Battery separator, secondary battery, and electrical apparatus

Abstract

The present application provides a battery separator, which is characterized by comprising a base film and a ceramic coating located on at least one side of the base film, wherein the difference between the contact angle of the base film and the contact angle of the ceramic coating is≤15 degrees. The battery separator of the present application has high adhesion, high liquid retention and high ionic conductivity, thereby improving the cycle characteristics and rate characteristics of batteries.

Description

Battery separator, secondary battery and electrical device

[0001] Cross-references

[0002] This application refers to Chinese Patent Application No. 202311622649.2, filed on November 29, 2023, entitled “Battery Separator, Secondary Battery and Electrical Device,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a battery separator, a secondary battery, and an electrical device. Background Art

[0004] In recent years, the application of secondary batteries has become increasingly widespread. They are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As secondary batteries have achieved great development, higher requirements have been placed on their energy density, cycle performance, and safety performance.

[0005] Currently, separators for secondary batteries are primarily made of PP and PE, key components of these batteries. These separators possess excellent pore size distribution, mechanical properties, chemical stability, electrolyte wettability, electronic insulation, and high-temperature closed-cell performance. However, because current PP and PE separators are non-polar and have low surface tension, their wettability to electrolytes and adhesion to surface coatings are relatively poor.

[0006] Summary of the Invention

[0007] The present application has been made in view of the above-mentioned problems, and its object is to provide a secondary battery separator having high adhesion, high liquid retention, and high ion conductivity, as well as a secondary battery and an electric device having the separator.

[0008] A first aspect of the present application provides a battery separator, characterized in that it includes a base film and a ceramic coating located on at least one side of the base film; wherein the difference between the contact angle of the base film and the contact angle of the ceramic coating is ≤15°.

[0009] Therefore, the present application adopts a battery separator with the structure described above, which can improve the wettability of the separator to the electrolyte, the adhesion of the surface coating (ceramic coating), and the adhesion between the separator and the positive and negative electrode sheets, thereby achieving high adhesion, high liquid retention and high ionic conductivity of the separator.

[0010] In any embodiment, the base film is a corona-treated base film, the corona treatment power P1 is 50W-200W, the voltage V1 is 100V-230V, and the time T1 is 0.1s-4s. In addition, the material forming the substrate is not particularly limited, and the base film includes one or more of polyethylene, polypropylene, polyimide, polyamide, polyethylene terephthalate, glass fiber, non-woven fabric, and high-temperature resistant polyester film, and optionally includes one or more of polyethylene and polypropylene.

[0011] In any embodiment, the ceramic coating is a corona-treated ceramic coating, wherein the corona treatment power P2 is 50W-500W, the voltage V2 is 100V-230V, and the time T2 is 0.1s-6s. Furthermore, the material forming the ceramic coating is not particularly limited, and the ceramic coating includes one or more of Al2O3, AlO(OH), SiO2, TiO2, MgO, CaO, ZnO2, ZrO2, and SnO2, and optionally includes Al2O3.

[0012] Therefore, by applying corona treatment to the substrate or ceramic coating, the surface energy of the material can be increased while preventing damage to the treated material. Based on the appropriate increase in the material's surface energy, the wettability of the separator to the electrolyte, the adhesion of the surface coating, and the adhesion between the separator and the positive and negative electrode sheets can be improved.

[0013] In any embodiment, the diaphragm further comprises a bonding coating, the bonding coating being located on a side of the ceramic coating away from the base film, and the difference between the contact angle of the ceramic coating and the contact angle of the bonding coating being 2°-15°. In addition, the material forming the bonding coating is not particularly limited and may be a polymer, specifically, may include one or more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene polymer, styrene-butadiene polymer, polyacrylic acid, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyamide, polyacrylonitrile, polyacrylate, polyacrylate, sodium hydroxymethyl cellulose, and optionally polyvinylidene fluoride.

[0014] By using the material to form the bonding coating and making the difference between the contact angle of the ceramic coating and the contact angle of the bonding coating within the above range, the surface energies of the bonding coating and the ceramic coating can be made close, thereby achieving a good bonding effect.

[0015] In any embodiment, the bonding coating is a bonding coating after corona treatment, the power P3 of the corona treatment is 50W-600W, the voltage V3 is 100V-230V, and the time T3 is 0.1s-5s.

[0016] Therefore, by setting the corona treatment to the above conditions, it is possible to achieve surface treatment of the material, that is, appropriately increase the surface energy of the material, while preventing damage to the corona-treated material.

[0017] In any embodiment, the contact angle of the base film is 60°-80°, the contact angle of the ceramic coating is 60°-80°, and the contact angle of the bond coating is 40°-60°.

[0018] By ensuring that the contact angle between the base film and the ceramic coating is within the above range, the surface energies between the base film and the ceramic coating can be close, thereby achieving good bonding between the two. By ensuring that the contact angle of the adhesive coating is within the above range, it can achieve better bonding between the separator and the electrode pad.

[0019] In any embodiment, the separator has a liquid absorption rate of 4.5 mm / s to 6 mm / s. By ensuring that the separator has a liquid absorption rate within this range, when immersed in an electrolyte, the electrolyte can quickly penetrate the separator, enabling rapid ion conduction, thereby improving the battery's ionic conductivity, and thereby enhancing the battery's cycle performance and rate characteristics.

[0020] In any embodiment, the bonding force between the base film and the ceramic coating is 2.5N / mm-4N / mm. By making the bonding force between the base film and the ceramic coating within the said range, the structure of the diaphragm is more compact, which enables the diaphragm to better perform its function, thereby improving the cycle performance and rate characteristics of the battery.

[0021] A second aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet and a separator.

[0022] The secondary battery of the present application has high cycle characteristics and high rate characteristics by including the separator of the present application.

[0023] In any embodiment, the separator further comprises a bonding coating located on a side of the ceramic coating away from the base film, wherein the difference between the contact angle of the positive electrode plate and the contact angle of the bonding coating is ≤ 20°; and / or the difference between the contact angle of the negative electrode plate and the contact angle of the bonding coating is ≤ 20°. The contact angle of the positive electrode plate is 40°-80°; and / or the contact angle of the negative electrode plate is 40°-80°.

[0024] By making the separator, positive electrode sheet and negative electrode sheet in the secondary battery have contact angles and contact angle differences within the said range respectively, good bonding between the separator, positive electrode sheet and negative electrode sheet can be achieved, thereby making the structure of the secondary battery more compact and the conduction of ions between the positive and negative electrode sheets and the separator smoother, thereby achieving high cycle characteristics and high rate characteristics of the secondary battery.

[0025] In any embodiment, the secondary battery includes at least one of a lithium secondary battery and a sodium secondary battery.

[0026] A third aspect of the present application provides an electrical device, characterized in that it includes the secondary battery. DETAILED DESCRIPTION

[0027] The following describes embodiments of a battery separator, a secondary battery, and an electrical device in detail. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of substantially identical structures may be omitted. This is done to avoid unnecessary redundancy and to facilitate understanding by those skilled in the art.

[0028] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0029] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0030] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0031] Unless otherwise specified, all steps of the present 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 may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0032] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0033] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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).

[0034] Battery separators, as a key component of secondary batteries, have a significant impact on battery performance. However, existing PP and PE separators are non-polar and have low surface tension, resulting in poor wettability to electrolytes and poor adhesion to surface coatings. By subjecting the battery separator and the various layers of the electrode structure to surface corona treatment, free radical reactions can be generated on the surface of the treated material, causing the polymers to crosslink. This roughens the surface and increases its wettability to polar solvents. The surface molecules of the treated material oxidize and polarize, and ions erode the surface, thereby increasing the adhesion of the treated surface. This can improve the battery separator's liquid retention and adhesion to the electrode, improving the cycle performance and rate characteristics of the secondary battery.

[0035] Based on this, the present application proposes a battery separator and a method for manufacturing the same, as well as a secondary battery and an electrical device having the separator, which are described in detail below.

[0036] [Battery separator]

[0037] The battery separator of the present application comprises a base film and a ceramic coating located on at least one side of the base film; wherein the difference between the contact angle of the base film and the contact angle of the ceramic coating is ≤15°, and optionally comprises an adhesive coating. The present application performs a surface corona treatment on each layer to enhance the surface energy of each layer, thereby increasing wettability and adhesion.

[0038] In some embodiments, the difference between the contact angle of the base film and the contact angle of the ceramic coating can be selected to be 15°, 14°, 13°, 12°, 11°, 10°, 9°, 8°, 7°, 6°, 5°, 4°, 3°, 2°, 1° or 0°, or a range between any two of the values.

[0039] The contact angle of the base film is adjusted by corona treatment of the base film surface. This treatment increases the surface energy of the material, thereby increasing the polarity of the material surface. By ensuring that the difference in contact angle between the layers falls within the specified range, the polarity of the base film surface is enhanced, thereby strengthening the adhesion between the base film and the coating. The coated separator is then subjected to a further corona treatment to increase the surface energy of the coated separator, thereby enhancing its adhesion and wettability to the electrolyte.

[0040] In any embodiment, the base film is a corona-treated base film, the corona treatment power P1 is 50W-200W, the voltage V1 is 100V-230V, and the time T1 is 0.1s-4s. In addition, the material forming the substrate is not particularly limited, and the base film includes one or more of polyethylene, polypropylene, polyimide, polyamide, polyethylene terephthalate, glass fiber, non-woven fabric, and high-temperature resistant polyester film, and optionally includes one or more of polyethylene and polypropylene.

[0041] In some embodiments, the power P1 of the corona treatment for the base film can be selected as 50W, 60W, 70W, 80W, 90W, 100W, 110W, 120W, 130W, 140W, 150W, 160W, 170W, 180W, 190W or 200W, or a range between any two of the values. In some embodiments, the power V1 of the corona treatment can be selected as 100V, 110V, 120V, 130V, 140V, 150V, 160V, 170V, 180V, 190V, 200V, 210V, 220V or 230V, or a range between any two of the values. In some embodiments, the corona treatment time T1 may be 0.1s, 0.5s, 1s, 1.5s, 2s, 2.5s, 3s, 3.5s or 4s, or a range between any two of the values.

[0042] In any embodiment, the ceramic coating is a corona-treated ceramic coating, wherein the corona treatment power P2 is 50-500W, the voltage V2 is 100V-230V, and the time T2 is 0.1s-6s. Furthermore, the material forming the ceramic coating is not particularly limited, and the ceramic coating includes one or more of Al2O3, AlO(OH), SiO2, TiO2, MgO, CaO, ZnO2, ZrO2, and SnO2, and optionally includes Al2O3.

[0043] In some embodiments, the power P2 of the corona treatment for the ceramic coating can be selected to be 50W, 60W, 70W, 80W, 90W, 100W, 110W, 120W, 130W, 140W, 150W, 160W, 170W, 180W, 190W, 200W, 210W, 220W, 230W, 240W, 250W, 260W, In some embodiments, the power V2 of the corona treatment may be selected from the group consisting of 100V, 110V, 120V, 130V, 140V, 150V, 160V, 170V, 180V, 190V, 200V, 210V, 220V or 230V, or a range between any two values. In some embodiments, the corona treatment time T2 can be selected as 0.1s, 0.5s, 1s, 1.5s, 2s, 2.5s, 3s, 3.5s, 4s, 4.5s, 5s, 5.5s or 6s, or a range between any two of the values.

[0044] Applying corona treatment to the substrate or ceramic coating increases the content of polar groups on the material's surface, thereby improving the material's polarity and surface energy, contributing to increased wettability and adhesion. Furthermore, the corona treatment prevents damage to the treated material, such as shrinkage caused by the energy released during the corona treatment, which could affect its mechanical strength. This increase in surface energy improves the separator's wettability to the electrolyte, the surface coating's adhesion, and the adhesion between the separator and the positive and negative electrodes.

[0045] In any embodiment, the diaphragm further comprises a bonding coating, the bonding coating being located on a side of the ceramic coating away from the base film, the difference between the contact angle of the ceramic coating and the contact angle of the bonding coating being 2°-15°. Furthermore, the material forming the bonding coating is not particularly limited and may be a polymer, specifically, may include one or more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene polymer, styrene-butadiene polymer, polyacrylic acid, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyamide, polyacrylonitrile, polyacrylate, polyacrylate, sodium hydroxymethyl cellulose, and optionally polyvinylidene fluoride.

[0046] In some embodiments, the difference between the contact angle of the ceramic coating and the contact angle of the bonding coating can be selected as 15°, 14°, 13°, 12°, 11°, 10°, 9°, 8°, 7°, 6°, 5°, 4°, 3° or 2°, or a range between any two of the values.

[0047] By using the material to form the bonding coating and making the difference between the contact angle of the ceramic coating and the contact angle of the bonding coating within the range, the surface energies of the bonding coating and the ceramic coating can be made close, thereby achieving a good bonding effect.

[0048] In any embodiment, the bonding coating is a bonding coating that has been corona treated, the power P3 of the corona treatment is 50-600W, the voltage V3 is 100V-230V, and the time T3 is 0.1s-5s.

[0049] In some embodiments, the power P3 of the corona treatment for the ceramic coating can be selected from 50W, 60W, 70W, 80W, 90W, 100W, 110W, 120W, 130W, 140W, 150W, 160W, 170W, 180W, 190W, 200W, 210W, 220W, 230W, 240W, 250W, 260W, 270W, 280W, 290W, 300W, 310W, 320W, 330W, 340W, 350W, 360W, 370W, 380W, 390W, 400W, 410W, 420W, 430W, 440W, 450W, 460W, 470W, 480W, 490W, 500W, 510W, 520W, 530W, 540W, 550W, 560W, 570W, 580W, 590W or 600W, or the range between any two values. In some embodiments, the power V3 of the corona treatment can be optionally 100V, 110V, 120V, 130V, 140V, 150V, 160V, 170V, 180V, 190V, 200V, 210V, 220V or 230V, or the range between any two values. In some embodiments, the corona treatment time T3 may be 0.1s, 0.5s, 1s, 1.5s, 2s, 2.5s, 3s, 3.5s, 4s, 4.5s or 5s, or a range between any two of the values.

[0050] Therefore, by setting the corona treatment to the above conditions, it is possible to achieve surface treatment of the material, that is, appropriately increase the surface energy of the material, while preventing damage to the corona-treated material.

[0051] In any embodiment, the contact angle of the base film is 60°-80°, the contact angle of the ceramic coating is 60°-80°, and the contact angle of the upper bonding coating is 40°-60°.

[0052] In some embodiments, the contact angle of the base film may be 60°, 62°, 64°, 66°, 68°, 70°, 72°, 74°, 76°, 78° or 80°, or a range between any two of the values.

[0053] By ensuring that the contact angle between the base film and the ceramic coating is within the above range, the surface energies between the base film and the ceramic coating can be close, thereby achieving good bonding between the two. By ensuring that the contact angle of the adhesive coating is within the above range, it can achieve better bonding between the separator and the electrode pad.

[0054] In any embodiment, the separator has a liquid absorption rate of 4.5 mm / s to 6 mm / s. By ensuring that the separator has a liquid absorption rate within this range, when the separator is immersed in the electrolyte, the electrolyte can quickly penetrate the separator, enabling rapid ion conduction, thereby improving the battery's ionic conductivity, and thereby improving the battery's cycle performance and rate characteristics.

[0055] In some embodiments, the liquid absorption rate of the diaphragm can be selected as 4.5mm / s, 4.6mm / s, 4.7mm / s, 4.8mm / s, 4.9mm / s, 5mm / s, 5.1mm / s, 5.2mm / s, mm / s, 5.3mm / s, 5.4mm / s, 5.5mm / s, 5.6mm / s, 5.7mm / s, 5.8mm / s, 5.9mm / s or 6mm / s, or a range between any two of the values.

[0056] In any embodiment, the bonding force between the base film and the ceramic coating is 2.5N / mm-4N / mm. By making the bonding force between the base film and the ceramic coating within the said range, the structure of the diaphragm is more compact, which enables the diaphragm to better perform its function, thereby improving the cycle performance and rate characteristics of the battery.

[0057] In some embodiments, the adhesion between the base film and the ceramic coating may be 2.5 N / mm, 2.6 N / mm, 2.7 N / mm, 2.8 N / mm, 2.9 N / mm, 3 N / mm, 3.1 N / mm, 3.2 N / mm, 3.3 N / mm, 3.4 N / mm, 3.5 N / mm, 3.6 N / mm, 3.7 N / mm, 3.8 N / mm, 3.9 N / mm or 4 N / mm, or a range between any two of the values.

[0058] In any embodiment, the separator further comprises a bonding coating located on a side of the ceramic coating away from the base film, wherein the difference between the contact angle of the positive electrode plate and the contact angle of the bonding coating is ≤ 20°; and / or the difference between the contact angle of the negative electrode plate and the contact angle of the bonding coating is ≤ 20°. The contact angle of the positive electrode plate is 40°-80°; and / or the contact angle of the negative electrode plate is 40°-80°.

[0059] In some embodiments, the difference between the contact angle of the positive electrode sheet and / or the negative electrode sheet and the contact angle of the bonding coating can be selected to be 20°, 19°, 18°, 17°, 16°, 15°, 14°, 13°, 12°, 11°, 10°, 9°, 8°, 7°, 6°, 5°, 4°, 3°, 2°, 1° or 0°, and the contact angle of the positive electrode sheet and / or the negative electrode sheet can be selected to be 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75° or 80°, or a range between any two of the values.

[0060] In the isolation membrane of the present application, by making the diaphragm, positive electrode sheet and negative electrode sheet in the secondary battery have contact angles and contact angle differences within the said range respectively, good bonding between the diaphragm, positive electrode sheet and negative electrode sheet can be achieved, thereby making the structure of the secondary battery more compact and the conduction of ions between the positive and negative electrode sheets and the diaphragm smoother, thereby achieving high cycle characteristics and high rate characteristics of the secondary battery.

[0061] [Positive electrode]

[0062] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on both sides of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0063] As an example, the positive electrode current collector has two opposite surfaces in its thickness direction, and the positive electrode film layers are disposed on the two opposite surfaces of the positive electrode current collector.

[0064] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0065] In some embodiments, the positive electrode active material may adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries 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 may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0066] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0067] In some embodiments, the positive electrode film layer may further include a conductive agent (Super P). As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0068] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0069] [Negative electrode]

[0070] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on both sides of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0071] As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode film layers are provided on both surfaces of the negative electrode current collector.

[0072] 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 base layer and a metal layer formed on at least one surface of the polymer base material. 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 base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0073] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0074] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0075] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0076] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0077] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0078] [Electrolytes]

[0079] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0080] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0081] 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0082] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0083] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0084] [Method for preparing battery separator]

[0085] The battery separator of the present application is prepared by the following method: the battery separator of the present application has a base film, a ceramic coating and an optional adhesive coating in sequence. First, the surface of the base film is corona treated to enhance the polarity of the base film surface and enhance the adhesion between the base film and the coating; the coated separator is corona treated again to enhance the surface energy of the coated separator, enhance the adhesion of the separator and the wettability of the electrolyte.

[0086] [Secondary battery]

[0087] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0088] The secondary battery of the present application has high cycle characteristics and high rate characteristics by including the separator of the present application.

[0089] Example

[0090] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0091] 1. Preparation method

[0092] Example 1

[0093] 1) Diaphragm

[0094] Polyethylene was used as the base film, the length of the base film was 100 cm, and the width was 10 cm. The base film was subjected to corona treatment with a power P1 of 200 W, a voltage V1 of 150 V, and a time T1 of 3.5 s.

[0095] A certain amount of ceramic material, Al2O3, was weighed and dispersed in water to form a ceramic slurry. The slurry was sprayed onto opposite surfaces of a corona-treated polyethylene base film to prepare a ceramic coating. After spraying, the coating was baked in a 60°C oven for 30 minutes. The baked ceramic coating surface was then corona-treated at a power P2 of 500W, a voltage V2 of 220V, and a time T2 of 5 seconds.

[0096] A certain amount of binder polyvinylidene fluoride was weighed and dissolved in solvent N-methyl-2-pyrrolidone to obtain a bonding slurry. The bonding slurry was sprayed on the opposite surfaces of the ceramic coating after corona treatment to prepare a bonding coating. After spraying, it was placed in a 60°C oven and baked for 30 minutes. The baked bonding coating surface was corona treated with a power P3 of 589 W, a voltage V3 of 200 V, and a time T3 of 4 seconds to obtain a diaphragm.

[0097] 2) Electrolyte

[0098] In an argon-filled glove box (water content <10 ppm, oxygen content <1 ppm), ethylene carbonate and ethyl methyl carbonate (volume ratio 3:7) were mixed uniformly. An appropriate amount of LiPF6 was slowly added to the non-aqueous organic solvent. Once the lithium salt was completely dissolved, a 1 mol / L electrolyte solution was obtained. The electrolyte conductivity was 8.5 mS / cm.

[0099] 3) Preparation of positive electrode sheet

[0100] The positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O2, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 90:5:5, and N-methylpyrrolidone (NMP) was added as a solvent. The mixture was stirred under vacuum until the system was homogeneous, obtaining a positive electrode slurry with a solid content of 65wt%. The positive electrode slurry was coated on a current collector aluminum foil and dried at 85°C before cold pressing. The positive electrode sheet was then trimmed, cut, and slit, and then dried under vacuum at 85°C for 4 hours to form the positive electrode sheet.

[0101] 4) Preparation of negative electrode sheet

[0102] Anode active material graphite, a certain amount of silicon, conductive agent Super P, thickener CMC, and binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 90:4:3:3 and dissolved in deionized water. A vacuum mixer was used to obtain the negative electrode slurry, which had a solids content of 55 wt%. The negative electrode slurry was then coated onto a current collector copper foil and dried at 85°C. The resulting sheet was then cold-pressed, trimmed, cut, and slit, and then dried at 120°C under vacuum for 12 hours to produce the negative electrode.

[0103] 5) Battery Preparation

[0104] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, so that the separator is placed between the positive and negative electrode sheets to isolate the positive and negative electrodes, and the bare battery cell is wound, the tabs are welded, and the bare battery cell is placed in an outer package. The prepared electrolyte is injected into the dried battery cell, packaged, allowed to stand, formed, shaped, and capacity tested to obtain the lithium secondary battery in Example 1.

[0105] In this application, the contact angle of the material surface is measured as follows:

[0106] Fix the electrode or film to a standard glass slide and place it on a table. Insert the needle into deionized water and slowly pump the deionized water into the syringe. With the needle pointing upward, squeeze the piston to expel the air from the syringe, and then place the needle back into the holder. Adjust the sample stage height so that the stage rises to receive the extruded droplet and form a droplet on the powder surface. Use a contact angle meter (SINDIN, Model SDC-200S) to automatically measure the contact angle, perform a fitting, and record the contact angle.

[0107] The secondary batteries of Examples 2-15 and Comparative Examples 1-3 are prepared in a similar manner to the secondary battery of Example 1, but with different corona treatment parameters of the base film, ceramic coating, and adhesive coating or contact angles of the positive / negative electrode sheets. Product parameters are detailed in Table 1.

[0108] 2. Performance Testing

[0109] 1. Diaphragm performance test

[0110] 1) Adhesion test

[0111] Use a sampler with a length of 100 mm and a width of 20 mm to take a sample. After wiping the stainless steel plate with alcohol, stick a double-sided tape of standard width (specification: 3M9730-100) evenly on the steel plate. Tear off the other side of the double-sided tape, stick the diaphragm evenly on it, install the fixture, and test the adhesion between the base film and the coating of the diaphragm on a tensile testing machine (model: INSTRON, Modle: 3365).

[0112] 2) Test of liquid absorption capacity

[0113] Sampling was performed using a sampler with a length of 100 mm and a width of 20 mm. The sample was immersed in a 1 mol / L LiPF6 / EC∶DEC=1∶1 electrolyte at 60°C for 4 h. The diaphragm was then taken out and suspended in the air for 30 s. The weight of the diaphragm before and after immersion was measured on an electronic balance ((weight after immersion - weight before immersion) / weight before immersion).

[0114] 3) Liquid absorption rate test

[0115] Use a sampler with a length of 100 mm and a width of 5 mm to take a sample. Fix the sample (suspend it horizontally in the air) and use a dropper to drop a drop of electrolyte (1 mol / L LiPF6 / EC:DEC=1:1) on the sample. Record the length of the liquid absorption strip after 60 seconds. The ratio of this length to time is the liquid absorption rate.

[0116] 2. Battery performance test

[0117] 1) Cycle performance

[0118] At 25°C, the prepared lithium secondary battery was charged at a constant current of 0.33C to 3.65V, then charged at a constant voltage of 0.05C, and then left for 10 minutes. Then, it was discharged at a constant current of 0.33C to 2.5V, and the discharge capacity was recorded as C0. 1000 cycles were performed according to the charge and discharge process. The discharge capacity after 1000 cycles was C1, and the cycle capacity retention rate of the battery = C1 / C0×100%.

[0119] 2) Fast charging performance

[0120] At 25°C, the prepared lithium secondary battery was charged at a constant current of 2C to 3.65V, and then charged at a constant voltage of 0.05C. The charging capacity at this time was C1. After that, it was left for 10 minutes and discharged at a constant current of 1C to 2.5V. The discharge capacity was recorded as C0. The fast charging performance is reflected by the value of C0 / C1. The larger the value, the better the fast charging performance.

[0121] 3. Analysis of test results of various embodiments and comparative examples

[0122] Batteries of various examples and comparative examples were prepared according to the method, and various performance parameters were measured. The results are shown in Table 1 below.

[0123] Table 1

[0124] As shown in Table 1, the diaphragms of Examples 1-15 of the present application include a base film and a ceramic coating located on at least one side of the base film; the difference between the contact angle of the base film and the contact angle of the ceramic coating is ≤15°, and the batteries manufactured using the diaphragms have a high capacity retention rate after 500 cycles, and the fast charging performance of the batteries is also excellent. The main reason for this is that the base film and the isolation film of the diaphragm are subjected to the corona treatment described in the present application, which improves the polarity and surface energy of the base film, the ceramic coating, and the bonding coating. Specifically, the contact angle between the layers is within the range described in the present application, thereby improving the bonding between the layers and improving the cycle performance and fast charging performance of the battery.

[0125] In addition, the inventors have found that in the later stages of the cycle of secondary batteries, battery attenuation is mainly affected by the amount of liquid retained. Therefore, increasing the liquid retention of the diaphragm helps to improve the cycle performance; in addition, the increased adhesion and increased liquid retention help to improve the interface state of the electrode, which is beneficial to the rate performance. In Examples 1-15 of the present application, after the membrane layer of the diaphragm is corona treated, the polarity of the material surface is enhanced, and the affinity with the electrolyte of the same polar substance is enhanced, resulting in a high liquid absorption rate of the diaphragm and a good liquid retention rate, which also helps to improve the cycle performance and fast charging performance of the battery.

[0126] In addition, according to Table 1, in Comparative Examples 1-3, the base film and ceramic coating of the diaphragm of Comparative Example 1 were not subjected to corona treatment; the ceramic coating and bonding coating of the diaphragm of Comparative Example 2 were not subjected to corona treatment; and the base film and bonding coating of the diaphragm of Comparative Example 3 were not subjected to corona treatment. As a result, the cycle characteristics and fast charging characteristics of the secondary batteries manufactured based on these diaphragms were significantly reduced and could not meet the requirements of this application.

[0127] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included within the technical scope of the present application. In addition, without departing from the scope of the present application, any other modifications that can be imagined by those skilled in the art to the embodiments, or any other methods constructed by combining some of the constituent elements in the embodiments are also included within the scope of the present application.

Claims

1. A diaphragm, characterized in that: comprising a base film and a ceramic coating located on at least one side of the base film; The difference between the contact angle of the base film and the contact angle of the ceramic coating is ≤15°, preferably ≤10°.

2. The diaphragm according to claim 1, characterized in that The base film is a base film after corona treatment, the power P1 of the corona treatment is 50W-200W, the voltage V1 is 100V-230V, and the time T1 is 0.1s-4s.

3. The diaphragm according to claim 1 or 2, characterized in that: The ceramic coating is a ceramic coating after corona treatment, the power P2 of the corona treatment is 50W-500W, the voltage V2 is 100V-230V, and the time T2 is 0.1s-6s.

4. The diaphragm according to any one of claims 1 to 3, characterized in that The diaphragm further comprises a bonding coating, wherein the bonding coating is located on a side of the ceramic coating away from the base film, and a difference between a contact angle of the ceramic coating and a contact angle of the bonding coating is 2°-15°.

5. The diaphragm according to any one of claims 1 to 4, characterized in that The bonding coating is a bonding coating after corona treatment, the power P3 of the corona treatment is 50W-600W, the voltage V3 is 100V-230V, and the time T3 is 0.1s-5s.

6. The diaphragm according to any one of claims 1 to 5, characterized in that The contact angle of the base film is 60°-80°.

7. The diaphragm according to any one of claims 1 to 6, characterized in that The contact angle of the ceramic coating is 60°-80°.

8. The diaphragm according to any one of claims 1 to 7, characterized in that The contact angle of the bonding coating is 40°-60°.

9. The diaphragm according to any one of claims 1 to 8, characterized in that The base film includes one or more of polyethylene, polypropylene, polyimide, polyamide, polyethylene terephthalate, glass fiber, non-woven fabric, and high-temperature resistant polyester film, and optionally includes one or more of polyethylene and polypropylene.

10. The diaphragm according to any one of claims 1 to 9, characterized in that The ceramic coating includes one or more of Al2O3, AlO(OH), SiO2, TiO2, MgO, CaO, ZnO2, ZrO2, SnO2, and optionally includes Al2O3.

11. The diaphragm according to any one of claims 1 to 10, characterized in that The bonding coating includes one or more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene polymer, styrene-butadiene polymer, polyacrylic acid, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyamide, polyacrylonitrile, polyacrylate, polyacrylate, sodium hydroxymethyl cellulose, and optionally includes polyvinylidene fluoride.

12. The diaphragm according to any one of claims 1 to 11, characterized in that The liquid absorption rate of the diaphragm is 4.5 mm / s-6 mm / s.

13. The diaphragm according to any one of claims 1 to 12, characterized in that The bonding force between the base film and the ceramic coating is 2.5N / mm-4N / mm.

14. A secondary battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and the separator according to any one of claims 1 to 13.

15. The secondary battery according to claim 14, characterized in that: The separator further comprises a bonding coating located on a side of the ceramic coating away from the base film, and the difference between the contact angle of the positive electrode sheet and the contact angle of the bonding coating is ≤20°; and / or The difference between the contact angle of the negative electrode plate and the contact angle of the bonding coating is ≤20°.

16. The secondary battery according to claim 14 or 15, characterized in that: The contact angle of the positive electrode plate is 40°-80°; and / or the contact angle of the negative electrode plate is 40°-80°.

17. The secondary battery according to any one of claims 14 to 16, characterized in that: The secondary battery includes at least one of a lithium secondary battery and a sodium secondary battery.

18. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 14 to 17.

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