Secondary battery and electric device

Abstract

This application provides a secondary battery and an electrical device. The secondary battery includes a positive electrode, a negative electrode, and a separator, with the separator located between the positive and negative electrodes. The separator includes a first polymer layer and a material layer disposed on the first polymer layer. The material layer includes an inorganic material, such as lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium aluminum germanium titanium phosphate, lithium aluminum tantalum titanium phosphate, lithium tetrathiophosphate, lithium germanium phosphorus sulfide, lithium phosphorus sulfide, and titanium dioxide, or one or more of these materials. In a longitudinal cross-section of the separator, the difference between the porosity of the material layer and the porosity of the first polymer layer is less than or equal to 10%. This secondary battery exhibits excellent high-rate cycle performance and a long service life.

Description

[0001] This application is a divisional application of Chinese patent application No. 202410458125.2, entitled "Secondary Battery and its Preparation Method and Electrical Device". Technical Field

[0002] This application relates to the field of secondary battery technology, and in particular to a secondary battery, its preparation method, and an electrical device thereof. Background Technology

[0003] In recent years, with the increasingly wide application of rechargeable batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. Due to the significant development of rechargeable batteries, higher requirements have been placed on their cycle performance. However, the cycle performance of existing rechargeable batteries needs further improvement. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery with good cycle performance.

[0005] A first aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, and a separator, wherein the separator is located between the positive and negative electrode, and the separator includes a first polymer layer and a material layer disposed on the first polymer layer, the material layer comprising an inorganic material. The inorganic materials include one or more of the following: lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium aluminum titanium germanium phosphate, lithium aluminum titanium phosphate, lithium aluminum titanium phosphate, lithium tetrathiophosphate, lithium germanium phosphorus sulfide, lithium phosphorus sulfide, iron oxide, copper oxide, titanium dioxide, tin dioxide, manganese dioxide, zinc oxide, zirconium dioxide, chromium nitride, vanadium nitride, nickel nitride, iron nitride, graphene oxide, graphene oxide, fluorinated graphite, fluorinated graphene, fluorinated carbon nanotubes, and fluorinated carbon fibers.

[0006] By incorporating inorganic materials such as lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium aluminum titanium germanium phosphate, lithium aluminum titanium phosphate, lithium aluminum titanium phosphate, lithium tetrathiophosphate, lithium germanium phosphorus sulfide, lithium phosphorus sulfide, iron oxide, copper oxide, titanium dioxide, tin dioxide, manganese dioxide, zinc oxide, zirconium dioxide, chromium nitride, vanadium nitride, nickel nitride, iron nitride, graphene oxide, graphene oxide, fluorinated graphite, fluorinated graphene, fluorinated carbon nanotubes, or fluorinated carbon fibers into the material layer of the separator, these inorganic materials can react with lithium metal and absorb lithium dendrites in contact with the material layer, causing the sharp lithium dendrites to transform into other lithium compounds. This reduces the risk of lithium dendrites continuing to puncture the separator and improves the cycle performance of the battery at high rates.

[0007] In any embodiment, the material layer is disposed on the side surface of the first polymer layer near the negative electrode sheet.

[0008] The material layer in the separator is disposed on the side surface of the first polymer layer near the negative electrode. The inorganic material can react quickly with the lithium dendrites grown on the negative electrode to absorb the lithium dendrites and improve the cycle performance of the battery at high rates.

[0009] In any embodiment, in a longitudinal cross-section of the diaphragm, the difference between the porosity of the material layer and the porosity of the first polymer layer is less than or equal to 10%.

[0010] The small difference in porosity between the material layer and the first polymer layer results in a smaller difference in lithium ion transport capacity between different layers and a smaller difference in lithium ion concentration between layers. This is beneficial to the overall uniformity of ion transport in the separator. At the same time, the small difference in porosity between layers can also reduce the interfacial effect between the layers of the separator, improve the compatibility between the layers of the separator, reduce the impedance of the separator, and help improve the cycle performance and rate performance of the battery.

[0011] In any embodiment, in a longitudinal section of the diaphragm, the porosity of the material layer is 10%-30%.

[0012] When the porosity of the material layer is within a suitable range, it ensures that the material layer has excellent ion transport performance and the diaphragm has low impedance, while also giving the material layer and diaphragm a certain mechanical strength, thus comprehensively improving the performance of the diaphragm.

[0013] In any embodiment, in a longitudinal cross-section of the diaphragm, the porosity of the first polymer layer is 10%-30%.

[0014] With the porosity of the first polymer layer within a suitable range, the first polymer layer has excellent ion transport performance and the membrane has low impedance, while the first polymer layer and the membrane also have a certain mechanical strength, thus comprehensively improving the performance of the membrane.

[0015] In any embodiment, the membrane further includes a second polymer layer, the material layer being located between the first polymer layer and the second polymer layer.

[0016] By setting a first polymer layer and a second polymer layer on both sides of the material layer, the material layer can be protected, reducing the risk of premature reduction and failure of inorganic materials caused by direct contact between inorganic materials and negative electrode sheets. At the same time, it can also improve the safety factor of the material layer and the separator, and further improve the cycle performance of the battery at high rates. In any embodiment, the difference between the porosity of the material layer and the porosity of the first polymer layer is less than or equal to 10% and / or the difference between the porosity of the material layer and the porosity of the second polymer layer is less than or equal to 10%.

[0017] Small differences in porosity between layers result in smaller differences in lithium-ion transport capacity across different layers and smaller differences in lithium-ion concentration between layers. This is beneficial for the overall uniformity of ion transport in the separator. At the same time, small differences in porosity between layers can also reduce the interfacial effect between the layers of the separator, improve the compatibility between the layers, and reduce the impedance of the separator, which is beneficial for improving the cycle performance and rate performance of the battery.

[0018] In any embodiment, in a longitudinal section of the diaphragm, the porosity of the material layer is 10%-30%.

[0019] When the porosity of the material layer is within a suitable range, it ensures that the material layer has excellent ion transport performance and the diaphragm has low impedance, while also giving the material layer and diaphragm a certain mechanical strength, thus comprehensively improving the performance of the diaphragm.

[0020] In any embodiment, in a longitudinal cross-section of the diaphragm, the porosity of the first polymer layer and / or the porosity of the second polymer layer is 10%-30%.

[0021] When the porosity of the first polymer layer and / or the porosity of the second polymer layer are within a suitable range, the first polymer layer and the second polymer layer have excellent ion transport performance and the membrane has low impedance. At the same time, the first polymer layer, the second polymer layer and the membrane also have a certain mechanical strength, thus comprehensively improving the performance of the membrane.

[0022] In any embodiment, the volume distribution particle size Dv50 of the inorganic material is 50nm-5000nm.

[0023] In any embodiment, the volumetric particle size Dv50 of the inorganic material is 50nm-1000nm.

[0024] When the volume distribution particle size Dv50 of the inorganic material is within a suitable range, on the one hand, the risk of excessively small particle size clogging the pores on the surface of the material layer is reduced, resulting in excellent air permeability and excellent ion transport channels for the membrane. On the other hand, it avoids adverse effects on processing performance due to excessively large inorganic material particle size, improves the uniformity of inorganic material distribution in the material layer, and also reduces the "powder shedding" phenomenon that occurs during the processing of excessively large inorganic material, which would affect the absorption of lithium dendrites by the inorganic material.

[0025] In any embodiment, the material layer further includes a third polymer, and the inorganic material has a mass content of 5%-50% based on the mass of the material layer; and / or, the third polymer has a mass content of 50%-95%.

[0026] In any embodiment, based on the mass of the material layer, the mass content of the inorganic material is 10%-50%; and / or, the mass content of the third polymer is 50%-90%.

[0027] By controlling the mass content of the third polymer or inorganic material in the material layer within a suitable range, the separator has low ionic impedance, and the battery has good cycle performance at high rates.

[0028] In any embodiment, the first polymer layer further includes a first polymer, and the second polymer layer further includes a second polymer. The first polymer, the second polymer, and the third polymer each independently comprise one or more of polyethylene, polypropylene, polyamide, polyester, polytetrafluoroethylene, polyvinylidene fluoride, and polyvinyl chloride.

[0029] In any embodiment, the first polymer, the second polymer, and the third polymer comprise polymers having the same material.

[0030] The first polymer, the second polymer, and the third polymer are polymers of the same material, and the separator has good compatibility, which improves the transport speed of lithium ions in the separator, reduces the ion impedance of the separator, and improves the cycle performance and rate performance of the battery.

[0031] In any embodiment, the thickness ratio of the first polymer layer, the material layer, and the second polymer layer is 1:(1~3):(0.8~1.2).

[0032] In any embodiment, the thickness ratio of the first polymer layer, the material layer, and the second polymer layer is 1:(1.5~2.5):(0.8~1.2).

[0033] When the thickness ratio of the first polymer layer, the material layer, and the second polymer layer is within a suitable range, the separator has low ion resistance, and the battery has good cycle performance at high rates.

[0034] In any embodiment, the thickness of the first polymer layer is 2.5 μm-4.5 μm; and / or, the thickness of the material layer is 3.5 μm-7.5 μm; and / or, the thickness of the second polymer layer is 2.5 μm-4.5 μm.

[0035] Within a suitable range, the first polymer layer, material layer, or second polymer layer of the separator has low ion resistance, a certain puncture strength, and the battery has good cycle performance and safety performance at high rates.

[0036] In any embodiment, the thickness of the diaphragm is 5 μm-25 μm.

[0037] In any embodiment, the thickness of the diaphragm is 10 μm-15 μm.

[0038] A second aspect of this application provides a method for preparing a secondary battery, comprising: An electrode assembly comprising a positive electrode, a negative electrode, and a separator is assembled to obtain a secondary battery. The separator comprises a first polymer layer and a material layer disposed on the first polymer layer, the material layer comprising an inorganic material. The inorganic materials include one or more of the following: lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium aluminum titanium germanium phosphate, lithium aluminum titanium phosphate, lithium aluminum titanium phosphate, lithium tetrathiophosphate, lithium germanium phosphorus sulfide, lithium phosphorus sulfide, iron oxide, copper oxide, titanium dioxide, tin dioxide, manganese dioxide, zinc oxide, zirconium dioxide, chromium nitride, vanadium nitride, nickel nitride, iron nitride, graphene oxide, graphene oxide, fluorinated graphite, fluorinated graphene, fluorinated carbon nanotubes, and fluorinated carbon fibers.

[0039] The separator of a secondary battery contains a material layer that absorbs lithium dendrites in contact with the material layer, causing the sharp lithium dendrites to transform into other lithium compounds. This reduces the risk of lithium dendrites continuing to puncture the separator and improves the battery's cycle performance at high rates.

[0040] In any embodiment, the membrane is prepared as follows: Step a: The raw materials for the first polymer layer, the raw materials for the material layer, and the raw materials for the second polymer layer are co-extruded to obtain a composite sheet; Step b: The composite sheet is stretched to form a thin film; Step c: Extract and heat-set the film to obtain a diaphragm.

[0041] The raw materials for the material layer include the inorganic materials. The membrane includes a first polymer layer, a material layer, and a second polymer layer, wherein the material layer is located between the first polymer layer and the second polymer layer.

[0042] The above preparation method can yield a separator comprising a first polymer layer, a material layer, and a second polymer layer. The material layer comprises an inorganic material that can react with lithium metal, causing sharp lithium dendrites to transform into other lithium compounds, reducing the risk of lithium dendrites continuing to puncture the separator, and improving the cycle performance of the battery at high rates. At the same time, the material layer is located between the first polymer layer and the second polymer layer, which can improve the safety performance of the material layer and further improve the cycle performance of the battery.

[0043] The third aspect of this application is an electrical device, characterized in that it comprises a secondary battery of the first aspect or a secondary battery obtained by the preparation method of the second aspect. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the diaphragm according to one embodiment of this application; Figure 2 This is a schematic diagram of the diaphragm according to one embodiment of this application. Figure 3 This is a schematic diagram of a secondary battery according to one embodiment of this application; Figure 4 yes Figure 3 An exploded view of a secondary battery according to an embodiment of this application is shown. Figure 5 This is a schematic diagram of a battery module according to one embodiment of this application; Figure 6 This is a schematic diagram of a battery pack according to one embodiment of this application; Figure 7 yes Figure 6 An exploded view of a battery pack according to one embodiment of this application is shown; Figure 8 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application; Figure 9 This is a scanning electron microscope image of the cross-section of the diaphragm prepared in Example 18; Figure 10 This is a scanning electron microscope image of the cross-section of the diaphragm prepared in Example 18; Figure 11 This is a scanning electron microscope image of the cross-section of the diaphragm prepared in Example 1; Figure 12 This is a scanning electron microscope image of a section of the diaphragm prepared in Example 1.

[0045] Figure label: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate; 10 Separator; 101 First polymer layer; 102 Material layer; 103 Second polymer layer. Detailed Implementation

[0046] The following detailed description, with appropriate reference to the accompanying drawings, discloses the secondary battery, its preparation method, and embodiments of the power-using device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0047] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0048] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0049] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0050] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0051] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0052] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0053] With the development of society, people have increasingly higher requirements for the safety of rechargeable batteries. However, after multiple cycles, metallic lithium will precipitate on the surface of the negative electrode. The metallic lithium dendrites can pierce the separator, causing the positive and negative electrodes to come into contact and resulting in a short circuit. Dendrites are especially prone to form during fast charging, affecting the cycle performance and safety performance of high-rate batteries.

[0054] [Rechargeable Battery] This application provides a secondary battery, including a positive electrode, a negative electrode, and a separator. The separator is located between the positive and negative electrode. The separator includes a first polymer layer and a material layer disposed on the first polymer layer. The material layer includes an inorganic material. The inorganic materials include one or more of the following: lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium aluminum titanium germanium phosphate, lithium aluminum titanium phosphate, lithium aluminum titanium phosphate, lithium tetrathiophosphate, lithium germanium phosphorus sulfide, lithium phosphorus sulfide, iron oxide, copper oxide, titanium dioxide, tin dioxide, manganese dioxide, zinc oxide, zirconium dioxide, chromium nitride, vanadium nitride, nickel nitride, iron nitride, graphene oxide, graphene oxide, fluorinated graphite, fluorinated graphene, fluorinated carbon nanotubes, and fluorinated carbon fibers.

[0055] Figure 1This is a schematic diagram of an embodiment of the diaphragm of this application. The diaphragm 10 includes a first polymer layer 101 and a material layer 102 disposed on the first polymer layer 101. In this paper, the term "graphene oxide" refers to graphene containing oxygen-containing functional groups, including but not limited to hydroxyl and carboxylic acid groups. Graphene oxide can be obtained by oxidizing graphene.

[0056] In this paper, the term "graphite oxide" refers to graphite containing oxygen-containing functional groups, including but not limited to hydroxyl and carboxylic acid groups. Graphene oxide can be obtained by oxidizing graphene.

[0057] In this article, the term "fluorinated graphite" refers to graphite containing fluorine atoms, and fluorinated graphene can be obtained by reacting graphite with F2.

[0058] In this article, the term "fluorinated graphene" refers to graphene containing fluorine atoms, which can be obtained by reacting graphene with F2.

[0059] In this paper, the term "fluorinated carbon nanotubes" refers to carbon nanotubes containing fluorine atoms, which can be obtained by reacting carbon nanotubes with F2.

[0060] In this article, the term "fluorinated carbon fiber" refers to carbon fiber containing fluorine atoms, which can be obtained by reacting carbon fiber with F2.

[0061] In some embodiments, the ratio of carbon atoms to oxygen atoms in graphene oxide or graphite oxide is 1:2 to 2:1.

[0062] In some embodiments, the ratio of carbon atoms to fluorine atoms in fluorinated graphite, fluorinated graphene, fluorinated carbon nanotubes, or fluorinated carbon fibers is 1:2 to 2:1.

[0063] By incorporating inorganic materials such as lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium aluminum titanium germanium phosphate, lithium aluminum titanium phosphate, lithium aluminum titanium phosphate, lithium tetrathiophosphate, lithium germanium phosphorus sulfide, lithium phosphorus sulfide, iron oxide, copper oxide, titanium dioxide, tin dioxide, manganese dioxide, zinc oxide, zirconium dioxide, chromium nitride, vanadium nitride, nickel nitride, iron nitride, graphene oxide, graphene oxide, fluorinated graphite, fluorinated graphene, fluorinated carbon nanotubes, or fluorinated carbon fibers into the material layer of the separator, these inorganic materials can react with lithium metal and absorb lithium dendrites in contact with the material layer, causing the sharp lithium dendrites to transform into other lithium compounds. This reduces the risk of lithium dendrites continuing to puncture the separator and improves the cycle performance of the battery at high rates.

[0064] In some embodiments, the material layer is disposed on the side surface of the first polymer layer near the negative electrode sheet.

[0065] The material layer in the separator is disposed on the side surface of the first polymer layer near the negative electrode sheet. The inorganic material can react quickly with the lithium dendrites grown on the negative electrode sheet to absorb the lithium dendrites and improve the cycle performance of the battery at high rates.

[0066] In some embodiments, in a longitudinal cross-section of the diaphragm, the difference between the porosity of the material layer and the porosity of the first polymer layer is less than or equal to 10%.

[0067] In some embodiments, in the longitudinal cross-section of the diaphragm, the difference between the porosity of the material layer and the porosity of the first polymer layer is less than or equal to 10%, and can be selected as any one of less than or equal to 2%, less than or equal to 3%, less than or equal to 4%, less than or equal to 5%, less than or equal to 6%, less than or equal to 7%, less than or equal to 8%, less than or equal to 9%, or less than or equal to 10%.

[0068] The porosity can be tested using any method known in the art, as exemplified below: Disassemble the battery to obtain the separator. Cut the separator into a sample of a certain size (e.g., 6mm × 6mm). Clamp the sample between two conductive and thermally conductive sheets (e.g., copper foil). Secure the sample to the sheets with adhesive (e.g., double-sided tape). Press the sample with a flat iron block of a certain mass (e.g., 400g) for a certain time (e.g., 1 hour) to minimize the gap between the sample and the copper foil. Trim the edges with scissors and attach the sample to a sample stage with conductive adhesive, ensuring the sample slightly protrudes from the edge of the sample stage. Then, mount the sample stage onto the sample holder and lock it in place. Turn on the argon ion cross-section polisher (e.g., IB-19500CP) and evacuate the system (e.g., 10Pa-4Pa). Set the argon flow rate (e.g., 0.15MPa), voltage (e.g., 8KV), and polishing time (e.g., 2 hours). Adjust the sample stage to swing mode and begin polishing. After polishing, scanning electron microscopy (SEM) images of the ion-polished cross-section (CP) of the sample are obtained using a scanning electron microscope (e.g., ZEISS Sigma300). The obtained SEM images are then segmented by grayscale using ImageJ software. Regions with grayscale values ​​between 0 and 115 are defined as porous regions, and regions with grayscale values ​​greater than 115 are defined as granular regions. Alternatively, the pore and granular regions can be automatically defined based on different grayscale values ​​using the auto mode. The porosity is then calculated by calculating the ratio of the area of ​​the porous region to the total area of ​​the image. During testing, 10 random SEM images can be selected to measure porosity, and the average value is taken to obtain the porosity of the sample.

[0069] The small difference in porosity between the material layer and the first polymer layer results in a smaller difference in the lithium ion transport capacity between different membrane layers and a smaller difference in lithium ion concentration between layers. This is beneficial to the overall uniformity of ion transport in the separator. At the same time, the small difference in porosity between layers can also reduce the interfacial effect between the layers of the separator, improve the compatibility between the layers of the separator, reduce the impedance of the separator, and help improve the cycle performance and rate performance of the battery.

[0070] In some embodiments, in a longitudinal section of the diaphragm, the porosity of the material layer is 10%-30%. In some embodiments, in a longitudinal section of the diaphragm, the porosity of the material layer can be selected as 10%, 15%, 20%, 25%, 30%, or any value range between two of these.

[0071] When the porosity of the material layer is within a suitable range, it ensures that the material layer has excellent ion transport performance and the diaphragm has low impedance, while also giving the material layer and diaphragm a certain mechanical strength, thus comprehensively improving the performance of the diaphragm.

[0072] In some embodiments, in a longitudinal section of the diaphragm, the porosity of the first polymer layer is 10%-30%. In some embodiments, in a longitudinal section of the diaphragm, the porosity of the first polymer layer can be selected as 10%, 15%, 20%, 25%, 30%, or any value range between two of these.

[0073] With the porosity of the first polymer layer within a suitable range, the first polymer layer has excellent ion transport performance and the membrane has low impedance, while the first polymer layer and the membrane also have a certain mechanical strength, thus comprehensively improving the performance of the membrane.

[0074] In some embodiments, the membrane further includes a second polymer layer, the material layer being located between the first polymer layer and the second polymer layer.

[0075] Figure 2 This is a schematic diagram of an embodiment of the diaphragm of this application. The diaphragm 10 includes a first polymer layer 101, a material layer 102, and a second polymer layer 103, wherein the material layer 102 is located between the first polymer layer 101 and the second polymer layer 103.

[0076] By setting a first polymer layer and a second polymer layer on both sides of the material layer, the material layer can be protected, reducing the risk of premature reduction and failure of inorganic materials caused by direct contact between inorganic materials and negative electrode sheets. At the same time, it can also improve the safety factor of the material layer and the separator, and further improve the cycle performance of the battery at high rates. In some embodiments, in a longitudinal cross-section of the diaphragm, the difference between the porosity of the material layer and the porosity of the first polymer layer is less than or equal to 10% and / or the difference between the porosity of the material layer and the porosity of the second polymer layer is less than or equal to 10%.

[0077] In some embodiments, in the longitudinal cross-section of the diaphragm, the difference between the porosity of the material layer and the porosity of the first polymer layer is less than or equal to 10%, and can be selected as any one of less than or equal to 2%, less than or equal to 3%, less than or equal to 4%, less than or equal to 5%, less than or equal to 6%, less than or equal to 7%, less than or equal to 8%, less than or equal to 9%, or less than or equal to 10%.

[0078] In some embodiments, in the longitudinal cross-section of the diaphragm, the difference between the porosity of the material layer and the porosity of the second polymer layer is less than or equal to 10%, and can be selected from any one of less than or equal to 2%, less than or equal to 3%, less than or equal to 4%, less than or equal to 5%, less than or equal to 6%, less than or equal to 7%, less than or equal to 8%, less than or equal to 9%, or less than or equal to 10%.

[0079] In some embodiments, in a longitudinal section of the diaphragm, the porosity of the material layer is 10%-30%. In some embodiments, in a longitudinal section of the diaphragm, the porosity of the material layer can be selected as 10%, 15%, 20%, 25%, 30%, or any value range between two of these.

[0080] When the porosity of the material layer is within a suitable range, it ensures that the material layer has excellent ion transport performance and the diaphragm has low impedance, while also giving the material layer and diaphragm a certain mechanical strength, thus comprehensively improving the performance of the diaphragm.

[0081] In some embodiments, in a longitudinal cross-section of the diaphragm, the porosity of the first polymer layer is 10%-30%.

[0082] In some embodiments, in a longitudinal cross-section of the diaphragm, the porosity of the first polymer layer can be selected as 10%, 15%, 20%, 25%, 30%, or any value between the two.

[0083] With the porosity of the first polymer layer within a suitable range, the first polymer layer has excellent ion transport performance and the membrane has low impedance, while the first polymer layer and the membrane also have a certain mechanical strength, thus comprehensively improving the performance of the membrane.

[0084] In some embodiments, in a longitudinal cross-section of the diaphragm, the porosity of the second polymer layer is 10%-30%.

[0085] In some embodiments, in a longitudinal cross-section of the diaphragm, the porosity of the second polymer layer can be selected as 10%, 15%, 20%, 25%, 30%, or any value between the two.

[0086] With the porosity of the second polymer layer within a suitable range, the second polymer layer has excellent ion transport performance and the membrane has low impedance, while also ensuring that the second polymer layer and the membrane have a certain mechanical strength, thus comprehensively improving the performance of the membrane.

[0087] In some embodiments, the inorganic material includes one or more of lithium titanium aluminum phosphate, lithium germanium aluminum phosphate, lithium titanium germanium aluminum phosphate, lithium titanium tantalum aluminum phosphate, lithium tetrathiophosphate, lithium germanium phosphorus sulfide, lithium phosphorus sulfide, graphene oxide, graphene oxide, fluorinated graphite, fluorinated graphene, fluorinated carbon nanotubes, and fluorinated carbon fibers.

[0088] Inorganic materials such as lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium aluminum titanium germanium phosphate, lithium aluminum titanium phosphate, lithium aluminum tantalum titanium phosphate, lithium tetrathiophosphate, lithium germanium phosphorus sulfide, and lithium phosphorus sulfide exhibit good ionic conductivity and low electronic conductivity, providing good ion conduction capability and electronic insulation. In addition, inorganic materials such as graphene oxide, graphite oxide, fluorinated graphite, fluorinated graphene, fluorinated carbon nanotubes, and fluorinated carbon fibers have high lithium intercalation capacity, can absorb a large number of lithium dendrites, and the reaction products with lithium dendrites include lithium fluoride or lithium oxide. Lithium fluoride or lithium oxide has good ionic conductivity. When the above materials are used to absorb lithium dendrites, they do not significantly increase the membrane impedance and inhibit the transfer of electrons through the membrane, which is beneficial to improving the cycle performance of the battery.

[0089] In some embodiments, the volume distribution particle size Dv50 of the inorganic material is 50nm-5000nm, and can be selected as 50nm-1000nm.

[0090] In some embodiments, the volume distribution particle size Dv50 of the inorganic material can be selected as 50nm, 100nm, 500nm, 1000nm, 1500nm, 2000nm, 2500nm, 3000nm, 3500nm, 4000nm, 4500nm, 5000nm or any value range between the two.

[0091] In this paper, the term "Dv50" refers to the particle size at which the cumulative volume distribution number of particles reaches 50% in the particle size distribution curve.

[0092] In this application, the volumetric particle size distribution (Dv50) of the inorganic material can be tested using methods known in the art. As an example, referring to GB / T 19077-2016, a laser particle size analyzer is used for determination. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0093] When the volume distribution particle size Dv50 of the inorganic material is within a suitable range, on the one hand, the risk of excessively small particle size clogging the pores on the surface of the material layer is reduced, resulting in excellent air permeability and excellent ion transport channels for the membrane. On the other hand, it avoids adverse effects on processing performance due to excessively large inorganic material particle size, improves the uniformity of inorganic material distribution in the material layer, and also reduces the "powder shedding" phenomenon that occurs during the processing of excessively large inorganic material, which would affect the absorption of lithium dendrites by the inorganic material.

[0094] In some embodiments, the material layer further includes a third polymer, and the inorganic material has a mass content of 5%-50%, optionally 10%-50%, based on the mass of the material layer.

[0095] In some embodiments, based on the mass meter of the material layer, the mass content of the inorganic material can be selected as 5%, 10%, 20%, 30%, 40%, 50%, or any value range between the two.

[0096] The inorganic material content is within a suitable range to ensure that there is enough inorganic material in the material layer to absorb lithium dendrites, thereby improving the cycle performance of the battery at high rates. At the same time, it reduces the impact of excessive inorganic material content on the compatibility between the first polymer layer or the second polymer layer and the material layer, reduces the interface effect, reduces the ion resistance of the separator, and improves the cycle performance and rate performance of the battery.

[0097] In some embodiments, the mass content of the third polymer is 50%-95%, optionally 50%-90%, based on the mass of the material layer.

[0098] In some embodiments, based on the mass meter of the material layer, the mass content of the third polymer can be selected as 50%, 60%, 70%, 80%, 90%, 95%, or any value range between the two.

[0099] The mass content of the third polymer is within a suitable range to ensure good compatibility between the material layer and the first or second polymer layer, reduce the interface effect, reduce the ion resistance of the separator, improve the cycle performance and rate performance of the battery, and at the same time enable the material layer to contain a certain amount of inorganic materials for absorbing lithium dendrites.

[0100] In some embodiments, the first polymer layer further includes a first polymer, and the second polymer layer further includes a second polymer. The first polymer, the second polymer, and the third polymer each independently comprise one or more of polyethylene, polypropylene, polyamide, polyester, polytetrafluoroethylene, polyvinylidene fluoride, and polyvinyl chloride.

[0101] In some embodiments, the first polymer, the second polymer, and the third polymer each independently comprise any one or more of medium-density polyethylene, high-density polyethylene, and ultra-high-density polyethylene.

[0102] In some implementations, the weight-average molecular weight of medium-density polyethylene is 150,000 to 200,000.

[0103] In some implementations, the weight-average molecular weight of high-density polyethylene is 200,000 to 400,000.

[0104] In some implementations, the weight-average molecular weight of ultra-high density polyethylene is greater than 1 million.

[0105] In some embodiments, the first polymer, the second polymer, and the third polymer comprise polymers having the same material.

[0106] The first polymer, the second polymer, and the third polymer are polymers of the same material, and the separator has good compatibility, which improves the transport speed of lithium ions in the separator, reduces the ion impedance of the separator, and improves the cycle performance and rate performance of the battery.

[0107] In some embodiments, the thickness ratio of the first polymer layer, the material layer and the second polymer layer is 1:(1~3):(0.8~1.2), and can be optionally 1:(1.5~2.5):(0.8~1.2).

[0108] In some embodiments, the thickness ratio of the first polymer layer, the material layer, and the second polymer layer can be selected as 1:1:1, 1:1.5:1, 1:2:1, 1:2.5:1, 1:3:1, 1:1:0.8, 1:1.5:1.2, 1:2:0.9, 1:2.5:0.8, 1:3:1.2, or any value range between the two.

[0109] The thickness ratio of the first polymer layer, the material layer, and the second polymer layer in the membrane can be tested using any method known in the art. For example, a scanning electron microscope (SEM) image of the membrane is obtained by referring to the test method for testing the porosity of the membrane layers described above. The thickness of each layer is then measured from the SEM image, and the thickness ratio of the first polymer layer, the material layer, and the second polymer layer can be obtained.

[0110] The thickness of the intermediate layer material, which absorbs lithium dendrites, is within a suitable range. On the one hand, this maximizes the absorption of lithium dendrites by the material layer, preventing them from continuing to grow and puncturing the separator. On the other hand, it also allows the polymers on both sides to provide some protection. At the same time, controlling the difference in thickness between the polymer layers on both sides minimizes the uniformity of lithium ion transport in the separator, reduces the phenomenon of local ion concentration differences between the layers of the separator, and comprehensively improves the cycle performance and rate performance of the battery.

[0111] In some embodiments, the thickness of the first polymer layer is 2.5 μm to 4.5 μm. In some embodiments, the thickness of the first polymer layer can be selected as 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, or any value range between the two.

[0112] In some embodiments, the thickness of the material layer is 3.5 μm to 7.5 μm. In some embodiments, the thickness of the material layer can be selected from 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, or any value range between the two.

[0113] In some embodiments, the thickness of the second polymer layer is 2.5 μm to 4.5 μm. In some embodiments, the thickness of the second polymer layer can be selected as 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, or any value range between the two.

[0114] By controlling the thicknesses of the first polymer layer, the material layer, and the second polymer layer within a suitable range, the material layer can effectively absorb lithium materials, while the first and second polymer layers on both sides can perform their respective protective functions, thereby comprehensively improving the electrochemical and safety performance of the battery.

[0115] In some embodiments, the thickness of the diaphragm is 5μm-25μm, and optionally 10μm-15μm.

[0116] In some embodiments, the thickness of the diaphragm can be selected as 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 15 μm, 16 μm, 18 μm, 20 μm, 22 μm, 25 μm or any value range between the two.

[0117] When the thickness of the separator is within a suitable range, the separator has low ion resistance and also has a certain mechanical strength, resulting in good cycle performance and safety performance at high rates.

[0118] In some embodiments, the first polymer layer and / or the second polymer layer further include an antioxidant.

[0119] In some embodiments, the antioxidant includes one or more of tris(2,4-di-tert-butylphenyl) phosphite, triphenyl phosphite, octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and pentaerythritol tetrakis(β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate).

[0120] The polymer layers on both sides contain antioxidants that can effectively reduce the rate of thermal and photo-oxidation reactions of the polymer layers, significantly improve the heat and light resistance of the polymer layers, delay the degradation and aging process of the polymer layers, and extend the service life of the membrane.

[0121] In some embodiments, the ionic impedance of the membrane is less than or equal to 0.40 Ω·cm. In some embodiments, the ionic impedance of the membrane is any one of 0.40 Ω·cm, 0.35 Ω·cm, 0.30 Ω·cm, 0.25 Ω·cm, 0.20 Ω·cm, or 0.15 Ω·cm.

[0122] The ionic impedance of the membrane can be tested using any method known in the art. For example, the membrane to be tested is cut into identical sizes (45.3 × 33.7 mm) and baked at 60°C for at least 4 hours, then quickly transferred to a glove box; Cu foil is used to test the Cu... The foil was used as the current collector to assemble blank symmetric cells. Green adhesive with centrally punched holes (14mm diameter) was used between the Cu foils. The aluminum-plastic film packaging bags needed to be baked at 60℃ for at least 4 hours before use, and then quickly transferred to a glove box. Using the negative electrode as the electrode, symmetric cells with different numbers of separator layers (1, 2, 3, 4, 5 layers) were assembled in situ in the glove box (5 parallel samples were assembled for each number of separator layers). The aluminum-plastic film packaging bags were side-sealed using a simple packaging machine, 300µL of electrolyte was injected, and then the bottom was sealed. The assembled symmetric cells were placed in the glove box overnight to allow the electrolyte to fully wet the separator. Before measuring EIS, the symmetric cells with different separator layer numbers were placed in a high-low temperature chamber for half an hour to maintain a constant temperature, and the EIS was measured at the set temperature (if the temperature is low, the holding time can be extended accordingly, such as about two hours). The EIS conditions were set to 1MHz. The perturbation voltage was set to 5mV at 1kHz. After the test, the data was linearly fitted to obtain the ionic impedance of the membrane.

[0123] The separator has low ion resistance, which helps to improve the ion transport rate in the separator and improve the cycle performance and rate performance of the battery.

[0124] This application also provides a method for preparing a secondary battery, comprising: An electrode assembly comprising a positive electrode, a negative electrode, and a separator is assembled to obtain a secondary battery. The separator comprises a first polymer layer and a material layer disposed on the first polymer layer, the material layer comprising an inorganic material. The inorganic materials include one or more of the following: lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium aluminum titanium germanium phosphate, lithium aluminum titanium phosphate, lithium aluminum titanium phosphate, lithium tetrathiophosphate, lithium germanium phosphorus sulfide, lithium phosphorus sulfide, iron oxide, copper oxide, titanium dioxide, tin dioxide, manganese dioxide, zinc oxide, zirconium dioxide, chromium nitride, vanadium nitride, nickel nitride, iron nitride, graphene oxide, graphene oxide, fluorinated graphite, fluorinated graphene, fluorinated carbon nanotubes, and fluorinated carbon fibers.

[0125] The separator of a secondary battery contains a material layer that absorbs lithium dendrites in contact with the material layer, causing the sharp lithium dendrites to transform into other lithium compounds. This reduces the risk of lithium dendrites continuing to puncture the separator and improves the battery's cycle performance at high rates.

[0126] In some embodiments, the membrane is prepared as follows: Step a: The raw materials for the first polymer layer, the raw materials for the material layer, and the raw materials for the second polymer layer are co-extruded to obtain a composite sheet; Step b: The composite sheet is stretched to form a thin film; Step c: Extract and heat-set the film to obtain a diaphragm.

[0127] The raw materials for the material layer include the inorganic materials. The membrane includes a first polymer layer, a material layer, and a second polymer layer, wherein the material layer is located between the first polymer layer and the second polymer layer.

[0128] The above preparation method can yield a separator comprising a first polymer layer, a material layer, and a second polymer layer. The material layer comprises an inorganic material that can react with lithium metal, causing sharp lithium dendrites to transform into other lithium compounds, reducing the risk of lithium dendrites continuing to puncture the separator, and improving the cycle performance of the battery at high rates. At the same time, the material layer is located between the first polymer layer and the second polymer layer, which can improve the safety performance of the material layer and further improve the cycle performance of the battery.

[0129] In some embodiments, step a specifically includes: melting and blending the first polymer layer raw material, the material layer raw material, and the second polymer layer raw material respectively, and then co-extruding them through a multi-channel co-extrusion die to obtain the composite sheet.

[0130] In some embodiments, the raw material for the first polymer layer includes the first polymer and a porogen, the raw material for the material layer includes the third polymer and an inorganic material, and the raw material for the second polymer layer includes the third polymer and the porogen.

[0131] The raw materials for the first and second polymer layers include a pore-forming agent, which is extracted during the extraction stage to leave micropores in the polymer layer, thereby improving the membrane's permeability and porosity.

[0132] In some embodiments, the pore-forming agent includes one or more of polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, mineral oil, kerosene, decahydronaphthalene, sodium chloride, potassium carbonate, and lithium chloride.

[0133] In some embodiments, the pore-forming agent has a mass content of 0.1%-5% based on the mass of the raw material of the first polymer layer.

[0134] In some embodiments, the pore-forming agent has a mass content of 0.1%-5% based on the mass of the second polymer layer raw material.

[0135] Adding an appropriate amount of pore-forming agent to the raw materials of each polymer layer is beneficial to forming a membrane with suitable gas content and porosity.

[0136] In some embodiments, the raw material of the first polymer layer, the raw material of the material layer, or the raw material of the second polymer layer each independently comprises one or more of polyethylene, polypropylene, polyamide, polyester, polytetrafluoroethylene, polyvinylidene fluoride, and polyvinyl chloride.

[0137] In some embodiments, the first polymer layer material and / or the second polymer layer material further include antioxidants.

[0138] In some embodiments, the antioxidant includes one or more of tris(2,4-di-tert-butylphenyl) phosphite, triphenyl phosphite, octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and pentaerythritol tetrakis(β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate).

[0139] Adding antioxidants to the raw materials can effectively reduce the rate of thermal and photo-oxidation reactions of the polymer layer, significantly improve the heat and light resistance of the polymer layer, delay the degradation and aging process of the polymer layer, and extend the service life of the membrane.

[0140] In some embodiments, the antioxidant content is 0.2%-0.4% by mass, based on the mass of the raw material of the first polymer layer.

[0141] In some embodiments, the antioxidant content is 0.2%-0.4% by mass, based on the mass of the second polymer layer raw material.

[0142] In some embodiments, the first polymer layer material and / or the second polymer layer material further include a nucleating agent.

[0143] Nucleating agents are used to form crystal nuclei in polymers, generating polymer layers with a semi-crystalline state.

[0144] In some embodiments, the nucleating agent includes one or more of phthalic acid, azelaic acid, adipic acid, and dibenzyl sorbitol.

[0145] In some embodiments, the nucleating agent has a mass content of 0.1%-5% based on the mass of the raw material of the first polymer layer.

[0146] In some embodiments, the nucleating agent has a mass content of 0.1%-5% based on the mass of the second polymer layer raw material.

[0147] In some implementations, step c specifically includes: The film is subjected to extraction treatment to obtain a microporous film; The microporous membrane is heat-set to obtain the diaphragm.

[0148] In some implementations, step c specifically includes: The film is subjected to heat setting treatment to obtain a first film; The first thin film is subjected to extraction treatment to obtain the diaphragm.

[0149] The secondary battery in this application includes lithium metal batteries or lithium secondary batteries.

[0150] Secondary batteries can be in the form of individual battery cells, battery modules, or battery packs. Battery modules and battery packs contain individual battery cells, and battery packs can also contain battery modules.

[0151] Typically, a battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through. The positive and negative electrodes, as well as the electrolyte, can be existing products used in metal-ion batteries.

[0152] [Positive electrode plate] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0153] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0154] In some embodiments, the positive 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 substrate and a metal layer formed on at least one surface of the polymer substrate. 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0155] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0156] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene (HFP)-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0157] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0158] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0159] [Negative electrode plate] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0160] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0161] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0162] In some implementations, the negative electrode active material is elemental lithium metal.

[0163] In some embodiments, the negative electrode active material can be an alloy of metallic lithium with other metallic or non-metallic elements. The metallic elements include any one or more of tin (Sn), zinc (Zn), aluminum (Al), magnesium (Mg), silver (Ag), gold (Au), gallium (Ga), indium (In), and phosphorus (Pt). The metalloid elements include one or more of boron (B), carbon (C), and silicon (Si).

[0164] In some implementations, the negative electrode sheet can be prepared by rolling the upper negative electrode active material onto the negative electrode current collector, and then cutting it to obtain the negative electrode sheet.

[0165] In some implementations, the negative electrode is a lithium metal sheet.

[0166] [Electrolytes] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0167] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0168] In some embodiments, the electrolyte salt may be selected from 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 dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0169] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl 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.

[0170] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0171] [Rechargeable Battery] In one embodiment of this application, a secondary battery is provided, including a positive electrode, a separator, a negative electrode, and an electrolyte.

[0172] In some embodiments, the secondary battery is a lithium-ion battery or a lithium metal battery. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrode plates. The electrolyte acts as a conductor of ions between the positive and negative electrode plates. A separator is disposed between the positive and negative electrode plates, primarily to prevent short circuits between the positive and negative electrodes, while simultaneously allowing ions to pass through.

[0173] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0174] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0175] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0176] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 This is an example of a square-structured secondary battery 5.

[0177] In some implementations, refer to Figure 4 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0178] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0179] Figure 5 This is battery module 4, used as an example. (See reference...) Figure 5In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0180] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0181] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0182] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0183] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0184] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0185] Figure 8 This is an example of an electrical device. The device could be 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 the secondary battery for this device, a battery pack or battery module can be used.

[0186] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0187] Example The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0188] I. Preparation Method Example 1 1) Diaphragm Inorganic material titanium dioxide (volume particle size distribution Dv50 of 50 nm), polyethylene with a weight average molecular weight of 1.6 million, and polyvinylpyrrolidone (PVP) porogen were fully dispersed in a high-speed mixer at a mass ratio of 15:85:1 to obtain the material layer raw material; polyethylene with a weight average molecular weight of 1.6 million, nucleating agent terephthalic acid, antioxidant tris(2,4-di-tert-butylphenyl) phosphite, and polyvinylpyrrolidone (PVP) porogen were fully dispersed in a high-speed mixer at a mass ratio of 99:0.7:0.3:1 to obtain the first polymer layer raw material and the second polymer layer raw material. The raw materials for the first polymer layer, the raw materials for the material layer, and the raw materials for the second polymer layer are melt-blended and plasticized in an eccentric rotor extruder at 200°C, and then fed into a three-layer co-extrusion die. The blend of the raw materials for the first polymer layer and the raw materials for the second polymer layer enters the outer sides, while the raw material for the material layer enters the inner side. After casting and cooling, a composite sheet is formed. The mass ratio of the extrusion amount of the first polymer layer raw material, the extrusion amount of the material layer raw material, and the extrusion amount of the second polymer layer raw material is 1:2:1. The obtained composite sheet was stretched on a synchronous biaxial stretching machine with a stretching ratio of 5×5 and a stretching temperature of 118℃. Then, it was heat-set at 130℃ with a pressure of 10 MPa and a time of 60 min to obtain the first film. The first film obtained was subjected to ultrasonic extraction with dichloromethane, soaking in alcohol, rinsing with deionized water, and drying to obtain a separating membrane.

[0189] 2) Preparation of positive electrode sheet Lithium iron phosphate (LiFePO4), carbon black (Super P), and polyvinylidene fluoride (PVDF) binder were mixed uniformly in an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1 to obtain a positive electrode slurry. The positive electrode slurry was then coated onto aluminum foil used as a positive electrode current collector. The positive electrode sheet was obtained through drying, cold pressing, slitting, and cutting processes. The areal density of the positive electrode was 0.207 mg / mm². 2 The compacted density is 3.5 g / cm³. 3 .

[0190] 3) Preparation of negative electrode sheet Lithium metal sheets are used as the negative electrode.

[0191] 4) Preparation of electrolyte Ethyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then LiPF6 was uniformly dissolved in the above solution to obtain an electrolyte with a concentration of 1 mol / L.

[0192] 5) Battery manufacturing The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then assembled, with the positive electrode having a diameter of 14 mm, the lithium metal sheet having a diameter of 16 mm, and the separator having a diameter of 16.5 mm. The electrode assembly is placed in an outer packaging, and the prepared electrolyte is injected into the dried electrode assembly. After vacuum sealing, settling, formation, and shaping, the battery is obtained.

[0193] Example 2 Compared with Example 1, the polyethylene with a weight average molecular weight of 1.6 million in the material layer raw material was replaced with polyvinylidene fluoride with a weight average molecular weight of 450,000. Other parameters are shown in Table 1.

[0194] Examples 3-6 Compared with Example 1, in Examples 3-6, the titanium dioxide in the material layer raw materials was replaced with lithium aluminum titanium phosphate (volume particle size distribution Dv50 of 500 nm), iron nitride (volume particle size distribution Dv50 of 100 nm), fluorinated graphite (volume particle size distribution Dv50 of 1000 nm, C atom to F atom ratio of 1:1), and graphene oxide (volume particle size distribution Dv50 of 1000 nm, C atom to O atom ratio of 2:1). Other parameters are shown in Table 1.

[0195] Examples 7-10 Compared with Example 3, in Examples 7-10, the mass ratio of lithium titanium aluminum phosphate to polyethylene in the raw materials of the material layer was adjusted to 5:95, 10:90, 40:60, and 50:50, respectively. Other parameters are shown in Table 1.

[0196] Examples 11-14 Compared with Example 3, Examples 11-14 adjust the mass ratio of the extrusion amount of the first polymer layer raw material, the extrusion amount of the material layer raw material, and the extrusion amount of the second polymer layer raw material, thereby adjusting the thickness ratio of the first polymer layer, the material layer, and the second polymer layer. Other parameters are shown in Table 1.

[0197] Example 15 Compared with Example 1, the difference lies in the adjustment of the membrane preparation and battery preparation processes, as follows: Polyethylene with a weight average molecular weight of 1.6 million, terephthalic acid as a nucleating agent, tris(2,4-di-tert-butylphenyl) phosphite as an antioxidant, and polyvinylpyrrolidone (PVP) as a pore-forming agent were fully dispersed in a high-speed mixer at a mass ratio of 99:0.7:0.3:1 to obtain the raw material for the first polymer layer. The first polymer layer raw material is melt-blended and plasticized at 200°C through an eccentric rotor extruder and then fed into a single-layer extrusion die. After casting and cooling, a sheet is obtained. The obtained sheet was stretched on a synchronous biaxial stretching machine with a stretching ratio of 5×5 and a stretching temperature of 118℃. Then, it was heat-set at 130℃ with a pressure of 10 MPa and a time of 60 min to obtain a film. The obtained film was subjected to ultrasonic extraction with dichloromethane, immersion in alcohol, rinsing with deionized water, and drying to obtain the first polymer layer.

[0198] Inorganic titanium dioxide (volume particle size distribution Dv50 of 50 nm) and polyvinylidene fluoride with a weight average molecular weight of 450,000 were dispersed in DMF solvent at a mass ratio of 15:85. The resulting slurry was coated onto a first polymer layer with a thickness of 6 μm. The thickness of the material layer was adjusted to 6 μm by controlling the thickness of the doctor blade. The material was first air-dried at room temperature, and then placed in a vacuum oven at 60°C for 24 h for vacuum drying. The membrane was then obtained.

[0199] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then assembled, with the positive electrode having a diameter of 14 mm, the lithium metal sheet having a diameter of 16 mm, and the separator having a diameter of 16.5 mm. The separator material layer is disposed on the surface of the first polymer layer near the positive electrode. The electrode assembly is placed in an outer packaging, and the prepared electrolyte is injected into the dried electrode assembly. After vacuum sealing, settling, formation, and shaping, the battery is obtained.

[0200] Example 16 Compared to Example 1, the difference lies in the adjustment of the orientation of the material layers in the diaphragm. The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then assembled, with the positive electrode having a diameter of 14 mm, the lithium metal sheet having a diameter of 16 mm, and the separator having a diameter of 16.5 mm. The separator material layer is disposed on the surface of the first polymer layer near the negative electrode. The electrode assembly is placed in an outer packaging, and the prepared electrolyte is injected into the dried electrode assembly. After vacuum sealing, settling, formation, and shaping processes, the battery is obtained.

[0201] Example 17 Compared with Example 1, the preparation methods of the separator and the secondary battery were adjusted as follows: Inorganic material titanium dioxide (volume particle size distribution Dv50 of 50 nm), polyethylene with a weight average molecular weight of 1.6 million, and polyvinylpyrrolidone (PVP) porogen were fully dispersed in a high-speed mixer at a mass ratio of 15:85:1 to obtain the material layer raw material; polyethylene with a weight average molecular weight of 1.6 million, nucleating agent terephthalic acid, antioxidant tris(2,4-di-tert-butylphenyl) phosphite, and polyvinylpyrrolidone (PVP) porogen were fully dispersed in a high-speed mixer at a mass ratio of 99:0.7:0.3:1 to obtain the first polymer layer raw material; The raw materials for the first polymer layer and the raw materials for the material layer are melt-blended and plasticized in an eccentric rotor extruder at 200°C and then fed into a two-layer co-extrusion die. After casting and cooling, a composite sheet is formed. The mass ratio of the extruded amount of the first polymer layer raw material to the extruded amount of the material layer raw material is 1:1. The obtained composite sheet was stretched on a synchronous biaxial stretching machine with a stretching ratio of 5×5 and a stretching temperature of 118℃. Then, it was heat-set at 130℃ with a pressure of 10 MPa and a time of 60 min to obtain the first film. The first film obtained was subjected to ultrasonic extraction with dichloromethane, soaking in alcohol, rinsing with deionized water, and drying to obtain a separating membrane.

[0202] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then assembled, with the positive electrode having a diameter of 14 mm, the lithium metal sheet having a diameter of 16 mm, and the separator having a diameter of 16.5 mm. The separator material layer is disposed on the surface of the first polymer layer near the negative electrode. The electrode assembly is placed in an outer packaging, and the prepared electrolyte is injected into the dried electrode assembly. After vacuum sealing, settling, formation, and shaping processes, the battery is obtained.

[0203] Example 18 Compared with Example 1, the difference lies in the adjustment of the membrane preparation process, as follows: Polyethylene with a weight average molecular weight of 1.6 million, terephthalic acid as a nucleating agent, tris(2,4-di-tert-butylphenyl) phosphite as an antioxidant, and polyvinylpyrrolidone (PVP) as a pore-forming agent were fully dispersed in a high-speed mixer at a mass ratio of 99:0.7:0.3:1 to obtain the polymer layer raw material. The base film raw material is melt-blended and plasticized at 200°C through an eccentric rotor extruder and then fed into a single-layer extrusion die. After casting and cooling, a sheet is obtained. The obtained sheet was stretched on a synchronous biaxial stretching machine with a stretching ratio of 5×5 and a stretching temperature of 118℃. Then, it was heat-set at 130℃ with a pressure of 10 MPa and a time of 60 min to obtain a film. The obtained film was subjected to ultrasonic extraction with dichloromethane, immersion in alcohol, rinsing with deionized water, and drying to obtain a polymer layer.

[0204] Inorganic titanium dioxide (volume particle size distribution Dv50 of 50 nm), polyvinylidene fluoride with a weight average molecular weight of 450,000, and DMF solvent were dispersed in a mass ratio of 15:85. The resulting slurry was coated onto a polymer layer with a thickness of 3 μm. The thickness of the material layer was adjusted to 6 μm by controlling the thickness of the doctor blade. Then, another polymer layer with a thickness of 3 μm was used to cover the surface. The mixture was first air-dried at room temperature, and then placed in a vacuum oven at 60°C for 24 h to dry under vacuum. The membrane was then removed.

[0205] Comparative Example 1 Compared with Example 1, the preparation method of the diaphragm was adjusted, as follows: Polyethylene with a weight average molecular weight of 1.6 million, terephthalic acid as a nucleating agent, tris(2,4-di-tert-butylphenyl) phosphite as an antioxidant, and polyvinylpyrrolidone (PVP) as a pore-forming agent were fully dispersed in a high-speed mixer at a mass ratio of 99:0.7:0.3:1 to obtain the polymer layer raw material. The base film raw material is melt-blended and plasticized at 200°C through an eccentric rotor extruder and then fed into a single-layer extrusion die. After casting and cooling, a sheet is obtained. The obtained sheet was stretched on a synchronous biaxial stretching machine with a stretching ratio of 5×5 and a stretching temperature of 118℃. Then, it was heat-set at 130℃ with a pressure of 10 MPa and a time of 60 min to obtain a film. The obtained film was subjected to ultrasonic extraction with dichloromethane, immersion in alcohol, rinsing with deionized water, and drying to obtain a polymer layer with a thickness of 12 μm.

[0206] II. Testing Methods 1. Cycling performance at high rates At 25℃, the coin cell battery was charged at a constant current of 2C to 3.65V, then charged at a constant voltage of 3.65V to a current of 0.05C, and then discharged at a constant current of 0.33C to 2.5V. This constitutes one charge-discharge cycle. The discharge capacity of the coin cell battery in the first cycle was recorded. The coin cell battery was charged and discharged for 100 cycles using the above method, and the discharge capacity in the 100th cycle was recorded. The discharge capacity retention rate of the coin cell battery was calculated using the following formula: Discharge capacity retention rate = discharge capacity in the 100th cycle / discharge capacity in the 1st cycle × 100%.

[0207] III. Analysis of Test Results for Each Embodiment and Comparative Example The separators and secondary batteries of each embodiment and comparative example were prepared according to the above method, and various parameters were measured. The results are shown in the table below.

[0208] Table 1

[0209] Table 2

[0210] The separator in the secondary battery of Embodiments 1-18 of this application includes a first polyethylene layer and a material layer disposed on the first polymer layer. The material layer includes inorganic materials such as titanium dioxide, lithium aluminum titanium phosphate, iron nitride, fluorinated graphite, or graphene oxide.

[0211] As can be seen from the comparison between Examples 1-18 and Comparative Example 1, the separator includes a material layer, which can reduce the ion resistance of the separator, improve the cycle performance of the battery at high rates, and extend the battery's service life.

[0212] As can be seen from the comparison between Example 16 and Example 15, the material layer of the separator is disposed on the surface of the first polymer layer near the negative electrode, which can further improve the cycle performance of the battery at high rates and extend the battery's service life.

[0213] As can be seen from the comparison between Example 17 and Example 16, and Example 2 and Example 18, in the longitudinal cross-sectional view of the separator, the difference between the porosity of the material layer and the porosity of the first polymer layer is less than or equal to 10%, which can reduce the ion resistance of the separator and improve the cycle performance of the battery at high rates.

[0214] As can be seen from the comparison between Example 2 and Example 17, the separator also includes a second polymer layer, which can further improve the cycle performance of the battery at high rates and extend the battery's lifespan.

[0215] As seen in Examples 3 and 7-10, based on the total mass of the material layers, the lithium titanium aluminum phosphate content is 5%-50%, and the polyethylene content is 50%-95%. This results in a separator with low ionic resistance and good cycle performance at high rates. Comparing Examples 3 and 8-10 with Example 7, it is evident that, based on the total mass of the material layers, a lithium titanium aluminum phosphate content of 10%-50% and a polyethylene content of 50%-90% can further reduce the ionic resistance of the separator, improve the cycle performance at high rates, and comprehensively improve both the cycle performance and rate performance of the battery.

[0216] As shown in Examples 3 and 11-14, when the thickness ratio of the first polymer layer, the material layer, and the second polymer layer is 1:(1~3):(0.8~1.2), the separator exhibits low ion resistance, and the battery demonstrates good cycle performance at high rates. Comparing Examples 3 and 12-13 with Examples 11 and 14, it is evident that a thickness ratio of 1:(1.5~2.5):(0.8~1.2) for the first polymer layer, the material layer, and the second polymer layer can further reduce the ion resistance of the separator and improve the battery's cycle performance at high rates.

[0217] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, characterized in that, The device includes a positive electrode, a negative electrode, and a separator, wherein the separator is located between the positive and negative electrode. The separator includes a first polymer layer and a material layer disposed on the first polymer layer, wherein the material layer includes an inorganic material. The inorganic materials include one or more of lithium titanium aluminum phosphate, lithium germanium aluminum phosphate, lithium titanium germanium aluminum phosphate, lithium titanium tantalum aluminum phosphate, lithium tetrathiophosphate, lithium germanium phosphorus sulfide, lithium phosphorus sulfide, and titanium dioxide. In the longitudinal cross-section of the diaphragm, the difference between the porosity of the material layer and the porosity of the first polymer layer is less than or equal to 10%.

2. The secondary battery according to claim 1, characterized in that, In the longitudinal cross-section of the diaphragm, the difference between the porosity of the material layer and the porosity of the first polymer layer is less than or equal to 5%.

3. The secondary battery according to claim 1, characterized in that, In the longitudinal cross-section of the diaphragm, the difference between the porosity of the material layer and the porosity of the first polymer layer is less than or equal to 3%.

4. The secondary battery according to claim 1, characterized in that, In the longitudinal section of the diaphragm, the difference between the porosity of the material layer and the porosity of the first polymer layer is less than or equal to 2%.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, In the longitudinal cross-section of the diaphragm, the porosity of the material layer is 10%-30%.

6. The secondary battery according to any one of claims 1 to 4, characterized in that, In the longitudinal section of the diaphragm, the porosity of the material layer is 15%-30%.

7. The secondary battery according to any one of claims 1 to 4, characterized in that, In the longitudinal cross-section of the diaphragm, the porosity of the first polymer layer is 10%-30%.

8. The secondary battery according to any one of claims 1 to 4, characterized in that, In the longitudinal cross-section of the diaphragm, the porosity of the first polymer layer is 15%-30%.

9. The secondary battery according to any one of claims 1 to 4, characterized in that, The thickness of the material layer is 3.5μm-7.5μm.

10. The secondary battery according to any one of claims 1 to 4, characterized in that, The thickness of the material layer is 3.5μm-6.0μm.

11. The secondary battery according to claim 9, characterized in that, The thickness of the diaphragm is 5μm-25μm.

12. The secondary battery according to claim 10, characterized in that, The thickness of the diaphragm is 10μm-15μm.

13. The secondary battery according to any one of claims 1-4, characterized in that, The inorganic material includes lithium titanium aluminum phosphate, or lithium titanium aluminum phosphate.

14. The secondary battery according to any one of claims 1 to 4, characterized in that, The volumetric particle size Dv50 of the inorganic material is 50nm-5000nm.

15. The secondary battery according to any one of claims 1 to 4, characterized in that, The volumetric particle size Dv50 of the inorganic material is 50nm-1000nm.

16. The secondary battery according to any one of claims 1 to 4, characterized in that, The material layer also includes a third polymer.

17. The secondary battery according to claim 16, characterized in that, Based on the mass of the material layer, the inorganic material has a mass content of 5%-50%; and / or, the third polymer has a mass content of 50%-95%.

18. The secondary battery according to claim 16, characterized in that, Based on the mass of the material layer, the inorganic material has a mass content of 10%-50%; and / or, the third polymer has a mass content of 50%-90%.

19. The secondary battery according to claim 16, characterized in that, The third polymer comprises one or more of polyethylene, polypropylene, polyamide, polyester, polytetrafluoroethylene, polyvinylidene fluoride, and polyvinyl chloride.

20. The secondary battery according to claim 16, characterized in that, The third polymer comprises polyethylene and / or polyvinylidene fluoride.

21. The secondary battery according to any one of claims 1 to 4, characterized in that, The first polymer layer includes a first polymer, which comprises one or more of polyethylene, polypropylene, polyamide, polyester, polytetrafluoroethylene, polyvinylidene fluoride, and polyvinyl chloride.

22. The secondary battery according to any one of claims 1 to 4, characterized in that, The first polymer layer includes a first polymer, which is polyethylene.

23. The secondary battery according to any one of claims 1 to 4, characterized in that, The ion resistance of the membrane is less than or equal to 0.40Ω. cm.

24. The secondary battery according to any one of claims 1 to 4, characterized in that, The material layer is disposed on the surface of the first polymer layer near the negative electrode sheet, or the material layer is disposed on the surface of the first polymer layer near the positive electrode sheet.

25. The secondary battery according to any one of claims 2 to 4, characterized in that, The membrane further includes a second polymer layer, the material layer being located between the first polymer layer and the second polymer layer, and the difference between the porosity of the material layer and the porosity of the second polymer layer is less than or equal to 10%.

26. The secondary battery according to claim 25, characterized in that, In the longitudinal cross-sectional view of the diaphragm, the porosity of the material layer and / or the porosity of the first polymer layer and / or the porosity of the second polymer layer is 10%-30%.

27. The secondary battery according to claim 25, characterized in that, The second polymer layer includes a second polymer, which comprises one or more of polyethylene, polypropylene, polyamide, polyester, polytetrafluoroethylene, polyvinylidene fluoride, and polyvinyl chloride.

28. The secondary battery according to claim 25, characterized in that, The thickness ratio of the first polymer layer, the material layer, and the second polymer layer is 1:(1~3):(0.8~1.2).

29. The secondary battery according to claim 27, characterized in that, The thickness ratio of the first polymer layer, the material layer, and the second polymer layer is 1:(1.5~2.5):(0.8~1.2).

30. The secondary battery according to claim 25, characterized in that, The thickness of the first polymer layer is 2.5 μm-4.5 μm; and / or the thickness of the material layer is 3.5 μm-7.5 μm; and / or the thickness of the second polymer layer is 2.5 μm-4.5 μm.

31. The secondary battery according to any one of claims 1-4, characterized in that, The positive electrode includes a current collector and a positive active material layer disposed on at least one side of the current collector, wherein the positive active material layer includes lithium iron phosphate as the positive active material.

32. The secondary battery according to any one of claims 1-4, characterized in that, The secondary battery further has one or more of the following characteristics: The positive electrode, negative electrode, and separator in the secondary battery are in a wound configuration. The secondary battery includes an outer packaging, which is a hard shell. The secondary battery is square in shape.

33. The secondary battery according to any one of claims 1-4, characterized in that, The secondary battery further includes an electrolyte, which is in a gel state.

34. An electrical appliance, characterized in that, The secondary battery includes any one of claims 1 to 33.

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