sublayer diaphragm, the porosity of the middle sublayer diaphragm in the first direction is greater than the porosity of the end portions and / or the pore size of the middle sublayer diaphragm in the first direction is greater than the pore size of the end portions.

[0051] Specifically, the porosity of the middle part of the intermediate sublayer diaphragm in the first direction is greater than the porosity of the end part and / or the pore size of the middle part of the intermediate sublayer diaphragm in the first direction is greater than the pore size of the end part, which means that the porosity of the middle part of the intermediate sublayer diaphragm in the first direction is greater than the porosity of the end part and / or the pore size of the middle part of the intermediate sublayer diaphragm in the first direction is greater than the pore size of the end part, and the outer sublayer diaphragm outside the intermediate sublayer diaphragm adopts conventional porosity and pore size settings. The intermediate sublayer diaphragm adopts the above porosity and / or pore size design, while the outer sublayer diaphragm adopts conventional porosity and pore size settings, which can further ensure the stability of the diaphragm and improve the liquid absorption capacity of the diaphragm, so that the design effect of the diaphragm is better.

[0052] In some embodiments, the middle sub-layer membrane is a base membrane; and the outer sub-layer membrane is a coated functional layer.

[0053] It can be understood that the material of the base film can be, but is not limited to, one of polypropylene, polyethylene, non-woven fabric, cellulose, and polyimide.

[0054] It is understandable that the material of the functional layer can be, but is not limited to, one of alumina coating, boehmite coating, PVDF coating, polymethyl methacrylate, polyvinylidene fluoride, and polyacrylonitrile. The outer sublayer diaphragm can be a functional layer coated on the base film, or a functional layer coated on the functional layer.

[0055] In a second aspect, the present application provides a lithium-ion battery, comprising the above-mentioned separator.

[0056] In some embodiments, the length direction of the separator corresponds to the length direction of the lithium-ion battery.

[0057] The lithium-ion battery is filled from both ends in the length direction.

[0058] The lithium-ion battery provided in the present application includes the above-mentioned diaphragm, which has strong liquid absorption capacity and good mass transfer characteristics, thereby improving the electrochemical performance and cycle life of the battery.

[0059] In a third aspect, the present application provides an electrical device comprising the lithium-ion battery described above.

[0060] Specifically, the electrical equipment may be an electric car, an electric motorcycle, an electric bicycle, a mobile power supply, a drone, a mobile phone, a computer, a camera, an electric tool, a smart home or a wearable device.

[0061] The electrical equipment provided in the embodiment of the present application has a lithium-ion battery, which has high charging and discharging efficiency, good safety and long cycle life, helps to improve the safety and cycle stability of the electrical equipment, and is beneficial to the long-term use of the electrical equipment.

[0062] The present invention is further described in detail below through embodiments.

[0063] Example 1

[0064] This embodiment is used to illustrate the diaphragm, electrode and lithium ion battery disclosed in the utility model, and includes the following steps:

[0065] 1. Preparation of diaphragms: The required diaphragms are prepared using a dry process. The molten resin material is made into a sheet-like crystalline film by extrusion and film blowing, and then a porous structure is formed by unidirectional or bidirectional stretching at high temperature. Diaphragms with uneven porosity and pore size can be prepared by controlling the different stretching temperatures in the width direction during the diaphragm preparation process.

[0066] The length L of the prepared diaphragm is 964 mm, the thickness D of the diaphragm is 15 μm, the porosity in the middle of the diaphragm is 0.45, the porosity at the end of the diaphragm is 0.3, the pore size in the middle of the diaphragm is 35 nm, and the pore size at the end of the diaphragm is 35 nm; the length L of the middle of the diaphragm is d The first end and the second end of the diaphragm have a length of 482 mm, respectively, and the first section and the second end of the diaphragm are symmetrical about the center line of the diaphragm.

[0067] 2. Preparation of positive electrode sheet: Mix lithium iron phosphate, conductive agent SuperP (superconducting carbon), and binder PVDF (polyvinylidene fluoride) in a mass ratio of 95:2.5:2.5 to form a slurry with a certain viscosity, apply it on aluminum foil, dry it at 85°C, roll it, and cut it into pieces to obtain the required positive electrode sheet.

[0068] 3. Preparation of negative electrode sheet: Graphite, conductive agent Super P (superconducting carbon), thickener CMC (sodium carboxymethyl cellulose), and binder SBR (styrene-butadiene rubber) are mixed evenly in a mass ratio of 96:2:1:1 to form a slurry with a certain viscosity, coated on copper foil, dried at 85°C, rolled, and cut to obtain the required negative electrode sheet.

[0069] 4. Preparation of electrodes: The negative electrode sheet, positive electrode sheet and separator prepared above are wound into a battery cell. The separator containing a liquid retaining structure corresponds to the upper part of the battery. After the assembly steps such as the pole ear welding and the cover lead-out plate welding, the lithium-ion battery is obtained through the subsequent steps such as liquid injection (the electrolyte is injected from the left and right ends of the length direction of the battery cell), formation, and capacity division.

[0070] Example 2

[0071] The difference between Example 2 and Example 1 is that the length of the middle portion of the diaphragm is different.

[0072] 1. Preparation of diaphragm:

[0073] The porosity of the prepared membrane is 0.45 in the middle, 0.3 at the ends, 35 nm in the middle, and 35 nm at the ends; the length L of the membrane in the middle is d The first end and the second end of the diaphragm are 241 mm long and 366 mm long respectively. The first end and the second end of the diaphragm are symmetrical about the center line of the diaphragm.

[0074] Example 3

[0075] The difference between Example 3 and Example 1 is that the length of the middle part of the diaphragm is different.

[0076] 1. Preparation of diaphragm:

[0077] The porosity of the prepared membrane is 0.45 in the middle, 0.3 at the ends, 35 nm in the middle, and 35 nm at the ends; the length L of the membrane in the middle is d The first end and the second end of the diaphragm have a length of 732 mm, and the lengths of the first end and the second end of the diaphragm are 120.5 mm respectively. The first end and the second end of the diaphragm are symmetrical about the center line of the diaphragm.

[0078] Example 4

[0079] The difference between Example 4 and Example 1 is that the porosity and pore size in the middle of the diaphragm are different.

[0080] 1. Preparation of diaphragm:

[0081] The porosity of the prepared membrane is 0.4 in the middle, the porosity of the membrane ends is 0.4, the pore size of the membrane in the middle is 40nm, and the pore size of the membrane ends is 30nm; the length L of the membrane in the middle is d The first end and the second end of the diaphragm have a length of 482 mm, respectively, and the first end and the second end of the diaphragm are symmetrical about the center line of the diaphragm.

[0082] Example 5

[0083] The difference between Example 5 and Example 2 is that the porosity and pore size in the middle of the diaphragm are different.

[0084] 1. Preparation of diaphragm:

[0085] The porosity of the prepared membrane is 0.4 in the middle, the porosity of the membrane ends is 0.4, the pore size of the membrane in the middle is 40nm, and the pore size of the membrane ends is 30nm; the length L of the membrane in the middle is d The first end and the second end of the diaphragm are 241 mm long and 366 mm long respectively. The first end and the second end of the diaphragm are symmetrical about the center line of the diaphragm.

[0086] Example 6

[0087] The difference between Example 6 and Example 3 is that the porosity and pore size in the middle of the diaphragm are different.

[0088] 1. Preparation of diaphragm:

[0089] The porosity of the prepared membrane is 0.4 in the middle, the porosity of the membrane ends is 0.4, the pore size of the membrane in the middle is 40nm, and the pore size of the membrane ends is 30nm; the length L of the membrane in the middle is d The first end and the second end of the diaphragm have a length of 732 mm, and the lengths of the first end and the second end of the diaphragm are 120.5 mm respectively. The first end and the second end of the diaphragm are symmetrical about the center line of the diaphragm.

[0090] Example 7

[0091] The difference between Example 7 and Example 1 is that the porosity and pore size in the middle of the diaphragm are different.

[0092] 1. Preparation of diaphragm:

[0093] The porosity of the prepared membrane is 0.4 in the middle, the porosity of the membrane end is 0.3, the pore size of the membrane in the middle is 45nm, and the pore size of the membrane end is 35nm; the length L of the membrane in the middle is d The first end and the second end of the diaphragm have a length of 482 mm, respectively, and the first end and the second end of the diaphragm are symmetrical about the center line of the diaphragm.

[0094] Example 8

[0095] The difference between Example 8 and Example 2 is that the porosity and pore size in the middle of the diaphragm are different.

[0096] 1. Preparation of diaphragm:

[0097] The porosity of the prepared membrane is 0.4 in the middle, the porosity of the membrane end is 0.3, the pore size of the membrane in the middle is 45nm, and the pore size of the membrane end is 35nm; the length L of the membrane in the middle is d The first end and the second end of the diaphragm are 241 mm long and 366 mm long respectively. The first end and the second end of the diaphragm are symmetrical about the center line of the diaphragm.

[0098] Example 9

[0099] The difference between Example 9 and Example 3 is that the porosity and pore size in the middle of the diaphragm are different.

[0100] 1. Preparation of diaphragm:

[0101] The porosity of the prepared membrane is 0.4 in the middle, 0.3 at the ends of the membrane, 45 in the middle, and 35 in the ends of the membrane; the length L of the middle of the membrane is d The first end and the second end of the diaphragm have a length of 723 mm, and the lengths of the first end and the second end of the diaphragm are 120.5 mm respectively. The first end and the second end of the diaphragm are symmetrical about the center line of the diaphragm.

[0102] Comparative Example 1

[0103] The difference between Comparative Example 1 and Example 1 is that the porosity and pore size in the middle and end portions of the diaphragm are the same.

[0104] 1. Preparation of diaphragm:

[0105] The length L of the prepared diaphragm is 964 mm, the thickness D of the diaphragm is 15 um, the porosity of the diaphragm is 0.4, and the pore size of the diaphragm is 35 nm.

[0106] Table 1 is a summary of the data parameters of various embodiments and comparative examples.

[0107]

[0108] From the data of Examples 1 to 9 and Comparative Example 1 in Table 1, it can be seen that by increasing the porosity and / or pore size in the middle of the diaphragm to make it larger than the porosity and / or pore size at the ends of the diaphragm, the impedance and air permeability t in the middle of the diaphragm are reduced. The smaller the air permeability t of the diaphragm, the stronger the liquid absorption and mass transfer capacity of the diaphragm. Therefore, increasing the porosity and / or pore size in the middle of the diaphragm increases the liquid absorption and mass transfer capacity of the middle of the diaphragm, saves the amount of electrode liquid injection, and reduces the manufacturing cost of the battery core.

[0109] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A diaphragm, characterized in that: In the first direction, the air permeability of the middle portion of the diaphragm is less than the air permeability of the end portion of the diaphragm, and the air permeability t of the diaphragm satisfies: Among them, 5.18 -3 is the empirical constant of the diaphragm, ε is the porosity, d is the pore size, and D is the thickness of the diaphragm; the first direction is the length direction of the diaphragm.

2. The diaphragm according to claim 1, characterized in that The porosity of the middle portion of the diaphragm is greater than the porosity of the end portions of the diaphragm and / or the pore size of the middle portion of the diaphragm is greater than the pore size of the end portions of the diaphragm.

3. The diaphragm according to claim 1, characterized in that The porosity of the diaphragm is 0.3-0.5, and the pore size of the diaphragm is 25 mm-45 mm.

4. The diaphragm according to claim 1, characterized in that The line passing through the midpoint of the diaphragm and perpendicular to the first direction is the center line. The ends of the diaphragm include a first end and a second end. The first end and the second end are symmetrical relative to the center line, and the middle of the diaphragm is symmetrical relative to the center line.

5. The diaphragm according to claim 4, characterized in that Taking the center line as a reference, the pore distribution of the diaphragm is symmetrical relative to the center line and / or the pore size distribution of the diaphragm is symmetrical relative to the center line.

6. The diaphragm according to claim 1, characterized in that The length of the diaphragm in the first direction is L, and the length of the middle part of the diaphragm in the first direction is L d , satisfying: L / 4≤L d ≤3L / 4.

7. The diaphragm according to claim 1, characterized in that In the thickness direction of the diaphragm, the diaphragm includes multiple sub-layer diaphragms, and the porosity of at least some of the sub-layer diaphragms in the middle in the first direction is greater than the porosity of the end portions and / or the pore size of at least some of the sub-layer diaphragms in the middle in the first direction is greater than the pore size of the end portions.

8. The diaphragm according to claim 7, characterized in that The diaphragm includes a middle sublayer diaphragm and an outer sublayer diaphragm, the porosity of the middle sublayer diaphragm in the first direction is greater than the porosity of the end portions and / or the pore size of the middle sublayer diaphragm in the first direction is greater than the pore size of the end portions.

9. The diaphragm according to claim 8, characterized in that The middle sub-layer membrane is a base membrane; the outer sub-layer membrane is a coated functional layer.

10. A lithium ion battery, characterized in that: The invention comprises the diaphragm according to any one of claims 1 to 9.

11. The lithium ion battery according to claim 10, characterized in that: The length direction of the separator corresponds to the length direction of the lithium-ion battery, and the lithium-ion battery is injected with liquid from both left and right ends of the length direction.

12. An electrical device, characterized in that: Includes the lithium ion battery according to claim 10 or 11.

Images