Separator and secondary battery

Abstract

A separator and a secondary battery. The separator of the present application comprises a base film layer, and a bonding layer and an inorganic ceramic layer are provided on the base film layer; the bonding layer is composed of a plurality of bonding points; in the bonding layer, the average longest diameter of the bonding points is 20-500 μm, and there are 20-150 bonding points in any region on the surface of the bonding layer, the length of a region being 3470 μm, and the width being 2600 μm. The bonding force of the surface of the separator is relatively strong, and the bonding force distribution is relatively uniform. When the separator is used in a secondary battery, the high-temperature cycle performance of the secondary battery can be improved.

Description

Separator and secondary battery

[0001] The present application claims priority to the Chinese patent application No. 202411272964.1, filed on September 11, 2024, and entitled "Separator and secondary battery", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the field of energy storage, in particular to a separator and a secondary battery. BACKGROUND

[0003] Secondary batteries are widely used in portable electronic products, electric vehicles, aerospace, energy storage and other fields as a kind of energy storage equipment. With the expansion of application fields, the energy density and charge rate of the current secondary batteries are also increasing, but the high-temperature cycle performance is still difficult to improve. SUMMARY

[0004] The present application can provide a separator and a secondary battery. The adhesion of the surface of the separator of the present application is strong, and the adhesion is uniformly distributed. When the separator of the present application is used in a secondary battery, the high-temperature cycle performance of the secondary battery can be improved.

[0005] In a first aspect, the present application provides a separator, which comprises a base film layer, the base film layer contains a bonding layer, the bonding layer is composed of a plurality of bonding points, the longest diameter of the bonding points is 20-500 μm on average in the bonding layer, and there are 20-150 bonding points in any region of the surface of the bonding layer, the length of the region is 3470 μm, and the width is 2600 μm.

[0006] The inventors found that because the energy density of the secondary battery is high, the separator is usually wide and thin, but this can cause the separator and the positive and negative electrodes on both sides of the separator to be easily deformed, and the cycle interface of the secondary battery is also prone to purple stain and lithium precipitation, which reduces the safety performance and service life of the secondary battery. In order to reduce the occurrence of this phenomenon, the current solution is usually to set a polyvinylidene fluoride coating in the separator, but the adhesion of the polyvinylidene fluoride coating is poor, which not only causes the separator and the positive and negative electrodes to be easily deformed, but also worsens the high-temperature cycle performance of the secondary battery.

[0007] Based on the above technical solutions of the present application, the inventors have further found that the adhesion layer composed of the adhesion points is arranged on the surface of the base film layer and the inorganic ceramic layer, and the adhesion points in any region with a length of 3470 μm and a width of 2600 μm in the adhesion layer are controlled to be in the range of 20-150, and the longest diameter of the adhesion points is controlled to be in the range of 20-500 μm. The adhesion points on the surface of the separator provide adhesion force. In this way, the surface of the separator has good adhesion force, and the distribution of the adhesion force is relatively uniform. This makes the separator and the positive and negative electrodes adhered to the surface of the separator tightly bonded, without obvious weak adhesion points. This can not only reduce the occurrence of the phenomenon of purple stain and lithium precipitation in the secondary battery, but also make the local and overall deformation less likely to occur. When the separator of the present application is used in a secondary battery, the high-temperature cycle performance of the secondary battery can be obviously improved. In addition, even if the secondary battery does not contain a polyvinylidene fluoride coating, the phenomenon of purple stain and lithium precipitation in the secondary battery is less likely to occur.

[0008] In an embodiment of the present application, the separator satisfies at least one of the following conditions: (1) in the adhesion layer, the distance between two adjacent adhesion points is 20-600 μm; (2) the projection area of all adhesion points in any region accounts for 20%-64.5% of the total area of the region; (3) there are 42-100 adhesion points in any region; and (4) the thickness of the adhesion layer is D1, and 0.2 μm≤D1≤4 μm.

[0009] Based on the above embodiment, the use of the separator satisfying the present application in a secondary battery can further improve the high-temperature cycle performance of the secondary battery.

[0010] In an embodiment of the present application, the separator satisfies at least one of the following conditions: (1) the longest diameter of the adhesion points is 200-420 μm; (2) in the adhesion layer, the distance between two adjacent adhesion points is 150-380 μm; (3) the projection area of all adhesion points in any region accounts for 20%-35% of the total area of the region; and (4) 0.5 μm≤D1≤2 μm.

[0011] Based on the above embodiment, the use of the separator satisfying the present application in a secondary battery can further improve the high-temperature cycle performance of the secondary battery.

[0012] In an embodiment of the present application, the projection shape of the adhesion points in the region is at least one of a circle, a circular ring, an ellipse, a square, or a rectangle.

[0013] Based on the above embodiment, the adhesion performance of the separator and the cycle performance of the secondary battery can be further improved.

[0014] In an embodiment of the present application, the area of the annular projection is x, the area of the outer circle corresponding to the annular projection is y, and 10%≤x / y≤50%.

[0015] Based on the above-mentioned embodiment, the kinetic performance of the secondary battery can be improved on the basis of ensuring adhesion.

[0016] In an embodiment of the present application, the adhesion layer comprises a water-based polymer, and the polymerized monomers of the water-based polymer comprise at least two of butadiene, methyl acrylate, methyl methacrylate, styrene, butyl methacrylate, isooctyl acrylate, ethylene, propylene, or vinylidene fluoride.

[0017] Based on the above-mentioned embodiment, the water-based polymer itself has good adhesion performance, and the main chain and the side chain of the water-based polymer can additionally graft the adhesion agent, which is conducive to improving the adhesion of the adhesion layer.

[0018] In an embodiment of the present application, the inorganic ceramic layer comprises 85% to 95% inorganic particles and 5% to 15% adhesion agent by mass fraction; the inorganic particles comprise at least one of alumina, silica, silicon dioxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zirconium oxide, zinc oxide, calcium oxide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate; and the adhesion agent comprises polyacrylate.

[0019] In an embodiment of the present application, one surface of the base film layer is provided with the adhesion layer, the other surface is provided with the inorganic ceramic layer, and the surface of the inorganic ceramic layer away from the base film layer is provided with the adhesion layer. Through the design of this special structure, the deformation of the positive and negative electrodes relative to the separator can be effectively reduced, so that the separator and the positive and negative electrodes adhered to the surface of the separator are tightly adhered, and there is no obvious adhesion weak point. Not only can the phenomenon of purple spot lithium precipitation in the secondary battery be reduced, but also the high-temperature cycle performance of the battery can be improved.

[0020] In a second aspect, the present application provides a secondary battery comprising an electrolyte and an electrode assembly, the electrode assembly comprising, in sequence along the thickness direction, a positive electrode, the separator described above, and a negative electrode, the positive electrode, the separator, and the negative electrode being stacked. Therefore, the electronic device provided by the present application has good use performance.

[0021] In an embodiment of the present application, the adhesion between the separator and the positive electrode is 2N / m to 12N / m at 80℃; and / or, the adhesion between the separator and the negative electrode is 2N / m to 12N / m.

[0022] In an embodiment of the present application, the electrolyte satisfies at least one of the following conditions: (1) the electrolyte comprises acetonitrile in a mass content of 35% to 80% based on the total mass of the electrolyte; (2) the electrolyte comprises 1,3-propane sultone in a mass content of 0.3% to 4.5% based on the total mass of the electrolyte.

[0023] Based on the above-mentioned embodiment, the low-temperature performance of the secondary battery can be obviously improved.

[0024] In an embodiment of the present application, the mass content ratio of acetonitrile and 1,3-propane sultone is 20 to 100 based on the total mass of the electrolyte.

[0025] Based on the above-mentioned embodiment, the low-temperature performance of the secondary battery can be further improved.

[0026] Advantages of the present application:

[0027] The present application provides a separator and a secondary battery. The separator comprises a base film layer, the surface of the base film layer is provided with an inorganic ceramic layer and a bonding layer, the bonding layer is uniformly distributed with bonding points, and the longest diameter of the bonding points in each bonding layer is 20 μm to 500 μm. By setting the bonding points to form the bonding layer and controlling the number and size of the bonding points in the bonding layer, the surface of the separator has good bonding force, and the bonding force is uniformly distributed. When one surface of the base film is provided with the inorganic ceramic layer and the other surface is provided with the bonding layer, the positive and negative electrodes can be more effectively and uniformly bonded. When the separator of the present application is used in the secondary battery, the high-temperature cycle performance of the secondary battery can be improved, and the purple discoloration and lithium precipitation phenomenon is less likely to occur in the secondary battery. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments of the present application. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0029] FIG. 1 is a CCD image of the bonding layer in the embodiments 1-5 of the present application.

[0030] Embodiments of the present application

[0031] In order to make the purposes, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. All other embodiments obtained by a person of ordinary skill in the art based on the present application shall fall within the scope of protection of the present application. If the specific conditions are not indicated in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are adopted. If the manufacturers of the reagents or instruments are not indicated, the conventional products that can be purchased in the market are adopted.

[0032] It should be noted that in the specific embodiments of the present application, the lithium ion battery is taken as an example of the secondary battery to explain the present application, but the secondary battery of the present application is not limited to the lithium ion battery.

[0033] The inventors found that in order to improve the energy density of the secondary battery to meet the use requirements, the separator, the positive electrode, and the negative electrode in the secondary battery are all set to be wide and thin. However, this will cause the separator to be easily deformed, and the cycle interface of the secondary battery is also prone to purple stain lithium precipitation, which reduces the safety performance of the secondary battery. Although there is a scheme of using a PCS coating in the separator at present, this will cause the cell of the secondary battery to be easily deformed, and also deteriorate the high-temperature cycle performance of the secondary battery. Based on this, the inventors found that when the separator in the present application is used in the secondary battery, not only the cycle performance of the secondary battery can be improved, but also the phenomenon of purple stain lithium precipitation in the secondary battery is less likely to occur. The secondary battery and the separator of the present application will be described below:

[0034] The secondary battery of the present application comprises an electrolyte and an electrode assembly, wherein the electrode assembly comprises a positive electrode, a separator, and a negative electrode in sequence along the thickness direction, and the positive electrode, the negative electrode, and the separator are stacked.

[0035] Separator

[0036] The diaphragm is used to isolate the positive electrode and the negative electrode to avoid direct contact between the two to cause short circuit. The diaphragm of the present application comprises a base film layer, a bonding layer and an inorganic ceramic layer are arranged on the base film layer, wherein the bonding layer is composed of a plurality of bonding points, and the longest diameter of the bonding points in the bonding layer is 20-500 μm, specifically 20 μm, 50 μm, 100 μm, 150 μm, 200 μm, 240 μm, 320 μm, 360 μm, 400 μm, 450 μm, 500 μm or any range between any two of the above values, preferably 200-400 μm, and there are 20-150 bonding points in any area of the surface of the bonding layer, specifically 20, 30, 40, 42, 55, 67, 86, 92, 100, 120, 150 or any range between any two of the above values, preferably 42-100; the length of the area is 3470 μm, and the width is 2600 μm. In the present application, the bonding points on the surface of the diaphragm not only have good bonding force, but also have uniform distribution of the bonding force, so that the diaphragm of the present application is not easy to deform, and the positive and negative electrodes bonded on both sides of the diaphragm are also not easy to deform. When the diaphragm of the present application is used in a secondary battery, not only can the generation of the secondary battery cycle interface purple lithium precipitation phenomenon be reduced, but also the high-temperature cycle performance of the secondary battery can be improved. In addition, the bonding layer of the present application can be arranged on the surface of the base film layer or the surface of the inorganic ceramic layer; when the bonding layer is arranged on the surface of the base film layer, the inorganic ceramic layer and the bonding layer are arranged on both sides of the base film layer, and the structure of the diaphragm is that the bonding layer, the base film layer and the inorganic ceramic layer are sequentially stacked; when the bonding layer is arranged on the surface of the inorganic ceramic layer, the inorganic ceramic layer and the bonding layer are arranged on the same side of the base film layer, and the inorganic ceramic layer is in contact with the base film layer, and the structure of the diaphragm is that the bonding layer, the inorganic ceramic layer and the base film layer are sequentially stacked. Of course, in some embodiments of the present application, in order to better improve the performance of the diaphragm, a bonding layer can also be arranged on one surface of the base film layer, an inorganic ceramic layer is arranged on the other surface, and a bonding layer is also arranged on the surface of the inorganic ceramic layer away from the base film layer, and the structure of the diaphragm is that the bonding layer, the inorganic ceramic layer, the base film layer and the bonding layer are sequentially stacked.

[0037] It should be noted that the shape of the bonding points is not particularly limited in the present application. Since the three-dimensional shape of the bonding points is not intuitive, the shape of the bonding points is described in terms of the projection shape of the bonding points in the area. Specifically, the projection shape of the bonding points in the area can be at least one of a circular shape, a circular ring shape, an elliptical shape, a square shape, or a rectangular shape. When the projection shape of the bonding points in the area is a circular ring shape, in some embodiments of the present application, the projection area of the circular ring shape is x, the area of the outer circle corresponding to the circular ring shape is y, and 10%≤x / y≤50%. It should also be noted that the "longest diameter" of the bonding points in the present application is also relative to the projection shape of the bonding points in the area, which refers to the distance between the two most distant points in the projection shape. Specifically, when the projection shape of the bonding points is a circular shape, the "longest diameter" refers to the diameter of the circle; when the projection shape is a circular ring shape, the "longest diameter" refers to the major radius of the circular ring; when the projection shape is an elliptical shape, the "longest diameter" refers to the length of the major axis of the ellipse; and when the projection shape is a square or rectangular shape, the "longest diameter" refers to the length of the diagonal of the square or rectangular shape.

[0038] In some embodiments of the present application, in order to further improve the kinetic performance of the diaphragm, the distance between adjacent two bonding points in the bonding layer of the diaphragm is 20 μm-600 μm, preferably 150 μm-380 μm. In the present application, the "distance between adjacent two bonding points" refers to the distance between the projections of adjacent two bonding points, which is the distance between the closest parts of the two projections.

[0039] The present application does not have a particular limitation on the distribution of the bonding points in the area. In actual production, the bonding points in the area are generally uniform and regular based on the need for preparation process, that is, the distance between adjacent two bonding points in the area is basically the same, and the projections of the bonding points in the area can form a pattern similar to a rectangle or a square. As an example, in the present embodiment, the bonding points in the area are uniformly distributed, and the projections of the bonding points can be arranged in a pattern similar to a rectangle. In addition, in the specific embodiments of the present application, since each bonding point has more than one adjacent point, and the arrangement of the bonding points in the present embodiment is relatively regular, the "distance between adjacent two bonding points" refers to the average distance, and the specific algorithm is: average distance = sum of distances between all adjacent two bonding points in the area / number of bonding points in the area.

[0040] In some embodiments of the present application, in order to further improve the surface bonding force of the diaphragm and make the diaphragm less likely to deform, the projection area of all the bonding points in any area of the bonding layer in the area generally accounts for 20%-64.5% of the total area of the area, preferably 20%-35%.

[0041] The thickness of the adhesive layer is not particularly limited in the present application. In actual use, in order to further improve the surface adhesion of the separator and make the separator less likely to deform, the thickness D1 of the adhesive layer is usually between 0.2 μm and 4 μm, preferably 0.5 μm≤D1≤2 μm. Moreover, when there are two adhesive layers, the thickness of the two adhesive layers can be the same or different. However, in actual operation, in order to reduce the difficulty of the process for preparing the adhesive layer, the thickness of the two adhesive layers is usually the same.

[0042] In addition, the adhesive layer in the separator is generally prepared by coating. The coating equipment can be selected from one of gravure, microgravure, screen printing, and extrusion coating. In order to more conveniently control the number, spacing, and size of the adhesive points, for example, the screen printing coating method is used to prepare the adhesive layer in the specific embodiments of the present application. When this method is used, the number, spacing, and size of the adhesive points in the adhesive layer can be changed by replacing the screen printing plate with different mesh.

[0043] In some embodiments of the present application, the adhesive layer comprises a water-based polymer. The polymerized monomers of the water-based polymer comprise at least two of butadiene, methyl acrylate, methyl methacrylate, styrene, butyl methacrylate, isooctyl acrylate, ethylene, propylene, or vinylidene fluoride. The water-based polymer has good adhesive properties. Moreover, the main chain and side chain of the water-based polymer can additionally be grafted with an adhesive, which is beneficial to improving the adhesion of the adhesive layer. For example, the water-based polymer can be grafted with acrylic acid, methyl methacrylate, butyl acrylate, octyl acrylate, isooctyl acrylate, butadiene, or acrylonitrile.

[0044] In addition, the material and thickness of the base film layer and the inorganic ceramic layer are not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the material of the base film layer can be at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric, or polypropylene-polyethylene-polypropylene porous composite film can be used. The inorganic ceramic layer can comprise 85% to 95% inorganic particles and 5% to 15% adhesive, wherein the inorganic particles comprise at least one of alumina, silica, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zirconium oxide, zinc oxide, calcium oxide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate; and the adhesive comprises polyacrylate.

[0045] Since the secondary battery in the present application contains the above-mentioned separator, the secondary battery of the present application has good high-temperature cycle performance. Moreover, the adhesion between the separator and the positive electrode, and the adhesion between the separator and the negative electrode of the secondary battery in the present application can reach 2 N / m to 12 N / m at 80°C.

[0046] electrolyte

[0047] The electrolyte can play a role in transmitting lithium ions and electrons, and ensure the formation of a path inside the electrochemical device. Currently, there are also solutions to reduce the phenomenon of purple lithium precipitation in secondary batteries by changing the components of the electrolyte, but this will cause the low-temperature performance of the secondary battery to deteriorate.

[0048] In some embodiments of the present application, in order to improve the low-temperature performance of the secondary battery, the electrolyte satisfies at least one of the following conditions: (1) the electrolyte includes acetonitrile with a mass content of 35% to 80% based on the total mass of the electrolyte; (2) the electrolyte includes 1,3-propane sultone with a mass content of 0.3% to 4.5% based on the total mass of the electrolyte. Further, the ratio of the mass contents of acetonitrile and 1,3-propane sultone can be in the range of 20 to 100 based on the total mass of the electrolyte, which can further improve the low-temperature performance of the secondary battery.

[0049] positive electrode

[0050] The positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. That is, in the present application, the positive electrode active material layer can be disposed on one surface in the thickness direction of the positive electrode current collector, or can be disposed on both surfaces in the thickness direction of the positive electrode current collector. Moreover, in the present application, the "surface of the positive electrode current collector" can be the entire area of the positive electrode current collector, or can be a partial area of the positive electrode current collector, and the present application is not particularly limited as long as the purpose of the present application can be achieved.

[0051] The components of the positive electrode active material layer include a positive electrode active material, which can be any material capable of reversibly intercalating and deintercalating Li + , Na + , etc. alkali metal ions to ensure that the electrochemical device can normally charge and discharge. For example, the positive electrode active material includes but is not limited to at least one of lithium iron phosphate (LiFePO4), lithium cobaltate (LiCoO2), lithium manganese oxide, lithium nickel oxide, ternary material, etc. The ternary material includes but is not limited to at least one of LiNi x Co y Mn z O2, LiNi x Co y Al z O2, etc., and the contents of Ni, Co, Mn, Al, etc. can be adjusted to ensure that x+y+z=1. For example, the ternary material can be LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.88 Co 0.08 Mn 0.04O2, LiNi 0.8 Co 0.15 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.88 Co 0.1 Mn 0.02 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.88 Co 0.1 Al 0.02 O2, etc.

[0052] In some embodiments of the present application, the component of the positive electrode active material layer further includes a positive electrode conductive agent; the present application does not limit the type of positive electrode conductive agent, and any known conductive material can be used. Specifically, the positive electrode conductive agent includes, but is not limited to, at least one of acetylene black, Super-P, or other carbon black, or amorphous carbon such as needle coke, or carbon nanotubes, or graphene, etc.

[0053] In some embodiments of the present application, the component of the positive electrode active material layer generally further includes a positive electrode binder, and the type of positive electrode binder used in the manufacture of the positive electrode active material layer is not particularly limited, and in the case of a coating method, it is only necessary to be a material that is soluble or dispersible in the liquid medium used in the manufacture of the electrode. The positive electrode binder includes, but is not limited to, any one or at least two of the following: polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, and other resin-based polymers; butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, isoprene rubber, polybutadiene rubber, ethylene-propylene rubber, and other rubber-like polymers; styrene-butadiene-styrene block copolymer or its hydrogenated product, ethylene-propylene-diene terpolymer (EPDM), styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer or its hydrogenated product, and other thermoplastic elastomer-like polymers; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, propylene-α-olefin copolymer, and other soft resin-like polymers; polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene-ethylene copolymer, and other fluorine-based polymers; and polymer compositions having ionic conductivity of alkali metal ions (particularly lithium ions), etc.

[0054] The type of the positive electrode current collector is not particularly limited, and can be any material known to be suitable for use as a positive electrode current collector. The material of the positive electrode current collector includes, but is not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, and the like; and materials such as carbon cloth, carbon paper, and the like. In addition, in order to reduce the electronic contact resistance between the positive electrode current collector and the positive electrode active material layer, the surface of the positive electrode current collector can be provided with a conductive additive or a conductive coating, or the like. The conductive additive includes, but is not limited to, carbon and noble metals such as gold, platinum, silver, and the like. The conductive coating can be a mixture layer of inorganic oxides, a conductive agent, and a positive electrode binder.

[0055] In the preparation of the positive electrode, the components in the positive electrode active material layer described above can be dissolved or dispersed in a solvent in a liquid state to form a positive electrode slurry, and then the positive electrode slurry can be coated on the positive electrode current collector and dried to form a positive electrode active material layer on the positive electrode current collector, thereby obtaining a positive electrode. In the preparation of the positive electrode using this method, the solvent in the positive electrode slurry is not particularly limited, as long as it can dissolve or disperse the components described above. Specifically, the solvent in the positive electrode slurry includes, but is not limited to, N-methyl pyrrolidone (NMP), ethylene carbonate (EC), and the like. In addition, in the preparation of the positive electrode, the components in the positive electrode active material layer can also be dry-mixed to form a sheet, and then the obtained sheet can be crimped to the positive electrode current collector.

[0056] Negative electrode

[0057] The negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, and the components of the negative electrode active material layer include a negative electrode active material. That is, in the present application, the negative electrode active material layer can be provided on one surface in the thickness direction of the negative electrode current collector, or can be provided on both surfaces in the thickness direction of the negative electrode current collector. Moreover, in the present application, the "surface of the negative electrode current collector" can be the entire area of the negative electrode current collector, or can be a partial area of the negative electrode current collector, and the present application is not particularly limited, as long as the purpose of the present application can be achieved.

[0058] The negative electrode active material layer generally contains a negative electrode active material, and the present application does not have a particular limitation on the negative electrode active material. Specifically, the negative electrode active material can include at least one of a carbon material or a silicon-based material. More specifically, the carbon material includes, but is not limited to, at least one of natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, or soft carbon; and the silicon-based material includes, but is not limited to, at least one of silicon, silicon-oxygen composite material, or silicon-carbon composite material.

[0059] In some embodiments of the present application, the negative electrode active material layer generally also contains a negative electrode conductive agent. The present application does not have a particular limitation on the type of the negative electrode conductive agent, as long as the purpose of the present application can be achieved. For example, the negative electrode conductive agent includes, but is not limited to, at least one of acetylene black, ketjen black, carbon nanotube, carbon fiber, carbon dot, or graphene, and the like.

[0060] In some embodiments of the present application, the negative active material layer can also contain a negative binder and a thickening agent. The present application does not have a particular limitation on the type of negative binder and thickening agent as long as the purpose of the present application can be achieved. For example, the negative binder can include, but is not limited to, at least one of polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene butadiene rubber, or acrylated styrene butadiene rubber; and the thickening agent in the negative slurry can include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose.

[0061] In the negative electrode, the material of the negative current collector includes, but is not limited to, copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or a polymer substrate coated with a conductive metal, and the present application does not have a particular limitation. Among them, the conductive metal includes, but is not limited to, copper, nickel, or titanium, and the material of the polymer substrate includes, but is not limited to, at least one of polyethylene, polypropylene, ethylene propylene copolymer, polyethylene terephthalate, polyethylene naphthalate, or poly-p-phenylene terephthalamide.

[0062] In addition, in the present application, the thickness of the negative current collector and the negative active material layer is not particularly limited as long as the purpose of the present application can be achieved. For example, the thickness of the negative current collector is 4 μm to 12 μm, and the thickness of the single-sided negative active material layer is 30 μm to 160 μm.

[0063] Further, in the preparation of the negative electrode, similar to the preparation of the positive electrode, either the negative electrode slurry can be prepared and then coated on the negative electrode current collector and dried to form the negative electrode active material layer on the negative electrode current collector, thereby obtaining the negative electrode, or the components in the negative electrode active material layer can be dry-mixed to form a sheet, and then the obtained sheet is crimped to the negative electrode current collector to form the negative electrode active material layer, thereby obtaining the negative electrode. The solvent in the negative electrode slurry includes any one of water-based solvents, organic-based solvents. The water-based solvents include, but are not limited to, mixed solvents of alcohol and water or water, etc. The organic-based solvents include, but are not limited to, aliphatic hydrocarbons such as hexane, etc.; aromatic hydrocarbons such as benzene, toluene, xylene, methylnaphthalene, etc.; heterocyclic compounds such as quinoline, pyridine, etc.; ketones such as acetone, methyl ethyl ketone, cyclohexanone, etc.; esters such as methyl acetate, methyl acrylate, etc.; amines such as diethylenetriamine, N,N-dimethylaminopropylamine, etc.; ethers such as diethyl ether, propylene oxide, tetrahydrofuran (THF), etc.; amides such as N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, etc.; aprotic polar solvents such as hexamethylphosphoramide, dimethyl sulfoxide, etc. In addition, in some other embodiments, in the case of using water-based solvents, a thickening agent and a styrene-butadiene rubber (SBR) emulsion are further included in the components of the negative electrode slurry to slurry the negative electrode slurry, so as to adjust the viscosity of the negative electrode slurry. The types of the thickening agent in the positive electrode slurry include, but are not limited to, at least one of carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphated starch, casein and salts thereof, etc.

[0064] The secondary battery of the present application can be used in electronic devices, and the use of the electrochemical device of the present application is not particularly limited, and it can be used in any electronic device known in the art. In some embodiments, the electrochemical device of the present application can be used in, but not limited to, notebook computers, pen input computers, mobile computers, electronic book players, portable telephones, portable facsimile machines, portable copying machines, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic organizers, calculators, memory cards, portable audio recorders, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting appliances, toys, game machines, timepieces, power tools, flashlights, cameras, home-use large storage batteries, and lithium-ion capacitors, etc.

[0065] Embodiments

[0066] The following examples and comparative examples are given to more specifically explain the embodiments of the electrochemical device of the present application, taking lithium-ion secondary batteries as examples. Those skilled in the art will understand that the preparation methods described in the present application are only examples, and any other suitable preparation method is within the scope of the present application.

[0067] Test methods and apparatuses:

[0068] Adhesion point number detection:

[0069] At any position on the surface of the separator, a region with a length of 3470 μm and a width of 2600 μm was selected, and a CCD (Charge-coupled Device) electronic microscope of the type VHX5000 of Keyence was used to observe and record the image information of the region after magnification of 100 times. Fig. 1 is a CCD image of Examples 1-5, and it can be seen from the figure that the projection shape of the adhesion point is a circular ring.

[0070] The adhesion point counting method in the region is as follows:

[0071] If the adhesion point in the region is not completely displayed, if the selected region is less than 50% of the entire adhesion point, it is not counted in the total number, and if it is equal to or greater than 50%, it is counted as one adhesion point.

[0072] Adhesion force test:

[0073] The adhesion force between the separator and the positive or negative electrode was tested according to the national standard GB / T 2790-1995, i.e. the 180° peeling test standard. The separator and the positive or negative electrode were cut into 54.2 mm x 72.5 mm samples, the separator and the positive or negative electrode were compounded, and a hot press was used for hot pressing. The hot pressing conditions were: temperature 85℃, pressure 1Mpa, hot pressing time 85s (seconds). The compounded sample was cut into 15mm x 54.2mm strips, and the adhesion force between the separator and the positive or negative electrode was tested according to the 180° peeling test standard at 80℃.

[0074] Low temperature performance test:

[0075] Step 1: In an environment of 25℃, the first charge and discharge of the secondary battery after formation was carried out. When discharging, it was discharged at 0.2C constant current to 3V, then the discharged secondary battery was left for 5min, then it was charged to 4.53V at 0.5C constant current, then it was charged to 0.02C constant voltage, and left for 60min.

[0076] Step 2: Discharge at 0.2C to 2.5V, and record the discharge capacity at this time, which is the discharge capacity of the first cycle of the secondary battery at 25℃. Then leave for 5min.

[0077] Step 3: The secondary battery was placed in 10℃, 0℃, -10℃, -20℃ environments in turn for discharging. When discharging, it was discharged at 0.2C constant current to 2.5V, and the final discharge capacity of the secondary battery at each temperature condition was recorded in turn. Before each discharge, the secondary battery was charged in a 25℃ environment. When charging, it was first charged to 4.53V at a charge rate of 0.5C, and then charged to 0.02C constant voltage.

[0078] Step 4: The low-temperature capacity retention rate of the secondary battery at -20°C was calculated using the following expression:

[0079] Low-temperature capacity retention rate = (Final discharge capacity of the secondary battery at -20°C / Discharge capacity of the first cycle of the secondary battery at 25°C) x 100%.

[0080] The greater the low-temperature capacity retention rate, the better the low-temperature performance of the secondary battery.

[0081] High-temperature cycle performance test:

[0082] The secondary battery was placed in a 45°C constant-temperature oven and allowed to stand for 30 minutes to allow the lithium ion battery to reach a constant temperature. Then the secondary battery was discharged at 0.2C to 3V, then rested for 5 minutes, and the initial discharge capacity C0 of the secondary battery was measured.

[0083] Then charging and discharging were performed, where one charge and one discharge were counted as one cycle, 800 cycles were performed, and the discharge capacity C1 of the secondary battery after 800 cycles was measured. The charging process was as follows: (1) 3.5C constant-current charging to 4.35V; (2) 3C constant-current charging to 4.35V, constant-voltage charging to 1.8C; (3) 1.8C constant-current charging to 4.4V, constant-voltage charging to 1.5C; (4) 1.5C constant-current charging to 4.53V, constant-voltage charging to 1.2C; (5) 1.2C constant-current charging to 4.58V, constant-voltage charging to 2100mA; (6) resting for 5 minutes; (7) 0.5C constant-current charging to 4.53V, constant-voltage charging to 0.05C. The discharge process was as follows: 0.7C constant-current discharging to 3.0V.

[0084] Capacity retention rate after 800 cycles at 45°C = C1 / C0 x 100%.

[0085] The higher the capacity retention rate, the better the high-temperature cycle performance of the secondary battery.

[0086] <Preparation of the separator>

[0087] Inorganic particles boehmite with a Dv50 of 1 µm were mixed with polyacrylate in a mass ratio of 90:10 and then dissolved in deionized water to form an inorganic coating slurry with a solid content of 50%. The resulting inorganic coating slurry was then uniformly coated onto one side of a base film layer made of polyethylene (PE) using a micro-concave coating method, and dried in an oven to obtain an inorganic ceramic layer.

[0088] 90 g of polymer particles (weight average molecular weight of 600,000, polymerized monomers are butadiene and methyl acrylate in a molar ratio of 1:1) were added to a stirrer, 10 g of sodium carboxymethyl cellulose was added, stirred and mixed uniformly, 5 g of wetting agent dimethyl silicone was added, then deionized water was added and stirred, the viscosity of the slurry was adjusted to 2000 mPa·s~5000 mPa·s, the solid content was 5%, and the binder layer slurry was obtained. Then the above binder layer slurry was uniformly coated on the surface of the inorganic ceramic layer and the base film layer by screen printing coating method, the coating weight was 0.5 g / m 2 , and then drying was completed in an oven to form a binder layer with a thickness of 1.7 μm.

[0089] <Preparation of the negative electrode>

[0090] The negative electrode active material artificial graphite, acetylene black, butadiene rubber and sodium carboxymethyl cellulose were mixed in a mass ratio of 96:1:1.5:1.5, then deionized water was added as a solvent, and a negative electrode slurry with a solid content of 70% was prepared, and then stirred uniformly in a vacuum stirrer. The negative electrode slurry was uniformly coated on one surface of a copper foil with a thickness of 8 µm, dried at 110°C, and after cold pressing, a negative electrode sheet with a 150 µm thick negative electrode active material layer coated on one surface was obtained, and then the above coating step was repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet with a negative electrode active material layer coated on both surfaces. The negative electrode sheet was cut into a size of 74 mm x 867 mm and the tab was welded for use.

[0091] <Preparation of the positive electrode>

[0092] The positive electrode active material lithium cobaltate, acetylene black and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 94:3:3, then N-methyl pyrrolidone (NMP) was added as a solvent, and a positive electrode slurry with a solid content of 75% was prepared, and then stirred uniformly in a vacuum stirrer. The positive electrode slurry was uniformly coated on one surface of an aluminum foil with a thickness of 12 µm, dried at 90°C, and after cold pressing, a positive electrode sheet with a 100 µm thick positive electrode active material layer coated on one surface was obtained, and then the above step was repeated on the other surface of the positive electrode sheet to obtain a positive electrode sheet with a positive electrode active material layer coated on both surfaces. The positive electrode sheet was cut into a size of 74 mm x 867 mm and the tab was welded for use.

[0093] <Preparation of the electrolyte>

[0094] In an environment with water content less than 10 ppm, non-aqueous organic solvents ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), vinylene carbonate (VC) are mixed in a mass ratio of 20:30:20:28:2, then lithium hexafluorophosphate (LiPF6) is added to the non-aqueous organic solvent to dissolve and mix uniformly to obtain an electrolyte. Based on the total mass of the electrolyte, the mass content of LiPF6 is 8%.

[0095] <Preparation of a secondary battery>

[0096] The positive electrode, the separator, and the negative electrode prepared above are stacked in order with the separator between the positive electrode and the negative electrode to play a role of isolation, and then wound to obtain an electrode assembly. The electrode assembly is loaded into an aluminum plastic film packaging bag, and water is removed at 80°C, and the prepared electrolyte is injected, and then vacuum packaging, standing, formation, shaping, and other processes are performed to obtain a secondary battery.

[0097] Examples 1-2 to 1-8

[0098] Except that the number of bonding points and the distance between adjacent bonding points are adjusted according to Table 1, the rest is basically the same as Example 1-1.

[0099] Examples 1-9 to 1-18

[0100] Except that the number of bonding points, the longest diameter, and the distance between adjacent bonding points are adjusted according to Table 1, the rest is basically the same as Example 1-3.

[0101] Examples 1-19 to 1-32

[0102] Except that the electrolyte is prepared in the following way, and the longest diameter of the bonding points is adjusted according to Table 1, the rest is basically the same as Example 1-4.

[0103] <Preparation of an electrolyte>

[0104] In an environment with water content less than 10 ppm, non-aqueous organic solvents EC, DEC, PC, PP, and VC are mixed in a mass ratio of 20:30:20:28:2 to form a base solvent, then LiPF6, acetonitrile, and 1,3-propane sultone are added to the base solvent, and mixed uniformly to obtain an electrolyte. Based on the total mass of the electrolyte, the mass content of LiPF6 is 8%, the contents of acetonitrile and 1,3-propane sultone are shown in Table 1, and the rest is the base solvent.

[0105] Examples 1-33 to 1-42

[0106] Except that the number of bonding points and the distance between adjacent bonding points are adjusted according to Table 1, the rest is basically the same as Example 1-4.

[0107] Comparative Examples 1-4

[0108] Except that the number of bonding points, the distance between adjacent bonding points or the longest diameter of the bonding points is adjusted according to Table 1, the rest is basically the same as Example 1-1.

[0109] Table 1

[0110]

[0111] Note: x / y means that in the projection shape of the bonding points, the area percentage of the projection area of the annular shape in the area of the corresponding outer circle of the annular shape; the same is true for Table 2 and Table 3.

[0112] Examples 2-1 to 2-10

[0113] Except that the longest diameter of the bonding points and the thickness of the bonding layer are adjusted according to Table 2, the rest is basically the same as Example 1-5.

[0114] Table 2

[0115]

[0116] Examples 3-1 to 3-3

[0117] Except that the thickness of the bonding layer and the type of aqueous polymer in the bonding layer are adjusted according to Table 3, the rest is basically the same as Example 2-1.

[0118] Table 3

[0119]

[0120] As shown in Tables 1 to 3, according to the examples and comparative examples, the adhesion of the separator of the application is strong and uniform. When used in a secondary battery, the high-temperature cycle performance of the secondary battery can be significantly improved.

[0121] In particular, when the thickness of the bonding layer is in the range of 0.5 μm to 2 μm, the high-temperature cycle performance of the secondary battery can be further improved.

[0122] In particular, when the electrolyte of the secondary battery contains 35% to 80% acetonitrile and / or 0.3% to 4.5% 1,3-propane sultone, the low-temperature performance of the secondary battery can be improved; and when the mass content ratio of acetonitrile and 1,3-propane sultone is 20 to 100, the low-temperature performance of the secondary battery can be further improved.

[0123] It should be noted that, in the present document, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0124] Various embodiments are described herein with reference to particular applications. Various modifications and changes can be made thereto by those skilled in the art without departing from the broader scope of the application as set forth in the appended claims along with the non-limiting embodiments. There are no intentions, expressed or implied, that any particular disclosed embodiment is more fair, suitable or effective than any other disclosed embodiments. The subsequent description is given primarily for preference and illustrative purposes.

[0125] The preferred embodiments of the present application are shown and described, but it should be understood that the application is not limited thereto since modifications can be made by those skilled in the art, and still be within the scope of the application.

Claims

1. A diaphragm, characterized by It comprises a base film layer, the base film layer contains a bonding layer and an inorganic ceramic layer, the bonding layer is composed of a plurality of bonding points, the average longest diameter of the bonding points is 20-500 μm in the bonding layer, there are 20-150 bonding points in any area of the bonding layer surface, the area is 3470 μm long and 2600 μm wide.

2. The separator according to claim 1, characterized in that It satisfies at least one of the following conditions: (1) In the bonding layer, the distance between two adjacent bonding points is 20-600 μm; (2) The projection area of all the bonding points in any area accounts for 20-64.5% of the total area of the area; (3) There are 42-100 bonding points in any area; (4) The thickness of the bonding layer is D1, 0.2 μm≤D1≤4 μm.

3. The diaphragm of claim 2, wherein, It satisfies at least one of the following conditions: (1) The average longest diameter of the bonding points is 200-420 μm; (2) In the bonding layer, the distance between two adjacent bonding points is 150-380 μm; (3) The projection area of all the bonding points in any area accounts for 20-35% of the total area of the area; (4) 0.5 μm≤D1≤2 μm.

4. The separator of claim 1, wherein One surface of the base film layer is provided with a bonding layer, and the other surface is provided with an inorganic ceramic layer, and the surface of the inorganic ceramic layer away from the surface of the base film layer is provided with the bonding layer.

5. The separator of claim 1, wherein The projection shape of the bonding points in the area is at least one of a circle, a circular ring, an ellipse, a square or a rectangle.

6. The diaphragm of claim 5, wherein The projection area of the circular ring is x, the area of the corresponding outer circle of the circular ring is y, and 10%≤x / y≤50%.

7. The separator according to any one of claims 1 to 6, wherein The bonding layer comprises a water-based polymer, and the polymerized monomers of the water-based polymer comprise at least two of butadiene, methyl acrylate, methyl methacrylate, styrene, butyl methacrylate, isooctyl acrylate, ethylene, propylene or vinylidene fluoride.

8. The separator of claim 1, wherein The inorganic ceramic layer comprises 85-95% inorganic particles and 5-15% binder by mass fraction; The inorganic particles comprise at least one of alumina, silica, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zirconium oxide, zinc oxide, calcium oxide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate; and the binder comprises polyacrylate.

9. A secondary battery characterized by comprising: It comprises an electrolyte and an electrode assembly, the electrode assembly comprises a positive electrode, a separator according to any one of claims 1-8 and a negative electrode in sequence along the thickness direction, and the positive electrode, the separator and the negative electrode are stacked.

10. The secondary battery according to claim 9, characterized by The bonding force between the separator and the positive electrode is 2-12 N / m at 80°C; and / or, The bonding force between the separator and the negative electrode is 2-12 N / m.

11. The secondary battery according to claim 9, characterized by The electrolyte satisfies at least one of the following conditions: (1) The electrolyte comprises acetonitrile with a mass content of 35-80% based on the total mass of the electrolyte; (2) the electrolyte comprises 1,3-propane sultone in a mass content of 0.3% to 4.5%, based on the total mass of the electrolyte.

12. The secondary battery according to claim 11, characterized by the electrolyte comprises acetonitrile and 1,3-propane sultone, and the mass content ratio of the acetonitrile and the 1,3-propane sultone is 20 to 100, based on the total mass of the electrolyte.

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