Battery diaphragm, secondary battery, and electric device

Abstract

The invention provides a battery diaphragm which is characterized by comprising a base membrane and a ceramic coating positioned on at least one side of the base membrane, wherein the difference value between the contact angle of the base film and the contact angle of the ceramic coating is less than or equal to 15 degrees. The battery diaphragm disclosed by the invention has high adhesion, high liquid retention capacity and high ionic conductivity, and the cycle characteristic and the rate characteristic of the battery can be improved.

Description

Technical Field

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

[0002] In recent years, with the increasingly wide application scope of secondary batteries, secondary batteries are widely used in energy storage power systems such as hydraulic power plants, thermal power plants, wind power plants, and solar power plants, as well as in multiple fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Due to the great development of secondary batteries, higher requirements are also put forward for their energy density, cycle performance, safety performance, etc.

[0003] At present, the separator materials for secondary batteries are mainly made of PP and PE materials, which are key components of secondary batteries. The separator materials have good pore size distribution, mechanical properties, chemical stability, electrolyte wettability, electronic insulation, and high-temperature shut-off performance. However, since the current PP and PE-based separators are all non-polar and have low surface tension, the wettability of the separator to the electrolyte and the adhesiveness of the surface coating are relatively poor. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide a secondary battery separator with high adhesiveness, high liquid retention, and high ionic conductivity, as well as a secondary battery and an electrical device having the separator.

[0005] In a first aspect of the present application, there is provided a battery separator, 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°.

[0006] Thus, by adopting the battery separator with the above structure, the present application can improve the wettability of the separator to the electrolyte, the adhesiveness of the surface coating (ceramic coating), and the adhesiveness between the separator and the positive and negative electrode plates, and achieve high adhesiveness, high liquid retention, and high ionic conductivity of the separator.

[0007] In any embodiment, the base film is a corona-treated base film, the power P1 of the corona treatment is 50W - 200W, the voltage V1 is 100V - 230V, and the time T1 is 0.1s - 4s. In addition, the material forming the base material 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.

[0008] In any embodiment, the ceramic coating is a corona-treated ceramic coating. The power P2 of the corona treatment is 50 W - 500 W, the voltage V2 is 100 V - 230 V, and the time T2 is 0.1 s - 6 s. In addition, the material forming the ceramic coating is not particularly limited, and the ceramic coating includes Al 2 O 3 , AlO(OH), SiO 2 , TiO 2 , MgO, CaO, ZnO 2 , ZrO 2 , SnO 2 or one or more of them, and optionally includes Al 2 O 3 .

[0009] Thus, by performing the corona treatment on the substrate or the ceramic coating, the surface energy of the material can be increased, and at the same time, damage to the treated material can be prevented. Based on the appropriate increase in the surface energy of the material, the wettability of the separator to the electrolyte, the adhesiveness of the surface coating, and the adhesiveness between the separator and the positive and negative electrode plates can be improved accordingly.

[0010] In any embodiment, the separator further includes an adhesive coating, which is located on the 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 adhesive coating is 2° - 15°. In addition, the material forming the adhesive coating is not particularly limited and can be a polymer. Specifically, it can 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 salt, sodium hydroxymethyl cellulose, and optionally includes polyvinylidene fluoride.

[0011] By using the above materials to form the adhesive coating and making the difference between the contact angle of the ceramic coating and the contact angle of the adhesive coating within the above range, the surface energies between the adhesive coating and the ceramic coating can be made close, thereby achieving a good bonding effect.

[0012] In any embodiment, the adhesive coating is a corona-treated adhesive coating. The power P3 of the corona treatment is 50 W - 600 W, the voltage V3 is 100 V - 230 V, and the time T3 is 0.1 s - 5 s.

[0013] Thus, by setting the corona treatment to the above conditions, surface treatment of the material can be achieved, that is, the surface energy of the material can be appropriately increased, and at the same time, damage to the corona-treated material can be prevented.

[0014] In any embodiment, the contact angle of the base film is 60°-80°. The contact angle of the ceramic coating is 60°-80°. The contact angle of the adhesive coating is 40°-60°.

[0015] By making the contact angles of the base film and the ceramic coating within the above range, the surface energies between the base film and the ceramic coating can be made similar, thus achieving a good bonding effect between the two. By making the contact angle of the adhesive coating within the above range, it can better achieve the effect of bonding the separator and the electrode tab.

[0016] In any embodiment, the liquid absorption rate of the separator is 4.5 mm / s - 6 mm / s. By making the separator have a liquid absorption rate within the above range, when the separator is immersed in the electrolyte, the electrolyte can quickly infiltrate the separator to achieve rapid ion conduction, thereby improving the ionic conductivity of the battery and further improving the cycle performance and rate characteristics of the battery.

[0017] In any embodiment, the adhesion between the base film and the ceramic coating is 2.5 N / mm - 4 N / mm. By making the adhesion between the base film and the ceramic coating within the above range, the structure of the separator is more compact, enabling the separator to better perform its function, and further improving the cycle performance and rate characteristics of the battery.

[0018] The second aspect of the present application provides a secondary battery, including a positive electrode tab, a negative electrode tab, and the separator described above.

[0019] The secondary battery of the present application has high cycle characteristics and high rate characteristics by having the separator of the present application.

[0020] In any embodiment, the separator further includes an adhesive coating on the side of the ceramic coating away from the base film, and the difference between the contact angle of the positive electrode tab and the contact angle of the adhesive coating ≤ 20°; and / or the difference between the contact angle of the negative electrode tab and the contact angle of the adhesive coating ≤ 20°. The contact angle of the positive electrode tab is 40°-80°; and / or the contact angle of the negative electrode tab is 40°-80°.

[0021] By making the separator, the positive electrode tab, and the negative electrode tab in the secondary battery have the contact angles and contact angle differences within the above ranges respectively, good bonding between the separator, the positive electrode tab, and the negative electrode tab can be achieved, thereby making the structure of the secondary battery more compact and the ion conduction between the positive and negative electrode tabs and the separator smoother, thus achieving the high cycle characteristics and high rate characteristics of the secondary battery.

[0022] In any embodiment, the secondary battery includes at least one of a lithium secondary battery and a sodium secondary battery.

[0023] A third aspect of the present application provides an electrical device, characterized by comprising the secondary battery described above. Detailed implementation manners

[0024] Hereinafter, the implementation manners of the battery separator, the secondary battery, and the electrical device will be described in detail. However, there may be cases where unnecessary details are omitted. For example, there are cases where the detailed description of well-known matters and the repeated description of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art.

[0025] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The range defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if the ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, it is understood that the ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values of 1 and 2 are listed, and if the maximum range values of 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0026] If there is no special description, all the implementation manners and optional implementation manners of the present application can be combined with each other to form a new technical solution.

[0027] If there is no special description, all the technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0028] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, and preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out sequentially, or may also include steps (b) and (a) carried out sequentially. For another example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or may also include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0029] Unless otherwise specified, "comprising" and "including" mentioned in this application mean open-ended or may also be closed-ended. For example, "comprising" and "including" may mean that other components not listed may also be included or comprised, or may only include or comprise the listed components.

[0030] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0031] As a key component of secondary batteries, the separator for batteries has a great influence on the performance of the batteries. However, the existing separators made of PP and PE materials are both non-polar and have a low surface tension, resulting in poor wettability of the separator to the electrolyte and poor adhesiveness of the surface coating. By performing surface corona treatment on each layer structure of the battery separator and the electrode sheet, free radical reactions can be generated on the surface of the object to be treated, causing cross-linking of the polymer. The surface becomes rough and its wettability to polar solvents increases. The surface molecules of the object to be treated are oxidized and polarized, and the surface is eroded by ion shock, so as to increase the adhesion ability of the surface of the object to be treated. Thereby, the liquid retention property of the battery separator and the adhesiveness with the electrode sheet can be improved, and the cycle performance and rate characteristics of the secondary battery can be improved.

[0032] Based on this, this application proposes a battery separator, its manufacturing method, a secondary battery having the separator, and an electrical device using the same, which will be described in detail below respectively.

[0033] [Battery Separator]

[0034] The battery separator of the present application 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°, and optionally contains a bonding coating. By subjecting each layer to surface corona treatment, the surface energy of each layer is increased, thereby increasing the wettability and adhesion.

[0035] In some embodiments, the difference between the contact angle of the base film and the contact angle of the ceramic coating can be optionally 15°, 14°, 13°, 12°, 11°, 10°, 9°, 8°, 7°, 6°, 5°, 4°, 3°, 2°, 1° or 0°, or the range between any two values.

[0036] Among them, the contact angle of the base film is adjusted by corona treatment on the surface of the base film. Through corona treatment, the surface energy of the material surface can be increased, thereby increasing the polarity of the material surface. By making the contact angle difference between the layers within the range, the polarity of the base film surface can be enhanced, and the adhesion between the base film and the coating can be enhanced; the separator after coating is subjected to corona surface treatment again to enhance the surface energy of the coated separator and enhance the adhesiveness and wettability of the separator to the electrolyte.

[0037] In any embodiment, the base film is a corona-treated base film. The power P1 of the corona treatment is 50W - 200W, the voltage V1 is 100V - 230V, and the time T1 is 0.1s - 4s. In addition, the material forming the base material is not particularly limited. The base film includes one or more of polyethylene, polypropylene, polyimide, polyamide, polyethylene terephthalate, glass fiber, non-woven fabric, and high-temperature polyester film, and optionally includes one or more of polyethylene and polypropylene.

[0038] In some embodiments, the power P1 of the corona treatment for the base film can be optionally 50W, 60W, 70W, 80W, 90W, 100W, 110W, 120W, 130W, 140W, 150W, 160W, 170W, 180W, 190W or 200W, or the range between any two values. In some embodiments, the power V1 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 time T1 of the corona treatment can be optionally 0.1s, 0.5s, 1s, 1.5s, 2s, 2.5s, 3s, 3.5s or 4s, or the range between any two values.

[0039] In any embodiment, the ceramic coating is a corona-treated ceramic coating. The power P2 of the corona treatment is 50 - 500 W, the voltage V2 is 100 V - 230 V, and the time T2 is 0.1 s - 6 s. In addition, the material forming the ceramic coating is not particularly limited, and the ceramic coating includes Al 2 O 3 , AlO(OH), SiO 2 , TiO 2 , MgO, CaO, ZnO 2 , ZrO 2 , SnO 2 and one or more of them, and optionally includes Al 2 O 3 .

[0040] In some embodiments, the power P2 of the corona treatment for the ceramic coating can be selected as 50 W, 60 W, 70 W, 80 W, 90 W, 100 W, 110 W, 120 W, 130 W, 140 W, 150 W, 160 W, 170 W, 180 W, 190 W, 200 W, 210 W, 220 W, 230 W, 240 W, 250 W, 260 W, 270 W, 280 W, 290 W, 300 W, 310 W, 320 W, 330 W, 340 W, 350 W, 360 W, 370 W, 380 W, 390 W, 400 W, 410 W, 420 W, 430 W, 440 W, 450 W, 460 W, 470 W, 480 W, 490 W or 500 W, or the range between any two of these values. In some embodiments, the voltage V2 of the corona treatment can be selected as 100 V, 110 V, 120 V, 130 V, 140 V, 150 V, 160 V, 170 V, 180 V, 190 V, 200 V, 210 V, 220 V or 230 V, or the range between any two of these values. In some embodiments, the time T2 of the corona treatment can be selected as 0.1 s, 0.5 s, 1 s, 1.5 s, 2 s, 2.5 s, 3 s, 3.5 s, 4 s, 4.5 s, 5 s, 5.5 s or 6 s, or the range between any two of these values.

[0041] By performing the corona treatment on the substrate or the ceramic coating, the content of polar groups on the material surface can be increased, thereby enhancing the polarity and surface energy of the material, which helps to increase the wettability and adhesion of the material. At the same time, the corona conditions can also prevent damage to the treated material, such as shrinkage of the material caused by the energy released during the corona treatment, which affects its mechanical strength. Based on the appropriate increase in the surface energy of the material, the wettability of the separator to the electrolyte, the adhesiveness of the surface coating, and the adhesiveness between the separator and the positive and negative electrode plates can be improved.

[0042] In any embodiment, the diaphragm further includes an adhesive coating located on the 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 adhesive coating is 2° - 15°. In addition, the material for forming the adhesive coating is not particularly limited and can be a polymer. Specifically, it 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 salt, sodium hydroxymethyl cellulose, and optionally includes polyvinylidene fluoride.

[0043] In some embodiments, the difference between the contact angle of the ceramic coating and the contact angle of the adhesive coating can be optionally 15°, 14°, 13°, 12°, 11°, 10°, 9°, 8°, 7°, 6°, 5°, 4°, 3° or 2°, or the range between any two of these values.

[0044] By using the material to form the adhesive coating and making the difference between the contact angle of the ceramic coating and the contact angle of the adhesive coating within the above range, the surface energy between the adhesive coating and the ceramic coating can be made close, thereby achieving a good bonding effect.

[0045] In any embodiment, the adhesive coating is an adhesive coating after corona treatment, and the power P3 of the corona treatment is 50 - 600W, the voltage V3 is 100V - 230V, and the time T3 is 0.1s - 5s.

[0046] 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 of these values. In some embodiments, the power V3 of the corona treatment can be selected from 100V, 110V, 120V, 130V, 140V, 150V, 160V, 170V, 180V, 190V, 200V, 210V, 220V or 230V, or the range between any two of these values. In some embodiments, the time T3 of the corona treatment can be selected from 0.1s, 0.5s, 1s, 1.5s, 2s, 2.5s, 3s, 3.5s, 4s, 4.5s or 5s, or the range between any two of these values.

[0047] Thus, by setting the corona treatment to the above conditions, surface treatment of the material can be achieved, that is, the surface energy of the material is appropriately increased while preventing damage to the corona-treated material.

[0048] In any embodiment, the contact angle of the base film is 60° - 80°. The contact angle of the ceramic coating is 60° - 80°. The contact angle of the upper bonding coating is 40° - 60°.

[0049] In some embodiments, the contact angle of the base film can be selected from 60°, 62°, 64°, 66°, 68°, 70°, 72°, 74°, 76°, 78° or 80°, or the range between any two of these values.

[0050] By making the contact angles of the base film and the ceramic coating within the above range, the surface energies between the base film and the ceramic coating can be made similar, thus achieving a good bonding effect between the two. By making the contact of the bonding coating within the above range, it can better achieve the effect of bonding the separator and the electrode tab.

[0051] In any embodiment, the liquid absorption rate of the separator is 4.5 mm / s - 6 mm / s. By making the separator have a liquid absorption rate within the above range, when the separator is immersed in the electrolyte, the electrolyte can quickly infiltrate the separator to achieve rapid ion conduction, thereby improving the ionic conductivity of the battery and further enhancing the cycle performance and rate characteristics of the battery.

[0052] In some embodiments, the liquid absorption rate of the separator can be selected from 4.5 mm / s, 4.6 mm / s, 4.7 mm / s, 4.8 mm / s, 4.9 mm / s, 5 mm / s, 5.1 mm / s, 5.2 mm / s, 5.3 mm / s, 5.4 mm / s, 5.5 mm / s, 5.6 mm / s, 5.7 mm / s, 5.8 mm / s, 5.9 mm / s or 6 mm / s, or the range between any two of these values.

[0053] In any embodiment, the adhesion between the base film and the ceramic coating is 2.5 N / mm - 4 N / mm. By making the adhesion between the base film and the ceramic coating within the above range, the structure of the separator is more compact, enabling the separator to better perform its functions, and further enhancing the cycle performance and rate characteristics of the battery.

[0054] In some embodiments, the adhesion between the base film and the ceramic coating can be selected from 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 the range between any two of these values.

[0055] In any embodiment, the separator further includes an adhesive coating on the side of the ceramic coating away from the base film, and the difference between the contact angle of the positive electrode plate and the contact angle of the adhesive coating ≤ 20°; and / or the difference between the contact angle of the negative electrode plate and the contact angle of the adhesive coating ≤ 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°.

[0056] In some embodiments, the difference between the contact angle of the positive electrode plate and / or the negative electrode plate and the contact angle of the adhesive coating may be selected from 20°, 19°, 18°, 17°, 16°, 15°, 14°, 13°, 12°, 11°, 10°, 9°, 8°, 7°, 6°, 5°, 4°, 3°, 2°, 1° or 0°. The contact angle of the positive electrode plate and / or the negative electrode plate may be selected from 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75° or 80°, or the range between any two of these values.

[0057] In the separator of the present application, by making the separator, the positive electrode plate and the negative electrode plate in the secondary battery have the contact angles and the contact angle differences within the above ranges respectively, good adhesion between the separator, the positive electrode plate and the negative electrode plate can be achieved, thereby making the structure of the secondary battery more compact and the conduction of ions between the positive and negative electrode plates and the separator smoother, thereby realizing the high cycle characteristics and high rate characteristics of the secondary battery.

[0058] [Positive electrode plate]

[0059] The positive electrode plate includes a positive current collector and positive electrode layers provided on both surface sides of the positive current collector. The positive electrode layers include positive active materials.

[0060] As an example, the positive current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode layers are provided on the two opposite surfaces of the positive current collector.

[0061] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (such as 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.).

[0062] In some embodiments, the positive active material may be a positive active material for a battery well-known in the art. As an example, the positive active material may include at least one of the following materials: lithium phosphate 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 conventional materials that can be used as battery positive active materials may also be used. These positive active materials may be used alone or in combination of two or more. Among them, examples of the lithium transition metal oxide may include, but are not limited to, lithium cobalt oxide (such as LiCoO 2) Lithium nickel oxides (such as LiNiO 2 ) Lithium manganese oxides (such as LiMnO 2 , LiMn 2 O 4 ), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (which can also be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (which can also be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (which can also be abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (which can also be abbreviated as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (which can also be abbreviated as NCM 811 ), lithium nickel cobalt aluminum oxides (such as LiNi 0.85 Co 0.15 Al 0.05 O 2 ) and at least one of their modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO 4 (which can also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of a composite material of lithium manganese iron phosphate and carbon.

[0063] In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0064] In some embodiments, the positive electrode film layer may further optionally 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.

[0065] In some embodiments, the positive electrode sheet can be prepared by the following method: dispersing the components for preparing the positive electrode sheet, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode sheet can be obtained.

[0066] [Negative electrode sheet]

[0067] The negative electrode sheet includes a negative electrode current collector and negative electrode film layers provided on both surface sides of the negative electrode current collector, and the negative electrode film layers include negative electrode active materials.

[0068] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layers are provided on the two surfaces of the negative electrode current collector.

[0069] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper 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.).

[0070] In some embodiments, the negative electrode active material can be a negative electrode active material for a battery 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, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material can be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as the negative electrode active material of the battery can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0071] In some embodiments, the negative electrode film layer may further optionally 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).

[0072] In some embodiments, the negative electrode film layer may further optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0073] In some embodiments, the negative electrode film layer may further optionally include other additives, such as a thickening agent (such as sodium carboxymethyl cellulose (CMC-Na)).

[0074] In some embodiments, the negative electrode plate can be prepared by the following method: dispersing the components for preparing the negative electrode plate, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (such as deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate can be obtained.

[0075] [Electrolyte]

[0076] The electrolyte functions to conduct ions between the positive electrode plate and the negative electrode plate. There is no specific limitation on the type of electrolyte in this application, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0077] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0078] 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 bis(oxalate) borate, lithium difluoro bis(oxalate) phosphate, and lithium tetrafluorooxalate phosphate.

[0079] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0080] In some embodiments, the electrolyte may further optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery properties, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0081] [Preparation Method of Battery Separator]

[0082] The battery separator of the present application is prepared by the following method: The battery separator of the present application sequentially has a base film, a ceramic coating, and an optional adhesive coating. First, corona treatment is performed on the surface of the base film to enhance the polarity of the base film surface and the adhesion between the base film and the coating; the coated separator is subjected to corona surface treatment again to enhance the surface energy of the coated separator, enhance the adhesiveness of the separator, and the wettability to the electrolyte.

[0083] [Secondary Battery]

[0084] Generally, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows ions to pass through.

[0085] The secondary battery of the present application has high cycle characteristics and high rate characteristics by having the separator of the present application.

[0086] Examples

[0087] Hereinafter, examples of the present application will be described. The examples described below are exemplary and are only used to explain the present application and should not be construed as a limitation of the present application. For those where specific technologies or conditions are not indicated in the examples, the technologies or conditions described in the literature in the art or according to the product specifications are followed. For reagents or instruments where the manufacturer is not indicated, they are all conventional products that can be obtained through commercial purchase.

[0088] I. Preparation Method

[0089] Example 1

[0090] 1) Separator

[0091] Using polyethylene as the base film, the length of the base film is 100 cm, the width is 10 cm, and corona treatment is performed on the base film, with the power P1 being 200 W, the voltage V1 being 150 V, and the time T1 being 3.5 s;

[0092] Weigh a certain amount of ceramic material Al 2 O 3Disperse it in water to obtain a ceramic material slurry. Spray the ceramic material slurry on the opposite two surfaces of the corona-treated base film polyethylene to prepare a ceramic coating. After spraying, place it in an oven at 60 °C and bake for 30 min. Perform corona treatment on the surface of the baked ceramic coating, with power P2 being 500 W, voltage V2 being 220 V, and time T2 being 5 s;

[0093] Weigh a certain amount of the binder polyvinylidene fluoride and dissolve it in the solvent N-methyl-2-pyrrolidone to obtain a binder slurry. Spray the binder slurry on the opposite two surfaces of the corona-treated ceramic coating to prepare a binder coating. After spraying, place it in an oven at 60 °C and bake for 30 min. Perform corona treatment on the surface of the baked binder coating, with power P3 being 589 W, voltage V3 being 200 V, and time T3 being 4 s to obtain a separator.

[0094] 2) Electrolyte

[0095] In a glove box filled with argon (water content < 10 ppm, oxygen content < 1 ppm), mix ethylene carbonate and ethyl methyl carbonate (volume ratio 3:7) in a certain proportion and mix them evenly. Then slowly add an appropriate amount of LiPF 6 to the non-aqueous organic solvent. After the lithium salt is completely dissolved, obtain an electrolyte with a concentration of 1 mol / L. The conductivity of the electrolyte is 8.5 mS / cm.

[0096] 3) Preparation of the positive electrode sheet

[0097] Mix the positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O 2 , conductive agent Super P, and binder polyvinylidene fluoride (PVDF) in a mass ratio of 90:5:5. Add the solvent N-methylpyrrolidone (NMP) and stir under vacuum until the system becomes homogeneous to obtain a positive electrode slurry with a solid content of 65 wt%. Coating the positive electrode slurry on the current collector aluminum foil, drying it at 85 °C, then performing cold pressing, and then trimming, cutting, and slitting. Then continue to dry it under vacuum at 85 °C for 4 h to make the positive electrode sheet.

[0098] 4) Preparation of the negative electrode sheet

[0099] The graphite as the negative electrode active material, a certain amount of silicon, the conductive agent Super P, the thickening agent CMC, and the binder styrene-butadiene rubber (SBR) are mixed in a mass ratio of 90:4:3:3 and dissolved in deionized water to prepare a negative electrode slurry. The negative electrode slurry is obtained under the action of a vacuum mixer, and the solid content in the negative electrode slurry is 55 wt%. The negative electrode slurry is coated on the current collector copper foil and dried at 85 °C, and then after cold pressing, trimming, slicing, and slitting, it is dried under vacuum conditions at 120 °C for 12 h to prepare a negative electrode plate.

[0100] 5) Preparation of the battery

[0101] The prepared positive electrode plate, separator, and negative electrode plate are stacked in sequence, with the separator placed in the middle of the positive and negative electrode plates to isolate the positive and negative electrodes, and then wound to obtain a bare battery core. The electrode tabs are welded, the bare battery core is placed in the outer package, and the prepared electrolyte is injected into the dried battery core, followed by encapsulation, standing, formation, shaping, capacity testing, etc., to obtain the lithium secondary battery in Example 1.

[0102] Among them, in this application, the contact angle on the material surface is measured as follows:

[0103] The electrode plate or film is fixed on a standard glass slide and then placed on the sample stage; the needle is inserted into deionized water, and the deionized water is slowly sucked into the syringe. The needle is held upward, the piston is squeezed to expel the air in the syringe, and then the needle is placed in the fixing seat. The height of the sample stage is adjusted so that the sample stage rises to receive the extruded liquid drop, which forms a liquid drop on the powder surface. The contact angle is automatically measured using a contact angle measuring instrument (SINDIN, model SDC-200S) and fitted to obtain the size, and the contact angle is recorded.

[0104] The secondary batteries in Examples 2-15 and the secondary batteries in Comparative Examples 1-3 are prepared in a similar manner to the secondary battery in Example 1, but the corona treatment parameters of the base film, ceramic coating, and adhesive coating or the contact angles between the positive electrode plate / negative electrode plate are different. The product parameters are shown in Table 1.

[0105] II. Performance testing

[0106] 1. Separator performance testing

[0107] 1). Testing of the adhesion force

[0108] A sampler with a length of 100 mm and a width of 20 mm is used to take samples. After wiping the stainless steel plate with alcohol, a standard-width double-sided tape (specification: 3M9730-100) is flatly pasted on the plate. The other side of the double-sided tape is torn off, and the separator is flatly pasted on it. The fixture is installed, and the adhesion force between the base film and the coating of the separator is tested on a tensile machine (model: INSTRON, Modle: 3365).

[0109] 2) Testing of liquid absorption capacity

[0110] Samples were taken using a sampler with a length of 100 mm and a width of 20 mm. The samples were immersed in an electrolyte of 1 mol / L LiPF 6 / EC∶DEC = 1∶1 at 60°C for 4 h. Then, the separator was taken out, suspended for 30 s, and the weight of the separator before and after immersion was measured on an electronic balance ((weight after immersion - weight before immersion) / weight before immersion).

[0111] 3) Testing of liquid absorption rate

[0112] Samples were taken using a sampler with a length of 100 mm and a width of 5 mm. The samples were fixed (suspended horizontally), and a drop (1 mol / L LiPF 6 / EC∶DEC = 1∶1) of the electrolyte was dropped onto the samples. The length of the liquid absorption strip after 60 s was recorded, and the ratio of this length to the time was the liquid absorption rate.

[0113] 2. Battery performance testing

[0114] 1) Cycling performance

[0115] 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. After that, it was left standing for 10 minutes, and then discharged at a constant current of 0.33C to 2.5V. The discharge capacity was recorded as C0. According to the above charge-discharge process, 1000 cycles were carried out. The discharge capacity after 1000 cycles was C1. The cycling capacity retention rate of the battery = C1 / C0 × 100%.

[0116] 2) Fast charging performance

[0117] At 25°C, the prepared lithium secondary battery was charged at a constant current of 2C to 3.65V, then charged at a constant voltage of 0.05C. The charging capacity at this time was C1. After that, it was left standing for 10 minutes, and then discharged at a constant current of 1C to 2.5V. The discharge capacity was recorded as C0. The fast charging performance was reflected by the value of C0 / C1. The larger this value, the better the fast charging performance.

[0118] III. Analysis of test results of each example and comparative example

[0119] Batteries of each example and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in Table 1 below.

[0120] Table 1

[0121]

[0122] As can be seen from Table 1, the separators 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°. The capacity retention rate of the battery manufactured using this separator after 500 cycles is relatively high, and at the same time, the fast charging performance of the battery is also excellent. The main reason is that through the corona treatment of the base film and the separator film of the present application, the polarity and surface energy of the base film, the ceramic coating, and the adhesive coating are improved. Specifically, the contact angles between the layers are within the range of the present application, thereby enhancing the adhesion between the layers and improving the cycle performance and fast charging performance of the battery.

[0123] In addition, the inventors have found through research that in the later stage of the cycle of secondary batteries, the battery decay is mainly affected by the liquid retention amount. Therefore, increasing the liquid retention amount of the separator helps to improve the cycle performance; in addition, the improvement of the adhesion and the increase of the liquid retention amount also help to improve the interface state of the electrode sheet, so it is beneficial to the rate performance. In Examples 1-15 of the present application, after the film layer of the separator is subjected to corona treatment, the polarity of the material surface is enhanced, and the affinity with the electrolyte, which is also a polar substance, is enhanced. Therefore, the liquid absorption rate of the separator is high and the liquid retention rate is good, which also helps to improve the cycle performance and fast charging performance of the battery.

[0124] In addition, as can be seen from Table 1, in Comparative Examples 1-3, the base film and the ceramic coating of the separator in Comparative Example 1 were not subjected to corona treatment; the ceramic coating and the adhesive coating of the separator in Comparative Example 2 were not subjected to corona treatment; the base film and the adhesive coating of the separator in 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 separators were significantly reduced and could not meet the requirements of the present application.

[0125] It should be noted that the present application is not limited to the above-described embodiments. The above embodiments are only examples, and embodiments having the same constitution and the same function and effect as the technical idea within the scope of the technical solution of the present application are included in the technical scope of the present application. In addition, within the scope not departing from the gist of the present application, various modifications that can be conceived by those skilled in the art to the embodiments and other ways constructed by combining some constituent elements of the embodiments are also included in the scope of the present application.

Claims

1. A separator, characterized in that, it comprises a base film and a ceramic coating 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°, preferably ≤ 10°.

2. The separator according to claim 1, characterized in that, the base film is a corona-treated base film, 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 separator according to claim 1 or 2, characterized in that, the ceramic coating is a corona-treated ceramic coating, 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 separator according to any one of claims 1 to 3, characterized in that, the separator further comprises an adhesive coating, the adhesive coating is located on the 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 adhesive coating is 2° - 15°.

5. The separator according to any one of claims 1 to 4, characterized in that, the adhesive coating is a corona-treated adhesive coating, 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 separator according to any one of claims 1 to 5, characterized in that, the contact angle of the base film is 60° - 80°.

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

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

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

10. The separator according to any one of claims 1 to 9, characterized in that, The ceramic coating includes Al 2 O 3 , AlO(OH), SiO 2 , TiO 2 , MgO, CaO, ZnO 2 , ZrO 2 , SnO 2 and one or more of the following, optionally including Al 2 O 3 .

11. The separator according to any one of claims 1 to 10, characterized in that, the adhesive coating comprises 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 salt, sodium hydroxymethyl cellulose, and optionally comprises polyvinylidene fluoride.

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

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

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

15. The secondary battery according to claim 14, wherein, the separator further includes an adhesive coating 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 adhesive coating is ≤20°; and / or the difference between the contact angle of the negative electrode sheet and the contact angle of the adhesive coating is ≤20°.

16. The secondary battery according to claim 14 or 15, wherein, the contact angle of the positive electrode sheet is 40° - 80°; and / or the contact angle of the negative electrode sheet is 40° - 80°.

17. The secondary battery according to any one of claims 14 to 16, wherein, the secondary battery includes at least one of a lithium secondary battery and a sodium secondary battery.

18. An electrical device, wherein, it includes the secondary battery according to any one of claims 14 to 17.

Images