Composite separator and preparation method therefor, and battery and electric device

Abstract

A composite separator and a preparation method therefor, and a battery and an electric device. The composite separator comprises a base membrane, wherein the base membrane has a first surface and a second surface arranged opposite each other, a non-woven fabric layer being provided on the first surface of the base membrane, the non-woven fabric layer comprising non-woven fabric material formed by polymer fibers, and the porosity of the non-woven fabric layer being at least 40%. The composite separator is used in the battery, the non-woven fabric layer being adjacent to a negative electrode sheet of the battery. The composite separator is formed by compounding the base membrane and the non-woven fabric formed by the polymer fibers, and when the composite separator is used in the battery, the non-woven fabric layer is close to the side of the negative electrode sheet; thus, on the basis of the characteristics of the non-woven fabric layer of the composite separator, the cycle stability, cycle life and safety of the battery are improved.

Description

Composite diaphragm and preparation method thereof, battery and electrical device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on January 24, 2024, with application number 202410102084.3 and invention name “Composite diaphragm and preparation method thereof, battery and electrical device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the field of battery material technology, and specifically relates to a composite diaphragm and a preparation method thereof, a battery and an electrical device. Background Art

[0003] Battery separator film (BSF), also known as battery diaphragm, is one of the core materials in batteries. Positioned between the positive and negative electrodes of a battery, the separator primarily separates the positive and negative active materials to reduce the risk of short circuits caused by contact between the electrodes. While allowing current-carrying ions to pass through, forming a charge and discharge circuit, it significantly impacts battery safety and cost.

[0004] During the charge and discharge process of secondary batteries, the negative electrode has the risk of dendrites. For example, the dendrite growth of the metal negative electrode can easily pierce the isolation membrane, thereby affecting the performance and life of the battery.

[0005] Summary of the Invention

[0006] In view of the above problems, the present application provides a composite diaphragm and its preparation method, a battery and an electrical device, aiming to solve the technical problem of how to reduce the risk of dendrite growth at the negative electrode of the battery.

[0007] In a first aspect, an embodiment of the present application provides a composite diaphragm, comprising a base membrane, the base membrane having a first surface and a second surface arranged opposite to each other, the first surface of the base membrane being provided with a non-woven fabric layer, the non-woven fabric layer comprising a non-woven fabric material formed of organic polymer fibers, the porosity of the non-woven fabric layer being at least 40%; the composite diaphragm is used in a battery, and the non-woven fabric layer is adjacent to the negative electrode plate of the battery.

[0008] A composite diaphragm is formed by combining a base film and a non-woven fabric formed by organic polymer fibers. When the composite diaphragm is used in a battery, the non-woven fabric layer is close to the side of the negative electrode. In this way, when dendrite growth occurs on the negative electrode, the non-woven fabric based on organic polymer fibers has a three-dimensional network fiber structure, which can provide a certain pre-growth space for the dendrite growth on the negative electrode. At the same time, the three-dimensional network fiber structure of the non-woven fabric can disperse the growth stress of the metal deposition of the negative electrode in all directions, thereby changing the vertical growth state of the dendrite from the surface of the negative electrode, that is, by controlling the metal deposition behavior, a uniform and dense deposition layer is formed on the surface of the negative electrode, thereby significantly reducing the risk of the composite diaphragm being pierced by the continuous growth of dendrites. In addition, the non-woven fabric material of organic polymer fibers itself is not only stable and not prone to thermal runaway, but also has good air permeability and large pores, which are conducive to electrolyte infiltration and promote ion transmission. Therefore, the composite diaphragm of the embodiment of the present application is used in the battery to improve the cycle stability, cycle life and safety of the battery.

[0009] In some embodiments, the porosity of the non-woven fabric layer is 47% to 70%.

[0010] The non-woven fabric layer with a porosity of 47% to 70% can provide sufficient pre-growth space for dendrite growth, and at the same time can reduce the potential barrier for ions to pass through the non-woven fabric, thereby promoting ion transmission.

[0011] In some embodiments, the thickness of the non-woven fabric layer is 10 μm to 35 μm; and / or,

[0012] The base film has a thickness of 5 μm to 20 μm.

[0013] By selecting the thickness of the non-woven fabric layer and the base film, the composite diaphragm formed by the non-woven fabric layer and the base film can have good mechanical properties and reduce the risk of dendrite growth at the negative electrode of the battery.

[0014] In some embodiments, the organic polymer fiber includes at least one of viscose fiber, acetate fiber, polyester fiber, polypropylene fiber, and polyimide fiber; and / or,

[0015] The material of the base film includes polyolefin.

[0016] The composite diaphragm formed by the combination of the above-mentioned organic polymer fibers and polyolefins is used in batteries, and the non-woven fabric layer close to the negative electrode plate can improve the cycle stability, cycle life and safety of the battery.

[0017] In some embodiments, a first coating is provided between the first surface of the base film and the non-woven fabric layer and / or a second coating is provided on the second surface of the base film, and the first coating and the second coating independently include at least one of organic nanomaterials, inorganic nanomaterials and organic-inorganic composite nanomaterials.

[0018] Applying a coating containing nanomaterials on one or both sides of the base membrane can enhance the overall mechanical strength of the composite membrane, thereby reducing the risk of dendrite growth piercing the composite membrane based on the increase in the mechanical properties of the composite membrane, while improving the electrolyte wettability. Furthermore, in particular, the first coating between the base membrane and the non-woven fabric layer can also increase the stability of the bond between the base membrane and the non-woven fabric layer. At the same time, the nanomaterial structure of the first coating can play a secondary protective role for dendrites. The combination with the non-woven fabric layer can further change the deposition morphology of the dendrites, allowing the metal to be evenly deposited at the interface, further significantly reducing the risk of internal short circuits in the battery.

[0019] In some embodiments, the materials of the first coating layer and the second coating layer include one or more of the following (1) to (3):

[0020] (1) The organic nanomaterial includes at least one of an aromatic ring polymer, an aromatic heterocyclic polymer, an aramid fiber, and a polyurethane fiber;

[0021] (2) the inorganic nanomaterial comprises at least one of tin dioxide nanoparticles, silicon dioxide nanoparticles and silver nanoparticles;

[0022] (3) The organic-inorganic composite nanomaterial includes at least one of a silicon-polyacrylic acid composite material, a silicon-polyacrylonitrile composite material, a tin-polyacrylic acid composite material, and a tin-polyacrylonitrile composite material.

[0023] On the basis that the first coating and the second coating enhance the mechanical strength of the composite membrane and reduce the risk of dendrite growth piercing the composite membrane, the coating can be further modified to better modify the base membrane by further selecting the types of organic nanomaterials, inorganic nanomaterials and organic-inorganic composite nanomaterials in the coating.

[0024] In some embodiments, the first surface of the base film is provided with the first coating layer, the second surface of the base film is provided with the second coating layer, and the first coating layer includes the organic nanomaterial, and the second coating layer includes the inorganic nanomaterial.

[0025] A first coating containing an organic nanomaterial is applied to the first surface of the base membrane, near the non-woven fabric layer, and a second coating containing an inorganic nanomaterial is applied to the second surface of the base membrane, away from the non-woven fabric layer. This allows the non-woven fabric layer to be more stably bonded to the base membrane due to the good adhesion of the organic nanomaterial, making it less likely to fall off. Furthermore, the inorganic nanomaterial's excellent hardness and wear resistance improve the mechanical strength of the composite membrane. Therefore, the combination of the first and second coatings provides the composite membrane with both stable resistance to dendrite penetration and the risk of dendrite penetration.

[0026] In some embodiments, the pore size of the first coating is 0.2 to 2 μm; and / or

[0027] The pore size of the second coating layer is 0.2-2 μm.

[0028] By selecting the pore sizes of the first coating and the second coating, the composite membrane can have good electrolyte wettability and improve the ion transmission efficiency.

[0029] In some embodiments, the porosity of the base film, the first coating layer, and the second coating layer as a whole is 28% to 46%; and / or,

[0030] The thickness of the base film, the first coating layer and the second coating layer as a whole is 7 μm to 25 μm.

[0031] The coating is combined with the surface of the base membrane to form a whole. By regulating the porosity and thickness of the base membrane and the coating as a whole, the composite membrane has good mechanical properties and is conducive to ion transmission.

[0032] In some embodiments, the composite membrane has one or more of the following (1) to (5):

[0033] (1) The porosity of the composite diaphragm is 38% to 55%;

[0034] (2) The Young's modulus of the composite diaphragm in the longitudinal direction is 8 MPa to 15 MPa;

[0035] (3) The Young's modulus of the composite diaphragm in the width direction is 6 MPa to 15 MPa;

[0036] (4) The thickness of the composite diaphragm is 15 μm to 55 μm;

[0037] (5) The air permeability of the composite membrane is 260s / 100cc to 390s / 100cc.

[0038] By selecting the overall porosity, Young's modulus, permeability and thickness of the composite diaphragm, the composite diaphragm can be used in batteries to better improve the cycle stability, cycle life and safety of the battery.

[0039] In a second aspect, an embodiment of the present application provides a method for preparing the above-mentioned composite diaphragm, comprising the following steps:

[0040] The first surface of the base film is laminated with the non-woven fabric layer to obtain the composite diaphragm.

[0041] This application creates a composite separator by laminating a base film and a non-woven fabric. This process is simple, and the resulting composite separator exhibits excellent stability and facilitates ion transport. When used in a battery, placing the non-woven fabric layer close to the negative electrode sheet significantly reduces the risk of dendrites from the negative electrode sheet piercing the composite separator. Therefore, the composite separator produced in this manner can improve the battery's cycle stability, cycle life, and safety.

[0042] In some embodiments, before laminating the first surface of the base film to the non-woven fabric layer, the method further comprises: coating the first surface of the base film with a first slurry containing at least one of an organic nanomaterial, an inorganic nanomaterial, and an organic-inorganic composite nanomaterial to obtain a first coating; and / or

[0043] Before or after laminating the first surface of the base film to the non-woven fabric layer, the method further includes: coating the second surface of the base film with a second slurry containing at least one of organic nanomaterials, inorganic nanomaterials and organic-inorganic composite nanomaterials to obtain a second coating.

[0044] By preparing a coating on at least one surface of the base membrane, the mechanical strength of the composite membrane can be enhanced and the risk of dendrite growth piercing the composite membrane can be further reduced.

[0045] In a third aspect, an embodiment of the present application provides a battery comprising a positive electrode sheet, a negative electrode sheet and an isolation membrane disposed between the positive electrode sheet and the negative electrode sheet, wherein the isolation membrane comprises the composite membrane provided in the first aspect of the embodiment of the present application and / or the composite membrane prepared by the preparation method provided in the second aspect of the embodiment of the present application, and the non-woven fabric layer in the composite membrane is located between the base membrane and the negative electrode sheet.

[0046] By using the composite membrane provided by the first aspect of the embodiment of the present application and / or the composite membrane prepared by the preparation method provided by the second aspect of the embodiment of the present application in a battery, the battery can have good cycle stability, cycle life and safety based on the good stability of the composite membrane, the ion transport being facilitated, and the significant reduction in the risk of the composite membrane being pierced by the continuous growth of dendrites of the negative electrode sheet.

[0047] In some embodiments, the battery is a metal battery.

[0048] In metal batteries, no embedded negative electrode active material is added to the negative electrode plate, and metal deposition occurs on the negative electrode current collector. Due to the high reactivity of the metal, uneven deposition is likely to occur, resulting in excessive local current density and promoting dendrite growth. However, the composite diaphragm based on the embodiment of the present application can effectively prevent the risk of piercing the dendrites growing on the surface of the negative electrode plate of the metal battery. Therefore, such a battery has the characteristics of high energy density, good cycle performance and long service life.

[0049] In some embodiments, the battery includes at least two electrode assemblies, and no buffer pad is provided between adjacent electrode assemblies.

[0050] During the initial stages of battery charge and discharge, metal deposition can easily cause compression of the electrode assemblies. Therefore, compressible cushioning pads are typically required to prevent compression of adjacent electrode assemblies and internal short circuits. However, the present embodiment incorporates a non-woven fabric into the composite separator, providing a certain degree of stress buffering. This eliminates the need for cushioning pads while maintaining excellent safety performance, further reducing battery costs.

[0051] In a fourth aspect, an embodiment of the present application provides an electrical device, comprising the battery provided in the third aspect of the present application.

[0052] By adopting the battery provided in the third aspect of the embodiment of the present application, such an electrical device has good cycle performance and service life and can work for a longer time.

[0053] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0055] FIG1 is a schematic structural diagram of a composite diaphragm according to an embodiment of the present application;

[0056] FIG2 is a schematic structural diagram of a composite diaphragm according to another embodiment of the present application;

[0057] FIG3 is a schematic structural diagram of a composite diaphragm according to another embodiment of the present application;

[0058] FIG4 is a schematic structural diagram of a composite diaphragm according to another embodiment of the present application;

[0059] FIG5 is a SEM image of a composite diaphragm prepared in one embodiment of the present application;

[0060] FIG6 is a schematic structural diagram of an embodiment of a secondary battery according to an embodiment of the present application;

[0061] FIG7 is an exploded schematic diagram of the secondary battery shown in FIG6 ;

[0062] FIG8 is a schematic structural diagram of an embodiment of a battery module according to the present application;

[0063] FIG9 is a schematic structural diagram of an embodiment of a battery pack according to the present application;

[0064] FIG10 is a schematic diagram of the exploded structure of the battery pack shown in FIG9 ;

[0065] FIG11 is a schematic diagram of an embodiment of an electrical device including a battery according to an embodiment of the present application as a power source.

[0066] Explanation of reference numerals: 11 - base film; 12 - non-woven fabric layer; 13 - first coating layer; 14 - second coating layer; 20 - battery cell; 21 - housing; 22 - top cover assembly; 23 - electrode assembly; 30 - battery module; 40 - battery pack; 41 - upper case; 42 - lower case. DETAILED DESCRIPTION

[0067] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0068] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0069] In the description of the embodiments of this application, the technical terms "first," "second," etc. are used only to distinguish different objects and should not be understood to indicate or imply relative importance or to implicitly indicate the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise specifically defined.

[0070] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0071] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0072] In the description of the embodiments of this application, the term "plurality" refers to two or more (including two). Similarly, "multiple groups" refers to two or more (including two groups), and "multiple sheets" refers to two or more (including two sheets). "At least one" refers to more than one (including one, two, three, etc.).

[0073] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they should not be understood as limiting the embodiments of the present application.

[0074] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0075] In the era of energy conservation and emission reduction, new energy technologies are developing rapidly, with battery research and application being the most significant. Separator membranes are one of the core materials in batteries. Located between the positive and negative electrodes of a battery, separator membranes primarily separate the positive and negative active materials to reduce the risk of short circuits caused by contact between the electrodes. While allowing current-carrying ions to pass through, forming a charge and discharge circuit, they significantly impact battery safety and cost.

[0076] A rechargeable battery, also known as a rechargeable battery, is a battery that can be recharged after discharge to activate the active material and continue to be used. During the charging and discharging process of a secondary battery, the negative electrode is at risk of dendrite formation. For example, in a metal battery (also known as a metal battery without embedded negative electrode active material), metal deposition occurs on the negative electrode. Due to the high reactivity of the metal, uneven deposition is likely to occur, resulting in excessive local current density. This "tip effect" promotes dendrite growth. If dendrite growth is allowed to continue, the dendrite will eventually pierce the diaphragm, causing a short circuit and battery failure. Therefore, an improved dendrite growth state is needed to reduce or even eliminate the risks posed by dendrite growth.

[0077] The diaphragm base film materials commonly used in batteries on the market currently have a single structure. For example, commonly used polymer substrates such as polyolefin base films such as polyethylene (PE) and polypropylene (PP) are affected by the synthesis process, and the structure presents a single transverse or longitudinal stretching. Such base films are prone to short circuits when used in metal batteries, so they generally need to be coated and modified on the surface. Although non-woven fabrics have a three-dimensional network structure, due to the large porosity of non-woven fabrics, single organic non-woven fabric materials cannot effectively avoid dendrite penetration as diaphragms, so they are difficult to use alone in metal batteries and generally need to be modified with inorganic fillers. Since single diaphragm base film materials are prone to short circuits in batteries, single organic non-woven fabric materials are also prone to short circuits, and the material processes of the two are different, and they are generally modified through coatings. Therefore, it is difficult for people to think of combining base film materials and organic non-woven fabric materials into composite diaphragms.

[0078] Currently, membrane modification is carried out through coating modification. For example, a modified coating is applied to the surface of the above-mentioned commonly used membrane base membrane or the commonly used non-woven fabric to form a composite membrane. Although the mechanical properties of the composite membrane can be enhanced, the ability to change or control the growth state of the dendrite is limited. Moreover, the modified coating is generally thicker, which reduces the energy density of the battery.

[0079] Based on the above considerations, and to reduce the risk of dendrite growth, the present invention proposes a composite separator, which is formed by laminating a conventional base film and an organic non-woven fabric. During use, the non-woven fabric layer of the composite separator is positioned adjacent to the negative electrode of the battery. This allows the composite separator to significantly reduce the risk of continued dendrite growth when dendrites form on the negative electrode. This is achieved by combining the non-woven fabric with the base film, based on its physical and chemical properties. The following technical solution is proposed.

[0080] Composite diaphragm and preparation method thereof

[0081] In a first aspect, embodiments of the present application provide a composite separator. As a summary of some embodiments of the present application, as shown in Figures 1-4 , the composite separator includes a base film 11 and a non-woven fabric layer 12: the base film 11 has a first surface and a second surface disposed opposite each other, and the non-woven fabric layer 12 is disposed on the first surface of the base film 11 and bonded to the base film 11. When the composite separator of the embodiments of the present application is used in a battery, the non-woven fabric layer 12 on the first surface of the base film 11 is adjacent to the negative electrode plate.

[0082] The base film 11 is a base film made of a separator substrate, which is a porous film formed of a polymer substrate. The base film made of a polymer substrate with a porous structure can meet the mechanical properties required by the battery separator and allow ions to pass through.

[0083] The non-woven fabric layer 12 is a non-woven fabric material formed of organic polymer fibers. Non-woven fabric is also called non-woven fabric or needle-punched cotton and is generally made by a needle-punching process. On the one hand, the non-woven fabric has a three-dimensional network fiber structure, has large pores, is relatively air-permeable, and has good wettability to the electrolyte. When combined with the base membrane 11, it will not affect the ion transmission efficiency between the positive and negative electrodes of the battery; on the other hand, the non-woven fabric has good thermal stability and mechanical stability, and is not prone to high-temperature failure. At the same time, the porosity of the non-woven fabric layer 12 is at least 40%. The non-woven fabric can provide space for metal deposition during initial charging and change the growth direction of dendrites through steric hindrance, thereby reducing the risk of dendrite growth on the negative electrode.

[0084] Based on this, the embodiment of the present application forms a composite separator by combining a base film 11 and a non-woven fabric layer 12 of organic polymer fibers. When used in a battery, the non-woven fabric layer 12 is positioned close to the negative electrode of the battery. When dendrites grow on the negative electrode, the non-woven fabric layer 12, with a certain porosity, has a three-dimensional network fiber structure, providing a "pre-growth" space for the dendrites. After the negative electrode nucleates and deposits on the electrode, it gradually grows away from the electrode base into the three-dimensional network framework of the non-woven fabric. The initial growth stress of the metal is large, and the non-woven fabric provides a "pre-growth" space for the metal. At the same time, the base film of the composite separator has certain mechanical properties, so that the composite separator allows dendrites to grow while avoiding the risk of dendrite tips piercing the separator due to continued growth. In addition, the mesh pores of the non-woven fabric change the vertical growth state of the dendrites. By controlling the metal deposition behavior, the growth stress is dispersed in all directions, shaping the deposition morphology, and finally forming a block-shaped, uniform, and dense deposition layer. At the same time, the good stability of the organic non-woven fabric material itself is conducive to the infiltration and ion transport of the electrolyte. Therefore, the composite diaphragm of the embodiment of the present application is used in a battery to improve the cycle stability, cycle life and safety of the battery.

[0085] In some embodiments, the porosity of the non-woven fabric layer 12 is 47% to 70%. For example, it can be 48%, 50%, 55%, 58%, 60%, 62%, 67%, 68%, 70%, etc. Porosity refers to the percentage of the pore volume in a porous material to the total volume of the material in its natural state. The ratio of the total volume of interconnected micro-voids in a porous material to the surface volume of the porous material is called effective porosity. The ratio of the total volume of all interconnected and non-interconnected micro-voids in a porous material to the surface volume of the porous medium is called absolute porosity or total porosity. In the embodiments of the present application, it may refer to effective porosity. The test of porosity can refer to the national standard "GB / T 24586-2009". If the porosity of the non-woven fabric layer 12 is too low, the barrier to ions passing through the fabric will increase, making ion transport more difficult. Excessive porosity will reduce the "anchoring" effect of the non-woven fabric layer 12's network structure on the deposited metal, making it difficult to provide sufficient space for metal "pre-growth." A non-woven fabric layer 12 with a porosity of 40% to 70% can provide sufficient pre-growth space for dendrite growth on the negative electrode sheet, while also further reducing the barrier to ions passing through the fabric, thereby promoting ion transport. Specifically, the porosity of the non-woven fabric layer 12 can be 48% to 56%.

[0086] In some embodiments, the thickness of the non-woven fabric layer 12 is 10 μm to 35 μm. For example, it can be 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 15 μm, 28 μm, 30 μm, 32 μm, 35 μm, etc. If the thickness of the non-woven fabric layer 12 is too large, it will increase the potential barrier for ions to pass through the non-woven fabric, thereby increasing the difficulty of ion transmission. If the thickness is too small, the network structure of the non-woven fabric layer 12 will reduce the "anchoring" effect of the deposited metal, making it difficult to provide sufficient metal "pre-growth" space. A non-woven fabric layer 12 with a thickness of 10 μm to 35 μm can provide sufficient pre-growth space for dendrite growth on the negative electrode sheet, and at the same time can better reduce the potential barrier for ions to pass through the non-woven fabric, thereby promoting ion transmission. Specifically, the thickness of the non-woven fabric layer 12 can be 15 μm to 18 μm.

[0087] In some embodiments, the air permeability of the non-woven fabric layer 12 is 5s / 100cc to 16s / 100cc. For example, it can be 5s / 100cc, 8s / 100cc, 10s / 100cc, 12s / 100cc, 14s / 100cc, 16s / 100cc, etc. Air permeability refers to the degree to which an object or medium allows gas to pass through under certain conditions. The air permeability in the embodiments of the present application is determined in accordance with the international standard "GB / T 458-2008". A non-woven fabric layer 12 that meets the above air permeability can effectively reduce the risk of the composite diaphragm being pierced by the continued growth of dendrites in the non-woven fabric layer 12 in the embodiments of the present application. Specifically, the air permeability of the non-woven fabric layer 12 can be 6s / 100cc to 10s / 100cc.

[0088] In some embodiments, the non-woven fabric material of the non-woven fabric layer 12 is an organic polymer fiber, including at least one of viscose fiber, acetate fiber, polyester fiber, polypropylene fiber, and polyimide fiber. The above non-woven fabric materials can well form the non-woven fabric layer 12 required by the embodiments of the present application. Specifically, the non-woven fabric material of the non-woven fabric layer 12 includes polyester fiber. Polyester fiber not only has excellent mechanical properties, thermal stability, and electrical insulation, and promotes efficient and stable ion migration, but also the R-COO-R groups in the polyester fiber have higher compatibility with the electrolyte, further improving the liquid retention capacity. For example, the polyester fiber can be polyethylene terephthalate.

[0089] In some embodiments, the non-woven fabric layer 12 is made of polyester fiber, and has a porosity of 48-56%, an air permeability of 6s / 100cc-10s / 100cc, and a thickness of 15μm-18μm. Under these conditions, the composite membrane formed has better overall effects.

[0090] In some embodiments, the surface of the base membrane 11 is provided with a coating containing nanomaterials. Specifically, as shown in FIG2 , the first surface of the base membrane 11 close to the non-woven fabric layer 12 is provided with a first coating 13. Alternatively, as shown in FIG3 , the second surface of the base membrane 11 away from the non-woven fabric layer 12 is provided with a second coating 14. Alternatively, as shown in FIG4 , the first surface of the base membrane 11 close to the non-woven fabric layer 12 is provided with a first coating 13, and the second surface of the base membrane 11 away from the non-woven fabric layer 12 is provided with a second coating 14. By applying a coating containing nanomaterials on one or both sides of the base membrane 11, the overall mechanical strength of the composite diaphragm can be enhanced, thereby increasing the mechanical properties of the composite diaphragm and further reducing the risk that dendrite growth may pierce the composite diaphragm. At the same time, the first coating 13 and the second coating 14 are coatings containing nanomaterials and have a certain porosity, which is conducive to improving the wettability of the electrolyte.

[0091] The first coating layer 13 includes at least one of an organic nanomaterial, an inorganic nanomaterial, and an organic-inorganic composite nanomaterial, and the second coating layer 14 includes at least one of an organic nanomaterial, an inorganic nanomaterial, and an organic-inorganic composite nanomaterial. By selecting the types of organic nanomaterial, inorganic nanomaterial, and organic-inorganic composite nanomaterial in the coating layer, the coating layer can better modify the base film 11.

[0092] Taking the first coating 13 as an example, the first coating 13 between the base film 11 and the non-woven fabric layer 12 can increase the stability of the bonding between the base film 11 and the non-woven fabric layer 12. At the same time, the nanomaterial structure of the first coating 13 can play a secondary protective role on dendrites. The combination with the non-woven fabric layer 12 can further change the deposition morphology of dendrites, which is beneficial for the first coating 13 to construct a suitable SEI layer to inhibit dendrite growth or eliminate dendrites, form a uniform deposition interface, further prevent dendrites from piercing the composite diaphragm, and significantly reduce the risk of internal short circuit in the battery.

[0093] In some embodiments, the organic nanomaterial includes at least one of an aromatic ring polymer, an aromatic heterocyclic polymer, an aramid fiber, and a polyurethane fiber. For example, the aromatic ring polymer may include at least one of polyethylene terephthalate or polybutylene terephthalate. The aromatic heterocyclic polymer may include at least one of polyaniline, polyimide, polybiphenyltetracarboximide, or biphenyltetracarboxylic dianhydride. The aramid fiber may include at least one of polyphenylene sulfide fiber, polyphenylene ether ketone fiber, or polyterephthalamide fiber. The polyurethane fiber may include polyurethane. Specifically, the organic nanomaterial includes aramid fiber, which has good heat resistance and viscosity, improves the stability and strength of the composite diaphragm, enhances the liquid absorption capacity of the composite diaphragm, and improves the wettability and conductivity. The combination of the nanostructured pores and the non-woven fabric layer 12 can better provide secondary protection for dendrites and improve the "shuttle effect" of metals.

[0094] In some embodiments, the inorganic nanomaterial includes at least one of tin dioxide nanoparticles, silicon dioxide nanoparticles, and silver nanoparticles. Specifically, the inorganic nanomaterial includes silicon dioxide nanoparticles; silicon dioxide not only has good thermal stability, but also can increase the wettability and liquid retention of the diaphragm. At the same time, it forms a surface structure interconnected with the base film 11, which can make the base film 11 and the coating more stable, thereby better improving the overall mechanical properties of the composite diaphragm. In addition, the inorganic nanomaterial can react with metals to form alloys, such as reacting with Na metal to form Na x Sn y / Na x Si y , which can effectively distribute the ion flux, enhance the electrolyte wettability, and make the sodium ions evenly distributed and nucleated.

[0095] In some embodiments, the organic-inorganic composite nanomaterial includes at least one of a silicon-polyacrylic acid (Si-PAA) composite material, a silicon-polyacrylonitrile (Si-PAN) composite material, a tin-polyacrylic acid (Sn-PAA) composite material, and a tin-polyacrylonitrile (Sn-PAN) composite material. The above-mentioned organic-inorganic composite nanomaterials can also react with metals to form ion conductors, such as reacting with Na metal to form Na x Sn y / Na x Si y and NaPAA / NaPAN ion conductors, which effectively distribute ion flux, enhance electrolyte wettability, and homogenize sodium ion distribution and nucleation. Specifically, organic-inorganic composite nanomaterials include tin-polyacrylonitrile composites. Sn and Na metals are highly reactive, while PAN can further enhance electrolyte wettability.

[0096] The materials and related parameters of the first coating layer 13 and the second coating layer 14 may be the same or different.

[0097] In some embodiments, a first coating 13 is provided on the first surface of the base film 11 near the non-woven fabric layer 12, and a second coating 14 is provided on the second surface of the base film 11 away from the non-woven fabric layer 12. The first coating 13 includes the above-mentioned organic nanomaterial, and the second coating 14 includes the above-mentioned inorganic nanomaterial or organic-inorganic composite nanomaterial. On the one hand, based on the good viscosity of the organic nanomaterial in the first coating 13, the non-woven fabric layer 12 can be more stably bonded to the base film 11 and not easily fall off. In addition, the strength and nanopore size of the cross-linked structure of the organic nanomaterial can block the growth of dendrites, making it easier to change the original vertical growth of dendrites to horizontal growth. On the other hand, based on the good hardness and wear resistance of the inorganic nanomaterial in the second coating 14, the mechanical strength of the composite diaphragm can be improved. At the same time, the inorganic nanomaterial or organic-inorganic composite nanomaterial reacts with metals such as sodium or potassium to play the role of "consuming sodium" and "consuming potassium", effectively distributing ion flux. Therefore, through the combination of the above-mentioned first coating 13 and second coating 14, the composite diaphragm has both stable anti-dendritic puncture risk capabilities.

[0098] In some embodiments, the pore size of the first coating 13 is 0.2 to 2 μm. In another embodiment, the pore size of the second coating 14 is 0.2 to 2 μm. The pore size of a coating refers to the size of the pores formed between the fibers or particles of the material in the coating, which may also be called pore throats. For example, the pore size of the first coating 13 may be 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.8 μm, or 2.0 μm; the pore size of the second coating 14 may be 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.8 μm, or 2.0 μm.

[0099] The first coating 13 and the second coating 14 are nanomaterial coatings. After the nanomaterial forms the coating, the surface contains pores, also known as pore throats. By selecting the pore size of the first coating 13 and the second coating 14, the composite membrane can have excellent electrolyte wettability and improve ion transmission efficiency. Specifically, the pore size of the first coating is 0.2-1 μm, and the pore size of the second coating is 0.2-1 μm.

[0100] In some embodiments, the material of base film 11 includes polyolefins, such as one or more of PE, PP, and PP / PE / PP multilayer microporous separators. The thickness of base film 11 can be 5 to 20 μm. The thickness of first coating layer 13 and second coating layer 14 can each be 1 to 2 μm, and the combined thickness of base film 11, first coating layer 13, and second coating layer 14 can be 7 to 25 μm, for example, 7 to 16 μm.

[0101] In some embodiments, the porosity of the base membrane 11, the first coating 13, and the second coating 14 as a whole is 28% to 46%. When only one surface of the base membrane is coated, the overall porosity of the base membrane and the coating is 28% to 46%. When both surfaces of the base membrane are coated, the overall porosity of the base membrane and the coatings on the two opposing surfaces is 28% to 46%. For example, the porosity can be 28%, 30%, 34%, 38%, 40%, 42%, 45%, etc. The base membrane 11 modified under these conditions has excellent mechanical properties and is also conducive to ion transport.

[0102] In some embodiments, the base film 11, the first coating layer 13, and the second coating layer 14 are integrally formed, and the air permeability is 245s / 100cc to 270s / 100cc. For example, the air permeability may be 245s / 100cc, 8s / 100cc, 250s / 100cc, 257s / 100cc, 260s / 100cc, 265s / 100cc, 270s / 100cc, etc. The base film 11 modified under these conditions meets the requirements of the composite separator in the battery.

[0103] In some embodiments, the base membrane 11, first coating 13, and second coating 14 have a porosity of 35% to 40%, an air permeability of 255s / 100cc to 260s / 100cc, and a thickness of 15μm to 16μm. The coatings are bonded to the surface of the base membrane 11 to form a single unit. By regulating the porosity, air permeability, and thickness of the base membrane 11 and the coatings, the composite membrane formed by the non-woven fabric combined with the base membrane 11 has excellent mechanical properties and facilitates ion transport.

[0104] In some embodiments, the porosity of the base film 11, first coating layer 13, and second coating layer 14 as a whole is less than the porosity of the non-woven fabric layer 12. For example, the porosity of the base film 11, first coating layer 13, and second coating layer 14 as a whole is 32% to 46%, while the porosity of the non-woven fabric layer 12 is 48% to 56%. The non-woven fabric layer 12 has a higher porosity near the negative electrode of the battery, providing more space for the initial bulk metal. The base film near the positive electrode of the battery has a lower porosity, which can regulate the state and direction of the tip dendrite growth. Because the tip dendrite is softer, the dense network structure more easily disperses the stress of the vertical growth of the dendrite, thereby causing the dendrite to grow horizontally.

[0105] The embodiments of the present application can improve the growth state of metal battery dendrites, reduce the risk of battery short circuit caused by dendrite tips, and achieve excellent cycle stability, cycle life and safety by regulating the material type, porosity and thickness of the non-woven fabric layer 12 and the coating (including the first coating 13 and / or the second coating 14).

[0106] In some embodiments, the porosity of the composite membrane is 38% to 55%, and can be 38%, 40%, 42%, 45%, 48%, 50%, 55%, etc. Composite membranes with the above porosity can greatly facilitate ion transport.

[0107] In some embodiments, the Young's modulus of the composite membrane in the length direction is 8MPa to 15MPa, for example, 8MPa, 10MPa, 12MPa, 15MPa, etc.; the Young's modulus of the composite membrane in the width direction is 6MPa to 15MP, for example, 6MPa, 8MPa, 10MPa, 12MPa, 15MPa, etc. Young's modulus is a physical quantity that describes the ability of a solid material to resist deformation. Young's modulus, also known as tensile modulus, is the most common type of elastic modulus or modulus of elasticity. The Young's modulus test method of the composite membrane of the embodiment of the present application refers to the national standard "GB / T7757-2009". The composite membrane formed by the above-mentioned Young's modulus parameters reflects that it has good mechanical properties and can be well used in batteries.

[0108] In some embodiments, the thickness of the composite separator is 15 μm to 55 μm, for example, 15 μm, 18 μm, 20 μm, 22 μm, 24 μm, 25 μm, 28 μm, 30 μm, 32 μm, 34 μm, 35 μm, 38 μm, 40 μm, 42 μm, 45 μm, 48 μm, 50 μm, 52 μm, 55 μm, etc. The composite separator having the above total thickness is formed by the thickness of the base film 11 (or the combined coating, such as the first coating 13 and / or the second coating 14) and the non-woven fabric layer 12, which has little effect on the energy density of the battery and can significantly reduce the risk of continued dendrite growth of the negative electrode sheet.

[0109] In some embodiments, the composite membrane has a porosity of 40% to 45%, a Young's modulus in the longitudinal direction of 9.5 MPa to 14 MPa, a Young's modulus in the width direction of 7.5 MPa to 14 MPa, and a total thickness of 25 μm to 34 μm. Specifically, the composite membrane can have a total air permeability of 260 s / 100 cc to 390 s / 100 cc.

[0110] In some embodiments, based on the needs of the battery, on the basis of providing a non-woven fabric layer on the first surface of the base membrane, the same or different non-woven fabric layer can also be provided on the second surface of the base membrane, and the specific material, thickness and porosity of the non-woven fabric layer on the second surface can be selected with reference to the non-woven fabric layer on the first surface. When there is no second coating on the second surface, the non-woven fabric layer is directly added to the second surface of the base membrane. When the second surface of the base membrane is provided with a second coating, a non-woven fabric layer is added on the second coating. The situation in which a non-woven fabric layer is provided on the second surface of the base membrane is also within the scope of protection of the technical solution of this application.

[0111] In a second aspect, an embodiment of the present application provides a method for preparing the above-mentioned composite diaphragm, comprising the following steps:

[0112] The first surface of the base film 11 is laminated to the non-woven fabric layer 12 to obtain a composite diaphragm.

[0113] In the present embodiment, a composite separator is obtained by laminating a base film 11 and a non-woven fabric layer 12. This process is simple, and the resulting composite separator exhibits excellent stability and facilitates ion transport. When used in a battery, the non-woven fabric layer is placed close to the negative electrode tab, significantly reducing the risk of dendrites from the negative electrode tab continuing to grow and piercing the composite separator. Therefore, the composite separator prepared in this manner can improve the battery's cycle stability, cycle life, and safety.

[0114] In some embodiments, before laminating the first surface of the base film 11 to the non-woven fabric layer 12, the process further includes: coating the first surface of the base film 11 adjacent to the non-woven fabric layer 12 with a first slurry containing at least one of an organic nanomaterial, an inorganic nanomaterial, and an organic-inorganic composite nanomaterial to obtain a first coating layer 13. That is, the aforementioned first coating layer 13 is prepared on the first surface of the base film 11.

[0115] Alternatively, before or after laminating the first surface of the base film 11 to the non-woven fabric layer 12, the process further includes: coating a second slurry containing at least one of an organic nanomaterial, an inorganic nanomaterial, and an organic-inorganic composite nanomaterial on a second surface of the base film 11 away from the non-woven fabric layer 12 to obtain a second coating layer 14. That is, the aforementioned second coating layer 14 is prepared on the second surface of the base film 11.

[0116] Alternatively, a first slurry containing at least one of an organic nanomaterial, an inorganic nanomaterial, and an organic-inorganic composite nanomaterial is coated on a first surface of the base film 11 near the non-woven fabric layer 12 to obtain a first coating layer 13, and a second slurry containing at least one of an organic nanomaterial, an inorganic nanomaterial, and an organic-inorganic composite nanomaterial is coated on a second surface of the base film 11 away from the non-woven fabric layer 12 to obtain a second coating layer 14. That is, the aforementioned first coating layer 13 and second coating layer 14 are prepared on both surfaces of the base film 11.

[0117] By preparing a coating on at least one surface of the base film, the mechanical strength of the composite membrane can be enhanced and the risk of dendrite growth piercing the composite membrane can be further reduced. The specific material selection and formation parameters of the first coating 13 and the second coating 14 are described above.

[0118] FIG5 is a SEM image of the composite diaphragm prepared in the embodiment, wherein the surface of the base membrane is combined with a non-woven fabric layer material having a three-dimensional network of fiber knots.

[0119] In some embodiments, the lamination process includes a roller lamination process, and the coating method can be spraying.

[0120] Battery

[0121] In a third aspect, an embodiment of the present application provides a battery comprising a positive electrode sheet, a negative electrode sheet, and a diaphragm disposed between the positive electrode sheet and the negative electrode sheet, wherein the diaphragm is a composite diaphragm provided in the first aspect of the embodiment of the present application and / or a composite diaphragm prepared by the preparation method provided in the second aspect of the embodiment of the present application.

[0122] By using the composite membrane provided by the first aspect of the embodiment of the present application and / or the composite membrane prepared by the preparation method provided by the second aspect of the embodiment of the present application in a battery, the non-woven fabric layer 12 in the composite membrane is located between the base membrane 11 and the negative electrode plate. Due to the good stability of the composite membrane, the ion transport is facilitated, and the risk of continued growth of dendrites from the negative electrode plate piercing the composite membrane is significantly reduced, the battery can have excellent cycle stability, cycle life, and safety.

[0123] In some embodiments, the battery is a secondary battery. In exemplary embodiments, the secondary battery may be a lithium metal battery or a sodium metal battery. Such secondary batteries in the embodiments of the present application have high energy density and good cycle stability. Furthermore, based on the advantages of the composite separators in the embodiments of the present application, such secondary batteries are well suited for use as power batteries or power sources for energy storage systems.

[0124] In some embodiments, the battery includes a plurality of electrode assemblies, for example, at least two electrode assemblies, and one electrode assembly includes a stacked positive electrode sheet, a composite diaphragm, and a negative electrode sheet. There is no buffer pad between adjacent electrode assemblies. Specifically, for metal batteries without embedded negative electrode active materials, metal is deposited on the negative electrode sheet, resulting in a large rebound of the negative electrode sheet, so a certain amount of metal deposition space is generally reserved to prevent rebound. However, if a large gap is left inside the battery cell directly during the production of the battery cell, the initial deposition process is not subject to force until the top shell of the battery cell expands to a certain extent, which can easily cause an internal short. The role of adding a buffer pad (with a certain amount of compression) is to subject it to a smaller shaping force during the initial deposition, so that the dendrite growth is not controlled and pierces the diaphragm. The internal space of the non-woven fabric here can replace the buffer pad. The embodiment of the present application is based on the addition of non-woven fabric to the composite diaphragm, which has a certain stress buffering effect, and can still have good safety performance without setting a buffer pad, thereby further reducing the cost of the battery.

[0125] In some embodiments, the battery is a metal battery, which is a battery in which the negative electrode plate does not use embedded negative electrode active materials such as carbon / silicon, but forms active metal on the surface of the negative electrode plate after recycling. For example, lithium metal batteries, sodium metal batteries, etc. Because the negative electrode plate does not have embedded negative electrode active materials such as carbon / silicon, metal deposition occurs on the negative electrode current collector. Due to the high reactivity of the metal reaction, uneven deposition is likely to occur, resulting in excessive local current density. The composite diaphragm based on the embodiment of the present application can effectively prevent the risk of dendrite piercing the surface of the negative electrode plate of the metal battery. Therefore, such a battery has the characteristics of high energy density, good cycle performance and long service life.

[0126] The negative electrode sheet of the metal battery can be a negative electrode current collector, for example, a metal foil or a composite current collector, for example, aluminum foil or copper foil.

[0127] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer bonded to the positive electrode current collector. The positive electrode active layer contains a positive electrode active material. When the secondary battery is a lithium metal battery, the positive electrode active material is a lithium-containing material. When the secondary battery is a sodium metal battery, the positive electrode active material is a sodium-containing material.

[0128] In some embodiments, the current collector of the positive electrode sheet, also known as the positive electrode current collector, may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate such as polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.

[0129] In some embodiments, the secondary battery of the present application may include any one of a battery cell, a battery module, and a battery pack.

[0130] A battery cell is a battery housing and an electrode assembly encapsulated within the housing. The shape of a battery cell is not particularly limited and can be cylindrical, square, or any other shape. A square-shaped battery cell 20 is shown in FIG6 .

[0131] In some embodiments, as shown in Figure 7, the outer packaging of the battery cell 20 may include a shell 21 and a top cover assembly 22. The shell 21 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 21 has an opening connected to the receiving cavity, and the top cover assembly 22 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the isolation membrane and the negative electrode sheet contained in the secondary battery of the embodiment of the present application can be formed into an electrode assembly 23 through a winding process and / or a lamination process. The electrode assembly 23 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 23. The number of electrode assemblies 23 contained in the battery cell 20 can be one or more, which can be adjusted according to actual needs.

[0132] The preparation method of the battery cell 20 is well known. In some embodiments, the positive electrode sheet, separator, and negative electrode sheet can be assembled with an electrolyte to form the battery cell 20. As an example, the positive electrode sheet, separator, and negative electrode sheet can be wound or laminated to form an electrode assembly 23. The electrode assembly 23 is then placed in an outer package, dried, and then injected with electrolyte. The battery cell 20 is then vacuum packaged, allowed to stand, formed, and shaped.

[0133] A battery module is assembled from the battery cells 20 , that is, it may contain a plurality of battery cells 20 , and the specific number can be adjusted according to the application and capacity of the battery module.

[0134] In some embodiments, FIG8 is a schematic diagram of an exemplary battery module 30. In the battery module 30, multiple battery cells 20 may be arranged sequentially along the length of the battery module 30. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 20 may be secured together using fasteners.

[0135] Optionally, the battery module 30 may further include a housing having an accommodation space, and the plurality of battery cells 20 may be accommodated in the accommodation space.

[0136] A battery pack is assembled from the battery cells 20 described above, and may contain multiple battery cells 20, wherein multiple battery cells 20 may be assembled into the battery module 30 described above. The specific number of battery cells 20 or battery modules 30 contained in a battery pack may be adjusted according to the application and capacity of the battery pack.

[0137] In the embodiment, Figures 9 and 10 are schematic diagrams of an exemplary battery pack 40. The battery pack 40 may include a battery box and multiple battery modules 30 disposed within the battery box. The battery box includes an upper box body 41 and a lower box body 42. The upper box body 41 covers the lower box body 42 and forms an enclosed space for accommodating the battery modules 30. The multiple battery modules 30 may be arranged in any manner within the battery box.

[0138] Electrical devices

[0139] Fourthly, embodiments of the present application further provide an electrical device comprising the battery of the aforementioned embodiments. The battery can serve as both a power source and an energy storage unit for the electrical device. Based on the advantages of the battery of the embodiments of the present application, the electrical device of the embodiments of the present application exhibits excellent cycle performance and safety.

[0140] Electrical devices may include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc. These electrical devices may use secondary batteries, battery modules, or battery packs based on their usage requirements.

[0141] Figure 11 is a schematic diagram of an exemplary electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device, a battery pack or battery module may be used.

[0142] As another example, the electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a secondary battery as a power source.

[0143] Example

[0144] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0145] Example 1

[0146] A composite diaphragm includes a base membrane and a non-woven fabric layer bonded to a first surface of the base membrane. The base membrane is made of polyethylene (PE) and has a thickness of 20 μm; the non-woven fabric layer is made of polyester fiber non-woven fabric and has a thickness of 10 μm. For details, see Table 1.

[0147] The preparation method of the composite diaphragm comprises: bonding and laminating the above-mentioned base film and non-woven fabric material to obtain the composite diaphragm.

[0148] Example 2

[0149] A composite membrane comprises a base membrane and a nonwoven fabric layer bonded to a first surface of the base membrane, with a first coating layer disposed between the base membrane and the nonwoven fabric layer. The base membrane is made of polyethylene (PE) with a thickness of 20 μm; the nonwoven fabric layer is made of polyester fiber with a thickness of 10 μm; and the first coating layer is made of an organic nanomaterial: aramid fiber (polyphenylene sulfide fiber) with a thickness of 1 μm. For details, see Table 1.

[0150] The preparation method of the composite diaphragm comprises: spraying aramid fiber nanomaterial on the surface of the base film to form a first coating layer, and laminating a non-woven fabric layer material on the first coating layer to obtain the composite diaphragm.

[0151] Example 3

[0152] A composite membrane comprises a base membrane and a nonwoven fabric layer bonded to the base membrane. A first coating is provided between the base membrane and the nonwoven fabric layer, and a second coating is provided on a second surface of the base membrane, distal from the nonwoven fabric layer. The base membrane is made of polyethylene (PE) with a thickness of 20 μm; the nonwoven fabric layer is made of polyester fiber with a thickness of 10 μm. Both the first and second coatings are made of organic nanomaterials: aramid fiber (polyphenylene sulfide fiber), with a thickness of 1 μm. See Table 1 for details.

[0153] The preparation method of the composite diaphragm includes: spraying aramid fiber nanomaterials on both surfaces of the base film to form a first coating layer and a second coating layer, and laminating a non-woven fabric layer material on the first coating layer to obtain the composite diaphragm.

[0154] Examples 4-20: See Table 1 for details.

[0155] Comparative Example 1

[0156] A composite diaphragm comprises a stacked polyethylene layer and a polypropylene layer, wherein the polyethylene layer has a thickness of 20 μm and the polypropylene layer has a thickness of 15 μm.

[0157] Comparative Example 2

[0158] A composite diaphragm comprises stacked polyethylene layers and a first coating layer. The first coating layer is made of an organic nano material: aramid fiber with a thickness of 15 μm. The polyethylene layer has a thickness of 20 μm.

[0159] Comparative Example 3

[0160] A composite diaphragm comprises a laminated base film and a first coating layer. The first coating layer is made of an inorganic nano material: silicon dioxide, and has a thickness of 15 μm. The base film is a polyethylene layer, and has a thickness of 20 μm.

[0161] Comparative Example 4

[0162] A composite diaphragm comprises a laminated base film and a first coating layer. The material of the first coating layer is an organic nano material: aramid fiber with a thickness of 15 μm. The base film is a polyester fiber non-woven fabric with a thickness of 20 μm.

[0163] Performance Testing

[0164] (1) Composite diaphragm performance

[0165] 1.1 Young's modulus: See GB / T7757-2009. Test method: Cut the composite diaphragm into test samples with a length of 50 mm and a width of 20 mm. Test the elastic modulus using a universal testing machine with a stretching distance of 50 mm and a test speed of 20 mm / min.

[0166] 1.2 Porosity: See GB / T 24586-2009. Test Principle: Utilizing the small molecular diameter inert gas (helium) displacement method, combined with Archimedes' principle and Bohr's law (PV = nRT), the true volume of the material being tested is accurately measured to determine the porosity of the composite membrane sample being tested.

[0167] Calculation formula: apparent volume V2 = S*H*A; porosity P = (V2-V1) / V2*100%.

[0168] Where: S-area, cm 2; H-thickness, cm; A-sample number, EA; V1-true volume of the sample, cm 3 ; V2-apparent volume of the sample, cm 3 ; P-porosity of sample, %.

[0169] 1.3 Thickness: Use micrometer or micro interface thickness measurement method.

[0170] 1.4 Air Permeability: Gurley air permeability analysis, see GB / T 458-2008. Test Principle: The time (s) required for 100cc of air to pass through a sample of a certain area.

[0171] 1.5 Coating pore size: Observe the structure through SEM and estimate the approximate pore size range.

[0172] Table 1 shows the material composition and test parameters of the composite diaphragms in the examples and comparative examples.

[0173] (2) Secondary battery cell test

[0174] Secondary battery cells, i.e. sodium ion full battery assembly:

[0175]

Positive electrode

[0176] The positive electrode active material is uniformly mixed with SuperP and PVDF in a mass ratio of 90:5:5, and then the positive electrode sheet is obtained by homogenization, coating, drying and cold pressing.

[0177]

Negative electrode

[0178] Cut the aluminum foil to use as the negative electrode.

[0179] [Diaphragm]

[0180] Composite diaphragms of Examples and Comparative Examples.

[0181] [Electrolyte]

[0182] 0.6122 g of sodium perchlorate was weighed and added to 10 ml of propylene carbonate solvent, and the mixture was stirred until the sodium perchlorate was completely dissolved. Then, 3% by mass of fluoroethylene carbonate was added as an additive, and the mixture was thoroughly stirred to prepare the electrolyte.

[0183]

Sodium-ion full battery

[0184] In an inert gas-protected glove box, the prepared negative electrode sheet, composite diaphragm and positive electrode sheet (the non-woven fabric layer in the composite diaphragm is close to the negative electrode sheet) are stacked tightly in sequence, and the electrolyte is added dropwise to completely soak the diaphragm. Then, the stacked part is encapsulated into a button battery shell to complete the battery assembly and obtain a full sodium ion battery.

[0185] Full battery charge and discharge test:

[0186] 2.1 Battery capacity test

[0187] At 25°C, the prepared battery was first charged to 3.65V at a constant current of 1C, further charged at a constant voltage to a current of 0.05C, and then discharged to 1.5V at a constant current of 1C. This is a charge and discharge cycle process, and the discharge capacity this time is used as the battery capacity.

[0188] 2.2 Battery cycle performance test

[0189] At 25°C, the prepared battery was first charged to 3.65V at a constant current of 1C, then further charged at a constant voltage to a current of 0.05C, and then discharged to 1.5V at a constant current of 1C. This constitutes one charge-discharge cycle, and the discharge capacity is the discharge capacity of the first cycle. The battery was subjected to cyclic charge and discharge tests in this manner. When the discharge capacity of the battery decayed to 80% of the discharge capacity of the first cycle, the test was stopped and the number of cycles of the battery was recorded.

[0190] 2.3 Battery internal resistance: DCR = ▲U / I; where ▲U is the voltage change within 30 seconds of discharge; I is the discharge current. The results are shown in Table 2. Table 2 shows the test results of batteries assembled with the composite separators of the examples and comparative examples.

[0191] Table 1

[0192] Table 2

[0193] It can be seen from the data in Table 2 above that: due to the use of the composite diaphragm unique to the embodiment of the present application, the battery of the embodiment of the present application has a smaller DCR internal resistance than the comparative example, and exhibits a better cycle life. Among them, the data of Example 1 and Examples 4-9 show that: the non-woven fabric layer using polyester fiber with a thickness of 10 to 18 μm has a better effect. By optimizing the material and thickness of the non-woven fabric layer in the composite diaphragm of the embodiment of the present application, and further adding a first coating and a second coating on both surfaces of the base film, the battery performance can be further improved. In Example 3, a non-woven fabric layer with a thickness of 15 μm of polyester fiber is used, and both the first coating and the second coating use aramid fiber with a thickness of 1 μm, and the corresponding battery effect is better.

[0194] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A composite separator, characterized in that, It includes a base film which has a first surface and a second surface arranged oppositely. The first surface of the base film is provided with a non-woven fabric layer. The non-woven fabric layer includes a non-woven fabric material formed by organic polymer fibers, and the porosity of the non-woven fabric layer is at least 40%. The composite separator is used in a battery, and the non-woven fabric layer is adjacent to the negative electrode plate of the battery.

2. The composite separator according to claim 1, wherein The porosity of the non-woven fabric layer is 47% - 70%.

3. The composite separator according to claim 1 or 2, characterized in that The thickness of the non-woven fabric layer is 10μm - 35μm; and / or, The thickness of the base film is 5μm - 20μm.

4. The composite separator according to any one of claims 1-3, characterized in that, The organic polymer fibers include at least one of viscose fiber, acetate fiber, polyester fiber, polypropylene fiber, and polyimide fiber; and / or, The material of the base film includes polyolefin.

5. The composite separator according to any one of claims 1-4, characterized in that A first coating is provided between the first surface of the base film and the non-woven fabric layer and / or a second coating is provided on the second surface of the base film. The first coating and the second coating independently include at least one of organic nano materials, inorganic nano materials, and organic-inorganic composite nano materials.

6. The composite separator according to claim 5, wherein The materials of the first coating and the second coating have one or more of the following (1) - (3): (1) The organic nano materials include at least one of aromatic ring polymers, heteroaromatic ring polymers, aramid fibers, and polyurethane fibers; (2) The inorganic nano materials include at least one of tin dioxide nano particles, silicon dioxide nano particles, and silver nano particles; (3) The organic-inorganic composite nano materials include at least one of silicon-polyacrylic acid composites, silicon-polyacrylonitrile composites, tin-polyacrylic acid composites, and tin-polyacrylonitrile composites.

7. The composite separator according to claim 5 or 6, characterized in that, The first coating is provided on the first surface of the base film, the second coating is provided on the second surface of the base film, and the first coating includes the organic nano materials, and the second coating includes the inorganic nano materials or the organic-inorganic composite nano materials.

8. The composite separator according to any one of claims 5-7, characterized in that, The pore size of the first coating is 0.2 - 2μm; and / or, The pore size of the second coating is 0.2 - 2μm.

9. The composite separator according to any one of claims 5-8, characterized in that, The overall porosity of the base film and the first coating and the second coating is 28% - 46%; and / or, The overall thickness of the base film and the first coating and the second coating is 7μm - 25μm.

10. The composite separator according to any one of claims 1-9, characterized in that, The composite separator has one or more of the following (1) - (5): (1) The porosity of the composite separator is 38% - 55%; (2) The Young's modulus in the length direction of the composite separator is 8MPa - 15MPa; (3) The Young's modulus in the width direction of the composite separator is 6MPa - 15MPa; (4) The thickness of the composite separator is 15μm - 55μm; (5) The air permeability of the composite separator is 260s / 100CC - 390s / 100CC.

11. A method for preparing a composite separator according to any one of claims 1-10, characterized in that, It includes the following steps: Bond the first surface of the base film with the non-woven fabric layer to obtain the composite separator.

12. The preparation method according to claim 11, wherein, Before laminating the first surface of the base film with the non-woven fabric layer, it further includes: coating a first slurry containing at least one of organic nanomaterials, inorganic nanomaterials, and organic-inorganic composite nanomaterials on the first surface of the base film to obtain a first coating; and / or, Before or after laminating the first surface of the base film with the non-woven fabric layer, it further includes: on the second surface of the base film Coating a second slurry containing at least one of organic nanomaterials, inorganic nanomaterials, and organic-inorganic composite nanomaterials to obtain a second coating.

13. A battery, characterized in that, It includes a positive electrode plate, a negative electrode plate, and a separator disposed between the positive electrode plate and the negative electrode plate. The separator includes the composite separator according to any one of claims 1 to 10 or the composite separator prepared by the preparation method according to any one of claims 11 to 12, and the non-woven fabric layer in the composite separator is located between the base film and the negative electrode plate.

14. The battery according to claim 13, characterized in that, The battery is a metal battery.

15. The battery according to claim 13 or 14, characterized in that, The battery includes at least two electrode assemblies, and there is no buffer pad between adjacent electrode assemblies.

16. An electrical device, characterized in that, The electrical device includes the battery according to any one of claims 13 to 15.

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