Battery diaphragm and secondary battery

Abstract

The invention relates to the technical field of battery diaphragms, in particular to a battery diaphragm and a secondary battery, the battery diaphragm comprises a base film and a first dispensing coating, and the base film is a porous film; the base film is provided with a first face and a second face which are oppositely arranged in the thickness direction of the base film. The first dispensing coating is mainly composed of organic polymer particles and a binder; the first dispensing coating is coated on at least one of the first surface and the second surface; wherein the distance D1 between two adjacent adhesive points in the first adhesive dispensing coating on the same surface is greater than the longest axis R of the adhesive points, and Rlt; d1lt; 2R; when the first surface and the second surface are both provided with the first dispensing coating, the orthographic projection of the first dispensing coating on the first surface and the orthographic projection of the first dispensing coating on the second surface on the same surface of the base film are staggered; impedance increment Clt before and after hot pressing of the battery diaphragm and the pole piece; 0.1 omega; the ventilation increment Plt of the base film before and after the first dispensing coating is coated; the volume is 15s / 100ml. The diaphragm and the battery have good ionic conductivity, bonding performance, energy density and cycle performance.

Description

Technical Field

[0001] This application relates to the technical field of battery separators, and more specifically to a battery separator and a secondary battery. Background Art

[0002] As the core power source of modern portable electronic devices and electric vehicles, the performance optimization of secondary batteries has always been a research hotspot. As a key inner component of the battery, the separator mainly functions to isolate the positive and negative electrodes to prevent short circuits, while allowing lithium ions to pass through freely. Although traditional polyolefin separators (such as PE, PP) have good mechanical properties, they have problems such as poor thermal stability (easy to shrink at high temperatures, leading to short circuits) and poor wettability to the electrolyte. To solve these problems, the industry generally adopts the method of coating a layer of inorganic ceramic particles (such as alumina, silica) or an organic polymer coating on the surface of the separator.

[0003] Existing coating technologies mainly include full coating. Full coating means uniformly coating a layer of slurry on the entire surface of the separator to form a continuous coating on the surface of the base film. However, the coating of the full coating process increases the weight and thickness of the separator, reduces the energy density of the battery. At the same time, the too thick coating will hinder ion conduction, increase the internal resistance, and increase the battery impedance after hot pressing. The bonding interface between the coating of the full coating and the base film is large, and peeling may occur during long-term cycling, thus affecting the battery life. Summary of the Invention

[0004] This application provides a battery separator and a secondary battery to at least partially or fully solve the above technical problems.

[0005] This application provides a battery separator, comprising:

[0006] A base film, which is a porous thin film; the base film has a first surface and a second surface oppositely arranged along its own thickness direction; and

[0007] A first dispensing coating, which is mainly composed of organic polymer particles and a binder; the first dispensing coating is coated on at least one of the first surface and the second surface;

[0008] Wherein, the distance D1 between two adjacent glue dots in the first dispensing coating on the same surface is greater than the longest axis R of the glue dot, and R < D1 < 2R; when the first dispensing coatings are provided on both the first surface and the second surface, the first dispensing coatings on the first surface and the first dispensing coatings on the second surface are staggeredly arranged in the orthographic projection on the same surface of the base film;

[0009] The impedance increment C of the battery separator before and after hot pressing with the electrode sheet is < 0.1Ω; the air permeability increment P of the base film before and after coating the first dispensing coating is < 15s / 100ml.

[0010] In some optional embodiments, the coverage of the first dispensing coating on the first surface is M1, 5% ≤ M1 ≤ 50%; and / or, the coverage of the first dispensing coating on the second surface is M2, 0 <M2≤50%。

[0011] In some optional embodiments, the distance D2 between two adjacent adhesive dots whose projections of the first dispensing coating on the first surface and the first dispensing coating on the second surface onto the same surface of the base film are greater than the longest axis R of the adhesive dots, and R <D2<2R。

[0012] In some optional embodiments, the adhesive dots of the first adhesive coating on the first surface form at least one preset pattern on the first surface; the orthographic projection of at least one adhesive dot of the first adhesive coating on the second surface onto the first surface is located at the center of the preset pattern.

[0013] In some optional embodiments, the adhesive dots of the first adhesive coating on the second surface are arranged in a one-to-one correspondence with the preset pattern.

[0014] In some optional embodiments, the preset pattern is a circular, regular polygonal, or array-like distribution structure.

[0015] In some optional embodiments, the battery separator further includes a second dispensing coating applied to the first surface and / or the second surface, and offset from the first dispensing coating on the same surface.

[0016] In some optional embodiments, the battery separator further includes a functional coating applied between the first surface and / or the second surface and the first adhesive coating. The functional coating includes at least one of the following functions: adhesion, cell closing, heat resistance, flame retardancy, enhanced ion conduction, adsorption of transition metal elements, and improvement of wettability between the base film and the electrolyte.

[0017] In some optional embodiments, the battery separator satisfies at least one of the following conditions (1)-(4):

[0018] (1) The longest axis R of the adhesive dot is in the range of 100μm-500μm;

[0019] (2) The distance D1 between two adjacent glue dots ranges from 100μm to 1000μm;

[0020] (3) The shape of the first adhesive coating includes at least one of the following: circle, ellipse, square, rhombus, cross, petal, star shape, and coffee ring;

[0021] (4) The height h of the glue dot is 1μm-10μm.

[0022] This application provides a secondary battery, including the battery separator described in any of the above claims.

[0023] The beneficial effects of this application are as follows: by utilizing the staggered adhesive coating on both sides of the base film, controlling the spacing between two adhesive dots on the same side, and reducing the increase in impedance after hot pressing and the increase in air permeability of the coated separator, the ionic conductivity and adhesion performance of the separator are improved. Simultaneously, the staggered adhesive dots help reduce the overall thickness of the separator, improving the energy density and cycle performance of the battery, and reducing the proportion of tab misalignment in the battery manufacturing process, thus lowering the battery manufacturing cost. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the battery separator structure in the first embodiment;

[0025] Figure 2 This is a schematic diagram of the battery separator structure in the second embodiment;

[0026] Figure 3 This is a schematic diagram of the battery separator structure in the third embodiment;

[0027] Figure 4 This is a schematic diagram of the battery separator structure in the fourth embodiment;

[0028] Figure 5 This is a schematic diagram of the battery separator in the fifth embodiment.

[0029] The reference numerals in the attached figures are as follows: 100, base film; 110, first side; 120, second side; 200, first dispensing coating; 300, second dispensing coating; 400, functional coating. Detailed Implementation

[0030] The present application will now be described in further detail with reference to the accompanying drawings and specific embodiments. Similar elements in different embodiments are referred to by related similar element reference numerals. In the following embodiments, many details are described to facilitate a better understanding of the present application. However, those skilled in the art will readily recognize that some features may be omitted in different situations, or may be replaced by other elements, materials, or methods. In some cases, certain operations related to the present application are not shown or described in the specification. This is to avoid obscuring the core parts of the present application with excessive description. For those skilled in the art, detailed description of these related operations is not necessary; they can fully understand the related operations based on the description in the specification and general technical knowledge in the art.

[0031] Furthermore, the features, operations, or characteristics described in the specification can be combined in any suitable manner to form various embodiments, and the operational steps involved in each embodiment can also be rearranged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the specification and drawings are only for clearly describing a particular embodiment and do not imply that they represent the necessary components and / or order.

[0032] The serial numbers assigned to components in this document, such as "first" and "second," are used only to distinguish the described objects and have no sequential or technical meaning. The terms "connection" and "linkage" used in this application, unless otherwise specified, include both direct and indirect connections (linkages).

[0033] In this application, the term "secondary battery" refers to a battery that can be recharged after discharge to reactivate its active materials and continue to be used. These batteries typically utilize the reversibility of chemical reactions; that is, once a chemical reaction converts into electrical energy, electrical energy can be used to repair the chemical system, and then the chemical reaction can be converted back into electrical energy. Common secondary batteries include, but are not limited to, nickel-metal hydride batteries, nickel-cadmium batteries, lead-acid (or lead-acid) batteries, lithium-ion batteries, polymer lithium-ion batteries, and sodium-ion batteries.

[0034] In this application, the term "battery separator" refers to a crucial component of a secondary battery. The battery separator is a thin film used during electrolysis to separate the positive and negative electrodes, preventing direct energy loss through reaction. The performance of the battery separator determines the battery's interface structure, internal resistance, and other characteristics, directly affecting its capacity, cycle life, and safety performance. A high-performance battery separator plays a vital role in improving the overall performance of the battery.

[0035] A separator typically consists of a base membrane and a coating layer applied to its surface. The base membrane, as the main component, is often a thin film with a specific microporous structure. These micropores act like precise channels, allowing lithium ions to freely move between the positive and negative electrodes while effectively preventing the direct passage of electrons, thus maintaining normal electrochemical reactions within the battery. The coating layer, on the other hand, uses different components to enhance various properties of the separator, such as improving its thermal stability and electrolyte wettability.

[0036] In this application, the term "overall coating" refers to uniformly coating a layer of slurry onto the surface of a base film to form a continuous coating on the base film surface.

[0037] In this application, the term "dot coating" refers to the process of transferring a coating pattern of regular size and shape onto the surface of a base film using a dot coating roller.

[0038] It should be noted that the coating formed during full coating increases the weight and thickness of the separator, reducing the energy density of the battery. At the same time, an excessively thick coating can hinder ion conduction and increase internal resistance. Moreover, the large interface between the coating and the base film may lead to peeling during long-term cycling, affecting battery life.

[0039] This application provides a diaphragm designed to overcome the shortcomings of full coating technology, specifically addressing the following core issues: (a) maximizing energy density retention: significantly reducing the amount of coating material used and the total coverage area; (b) optimizing ion conduction pathways: minimizing hindrance to ion migration while ensuring safety; (c) enhancing coating adhesion and flexibility: avoiding large-area continuous interfaces, reducing the risk of coating peeling, and improving the adhesion between the diaphragm and the electrode; (d) increasing electrolyte retention and wetting speed: rapidly adsorbing and storing electrolyte by utilizing the gaps between the dotted structures.

[0040] The separator in this application utilizes a dot-coating technique on different surfaces of a base membrane to form a dispensing coating. The structure of the dispensing coating has been optimized, reducing the increase in impedance after hot pressing and the increase in gas permeability of the coated separator. Because the dispensing coating has sufficient adhesion to the electrode, it improves the interface between the separator and the electrode. The dot-coating method reduces the amount of coating material used by up to 30%-50%, significantly improving the weight and volumetric energy density of the battery. Ions can rapidly migrate in the uncoated areas between the dispensing dots, reducing the battery's internal resistance. The gaps between the dispensing dots form efficient electrolyte channels and reservoirs, giving the separator excellent electrolyte wettability. The independently distributed dispensing coating avoids stress concentration, resulting in stronger adhesion, better bonding, and improved separator flexibility.

[0041] Please see Figure 1 In some embodiments, the battery separator includes a base film 100 and a first adhesive coating 200. The base film 100 has a first surface 110 and a second surface 120 disposed opposite to each other along its own thickness direction. The first adhesive coating 200 is composed of a plurality of adhesive dots. The base film 100 is a porous film, specifically a polyolefin microporous film. For example, the base film 100 can be a polyethylene (PE) base film 100, a polypropylene (PP) base film 100, or a composite base film 100 composed of polyethylene (PE) and polypropylene (PP). The first adhesive coating 200 is disposed on at least one surface of the base film 100, that is, the first adhesive coating 200 is coated on at least one of the first surface 110 and the second surface 120. The first adhesive coating 200 is mainly composed of organic polymer particles and an adhesive. The impedance increase C before and after hot pressing the battery separator with the electrode is <0.1Ω; the air permeability increase P of the base film 100 before and after coating with the first adhesive coating 200 is <15s / 100ml.

[0042] The statement "the first glue coating layer 200 is coated on at least one of the first surface 110 and the second surface 120" can be understood as that the first glue coating layer 200 is provided on the first surface 110 or the second surface 120, or the first glue coating layer 200 is provided on both the first surface 110 and the second surface 120.

[0043] Please refer to Figure 2 and Figure 3 , when the first glue coating layer 200 is coated on at least one of the first surface 110 and the second surface 200, the distance D1 between two adjacent glue dots in the first glue coating layer 200 is greater than the longest axis R of the glue dot, and R < D1 < 2R. When the first glue coating layer 200 is provided on both the first surface 110 and the second surface 120, the orthographic projections of the first glue coating layer 200 on the first surface 110 and the first glue coating layer 200 on the second surface 120 on the same surface of the base film 100 (such as the first surface 110) are staggeredly arranged. For example, the distance D1 between two adjacent glue dots in the first glue coating layer 200 on the first surface 110 is 1.1R, 1.2R, 1.3R, 1.4R, 1.5R, 1.6R, 1.7R, 1.8R or 1.9R. Similarly, the first glue coating layer 200 on the second surface 120 also satisfies this condition. As Figure 2 and 3 shown, when the first glue coating layer 200 is provided on the first surface 110 and the second surface 120, the orthographic projection of the glue coating layer 200 on the first surface 110 on the first surface 110 of the base film 100 ( Figure 2 and Figure 3 the solid line structure in) and the orthographic projection of the glue coating layer 200 on the second surface 120 on the first surface 110 of the base film 100 ( Figure 2 and Figure 3 the dotted line structure in) are staggeredly arranged, avoiding the overlap of the glue dots on the two surfaces to increase the overall thickness of the diaphragm, so as to ensure the thin design of the diaphragm, which helps to improve the volume energy density of the battery cell, and at the same time, it can also reduce the proportion of ear misalignment in the battery cell manufacturing process and reduce the manufacturing cost of the battery cell.

[0044] It should be noted that the staggered arrangement refers to the spaced arrangement of the orthographic projections of the two structures, without an overlapping area (or an intersecting area), and the edge lines do not tangent either. The orthographic projections of the first glue coating layers on the first surface and the second surface on the same surface of the base film are staggeredly arranged, which can also be understood as that the orthographic projections of all the glue dots of the two glue coating layers on the base film are staggeredly arranged.

[0045] In this application, the "long axis" refers to the longest axis of symmetry in a symmetric figure or component. For example, when the glue dot is oval, its longest diameter is the long axis; when the glue dot is a symmetric petal shape, its long axis is the axis along the longest dimension direction.

[0046] In this application, "orthographic projection" refers to the projection generated when the projection rays are perpendicular to the projection plane, and is also called orthogonal projection.

[0047] The core function of hot pressing is to compact the electrode sheet and improve the adhesion between the electrode sheet and the separator. Hot pressing the battery separator and the electrode sheet is a key step in preparing the battery cell. It is inevitable that the impedance increases and the air permeability decreases after hot pressing. However, the increase in impedance will affect the cycle performance and ion transport efficiency (or ionic conductivity) of the battery, and the decrease in air permeability will also affect the ion transport efficiency (or ionic conductivity). Exemplarily, the hot pressing temperature is 80°C ± 5, the hot pressing time is 55 s - 65 s, and the hot pressing intensity is 1 MPa - 3 MPa. For example, the hot pressing temperature is 80°C, the hot pressing time is 60 s, and the hot pressing intensity is 2 MPa. The impedance increase value C < 0.1 Ω before and after hot pressing, and the air permeability increase value P < 15 s / 100 ml of the base film 100 before and after coating the first adhesive coating 200 effectively alleviate the negative impact of the hot pressing process on the key performance of the battery.

[0048] The size consistency of the glue dots in this application is good. For example, the consistency deviation of the glue dot size (or the longest axis dimension) and height is ≤ 10%, or even ≤ 5%. Exemplarily, the longest axis of the glue dots on the separator is 380 μm - 400 μm, and the height is 1.9 μm - 2 μm.

[0049] It can be understood that under the condition of the same coating amount, the better the height consistency of the glue dots, the smaller the change in the coating thickness before and after hot pressing, that is, the more difficult it is for the glue dots to be compressed. Therefore, the gaps between particles and between the coating material and the base film are larger, the resistance to air and lithium ions is smaller, and the air permeability increase value and impedance increase value are smaller.

[0050] In some embodiments, the coverage rate of the first adhesive coating 200 on the first surface 110 is M1, 5% ≤ M1 ≤ 50%; and / or, the coverage rate of the first adhesive coating 200 on the second surface 120 is M2, 0 < M2 ≤ 50%. The coverage rate can be understood as the ratio of the area of the glue dots to the area of the base film. For example, the first adhesive coating 200 is provided on both the first surface 110 and the second surface 120. The ratio of the sum of the areas of the glue dots of the first adhesive coating 200 on the first surface 110 to the area of the base film is 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%, and that on the second surface 120 is 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%. This design enables the first adhesive coating 200 to be firmly bonded to the electrode sheet and ensures effective air-permeable pores to ensure the ionic conductivity, cycle performance and energy density of the battery.

[0051] In some embodiments, the distance D2 between adjacent glue dots in the orthographic projection of the first glue coating 200 on the first surface 110 and the first glue coating 200 on the second surface 120 on the same surface of the base film 100 (i.e., the first surface 110) is greater than the longest axis R of the glue dot, and R < D2 < 2R. It can also be understood that the distance between the orthographic projection of the glue dots on the first surface 100 on the base film 100 and the orthographic projection of the glue dots on the second surface 120 on the base film 100 is D2. D2 can be 1.1R, 1.2R, 1.3R, 1.4R, 1.5R, 1.6R, 1.7R, 1.8R or 1.9R.

[0052] In some embodiments, the glue dots of the first glue coating 200 on the first surface 110 form at least one preset pattern on the first surface 110; the orthographic projection of at least one glue dot of the first glue coating 200 on the second surface 120 on the first surface 110 is located at the center of the preset pattern. It can also be understood that the glue dots on the second surface 120 are located at the center of the geometric pattern composed of multiple glue dots on the first surface 110. That is, the distance between the orthographic projection of at least one glue dot of the first glue coating 200 on the second surface 120 on the first surface 110 and all the glue dots forming the preset pattern on the first surface 110 is the same. For example, please refer to Figure 3 , 4 glue dots on the first surface 110 form a square, and the glue dot on the second surface 120 is located at the center of the square, and the distance from the four glue dots is the same.

[0053] In some embodiments, the glue dots of the first glue coating 200 on the second surface 120 are arranged in one-to-one correspondence with the preset pattern. It can also be understood that a glue dot on the second surface 120 is provided at the center of each preset pattern formed by the glue dots on the first surface 110. Of course, in other embodiments, 2, 3 or more than 3 glue dots of the first glue coating 200 on the second surface 120 can also be correspondingly provided within a preset pattern formed by the glue dots on the first surface 110.

[0054] In some embodiments, the preset pattern is a circle, a regular polygon or an array distribution structure. The array distribution structure refers to a regular distribution form in which multiple glue dots are neatly and repeatedly arranged according to preset rules (such as row and column spacing, arrangement angle). For example, multiple glue dots form a two-dimensional rectangular array, a circular array or a honeycomb array, and a glue dot on the second surface 120 can be arranged at the center of the smallest unit of these arrays.

[0055] In some embodiments, the battery separator further includes a second dispensing coating 300, which is applied to the first surface 110 and / or the second surface 120 and is offset from the first dispensing coating 200 on the same surface. Alternatively, it can be understood that the first surface 110 and the second surface 120 both have the first dispensing coating 200, and the first surface 110 has the second dispensing coating 300; or the first surface 110 and the second surface 120 both have the first dispensing coating 200, and the second surface 120 has the second dispensing coating 300; or the first surface 110 has both the first dispensing coating 200 and the second dispensing coating 300, and the second surface 120 has the second dispensing coating 300; or the second surface 120 has both the first dispensing coating 200 and the second dispensing coating 300, and the first surface 110 has the second dispensing coating 300; or both the first surface 110 and the second surface 120 have both the first dispensing coating 200 and the second dispensing coating 300. When two adhesive coatings are applied to the same surface, the first adhesive coating 200 and the second adhesive coating 300 are staggered, and there are no intersecting or tangent areas. For example, such as... Figure 4 As shown, a first adhesive coating 200 and a second adhesive coating 300 are provided on the first surface 110, wherein the blank area is the first adhesive coating 200 and the shaded area is the second adhesive coating 300. The first adhesive coating 200 and the second adhesive coating 300 can be the same coating made of the same slurry. Of course, in some embodiments, they can also be made of different slurries. By providing the first adhesive coating 200 and the second adhesive coating 300 on the same surface, the coating coverage and area on that surface of the base film can be increased, which helps to improve the adhesion between the separator and the electrode. The first adhesive coating 200 and the second adhesive coating 300 are staggered, and the first adhesive coating 200 or the second adhesive coating 300 on the two surfaces are also staggered, which also helps to minimize the separator thickness and further effectively improve the energy density of the cell.

[0056] Please see Figure 5In some embodiments, the battery separator further includes a functional coating 400, which is applied between the first surface 110 and / or the second surface 120 and the first adhesive coating 200. The functional coating 400 includes at least one function among adhesion, cell closing, heat resistance, flame retardancy, enhanced ion conduction, adsorption of transition metal elements, and improved wettability of the base membrane and electrolyte, thereby improving the separator's adhesion, cell closing, heat resistance, flame retardancy, ionic conductivity, adsorption of metal elements, and wettability. For example, the functional coating 400 includes a cell closing function, and may also be referred to as a cell-closing coating. It includes materials capable of melting below 130°C and spreading on the surface of the base membrane 100 to form a dense layer. For example, the slurry of the functional coating 400 includes ethylene polymers such as polyethylene (PE) or ethylene-vinyl acetate copolymer (EVA), effectively improving the cell closing performance of the separator. The functional coating 400 may include heat-resistant properties. For example, the slurry of the functional coating 400 may include, but is not limited to, heat-resistant ceramics such as alumina, boehmite, silica, barium carbonate, magnesium oxide, and magnesium hydroxide, and may also include cellulose, polyimide (PI), aramid, etc., to improve the heat resistance of the separator. Alumina not only improves heat resistance but also enhances the wettability of the base film and electrolyte. The functional coating 400 may also include adhesive properties. The slurry of the functional coating 400 may include, but is not limited to, polymers such as polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), and olefin polymers, to improve adhesion to the electrode. Finally, the functional coating 400 may include flame-retardant properties. For example, the slurry of the functional coating 400 may include ammonium polyphosphate (APP) or aluminum hydroxide, to inhibit the spread of battery combustion. The functional coating 400 may include ion conduction enhancement functions. For example, the slurry of the functional coating 400 may include, but is not limited to, MOFs, solid electrolyte materials (oxides, polymers, sulfides), etc., to provide a fast channel for ion transport, reduce ion transport impedance, and improve ion conductivity. The MOF may also adsorb transition metal elements. The functional coating 400 may also include transition metal adsorption functions. For example, the slurry of the functional coating 400 may include, but is not limited to, nitrogen-containing compounds, LiOH, polyacrylic acid (PAA), or polymethyl methacrylate (PMAA), etc., to adsorb Co dissolved from the positive electrode. 3+ Ni 2+ Mn 2+ Transition metal ions are present to prevent them from depositing on the negative electrode and inducing lithium dendrite formation. The functional coating 400 may include materials that improve the wetting function of the separator and the electrolyte. For example, the slurry of the functional coating 400 may include surfactants (such as fluorocarbon surfactants (such as FC-4430)), hydrophilic polymers (such as polyvinylpyrrolidone (PVP)) and inorganic hydrophilic fillers (such as silicon dioxide (SiO2)), etc., to reduce the surface tension of the separator, allowing the electrolyte to quickly and uniformly wet the separator and reduce interfacial resistance.

[0057] In some embodiments, the longest axis R of the adhesive dot ranges from 100μm to 500μm, which can also be understood as the longest diameter of the adhesive dot in the first adhesive coating 200 and the second adhesive coating 300 being 100μm to 500μm. For example, the diameter of the adhesive dot can be 100μm, 150μm, 200μm, 250μm, 300μm, 350μm, 400μm, 450μm, or 500μm, or any two of the above values.

[0058] In some embodiments, the distance D1 between two adjacent adhesive dots ranges from 100μm to 1000μm. For example, the center-to-center distance between two adjacent adhesive dots can be 200μm, 250μm, 300μm, 350μm, 400μm, 450μm, 500μm, 600μm, 700μm, 800μm, 900μm, or 1000μm, or any two of the above values. When a second adhesive coating 300 is provided on the base film 100, the distance between its adhesive dots can also be designed within the above range, and the distance between the adhesive dots of the first adhesive coating 200 and the second adhesive coating 300 can be the same or different.

[0059] In some embodiments, the shape of the first adhesive coating 200 includes at least one of the following: circular, elliptical, square, rhomboid, cross-shaped, petal-shaped, star-shaped, and coffee-ring-shaped. The shape of the second adhesive coating 300 may be selected from at least one of the above patterns, and its specific pattern may be the same as or different from that of the first adhesive coating 200.

[0060] It should be noted that the coffee-ring adhesive dots have an overall annular raised structure, which is different from traditional solid circular adhesive dots. When observed on the membrane surface, obvious coating accumulation can be seen at the edge of each individual adhesive dot, forming a continuous or discontinuous ring. That is, the functional components of the coating are enriched in the ring area, while the central area inside the ring is basically uncoated, maintaining the original microporous structure of the membrane base.

[0061] In some embodiments, the height h of the adhesive dots in the first adhesive dot coating 200 is between 1 μm and 10 μm. For example, the height of the adhesive dots can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, or any two of the above values. When the base film 100 is provided with a second adhesive dot coating 300, the height of its adhesive dots can also be designed within the above range, and the heights of the adhesive dots in the first adhesive dot coating 200 and the second adhesive dot coating 300 can be the same or different. Through the design of the adhesive dot height, under the premise of satisfying the adhesion to the positive and negative electrodes and the feasibility of the coating process, a thinner thickness is better, which is beneficial to improving the energy density of the battery cell.

[0062] In some embodiments, the first dispensing coating 200 and the second dispensing coating 300 also satisfy the following conditions: M = dispensing adhesion force / spraying adhesion force, 10 < M < 50, N = dispensing adhesion force / topcoat adhesion force, 2 < N < 8.

[0063] The embodiments of this application also provide a method for preparing a diaphragm, characterized in that the diaphragm is the diaphragm in any of the above embodiments, and the preparation method includes:

[0064] S101: Prepare base film 100 and first adhesive coating slurry.

[0065] The first dispensing coating slurry can be a functional coating slurry, such as polyvinylidene fluoride coating slurry, polymethyl methacrylate coating slurry, polyolefin wax coating slurry, heat-resistant ceramic coating slurry, polymethyl methacrylate mixed ceramic coating slurry, etc. Alternatively, the first dispensing coating adhesive can be a slurry composed of organic matter, dispersants, binders, deionized water, thickeners, wetting agents, and functional additives. Specifically, the following ingredients are used: 10-20 parts organic powder, 0.2-0.8 parts dispersant, 6-15 parts binder, 60-80 parts deionized water, 0.5-3 parts thickener, 0.5-1.5 parts wetting agent, and 0-1 parts other functional additives, such as defoamer, which can be added selectively as needed. First, the dispersant, binder A, thickener, and water are mixed and stirred. Then, the organic powder is added and stirred and dispersed. Next, it is transferred to a sand mill for sand milling and dispersion. Then, binder B and wetting agent are added and stirred and mixed. Finally, the defoamer is added and stirred at low speed to remove bubbles to obtain the slurry.

[0066] S102: A first dispensing coating slurry is coated on at least one surface of the base film 100 to form a first dispensing coating 200, that is, the first dispensing coating 200 can be provided on one surface of the base film 100 or on both surfaces.

[0067] In some embodiments, the viscosity of the first dispensing coating slurry is controlled to be between 10 cP and 1000 cP to ensure good transfer rate and dot shape retention. For example, the viscosity of the first dispensing coating slurry is controlled to be 10 cP, 100 cP, 200 cP, 300 cP, 400 cP, 500 cP, 600 cP, 700 cP, 800 cP, 900 cP, or 1000 cP, or any two of the above values.

[0068] In some embodiments, the solid content of the first dispensing coating slurry is between 8% and 30%. For example, the solid content of the first dispensing coating slurry is 8%, 10%, 15%, 20%, 25%, or 30%, or any two of the above values.

[0069] In some embodiments, the particle size D50 of the first dispensing coating slurry is 1μm-8μm. For example, the particle size D50 of the second coating slurry is 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm or 8μm, or any two of the above values.

[0070] In some embodiments, the preparation method further includes: performing a hydrophilic modification treatment on the location of the first dispensing coating 200 to be applied on the base film 100 before applying the first dispensing coating 200, so as to further enhance the adhesion and spreading of the coating slurry at the specific location and make the shape of the dispensing coating more perfect. Specifically, the base film can be hydrophilic modified by methods such as ultraviolet light irradiation and corona treatment.

[0071] In some embodiments, the method further includes preparing a second dispensing coating slurry and coating the second dispensing coating slurry on at least one surface of the base film 100 to form a second dispensing coating 300. The adhesive dots of the second dispensing coating 300 are staggered from the adhesive dots of the first dispensing coating 200, and the orthogonal projections of the adhesive dots of the first dispensing coating 200 and the second dispensing coating 300 on different surfaces onto the base film 100 are also staggered. The second dispensing coating slurry may also be a functional coating slurry, such as a polyvinylidene fluoride coating slurry, a polymethyl methacrylate coating slurry, a polyolefin wax coating slurry, a heat-resistant ceramic coating slurry, a polymethyl methacrylate mixed ceramic coating slurry, etc. Alternatively, the first dispensing coating slurry may be a slurry composed of organic matter, a dispersant, a binder, deionized water, a thickener, a wetting agent, and functional additives, which may be the same as or different from the slurry of the first dispensing coating.

[0072] In some embodiments, the viscosity of the second dispensing coating slurry is controlled to be 10 cP-1000 cP; and / or, the slurry solid content of the second dispensing coating slurry is 8%-30%; and / or, the slurry particle size D50 of the second dispensing coating slurry is 1 μm-8 μm.

[0073] In some embodiments, a functional coating 400 is further disposed on the base film 100. The raw materials of the functional coating 400 include at least one of the following functions: adhesion, cell closing, heat resistance, flame retardancy, ion conduction enhancement, adsorption of transition metal elements, and improvement of the wettability of the base film to the electrolyte. A first dispensing coating 200 and / or a second dispensing coating 300 are disposed on the functional coating 400. The specific composition of the functional coating 400 has been described above and will not be repeated here.

[0074] This application also provides a battery, which can be a secondary battery, including a lithium-ion battery or a sodium-ion battery. The secondary battery includes the separator from any of the above embodiments, or a separator prepared by any of the above preparation methods. The separator and preparation methods have been described in detail above and will not be repeated here.

[0075] The effects of the diaphragm of this application will be described in detail below with specific embodiments. It should be noted that the embodiments of this application are only for better illustrating the solution of this application, and are not intended to limit this application. Some test or experimental methods involved in this application, unless otherwise specified, are conventional means used in testing or experimentation in the art.

[0076] Example 1

[0077] A commercially available 12μm PP base film was selected. A first adhesive coating was applied to both the first and second surfaces. The diameter R of the adhesive dots on both surfaces was 100μm, and the height of the dots was 5μm. The distance D1 between two adjacent dots on the same surface was 150μm. The coverage of the first adhesive coating on the first surface was 30%, and on the second surface, it was 5%. The orthographic projections of the adhesive dots on the first and second surfaces onto the same surface of the base film were staggered, but the dots on one surface were not centered on the preset pattern formed by the first adhesive coating on the other surface. The coating amount was 0.41g / m². 2 The breathability increase is 5s / 100ml, and the resistance increase before and after hot pressing is 0.04Ω.

[0078] Example 2

[0079] A commercially available 12μm PP base film was selected. A first adhesive coating was applied to both the first and second surfaces. The diameter R of the adhesive dots on both surfaces was 100μm, and the height of the dots was 5μm. The distance D1 between two adjacent dots on the same surface was 150μm. The coverage of the first adhesive coating on the first surface was 30%, and on the second surface, it was 5%. The orthographic projections of the adhesive dots on the first and second surfaces onto the same surface of the base film were staggered, with the center of the preset pattern formed by the adhesive dots on one surface and the first adhesive coating on the other surface. The distance D2 between two adjacent dots in the orthographic projections of the two first adhesive coatings onto the same surface of the base film was 106μm. The coating amount was 0.43g / m². 2 The breathability increase is 6s / 100ml, and the resistance increase before and after hot pressing is 0.04Ω.

[0080] Example 3

[0081] A commercially available 12μm PP base film was selected. A first adhesive coating was applied to both the first and second surfaces. The diameter R of each adhesive dot in the first adhesive coating was 100μm, and the height of each dot was 5μm. The distance D1 between two adjacent adhesive dots on the same surface was 150μm. The coverage of the first adhesive coating on the first surface was 5%, and the coverage on the second surface was 1%. The orthographic projections of the adhesive dots on the first and second surfaces onto the same surface of the base film were staggered, with the center of the preset pattern formed by the adhesive dots on one surface and the first adhesive coating on the other surface. The distance D2 between two adjacent adhesive dots in the orthographic projections of the two first adhesive coatings onto the same surface of the base film was 106μm. The coating amount was 0.36g / m². 2 The air permeability increased by 2s / 100ml, and the impedance increased by 0.02Ω before and after hot pressing.

[0082] Example 4

[0083] A commercially available 12μm PP base film was selected. A first adhesive coating was applied to both the first and second surfaces. The diameter R of each adhesive dot in the first adhesive coating was 100μm, and the height of each dot was 5μm. The distance D1 between two adjacent adhesive dots on the same surface was 150μm. The coverage of the first adhesive coating on the first surface was 30%, and the coverage on the second surface was 5%. The orthographic projections of the adhesive dots on the first and second surfaces onto the same surface of the base film were staggered, with the center of the preset pattern formed by the adhesive dots on one surface and the first adhesive coating on the other surface. The distance D2 between two adjacent adhesive dots in the orthographic projections of the two first adhesive coatings onto the same surface of the base film was 106μm. The coating amount was 0.44g / m². 2 The breathability increase is 5s / 100ml, and the resistance increase before and after hot pressing is 0.05Ω.

[0084] Example 5

[0085] A commercially available 12μm PP base film was selected. A first adhesive coating was applied to both the first and second surfaces. The diameter R of each adhesive dot in the first adhesive coating was 100μm, and the height of each dot was 5μm. The distance D1 between two adjacent adhesive dots on the same surface was 150μm. The coverage of the first adhesive coating on the first surface was 30%, and the coverage on the second surface was 5%. The orthographic projections of the adhesive dots on the first and second surfaces onto the same surface of the base film were staggered, with the center of the preset pattern formed by the adhesive dots on one surface and the first adhesive coating on the other surface. The distance D2 between two adjacent adhesive dots in the orthographic projections of the two first adhesive coatings onto the same surface of the base film was 106μm. The coating amount was 0.42g / m². 2 The breathability increase is 7s / 100ml, and the resistance increase before and after hot pressing is 0.05Ω.

[0086] Example 6

[0087] A commercially available 12μm PP base film was selected. A first adhesive coating was applied to both the first and second surfaces. The diameter R of each adhesive dot in the first adhesive coating was 100μm, and the height of each dot was 2μm. The distance D1 between two adjacent adhesive dots on the same surface was 150μm. The coverage of the first adhesive coating on the first surface was 30%, and the coverage on the second surface was 5%. The orthographic projections of the adhesive dots on the first and second surfaces onto the same surface of the base film were staggered, with the center of the preset pattern formed by the adhesive dots on one surface and the first adhesive coating on the other surface. The distance D2 between two adjacent adhesive dots in the orthographic projections of the two first adhesive coatings onto the same surface of the base film was 106μm. The coating amount was 0.38g / m². 2 The breathability increase is 5s / 100ml, and the resistance increase before and after hot pressing is 0.03Ω.

[0088] Example 7

[0089] A commercially available 12μm PP base film was selected. A first adhesive coating was applied to the first surface. The diameter R of the adhesive dots in the first coating was 100μm, the height of the dots was 5μm, and the distance D1 between adjacent dots was 150μm. The coverage of the first adhesive coating was 30%, and the coating amount was 0.35g / m². 2 The breathability increase is 3s / 100ml, and the resistance increase before and after hot pressing is 0.03Ω.

[0090] Example 8

[0091] A commercially available 12μm PP base film was selected. A first adhesive coating was applied to the first surface. The diameter R of the adhesive dots in the first coating was 300μm, the height of the dots was 5μm, and the distance D1 between adjacent dots was 500μm. The coverage of the first adhesive coating was 30%, and the coating weight was 0.37g / m². 2 The breathability increase is 4s / 100ml, and the resistance increase before and after hot pressing is 0.03Ω.

[0092] Example 9

[0093] A commercially available 12μm PP base film was selected. A first adhesive coating was applied to the first surface. The diameter R of the adhesive dots in the first coating was 500μm, the height of the dots was 5μm, and the distance D1 between two adjacent dots was 850μm. The coverage of the first adhesive coating was 30%, and the coating amount was 0.35g / m². 2 The air permeability increased by 4s / 100ml, and the impedance increased by 0.02Ω before and after hot pressing.

[0094] Example 10

[0095] A commercially available 12μm PP base film was selected. A first adhesive coating was applied to the first surface. The diameter R of the adhesive dots in the first coating was 100μm, the height of the dots was 5μm, and the distance D1 between adjacent dots was 150μm. The coverage of the first adhesive coating was 50%, and the coating weight was 0.36g / m². 2 The breathability increase is 5s / 100ml, and the resistance increase before and after hot pressing is 0.03Ω.

[0096] Comparative Example 1

[0097] The adhesive dots on the first and second surfaces completely overlap: A commercially available 12μm PP base film is used. A first adhesive coating is applied to both the first and second surfaces. The diameter R of each adhesive dot in the first adhesive coating is 100μm, and the height of each dot is 5μm. The distance D1 between two adjacent adhesive dots on the same surface is 150μm. The coverage of the first adhesive coating on the first surface is 30%, and the coverage on the second surface is 5%. The orthographic projection of the adhesive dots on the second surface onto the base film completely overlaps with the orthographic projection of the adhesive dots on the first surface onto the base film. That is, the distance D2 between two adjacent adhesive dots on the same surface of the two first adhesive coatings is 0μm. The coating amount is 0.4g / m². 2 The breathability increase is 10s / 100ml, and the impedance increase before and after hot pressing is 0.1Ω.

[0098] Comparative Example 2

[0099] The adhesive dots on the first and second surfaces are tangent and have no overlapping area: A commercially available 12μm PP base film is used. A first adhesive coating is applied to both the first and second surfaces. The diameter R of each adhesive dot in the first adhesive coating is 100μm, and the height of each dot is 5μm. The distance D1 between two adjacent adhesive dots on the same surface is 150μm. The coverage of the first adhesive coating on the first surface is 30%, and the coverage on the second surface is 5%. The orthographic projections of the adhesive dots on the first and second surfaces onto the same surface of the base film are tangent. The distance D2 between two adjacent adhesive dots of the orthographic projections of the two first adhesive coatings onto the same surface of the base film is 50μm. The coating amount is 0.44g / m². 2 The breathability increase is 7s / 100ml, and the resistance increase before and after hot pressing is 0.06Ω.

[0100] Comparative Example 3

[0101] The adhesive dots on the first and second surfaces do not overlap: A commercially available 12μm PP base film is used. A first adhesive coating is applied to both the first and second surfaces. The diameter R of the adhesive dots in the first adhesive coating is 100μm. The height of the adhesive dots on the first surface is 2μm, and the height of the adhesive dots on the second surface is 5μm. The distance D1 between two adjacent adhesive dots on the same surface is 50μm. The coverage of the first adhesive coating on the first surface is 100%, and the coverage of the first adhesive coating on the second surface is 5%. The orthographic projection of the adhesive dots on the second surface onto the base film completely overlaps with the orthographic projection of the adhesive dots on the first surface onto the base film. That is, the distance D2 between two adjacent adhesive dots on the same surface of the two first adhesive coatings is 0μm. The coating amount is 0.42g / m². 2 The breathability increase is 15s / 100ml, and the resistance increase is 0.15Ω before and after hot pressing.

[0102] Comparative Example 4

[0103] The first surface has an adhesive dot coating: a commercially available 12μm PP base film is used, and a first adhesive dot coating is applied to the first surface. The diameter R of each adhesive dot in the first adhesive dot coating is 100μm, the height is 5μm, the distance D1 between two adjacent adhesive dots is 50μm, the coverage is 100%, and the coating amount is 0.36g / m². 2 The breathability increase is 10s / 100ml, and the resistance increase before and after hot pressing is 0.12Ω.

[0104] All the separators prepared in the examples and comparative examples were hot-pressed with electrodes at a temperature of 80°C, a hot-pressing time of 60 s, and a hot-pressing strength of 2 MPa to prepare battery cell samples. The positive electrode adhesion force, ionic conductivity, DC internal resistance (DCR) value of the 280Ah energy storage cell, and the temperature rise during the heating test of the 280Ah energy storage cell were tested for all prepared battery cell samples. The specific test methods are as follows:

[0105] Positive electrode adhesion test: After hot pressing the separator and positive electrode together, the force of peeling between the two is tested using a universal testing machine.

[0106] Ionic conductivity testing: The AC impedance (EIS) of the battery cell was measured using an electrochemical workstation to obtain the Nyquist plot. The intercept of the high-frequency region of the Nyquist plot with the real axis is the ohmic impedance R. Ω According to the formula σ=L / (R) Ω The ionic conductivity is calculated using the formula ⋅S. Here, L is the electrolyte thickness (membrane thickness for liquid electrolytes; electrolyte layer thickness for solid electrolytes), and S is the effective area of ​​the electrode.

[0107] Membrane thickness testing: Measured using a Maer thickness gauge, unit is μm. Testing reference is GB / T36363-2018 "Polyolefin Separators for Lithium-ion Batteries".

[0108] 280Ah energy storage cell DC internal resistance (DCR) test: With the cell SOC at approximately 50%, the internal resistance of the cell during charging and discharging under constant current is tested using an AC internal resistance tester. The average of the charging and discharging internal resistances is then taken as the DC internal resistance (DCR).

[0109] 280Ah Energy Storage Cell Heating Test: The cell was discharged to 2.5V@0%SOC and then left to stand for a period of time. In a 25℃ incubator, the ambient temperature was kept constant, and no active cooling treatment was applied to the cell. The charge / discharge rate was set to a constant current of 0.5C@140A. Each cell underwent one full charge and full discharge test (>4h), and the change in cell surface temperature was observed to measure the temperature rise. The temperature sampling point for the cell was located at the center of the front side.

[0110] Table 1 below shows the test results of the separator and cell samples prepared in Examples 1 to 10 and Comparative Examples 1 to 4.

[0111] Table 1

[0112]

[0113]

[0114] As can be seen from the table, the design of the adhesive dot spacing and the staggered design of adhesive dots on different surfaces, as well as the optimization of impedance increase and air permeability increase before and after hot pressing, help to improve the cell adhesion and ionic conductivity performance, and also help to reduce the overall thickness of the separator, thereby improving the energy density and cycle performance of the battery.

[0115] The positions of the adhesive dots on the second surface differ between Example 1 and Example 2. In Example 2, the projection of the adhesive dots on the second surface is at the center of the projection of the adhesive dots on the first surface, which can improve the ionic conductivity (from 1.52 mS / cm to 1.56 mS / cm).

[0116] Examples 1 to 6 show a first adhesive coating on both sides of the base membrane. These examples demonstrate that reducing the adhesive dot height helps decrease the overall thickness of the separator. Simultaneously, the DC internal resistance (DCR) value and the temperature rise during the heating test of the 280Ah energy storage cell are relatively small, indicating that reducing the adhesive dot height helps improve the cell's energy efficiency, cycle life, and safety performance. Examples 4 and 5 show that reducing the increase in air permeability can improve ionic conductivity, reduce separator thickness, and effectively improve the cell's energy efficiency, cycle life, and safety performance.

[0117] A comparison of Examples 2 and 7 shows that the single-sided adhesive coating can also effectively reduce the separator thickness, thereby improving the battery's energy density and cycle performance, as well as the cell adhesion and ionic conductivity.

[0118] Comparing Examples 1 and 2 with Comparative Examples 1 and 2, and Examples 7 to 10 with Comparative Example 4, it can be seen that the staggered arrangement of adhesive dots can effectively improve ionic conductivity and enhance the energy density and cycle performance of the battery.

[0119] The above examples illustrate this application only to aid understanding and are not intended to limit its scope. Those skilled in the art to which this application pertains can make various simple deductions, modifications, or substitutions based on the ideas presented.

Claims

1. A battery separator, characterized in that, Comprising: A base film, the base film being a porous thin film; the base film has a first surface and a second surface oppositely disposed along its own thickness direction; And A first dot coating layer, the first dot coating layer mainly composed of organic polymer particles and a binder; the first dot coating layer is coated on at least one of the first surface and the second surface; Wherein, the distance D1 between two adjacent glue dots in the first dot coating layer on the same surface is greater than the longest axis R of the glue dot, and R < D1 < 2R; when the first dot coating layer is provided on both the first surface and the second surface, the first dot coating layer on the first surface and the first dot coating layer on the second surface are staggeredly arranged in the orthographic projection on the same surface of the base film; The impedance increase value C of the battery separator before and after hot pressing with the electrode sheet is < 0.1 Ω; the air permeability increase value P of the base film before and after coating the first dot coating layer is < 15 s / 100 ml.

2. The battery separator according to claim 1, characterized in that, The coverage rate of the first dot coating layer on the first surface is M1, 5% ≤ M1 ≤ 50%; and / or, the coverage rate of the first dot coating layer on the second surface is M2, 0 < M2 ≤ 50%.

3. The battery separator according to claim 1, characterized in that, The distance D2 between two adjacent glue dots in the orthographic projection on the same surface of the base film of the first dot coating layer on the first surface and the first dot coating layer on the second surface is greater than the longest axis R of the glue dot, and R < D2 < 2R.

4. The battery separator according to claim 3, characterized in that, The glue dots of the first dot coating layer on the first surface form at least one preset pattern on the first surface; the orthographic projection of at least one of the glue dots of the first dot coating layer on the second surface on the first surface is located at the center of the preset pattern.

5. The battery separator according to claim 4, characterized in that, The glue dots of the first dot coating layer on the second surface are arranged in one-to-one correspondence with the preset pattern.

6. The battery separator according to claim 4, characterized in that, The preset pattern is a circular shape, a regular polygon or an array distribution structure.

7. The battery separator according to claim 1, characterized in that, The battery separator further includes a second dot coating layer, the second dot coating layer is coated on the first surface and / or the second surface, and is staggeredly arranged with the first dot coating layer on the same surface.

8. The battery separator according to claim 1, characterized in that, The battery separator further includes a functional coating layer, the functional coating layer is coated between the first surface and / or the second surface and the first dot coating layer, and the functional coating layer includes at least one of the functions of bonding, closed pore, heat resistance, flame retardance, ion conduction enhancement type, adsorption of transition metal elements, and improvement of the wettability between the base film and the electrolyte.

9. The battery separator according to claim 1, characterized in that, The battery separator satisfies at least one of the following conditions (1)-(4): (1) The value range of the longest axis R of the glue dot is 100 μm - 500 μm; (2) The value range of the distance D1 between two adjacent glue dots is 100 μm - 1000 μm; (3) The shape of the first dot coating layer includes at least one of circular, elliptical, square, rhombus, cross-shaped, petal-shaped, star-shaped and coffee-ring-shaped; (4) The value of the height h of the glue dot is 1 μm - 10 μm.

10. A secondary battery, characterized in that, Comprising the battery separator according to any one of claims 1-9.

Images