Composite separator, secondary battery, and electrical device

Abstract

The present application discloses a composite separator, a secondary battery, and an electrical device. The secondary battery includes: a composite separator, a positive electrode active material layer located on one side of the composite separator, and a negative electrode active material layer located on the other side of the composite separator. The composite separator includes a polymer layer and conductive structures located on both sides of the polymer layer. The conductive structure has through holes. The porosity of the composite separator is 15 - 30%, and the average pore diameter of the pore structure is 100 nm - 20 μm. The secondary battery can alleviate the decline in cycle performance caused by poor electrolyte infiltration, and thus has good cycle performance and safety.

Description

Technical Field

[0001] The present application relates to the field of secondary batteries, and more particularly, to a composite separator, a secondary battery, and an electrical device. Background Art

[0002] With the development and popularization of battery technologies, secondary batteries such as lithium-ion batteries are applied to various electrical devices to provide clean electrical energy. The secondary battery stores and supplies electrical energy by the insertion and extraction of energy-storing ions, such as lithium ions, between the positive electrode and the negative electrode. During the battery cycling process, the positive and negative electrode active materials will expand in volume, resulting in the electrolyte between the internal electrode sheets of the battery being extruded, thus causing poor electrolyte infiltration.

[0003] Therefore, the current composite separators, secondary batteries, battery devices, and electrical devices still need to be improved. Summary of the Invention

[0004] In view of the above problems, the present application provides a composite separator, a secondary battery, and an electrical device.

[0005] In one aspect of the present application, a secondary battery is proposed. The secondary battery includes: a composite separator, a positive electrode active material layer located on one side of the composite separator, and a negative electrode active material layer located on the other side of the composite separator. The composite separator includes a polymer layer and conductive structures located on both sides of the polymer layer. The conductive structure has through holes. The porosity of the composite separator is 15%-30%, and the average pore diameter of the polymer layer is 100 nm - 20 μm. This secondary battery uses a composite separator with a conductive function, and the electrolyte stored in the polymer layer is used to infiltrate the electrode active layer, which can alleviate the decline in cycling performance caused by poor electrolyte infiltration. Therefore, it has good cycling performance and safety. That is to say, the present application provides a composite separator with a certain pore diameter, porosity, and conductive function, which improves the ability of the electrolyte to infiltrate the active material layer. When the active material expands, the electrolyte stored in the polymer layer of the composite separator is released.

[0006] According to an embodiment of the present application, the polymer layer includes a first sub-layer and a second sub-layer. The first sub-layer is located on the side close to the positive electrode active material layer, and the second sub-layer is located on the side close to the negative electrode active material layer. The first sub-layer has a plurality of first holes, and the second sub-layer has a plurality of second holes. The average pore diameter of the first holes is 10 nm - 20 μm, and the average pore diameter of the second holes is 500 nm - 20 μm. Thereby, the ability of the polymer layer to accommodate the electrolyte can be further improved.

[0007] According to an embodiment of the present application, the average pore diameter of the first hole is the same as that of the second hole. Thus, the steps of preparing the polymer layer can be simplified and the production cost can be reduced.

[0008] According to an embodiment of the present application, the average pore diameter of the first hole is different from that of the second hole. The average pore diameter of the first hole is 10 nm - 1 μm, and the average pore diameter of the second hole is 1 μm - 20 μm. Thus, the ability of the polymer layer to accommodate the electrolyte can be further improved.

[0009] According to an embodiment of the present application, the porosity of the first sub-layer is 10 - 20%, and the porosity of the second sub-layer is 20 - 30%. Thus, while maintaining a certain ability of the polymer layer to accommodate the electrolyte, the mechanical properties of the film layer can be maintained to meet the requirements of the battery.

[0010] According to an embodiment of the present application, the material of the polymer layer includes at least one of epoxy resin, terephthalate, polyethylene, polypropylene, poly(p-phenylene terephthalamide), polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, and polyamide. The polymer layer formed by the above materials has appropriate mechanical properties.

[0011] According to an embodiment of the present application, the conductive structure includes a first conductive layer and a second conductive layer. The first conductive layer is in contact with the positive electrode active material, the second conductive layer is in contact with the negative electrode active material. The first conductive layer has a first through-hole, the second conductive layer has a second through-hole, and the average pore diameters of the first through-hole and the second through-hole are independently 500 nm - 20 μm. Thus, the structure of the secondary battery can be further simplified.

[0012] According to an embodiment of the present application, the average pore diameters of the first through-hole and the second through-hole are independently 1 μm - 10 μm. Thus, the electrolyte wettability of the composite separator can be further improved.

[0013] According to an embodiment of the present application, the porosities of the first conductive layer and the second conductive layer are independently 15 - 30%. Thus, the electrolyte wettability of the composite separator can be further improved.

[0014] According to an embodiment of the present application, the conductive structure includes at least one of aluminum, aluminum alloy, copper, copper alloy, nickel, nickel alloy, iron, iron alloy, titanium, titanium alloy, silver, and silver alloy. The positive electrode active material layer includes at least one of lithium-containing phosphate and lithium transition metal oxide. The negative electrode active material layer includes at least one of artificial graphite and natural graphite.

[0015] According to an embodiment of the present application, the secondary battery is a wound battery, the wound battery includes a plurality of the composite separator films, the plurality of the composite separator films are spaced apart by an insulating separator, the composite separator film includes a plurality of flat portions and a plurality of bent portions, and adjacent flat portions are connected by the bent portions. Thereby, the performance of the secondary battery can be further improved.

[0016] In another aspect of the present application, the present application provides a composite separator film. The composite separator film includes: a polymer layer, and conductive structures located on both sides of the polymer layer, the conductive structures having through holes, the porosity of the composite separator film being 15-30%, and the average pore size of the polymer layer being 100 nm-20 μm. The composite separator film has a good ability to store electrolyte and has the function of a current collector. An active material layer can be directly formed on the conductive structure, so that the decline in cycle performance caused by poor electrolyte infiltration can be alleviated, and thus it has good cycle performance and safety.

[0017] According to an embodiment of the present application, the polymer layer includes a first sub-layer and a second sub-layer, the first sub-layer having a plurality of first holes, the second sub-layer having a plurality of second holes, the average pore size of the first holes being 10 nm-1 μm, and the average pore size of the second holes being 1 μm-20 μm. Thereby, the performance of the composite separator film can be further improved.

[0018] According to an embodiment of the present application, the conductive structure includes a first conductive layer and a second conductive layer, the first conductive layer being located on one side of the first sub-layer, the second conductive layer being located on one side of the second sub-layer, the first conductive layer having a first through hole, the second conductive layer having a second through hole, the average pore sizes of the first through hole and the second through hole being independently 1-10 μm, and the porosities of the first conductive layer and the second conductive layer being independently 10-30%. Thereby, the performance of the composite separator film can be further improved.

[0019] In another aspect of the present application, the present application provides an electrical device. The electrical device includes the secondary battery described above. Thereby, the electrical device has all the features and advantages of the aforementioned secondary battery and composite separator film. Generally speaking, the electrical device has good cycle performance and safety. Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions of the present application, the drawings used in the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained according to the drawings without creative efforts.

[0021] Figure 1 Schematic structural diagram of a secondary battery according to an embodiment of the present application;

[0022] Figure 2 Exploded schematic structural diagram of a secondary battery according to an embodiment of the present application;

[0023] Figure 3 Schematic structural diagram of a composite separator according to an embodiment of the present application;

[0024] Figure 4 Schematic structural diagram of a composite separator according to another embodiment of the present application;

[0025] Figure 5 Schematic structural diagram of a secondary battery according to an embodiment of the present application;

[0026] Figure 6 Schematic structural diagram of an electrical device according to an embodiment of the present application. Detailed implementation manners

[0027] Hereinafter, embodiments of the technical solutions of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to illustrate the technical solutions of the present application more clearly, and thus are only examples and should not be used to limit the protection scope of the present application.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field 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 are intended to cover non-exclusive inclusion.

[0029] Referring to "embodiments" herein means that specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of this application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0030] In the description of the embodiments of this application, the term "and / or" is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " herein generally represents an "or" relationship between the associated objects before and after.

[0031] In the description of the embodiments of the present application, the term "plurality" means two or more (including two). Similarly, "multiple groups" means two or more groups (including two groups), and "multiple sheets" means two or more sheets (including two sheets).

[0032] In the description of the embodiments of the present application, the orientation or positional relationship indicated by technical terms such as "upper", "lower", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the embodiments of the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, so it should not be construed as a limitation to the embodiments of the present application.

[0033] Unless otherwise specified, the terms used in the present application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values of the various parameters mentioned in the present application can be measured by various common measurement methods in the art (for example, they can be tested according to the methods given in the embodiments of the present application).

[0034] During the cycling process of lithium-ion batteries, volume expansion will occur, especially in anode active material systems such as graphite and silicon. This process will cause the electrolyte between the electrode sheets inside the battery cell, as well as the electrolyte inside the electrode sheets, to be extruded due to the volume expansion of the active material, resulting in poor electrolyte infiltration of the electrode sheets. Especially for wound batteries, due to the greater expansion force and stress concentration at the corners, the problem of poor electrolyte infiltration at the corner positions is particularly serious. Poor electrolyte infiltration will cause some lithium ions to accumulate on the surface of the anode material, resulting in lithium deposition, further leading to the formation of lithium dendrites, and may pierce the separator, causing short circuit between the positive and negative electrodes.

[0035] In some embodiments, the storage capacity of the electrode assembly for the electrolyte can be improved by introducing a hole structure into the current collector or increasing the thickness of the separator. However, the above improvements often require complicating the structure of the current collector.

[0036] In view of this, the present application proposes a composite separator and a secondary battery. By adopting a polymer layer with an appropriate average pore size and porosity, a sufficient amount of electrolyte can be stored inside the polymer layer, and through the conductive structure, it has the function of a current collector. Therefore, better infiltration of the active material layer can be achieved: the active material layer is formed on the conductive structures on both sides of the polymer layer. On the one hand, when the electrode active material expands, this structure can release the electrolyte stored in the polymer layer to improve the electrolyte infiltration condition on the surface of the electrode sheet, thereby alleviating the problems caused by poor electrolyte infiltration. On the other hand, it can also increase the integration degree of the internal structure of the battery and achieve infiltration of the active layer with a simple structure.

[0037] In one aspect of the present application, a secondary battery is proposed. The secondary battery includes a composite separator, a positive electrode active material layer, and a negative electrode active material layer. The positive electrode active material layer is located on one side of the composite separator, and the negative electrode active material layer is located on the other side of the composite separator. Refer to Figure 3 , the composite separator includes a polymer layer 110 and conductive structures located on both sides of the polymer layer 110, such as 120A and 120B shown in the figure. The polymer layer 110 has a pore structure (not shown in the figure), which can be used to absorb the electrolyte and release the electrolyte when squeezed by the active material. The conductive structure has through-holes (not shown in the figure) to provide a flow path for the electrolyte stored in the polymer layer. The porosity of the composite separator is 15 - 30%, and the average pore diameter of the polymer layer is 100 nm - 20 μm. The secondary battery uses a composite separator with a good liquid retention ability due to its pore structure and a conductive function, so it has a good ability to store the electrolyte and a simple structure with a high degree of integration, which can alleviate the decline in cycle performance caused by poor electrolyte infiltration, and thus has good cycle performance and safety.

[0038] Specifically, the secondary battery proposed in the present application adopts the method of a composite separator to integrate the positive and negative current collectors on both sides of the polymer layer. Through the conductive structure with through-holes, a flow path for the electrolyte is provided to achieve the conductive function, and the internal structure of the battery can be further simplified. Moreover, by using a polymer layer with an appropriate average pore diameter, it can play a role in separating the conductive structures carrying the positive and negative electrode active materials, and at the same time, the above-mentioned pore diameter can be used to store a sufficient amount of electrolyte inside the polymer layer. Even if the positive and negative electrode active materials expand during the cycle and the electrolyte on the electrode surface is extruded, the electrolyte in the pore structure loaded in the polymer layer can be released by extrusion at this time, thereby maintaining good electrolyte infiltration on the overall surface of the composite separator.

[0039] Porosity

[0040] In the present application, the porosity is used to evaluate the proportion between the solid structure and the pores / through-holes in the membrane layer. The larger the porosity, the higher the proportion of pores and / or through-holes in the membrane layer structure. Those skilled in the art can understand that in a membrane layer structure with the same material and the same thickness, the larger the porosity, the smaller the mechanical strength.

[0041] The porosity in the present application can be detected by the weighing method. For example, first weigh the weight of a membrane layer with pores / through-holes with a volume of V and record it as m0. Immerse the weighed membrane layer completely in the n-hexadecane reagent for a period of time, such as 2 h. Then take out the membrane layer and wipe off the residual reagent on its surface with a dust-free paper, and weigh the membrane layer and record it as m1. The porosity is calculated using the following formula:

[0042]

[0043] In the above formula is the porosity, with the unit of %; is the density of n-hexadecane, with the unit of g / cm 3 .

[0044] Average pore size

[0045] In the present application, the average pore diameter is used to evaluate the size of the solid structure and the pores / through-holes in the membrane layer. For the polymer layer, the average pore diameter is the average pore diameter of the pore structure; for the conductive structure, the average pore diameter is the average pore diameter of the through-holes. The average pore diameter in the present application can be obtained by the following method:

[0046] The battery cell is placed in a 1.0 mol / L aqueous sodium hydroxide solution at room temperature for discharging treatment. After discharging is completed, the composite separator loaded with the active material is obtained by manual disassembly; the composite separator loaded with the active material is finely sliced layer by layer at different thickness positions by using cryogenic focused ion beam (FIB) (the minimum scale can reach nanoscale thin slices), the polymer layer is separated, and then different area regions of the polymer layer are cut to obtain a plurality of specimens.

[0047] The test instrument used is an ASAP2460 - physical adsorption analyzer. Each specimen sample after drying and degassing treatment is placed in liquid nitrogen, different test pressures are adjusted, the adsorption amounts of nitrogen are measured respectively, and the adsorption and desorption isotherms are plotted. Then, the pore volume and specific surface area of the porous carbon material are obtained according to the adsorption and desorption isotherms, and the average pore diameter is further calculated. The average value of multiple specimens is taken to obtain the average pore diameter of the membrane layer to be measured.

[0048] According to the embodiments of the present application, when the overall porosity of the composite separator is 10 - 30%, it is beneficial to maintain the overall mechanical properties of the composite separator to meet the requirements of the battery, support the positive and negative active materials formed on the conductive structure, and keep the overall mechanical structure of the composite separator stable during preparation, transportation and use. The average pore diameter of the polymer layer in the composite separator can be 100 nm - 20 μm. When the average pore diameter is within the above range, the resistance of the electrolyte to enter the internal pore structure can be reduced, which is beneficial to storing the electrolyte by using the pore structure. In some embodiments, the average pore diameter of the pore structure can be 1 μm - 20 μm. Thus, the resistance of the electrolyte to enter the internal pore structure can be further reduced.

[0049] In some embodiments, the pore structure of the polymer layer can be through-holes. That is, the electrolyte can flow through the pore structure from one side of the polymer layer to the other side. Thus, the ability of the polymer layer to release the electrolyte when being squeezed can be improved.

[0050] According to the embodiments of the present application, the material for forming the polymer layer is not particularly limited, and those skilled in the art can use familiar polymers with insulating properties to form the polymer layer. For example, the polymer layer material can be selected to be a polymer material with good stability in the electrolyte, and this polymer may not have the ability to swell in the electrolyte. As mentioned above, the polymer layer of the present application realizes the storage of the electrolyte through an open pore structure. Therefore, the polymer material itself may not have the ability to adsorb the electrolyte. The polymer layer formed by a polymer without swelling performance can maintain a relatively stable volume during use, thereby improving the stability of the conductive structure loaded thereon and reducing the probability of the conductive structure peeling off from the polymer layer.

[0051] In some specific embodiments, the polymer layer can be formed by using the diaphragm material of a common secondary battery. The diaphragm material has good electrolyte stability and relatively low production cost. For example, the material for forming the polymer layer can include at least one of epoxy resin, terephthalate, polyethylene, polypropylene, poly(p-phenyleneterephthalamide), polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, and polyamide. For example, the following polymer materials can be used as the principle for forming the polymer layer: any one or more of terephthalate, polyethylene, polypropylene, epoxy resin, polyamide, polyimide, polyester, polyolefin, polyyne, silicone polymer, polyether, polyol, polysulfone, polysaccharide polymer, amino acid polymer, polythiazyl polymer, aromatic ring polymer, as well as aromatic heterocyclic polymer, epoxy resin, phenolic resin, their derivatives, crosslinked products, and / or copolymers. The polymer layer formed by the above materials has appropriate mechanical properties and can further improve the performance of the composite separator.

[0052] In some examples, the secondary battery can be a wound battery. The wound battery includes a plurality of the composite separators, and the plurality of composite separators are spaced apart by an insulating diaphragm. The composite separator includes a plurality of planar portions and a plurality of bent portions, and adjacent planar portions are connected by the bent portions. Since the composite separator proposed in the present application has a certain ability to store the electrolyte, it can better alleviate the problems of large stress and serious electrolyte extrusion at the corners of the wound battery.

[0053] Next, taking the secondary battery as a wound battery as an example, each structure of the secondary battery will be described in detail. Those skilled in the art can understand that the following embodiments are only for illustrating the secondary battery proposed in the present application and cannot be construed as a limitation on the type of the secondary battery.

[0054] In this embodiment, the pore structure in the polymer layer of the composite separator membrane may have different average pore diameters and / or distribution densities in different regions. For example, the region corresponding to the corner of the wound battery in the polymer layer may have a higher porosity to store more electrolyte, and the region corresponding to the large face of the battery may have a lower porosity to provide better mechanical support. In this embodiment, the average pore diameter of the polymer may be the average value of the pore diameters in all regions, and the porosity may also be the average porosity of all regions.

[0055] In some other examples, the pore structure in the polymer layer may be uniformly distributed, that is, the density of the pore structure and the average pore diameter of the pores at different positions in the polymer layer may be the same. Thus, on the one hand, the preparation cost of the polymer layer can be reduced, and on the other hand, the entire polymer layer can have more uniform mechanical properties, and when dealing with stresses such as expansion caused by the active material, the stress can also be more evenly distributed.

[0056] In some embodiments, referring to Figure 4 , the polymer layer may include a first sub-layer 110A and a second sub-layer 110B. The first sub-layer 110A is located on the side close to the positive electrode active material, and the second sub-layer 110B is located on the side close to the negative electrode active material. The first sub-layer 110A has a plurality of first pores, and the second sub-layer 110B has a plurality of second pores. In this embodiment, the materials constituting the first sub-layer 110A and the second sub-layer 110B may be the same or different, and the average pore diameters and distribution densities of the first and second pores may be the same or different. The polymer layer is composed of two sub-layers, which can reduce the depth of the pores forming the pore structure penetrating the whole polymer layer. On the one hand, it can reduce the probability that the pores do not penetrate the polymer due to the large pore depth and the electrolyte can only enter and exit from one side of the polymer membrane. On the other hand, it can also reduce the difficulty of forming the pore structure.

[0057] According to the embodiments of the present application, the first sub-layer and the second sub-layer can be bonded and fixed through an adhesive. For example, an adhesive such as polyvinylidene fluoride (PVDF) can be mixed with deionized water to form a uniform slurry, and this slurry is used to bond the large faces of the two polymer sub-layers together to realize the fixation of the first sub-layer and the second sub-layer.

[0058] According to the embodiments of the present application, the first pores are close to the side of the positive electrode active material layer. During the battery cycling process, the expansion of the positive electrode active material is relatively small. Therefore, the first pores may have a relatively small average pore diameter. For example, the average pore diameter of the first pores can be 10 nm - 20 μm. The second pores are close to the side of the negative electrode active material layer. During the battery cycling process, the expansion of the negative electrode active material is relatively large. Therefore, the first pores may have a relatively large average pore diameter, for example, it can be 500 nm - 20 μm.

[0059] In some embodiments, by adjusting the pore structure in the polymer layer, the Young's modulus of the polymer layer can be made to be from 1 MPa to 100 MPa. Thus, the film layer has appropriate rigidity and toughness and is suitable for providing support for the conductive structure and the subsequent loaded electrode active material.

[0060] In this application, the definition and measurement method of Young's modulus can include any conventional method in the art. For example, Young's modulus can be measured through the following process: Cut the sample to be measured into a specimen of 15 mm × 200 mm, measure the thickness h (μm) of the specimen with a micrometer, and conduct a tensile test using a Gotech tensile machine under normal temperature and pressure (25 degrees Celsius, 0.1 MPa). Set the initial position so that the length of the sample between the clamps is 50 mm, and the tensile speed is 5 mm / min. Record the tensile load L (N) and the equipment displacement y (mm) until the specimen breaks, then calculate the stress ε (GPa) = L / (15 × h), the strain η = y / 50, draw the stress-strain curve, and take the initial linear region of the curve. The slope of the curve is the Young's modulus.

[0061] In some specific embodiments, the average pore diameter of the first pores can be from 10 nm to 1 μm, and the porosity of the first sub-layer 110A can be from 10% to 20%. The average pore diameter of the second pores can be from 1 μm to 20 μm, and the porosity of the second sub-layer 110B can be from 20% to 30%.

[0062] In some embodiments, when the average pore diameters of the first and second pores are inconsistent, in order to make the mechanical properties of the polymer layer more uniform and reduce the probability of excessive local stress, the porosity of the first and second sub-layers can be made the same by adjusting the pore content.

[0063] In some embodiments of this application, the polymer layer and the pore structure therein can be prepared by methods commonly used in the art for forming pore structures in polymer materials. For example, polymer particles can be made into an organic polymer cast sheet through melting, mixing, molding extrusion, etc. The organic polymer cast sheet is stretched a certain multiple along the length direction using a biaxial asynchronous stretching machine, and then stretched along the width direction of the organic polymer cast sheet. By controlling the stretching multiples in the length and width directions, a pore structure with different average pore diameters can be prepared, and then a polymer layer with an appropriate porosity can be obtained. When the polymer layer includes the first and second sub-layers, the stretching multiples in the length and width directions when preparing the first and second sub-layers can be determined according to the target pore diameter and porosity of each sub-layer. When the prepared polymer layer needs to have different porosities and / or average pore diameters in different regions, the polymer layer can be stretched in the width or length direction respectively for different regions, and the stretching multiples when stretching different regions along the same direction are different.

[0064] According to the embodiments of this application, refer to Figure 4, the conductive structure may include a first conductive layer 120A and a second conductive layer 120B. The first conductive layer 120A is in contact with the positive electrode active material and is used to carry the positive electrode active material. The second conductive layer 120B is in contact with the negative electrode active material. The first conductive layer has a first through hole, as shown in reference Figure 4 , so that the electrolyte stored in the first sub-layer 110A can penetrate through the first conductive layer. The second conductive layer has a second through hole, as shown in reference Figure 4 , so that the electrolyte stored in the second sub-layer 110B can penetrate through the second conductive layer. The sizes of the first through hole and the second through hole are independently 500 nm - 20 μm respectively. Thus, the performance of the composite separator can be further improved.

[0065] In some embodiments, the conductive structure may be formed of a material with conductivity such as a metal. For example, the metal includes any one or more of aluminum, aluminum alloy, copper, copper alloy, nickel, nickel alloy, iron, iron alloy, titanium, titanium alloy, silver and silver alloy. For example, the first conductive layer in contact with the positive electrode active material layer can be formed of aluminum metal, and the second conductive layer in contact with the negative electrode active material layer can be formed of copper metal.

[0066] In the present application, the size of the through hole may be the average pore diameter determined by the foregoing definition and measurement method.

[0067] According to the embodiments of the present application, similar to the first and second holes, the sizes of the first through hole and the second through hole, that is, the average pore diameters, may be the same or different. In some embodiments, the average pore diameters of the first through hole and the second through hole may be independently 1 μm - 10 μm respectively, and the porosities of the first conductive layer and the second conductive layer are independently 15 - 30% respectively. Thus, the electrolyte wettability of the composite separator can be further improved.

[0068] In some embodiments, when the composite separator includes a first sub-layer and a second sub-layer, the average pore diameter of the first through hole may be consistent with the average pore diameter of the first hole in the first sub-layer, and the average pore diameter of the second through hole may be consistent with the average pore diameter of the second hole in the second sub-layer. Similarly, the porosity of the first conductive layer may be consistent with the porosity of the first sub-layer, and the porosity of the second conductive layer may be consistent with the porosity of the second sub-layer. Thus, the consistency of the polymer sub-layer and the conductive structure on the same side can be improved, facilitating the circulation of the electrolyte, and the uneven stress distribution during the cycle caused by the difference in their structures can also be alleviated, thereby affecting the overall structural stability of the composite separator.

[0069] For example, in some embodiments, a conductive structure can be formed on the surface of the polymer layer by, but not limited to, methods such as vapor deposition, electroless plating, evaporation plating, and adhesion. Specifically, the prepared polymer layer can be cleaned by pickling, alkali washing, etc., and then placed in a vacuum evaporation chamber. A mask plate is placed on the polymer surface, and a conductive metal is deposited on the surface of the polymer layer at an evaporation temperature of 1300 °C to 2000 °C. Alternatively, a metal layer can also be formed by deposition and other methods, and a through-hole can be formed by laser etching to obtain a conductive structure.

[0070] When the polymer layer includes a first and a second sub-layer, a first conductive layer can be first formed on the surface of the first sub-layer, and a second conductive layer can be formed on the surface of the second sub-layer. Subsequently, the sides of the two insulating sub-layers without the conductive structure are bonded by adhesion.

[0071] In the present application, the thickness of the polymer layer can be adjusted according to the material and porosity of the formed polymer, as long as it can meet the requirements of mechanical properties, achieve self-support and be sufficient to load the conductive structure and the positive and negative active materials. Similarly, the thickness of the conductive structure can also be adjusted according to conditions such as the size and proportion of the through-holes, and the metal forming the conductive structure, and it can play a role in loading the positive and negative active materials and forming a stable solid connection with the polymer layer. For example, in some embodiments of the present application, the thickness of the polymer layer can be 1 μm to 10 μm, and the thickness of the conductive structure can be 1 μm to 10 μm. Specifically, the thickness of the conductive structure can be lower than the thickness of the polymer layer. Specifically, the sum of the thicknesses of the conductive structures on both sides of the polymer layer does not exceed the thickness of the polymer layer.

[0072] It should be particularly noted here that when the polymer layer includes a first and a second sub-layer, the thickness of the polymer layer is the sum of the thicknesses of the two sub-layers, and the sum of the thicknesses of the two sub-layers can be 1 μm to 10 μm. The conductive structures are arranged on two opposite surfaces of the polymer layer, so the thickness of the conductive structure is the thickness of the conductive structure on the single-side surface of the polymer layer. That is to say, the thicknesses of the first conductive layer 120A and the second conductive layer 120B can be independently 1 μm to 10 μm respectively.

[0073] According to the embodiments of the present application, the specific methods for forming the positive active material and the negative active material on the conductive structure can be selected from the common methods in the art, such as coating, deposition, etc. Coating includes any one or more of roll coating, extrusion coating, knife coating, and gravure coating. Deposition includes any one or more of physical deposition and chemical deposition.

[0074] According to an embodiment of the present application, the electrolyte may be a commonly used liquid electrolyte in the art. For example, the electrolyte may include solvents such as cyclic carbonates and chain carbonates, and may also have a lithium salt, as well as additives having functions such as improving gas generation and stabilizing the SEI film. For example, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. The solvent may also be an ether solvent. The ether solvent may include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyltetrahydrofuran, diphenyl ether, and crown ether. The lithium salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalato)borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate. The additive may include a negative electrode film-forming additive, may also include a positive electrode film-forming additive, and may further include an additive capable of improving certain performance of the lithium ion secondary battery, such as an additive for improving the overcharge / quick charge performance of the lithium ion secondary battery, an additive for improving the high temperature performance of the lithium ion secondary battery, an additive for improving the low temperature performance of the lithium ion secondary battery, etc. For example, it may include at least one of cyclic sulfonic esters, 1,3-propane sultone, butylene carbonate (BC), fluoroethylene carbonate (FEC), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0075] In some specific embodiments, the electrolyte may contain EC (ethylene carbonate), PC (polycarbonate), DMC (dimethyl carbonate), the additive may include VC, DTD, PS, etc., and the lithium salt may include lithium hexafluorophosphate.

[0076] According to an embodiment of the present application, the positive electrode active material layer includes at least one of lithium-containing phosphates and lithium transition metal oxides. In some embodiments, the lithium-containing phosphates and / or lithium transition metal oxides included in the positive electrode active material may further include lithium iron phosphate and / or modified products of lithium transition metal oxides, and include at least one of lithium manganese phosphate and lithium-rich manganese-based materials, including but not limited to. The negative electrode active material layer includes at least one of a graphite negative electrode material and a silicon-based negative electrode material, and may include at least one of artificial graphite and natural graphite, for example.

[0077] According to an embodiment of the present application, refer to Figure 5, on both sides of the composite separator 100, an insulating separator is further provided. Specifically, the insulating separator can be a secondary battery separator commonly used in the art, and is used to insulate and isolate the electrode active materials on the surfaces of multiple composite separators. For example, referring to Figure 5 , it may include a first separator 200 and a second separator 300 to achieve insulation between the positive electrode and the negative electrode when forming a wound battery or other forms.

[0078] According to an embodiment of the present application, the secondary battery proposed by the present application can be a square shell battery or a cylindrical battery. According to an embodiment of the present application, the secondary battery can be a soft package battery or a hard shell battery. Figure 1 It is a secondary battery 10 with a square structure as an example. Referring to Figure 2 , the secondary battery may have an outer package, and the outer package may include a housing 101 and a cover plate 103. Among them, the housing 101 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 101 has an opening communicating with the receiving cavity, and the cover plate 103 can be disposed on the opening to close the receiving cavity. One or more electrode assemblies 102 can be accommodated in the receiving cavity, the electrolyte is infiltrated in the electrode assemblies 102, and the aforementioned composite separator can be sealed in the electrode assemblies 102 by winding or other means.

[0079] In another aspect of the present application, the present application proposes a composite separator. Referring to Figure 3 , the composite separator includes a polymer layer 110 and conductive structures located on both sides of the polymer layer, such as 120A and 120B shown in the figure. The composite separator can be the composite separator in the aforementioned secondary battery. Specifically, the polymer layer has pores that can pass through the electrolyte, and the conductive structure has through holes to provide a flow path for the electrolyte. The porosity of the composite separator is 15%-30%, and the average pore diameter of the polymer layer is 10 nm - 20 μm. The composite separator has an average pore diameter suitable for storing the electrolyte and has the function of a current collector, which can alleviate the decline in cycle performance caused by poor electrolyte infiltration, so it has good cycle performance and safety.

[0080] According to an embodiment of the present application, referring to Figure 4 , the polymer layer may include a first sub-layer 110A and a second sub-layer 110B. The first sub-layer has a plurality of first holes, the second sub-layer has a plurality of second holes, the average pore diameter of the first holes is 10 nm - 1 μm, and the average pore diameter of the second holes is 1 μm - 20 μm. Thus, the performance of the composite separator can be further improved. Similarly, terms such as "first hole", "second hole", and "average pore diameter" in the composite separator can also have the same meaning as the corresponding terms in the composite separator of the aforementioned secondary battery.

[0081] According to an embodiment of the present application, similarly, the conductive structure includes a first conductive layer 120A and a second conductive layer 120B. The first conductive layer is located on one side of the first sub-layer, and the second conductive layer is located on one side of the second sub-layer. The first conductive layer has a first through-hole, and the second conductive layer has a second through-hole. The average pore diameters of the first through-hole and the second through-hole are independently 1-10 μm respectively, and the porosities of the first conductive layer and the second conductive layer are independently 10-30%. Thereby, the performance of the composite separator can be further improved. Similarly, the sizes of the first and second through-holes can be the average pore diameters of the through-holes. The size of the first through-hole can be consistent with the average pore diameter of the first hole in the first sub-layer, and the size of the second through-hole can be consistent with the average pore diameter of the second hole in the second sub-layer.

[0082] Generally speaking, the polymer layer of the composite separator has an average pore diameter suitable for storing the electrolyte, and the through-holes of the conductive structure allow the electrolyte to flow through the conductive structure. When the positive and negative active materials loaded on the composite separator, especially the negative active material expands during cycling, the electrolyte stored in the pore structure of the polymer layer can be extruded to achieve the effect of wetting the surface of the composite separator. The overall porosity of the composite separator can ensure the mechanical properties of the composite membrane and meet the requirements of the secondary battery for the mechanical strength and other properties of the current collector.

[0083] In another aspect of the present application, the present application proposes a battery device. The battery device includes the secondary battery or the composite separator described above. Thereby, the battery device has all the features and advantages of the aforementioned secondary battery and composite separator. Generally speaking, the battery device has good cycling performance and safety.

[0084] In another aspect of the present application, the present application proposes an electrical device. The electrical device includes the battery device described above. Thereby, the electrical device has all the features and advantages of the aforementioned battery device, secondary battery and composite separator. Generally speaking, the electrical device has good cycling performance and safety.

[0085] In the present application, the electrical device can be such as a mobile phone, a tablet computer, a laptop computer, an electric toy, an electric tool, a battery car, an electric vehicle, a ship, a spacecraft, etc. Among them, the electric toy can include a fixed or mobile electric toy, for example, a game console, an electric vehicle toy, an electric ship toy, an electric aircraft toy, etc., and the spacecraft can include an airplane, a rocket, a space shuttle, a spaceship, etc.

[0086] Figure 6The electric device 2 is taken as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electric device for the battery, a battery pack or a battery module can be adopted.

[0087] The electric device as another example can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires to be thin and light, and a lithium-ion secondary battery can be adopted as the power source.

[0088] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and cannot be construed as a limitation to the present application. For those specific technologies or conditions not specified in the embodiments, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product specification. For the reagents or instruments not specified in the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0089] Embodiment 1

[0090] Step 1: The organic polymer polypropylene particles are melted, kneaded, and formed by extrusion to obtain an organic polymer cast sheet. The cast sheet is stretched along the length direction and the width direction by a biaxial asynchronous stretching machine, and the first sub-layer with the required size is obtained by die cutting; the second sub-layer is obtained in the same way. The pore size and porosity of the polymer layer are tested, and the average pore size of the first sub-layer in Embodiment 1 is 100 nm, and the porosity is 12%; the average pore size of the second sub-layer is 3 μm, and the porosity is 21%. A binder such as polyvinylidene fluoride (PVDF) is mixed with deionized water to form a uniform slurry, and this slurry is used to bond the first polymer layer and the second polymer layer together on the large surface.

[0091] Step 2: A mask with a porosity of 20% and a pore size of 10 μm is covered on the side of the first sub-layer away from the second sub-layer, and a mask without voids is covered on the side of the second sub-layer away from the first sub-layer. Then, a porous aluminum-based conductive layer with a thickness of 3 μm is obtained on the side of the first sub-layer away from the second sub-layer by physical vapor deposition. In the same way, a porous copper-based conductive layer is obtained on the side of the second sub-layer away from the first sub-layer.

[0092] Step 3: Graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and binder sodium carboxymethyl cellulose (CMC) are mixed according to a certain mass ratio, and deionized water as the solvent is added, and they are fully stirred and mixed evenly to obtain a negative electrode slurry. The lithium-rich cathode material 0.4Li2MnO3·0.6LiNi 0.5 Mn 0.5O2, conductive agent acetylene black, and binder PVDF (polyvinylidene fluoride) are mixed in a weight ratio of 94:4:2, and solvent N-methylpyrrolidone is added, and the mixture is stirred and mixed to obtain positive electrode slurry. The negative electrode slurry is applied to the copper-based conductive layer of the composite isolation membrane on the side away from the second sublayer, and the positive electrode slurry is applied to the aluminum-based conductive layer of the composite fluid on the side away from the first sublayer, and then a pole piece with a positive electrode on one side and a negative electrode on the other side is formed through baking, cold pressing, die cutting and other processes.

[0093] Step 4: Provide an electrolyte. In an argon atmosphere glove box with a water content of <10 ppm, mix EC (ethylene carbonate), PC (polycarbonate), and DMC (dimethyl carbonate) in a weight ratio of EC:PC:DMC=3:3:3, and then add LiPF6, VC, DTD and PS. After stirring evenly, an electrolyte is obtained, wherein the concentration of LiPF6 in the lithium-ion battery electrolyte is 1 mol / L, and the mass percentages of VC, DTD, and PS are 3%, 1%, and 1%, respectively, to obtain an electrolyte.

[0094] Step 5: Form a bare cell by winding the die-cut multiple groups of membranes, each group of membranes is composed of a first diaphragm, a composite electrode, and a second diaphragm stacked in sequence. Put the bare cell into an outer package and inject the electrolyte, and then obtain a lithium-ion secondary battery through formation, aging and other processes.

[0095] Embodiment 2:

[0096] The remaining operations are the same as those in Example 1, except that in step 1, the average pore size of the second sublayer is 10 μm, the porosity is 25%, and the other steps and conditions remain unchanged.

[0097] Embodiment 3:

[0098] The difference from Example 1 is that in step 1, the average pore size of the second sublayer is 18 μm, the porosity is 28%, and the other steps and conditions remain unchanged.

[0099] Embodiment 4:

[0100] The difference from Example 1 is that in step 1, the average pore size of the first sublayer is 500 nm, the porosity is 15%, and the other steps and conditions remain unchanged.

[0101] Embodiment 5:

[0102] The difference from Example 2 is that in step 1, the average pore size of the first sublayer is 500 nm, the porosity is 15%, and the other steps and conditions remain unchanged.

[0103] Embodiment 6:

[0104] The difference from Example 3 is that the average pore diameter of the first sub-layer in Step 1 is 500 nm and the porosity is 15%, and the other steps and conditions remain unchanged.

[0105] Example 7:

[0106] The difference from Example 1 is that the average pore diameter of the first sub-layer in Step 1 is 1 μm and the porosity is 19%, and the other steps and conditions remain unchanged.

[0107] Example 8:

[0108] The difference from Example 2 is that the average pore diameter of the first sub-layer in Step 1 is 1 μm and the porosity is 19%, and the other steps and conditions remain unchanged.

[0109] Example 9:

[0110] The difference from Example 3 is that the average pore diameter of the first sub-layer in Step 1 is 1 μm and the porosity is 19%, and the other steps and conditions remain unchanged.

[0111] Example 10:

[0112] The remaining operations are the same as those in Example 1. The difference from Example 1 is that in Step 1, the average pore diameters of the first and second sub-layers are both 10 μm and the porosities are both 25%, and the other steps and conditions remain unchanged.

[0113] Example 11:

[0114] The remaining operations are the same as those in Example 1. The difference from Example 1 is that in Step 1, the average pore diameter of the second sub-layer is 1 μm and the porosity is 19%, and the other steps and conditions remain unchanged.

[0115] Comparative Example 1:

[0116] The difference from Example 1 is that there is no need to create pores on the first polymer layer, the second polymer layer, and the conductive layer.

[0117] Comparative Example 2

[0118] The difference from Example 1 is that the average pore diameters of the first and second polymer layers are both 25 μm and the porosities are both 50%, and the other steps and conditions remain unchanged.

[0119] Comparative Example 3

[0120] The difference from Example 1 is that the average pore diameters of the first and second sub-layers are both 100 nm and the porosities are both 12%, and the other steps and conditions remain unchanged.

[0121] Perform performance tests on the composite separator membranes and secondary batteries prepared in the above examples and comparative examples:

[0122] Pore size test of the composite separator:

[0123] Samples were taken from the first polymer layer and the second polymer layer respectively. Photographs of the samples magnified 30,000 times were obtained through a scanning electron microscope, and the average pore size of the pores in the samples was obtained by combining software such as Nano Measurer and Origin.

[0124] Porosity test of the composite separator:

[0125] The porosity of the first polymer layer and the second polymer layer was detected by the weighing method. First, the weight of the polymer layer with a volume of V was weighed and recorded as m0. The weighed polymer layer was completely immersed in n-hexadecane reagent for 2 h, and then the polymer layer was taken out and the residual reagent on its surface was wiped off with dust-free paper. The weight of the polymer layer was weighed and recorded as m1. The porosity of the polymer layer was calculated using the following formula:

[0126]

[0127] In the above formula is the porosity, with the unit of %; is the density of n-hexadecane, with the unit of g / cm 3 .

[0128] Liquid retention rate test of the electrode sheet:

[0129] Take 20 layers of the composite separator with a conductive structure (hereinafter simply referred to as the electrode sheet) prepared by the described method, with a size of 100 mm * 100 mm. Stack the electrode sheets together and clamp them with two aluminum clamps, and weigh the weight and record it as m0; then soak it together with the clamps in the electrolyte for 2 h and take it out. Wait until the electrolyte is in a dripping state and wipe off the residual electrolyte on the surface of the aluminum clamps with dust-free paper, and weigh the weight and record it as m1; then use an automatic press to apply a pressure of 3000 N on both sides of the clamps (simulating the state of the battery in the battery pack), and weigh the weight and record it as m2 after maintaining for 3 min. The liquid retention rate of the electrode sheet is calculated according to the following formula:

[0130]

[0131] In the above formula is the liquid retention rate, with the unit of %.

[0132] The test results of the above examples and comparative examples are shown in Table 1 below:

[0133] Table 1

[0134]

[0135] From the above results, it can be seen that the pore-forming design of the organic polymer layer and the conductive layer has an obvious effect on improving the liquid retention rate of the electrode sheet. From the results of the examples, when the pore size and porosity of the first sub-layer remain unchanged, when the pore size of the second sub-layer increases from 3 μm to 10 μm, the liquid retention rate of the electrode sheet increases significantly; however, when the pore size of the second sub-layer increases from 10 μm to 18 μm, the liquid retention rate of the electrode sheet remains basically unchanged. When the pore size and porosity of the first polymer remain unchanged, as the pore size and porosity of the second polymer layer increase, the liquid retention rate of the electrode sheet increases to some extent, but the increased value is not large.

[0136] Lithium-ion secondary battery cycle performance test:

[0137] In a constant temperature environment of 25 °C, charge at a constant current of 1C to 4.4V, then charge at a constant voltage of 4.4V until the current drops to 0.05C, and then discharge at a constant current of 1C to 2.5 V to obtain the first-week discharge specific capacity (C d1 ); Repeat charging and discharging in this way until the 500th week, and the discharge specific capacity after 500 cycles is recorded as C dn .

[0138] Capacity retention rate (%) = Discharge specific capacity after 500 cycles (C dn ) / First-week discharge specific capacity (C d1 ).

[0139] Lithium-ion secondary battery corner lithium deposition test after cycling

[0140] Charge the lithium-ion secondary battery after 500 cycles at a constant current of 1C to 4.4V, then charge at a constant voltage of 4.4V until the current drops to 0.05C, and then disassemble it to determine the lithium deposition at the corner of the anode electrode sheet interface, and grade the lithium deposition at the corners of the concave and convex surfaces of the anode according to the judgment grades shown in Table 2 below.

[0141] The judgment grades for lithium deposition at the corner interface of the anode of the lithium-ion secondary battery after 500 cycles are shown in Table 2 below, where JR in Table 2 is the number of electrode components in the secondary battery:

[0142] Table 2

[0143]

[0144] The cycle capacity retention rate and the corner lithium deposition grade of the above examples and comparative examples are shown in Table 3 below:

[0145] Table 3

[0146]

[0147] In terms of the cycle performance and the lithium deposition level at the anode corner, as the pore size and porosity of the first polymer layer and the second polymer layer increase, the liquid retention rate of the electrode sheet is improved. Therefore, the electrolyte infiltration at the battery corner position is improved, which in turn improves the lithium deposition at the corner position, and finally improves the cycle performance of the battery. However, when the pore size of the second sub-layer is 10 μm and 18 μm, and the corresponding pore sizes of the first sub-layer are 500 nm and 1 μm, the lithium deposition levels at the battery corner positions are both grade one.

[0148] 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 foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be covered by the scope of the claims and the specification of the present application. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed in the text, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A secondary battery, characterized in that, Comprising: A composite separator, a positive electrode active material layer on one side of the composite separator, and a negative electrode active material layer on the other side of the composite separator, The composite separator includes a polymer layer, and conductive structures on both sides of the polymer layer, the conductive structures having through holes, The porosity of the composite separator is 15 - 30%, and the average pore diameter of the polymer layer is 100 nm - 20 μm, The polymer layer includes a first sub-layer and a second sub-layer, the first sub-layer is on the side close to the positive electrode active material layer, the second sub-layer is on the side close to the negative electrode active material layer, the first sub-layer has a plurality of first holes, and the second sub-layer has a plurality of second holes, The average pore diameters of the first holes and the second holes are different, the average pore diameter of the first holes is 10 nm - 1 μm, and the average pore diameter of the second holes is 1 μm - 20 μm.

2. The secondary battery according to claim 1, wherein The porosity of the first sub-layer is 10 - 20%, and the porosity of the second sub-layer is 20 - 30%.

3. The secondary battery according to claim 1, characterized in that, The material of the polymer layer includes at least one of epoxy resin, terephthalate, polyethylene, polypropylene, poly(p-phenyleneterephthalamide), polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, and polyamide.

4. The secondary battery according to claim 1, characterized in that, The conductive structure includes a first conductive layer and a second conductive layer, the first conductive layer is in contact with the positive electrode active material, and the second conductive layer is in contact with the negative electrode active material, The first conductive layer has first through holes, and the second conductive layer has second through holes, The average pore diameters of the first through holes and the second through holes are independently 500 nm - 20 μm.

5. The secondary battery according to claim 4, characterized in that, The average pore diameters of the first through holes and the second through holes are independently 1 μm - 10 μm.

6. The secondary battery according to claim 4, wherein The porosities of the first conductive layer and the second conductive layer are independently 10 - 30%.

7. The secondary battery according to claim 1, characterized in that, The secondary battery is a wound battery, The wound battery includes a plurality of the composite separators, and the plurality of composite separators are separated by an insulating separator. The composite separator includes a plurality of flat portions and a plurality of bent portions, and adjacent flat portions are connected by the bent portions.

8. A composite separator, characterized in that, Comprising: A polymer layer, and conductive structures on both sides of the polymer layer, the conductive structures having through holes, The porosity of the composite separator is 15 - 30%, and the average pore diameter of the polymer layer is 100 nm - 20 μm, The polymer layer includes a first sub-layer and a second sub-layer, the first sub-layer has a plurality of first holes, the second sub-layer has a plurality of second holes, the average pore diameters of the first holes and the second holes are different, the average pore diameter of the first holes is 10 nm - 1 μm, and the average pore diameter of the second holes is 1 μm - 20 μm.

9. The composite separator film according to claim 8, wherein, The conductive structure includes a first conductive layer and a second conductive layer, the first conductive layer is on one side of the first sub-layer, and the second conductive layer is on one side of the second sub-layer, The first conductive layer has first through holes, and the second conductive layer has second through holes, The average pore diameters of the first through-hole and the second through-hole are independently 1-10 μm, The porosities of the first conductive layer and the second conductive layer are independently 10-30%.

10. An electrical device, characterized in that, A secondary battery comprising any one of claims 1-7.

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