Separator and secondary battery

Abstract

A separator and a secondary battery. The separator comprises a base film layer, wherein one surface of the base film layer is provided with an inorganic ceramic layer, and the other surface of the base film layer is provided with linear adhesives. The thickness of each linear adhesive is D2, the width is W2, and 1μm≤D2≤5μm and 20μm≤W2≤400μm. When the separator is used in a secondary battery, the cycle performance of the secondary battery can be improved.

Description

Separator and secondary battery

[0001]

[0002] The present application claims priority to the Chinese patent application No. 202411272966.0, filed on September 11, 2024, and entitled "Separator and secondary battery", the content of which is incorporated herein by reference in its entirety.

[0003] TECHNICAL FIELD

[0004] The present application relates to the field of energy storage, in particular to a separator and a secondary battery. BACKGROUND

[0005] As a kind of energy storage equipment, secondary batteries are widely used in portable electronic products, electric vehicles, aerospace, energy storage and other fields. With the expansion of application fields, the energy density and charge rate of the current secondary batteries are also increasing, but their high-temperature cycle performance is still difficult to improve. SUMMARY

[0006] The present application can provide a separator and a secondary battery. When the separator of the present application is used in a secondary battery, the high-temperature cycle performance of the secondary battery can be effectively improved.

[0007] In a first aspect, the present application provides a separator, which comprises a base film layer, one surface of the base film layer is provided with an inorganic ceramic layer, and the other surface is provided with linear adhesives; each linear adhesive has a thickness D2 and a width W2, 1 μm≤D2≤5 μm, and 20 μm≤W2≤400 μm.

[0008] Based on the above technical solution, the inventors found that when the flow guide layer formed by all the linear adhesives is arranged on one surface of the base film layer, the gap between adjacent linear adhesives can serve as an electrolyte transmission channel, which can effectively improve the electrolyte supply capacity, the electrolyte can better infiltrate the separator, and the high-temperature cycle performance of the secondary battery can also be improved. In addition, since the linear adhesives in the flow guide layer also have certain adhesion, the linear adhesives can play a role in fixing the separator, so that the separator is not easy to deform, and the high-temperature cycle performance of the secondary battery can also be improved to some extent.

[0009] In an embodiment of the present application, the separator satisfies at least one of the following conditions: (1) all the linear adhesives are parallel to each other; (2) the sum of the projection areas of all the linear adhesives on the base film layer accounts for 10% to 30% of the area of the base film layer; (3) 2 μm≤D2≤4 μm; (4) 150 μm≤W2≤250 μm; (5) the distance between adjacent linear adhesives is 50 μm to 500 μm.

[0010] Based on the above-mentioned embodiments, the high-temperature cycle performance of the secondary battery containing the above-mentioned separator can be more obviously improved.

[0011] In an embodiment of the present application, the distance between adjacent linear binders is more preferably 110 μm ~ 360 μm, which can effectively improve the high-temperature cycle performance and low-temperature performance of the secondary battery.

[0012] In an embodiment of the present application, the inorganic ceramic layer is provided with point-like binders away from the surface of the base film layer, all the point-like binders constitute a binder layer, the longest diameter of each point-like binder is 20 μm ~ 500 μm, and there are 20 ~ 150 point-like binders in any area of the surface of the binder layer, the length of the area is 3470 μm, and the width of the area is 2600 μm.

[0013] Based on the above-mentioned embodiments, the distribution of the binding force of the separator is more uniform, and when used in a secondary battery, the phenomenon of purple stain and lithium precipitation of the secondary battery can be better reduced, thereby improving the high-temperature cycle performance of the secondary battery.

[0014] In an embodiment of the present application, the thickness of the binder layer is D1, and the separator satisfies at least one of the following conditions: (1) the distance between two adjacent point-like binders is 20 μm ~ 1000 μm; (2) the projection area of all the point-like binders in any area accounts for 20% ~ 60% of the total area of the area; (3) 0.2 μm ≤ D1 ≤ 4 μm; (4) 1 ≤ D2 / D1 ≤ 2.

[0015] Based on the above-mentioned embodiments, the interface performance of the separator is better, and the high-temperature cycle performance of the secondary battery using the above-mentioned separator is also better.

[0016] In an embodiment of the present application, the projection shape of the binding point in the area is at least one of a circle, a circular ring, an ellipse, a square or a rectangle.

[0017] In an embodiment of the present application, the binder layer comprises a first aqueous polymer, and the polymerized monomers of the first aqueous polymer comprise at least two of butadiene, methyl acrylate, methyl methacrylate, styrene, butyl methacrylate, isooctyl acrylate, ethylene, propylene or vinylidene fluoride.

[0018] Based on the above-mentioned technical solutions, the first aqueous polymer itself has good binding force, and when the above-mentioned separator is used in a secondary battery, the high-temperature cycle performance of the secondary battery can be further improved.

[0019] In an embodiment of the present application, all the linear binders constitute a flow guide layer, the flow guide layer comprises a second aqueous polymer, and the monomers of the second aqueous polymer comprise at least two of styrene, butyl methacrylate, propylene, vinylidene fluoride or hexafluoropropylene.

[0020] Based on the above technical solution, the second water-based polymer itself has good adhesion, and the above-mentioned diaphragm can further improve the high-temperature cycle performance of the secondary battery when used in the secondary battery.

[0021] In a second aspect, the application provides a secondary battery, comprising an electrolyte and an electrode core, the electrode core is sequentially stacked in the thickness direction of the electrode core with a positive electrode, the above-mentioned diaphragm and a negative electrode, the positive electrode is arranged on the surface of the flow guide layer; the edge of the positive electrode is also provided with a tab, and the tab is located on the extension line of at least part of the linear adhesive.

[0022] Based on the secondary battery of the application, the linear adhesive on the flow guide layer can form a through electrolyte transmission channel between the diaphragm and the positive electrode, effectively improve the electrolyte supply capacity, improve the interface performance of the positive electrode and the diaphragm, and result in better high-temperature cycle performance of the secondary battery. In addition, since the tab is located on the extension line of at least part of the linear adhesive, the electrolyte at both ends of the electrode core can be transmitted to the main body of the electrode core, thereby prolonging the high-temperature cycle performance of the electrode core and reducing the risk of lithium precipitation at the end.

[0023] In an embodiment of the application, the electrolyte transmission rate of the flow guide layer is greater than the electrolyte transmission rate of the adhesive layer.

[0024] In an embodiment of the application, the electrolyte transmission rate of the adhesive layer is 5mm / min~40mm / min, and the electrolyte transmission rate of the flow guide layer is 15mm / min~60mm / min.

[0025] In an embodiment of the application, the electrolyte comprises ethylene glycol diethyl cyan ether and lithium tetrafluoroborate; and / or, the electrolyte comprises adiponitrile and fluorobenzene.

[0026] Based on the above embodiment, the low-temperature performance of the secondary battery can be obviously improved.

[0027] In an embodiment of the application, the electrolyte comprises ethylene glycol diethyl cyan ether and lithium tetrafluoroborate, and the ratio of the mass content of ethylene glycol diethyl cyan ether to the mass content of lithium tetrafluoroborate based on the total mass of the electrolyte is 10~150.

[0028] In an embodiment of the application, the ratio of the mass content of ethylene glycol diethyl cyan ether to the mass content of lithium tetrafluoroborate is 30~75.

[0029] Based on the above embodiment, the low-temperature performance of the secondary battery can be further improved.

[0030] In an embodiment of the application, the electrolyte comprises adiponitrile and fluorobenzene, and the sum of the mass content of adiponitrile and the mass content of fluorobenzene based on the total mass of the electrolyte is 4.5%~10%.

[0031] Based on the above embodiments, the low-temperature performance of the secondary battery can be further improved.

[0032] Advantages of the present application:

[0033] The present application provides a separator and a secondary battery. The separator comprises a base film layer, one surface of the base film layer is provided with an inorganic ceramic layer, and the other surface is provided with a flow guide layer. The flow guide layer is provided with linear adhesives. The thickness of each linear adhesive is D2, and the width is W2. 1 μm≤D2≤5 μm, and 20 μm≤W2≤400 μm. By setting the linear adhesives to form the flow guide layer, and controlling the width and thickness of the linear adhesives in the flow guide layer, an electrolyte transmission channel can be formed, and the electrolyte supply capacity can be effectively improved. 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. BRIEF DESCRIPTION OF DRAWINGS

[0034] 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. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0035] FIG. 1 is a demonstration diagram of the electrolyte transmission rate test of the embodiments of the present application;

[0036] FIG. 2 is a CCD diagram of the adhesive layer in the embodiments 3-4 of the present application.

[0037] Embodiments of the present application

[0038] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, 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, not all. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application. The specific conditions are not specified in the embodiments, and are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be purchased on the market.

[0039] It should be noted that in the specific embodiments of the present application, lithium ion batteries are used as examples of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium ion batteries.

[0040] The inventors found that in order to improve the energy density and charging rate of the secondary battery to meet the use requirements, the separator, positive and negative electrodes in the secondary battery are all set to be wide and thin; but this will cause the separator to be easily deformed, and the cycle interface of the secondary battery is also prone to purple stain and lithium precipitation, resulting in a decrease in the safety performance of the secondary battery. Although there is a scheme of using a PCS coating in the separator, 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, the high-temperature cycle performance of the secondary battery can be improved without basically affecting the cycle interface of the secondary battery. The secondary battery and the separator of the present application are described below:

[0041] The secondary battery of the present application comprises an electrolyte and a cell, wherein the cell 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.

[0042] The separator

[0043] The separator is used to isolate the positive electrode and the negative electrode to avoid direct contact between them to cause short circuit. The separator of the present application comprises a base film layer, one surface of the base film layer is provided with an inorganic ceramic layer, and the other surface is provided with a linear adhesive, all the linear adhesives constitute a flow guide layer, the thickness of each linear adhesive is D2, the width is W2, 1 μm≤D2≤5 μm, preferably 2 μm≤D2≤4 μm; 20 μm≤W2≤400 μm, preferably 150 μm≤W2≤250 μm. The width is the width of each linear adhesive in the width direction of the separator, and the length direction of the separator is the winding direction of the cell, and the width direction is perpendicular to the winding direction of the cell.

[0044] When the flow guide layer composed of the linear adhesives is provided in the separator in the present application, the gap between the adjacent linear adhesives can serve as an electrolyte transmission channel, which can effectively improve the electrolyte supply capacity, the electrolyte can better infiltrate the separator, improve the cycle interface of the separator, and the high-temperature cycle performance of the secondary battery can also be improved. Moreover, since the uniformly distributed linear adhesives also have certain adhesion, the flow guide layer can fix the separator to a certain extent, so that the separator is not easily deformed, thereby improving the high-temperature cycle performance of the secondary battery.

[0045] In some embodiments of the present application, the distance between adjacent linear adhesives is 50-500 μm, preferably 110-360 μm; and the linear adhesives can be parallel to each other, so that the high-temperature cycle performance of the secondary battery can be more obviously improved. In addition, in some embodiments of the present application, the sum of the projected areas of all linear adhesives on the base film layer accounts for 10-30% of the area of the base film layer, so as to ensure the adhesive force and the power kinetics of the battery cell. In addition, in the embodiments of the present application, the linear adhesives also have a length, but since the gap between adjacent linear adhesives needs to be used as an electrolyte transmission channel, the electrolyte transmission channel usually needs to be the same as the length of the base film layer, so as to better transmit the electrolyte; therefore, for the same size of the base film layer, the length of the linear adhesives is usually fixed and the same as the length of the base film layer.

[0046] In addition, in some embodiments of the present application, the flow guide layer comprises a second water-based polymer; the monomers of the second water-based polymer comprise at least two of styrene, butyl methacrylate, propylene, vinylidene fluoride or hexafluoropropylene. The second water-based polymer itself has good adhesive properties, and the main chain and the branch chain of the second water-based polymer can additionally graft adhesives, which is conducive to improving the adhesive force of the adhesive layer.

[0047] In some embodiments of the present application, in order to make the strength distribution of the adhesive force of each region on the surface of the separator substantially the same, the inorganic ceramic layer is provided with a point adhesive away from the surface of the base film layer, all the point adhesives on the same surface constitute an adhesive layer, the longest diameter of each point adhesive 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 point adhesives in any region on the surface of the adhesive layer, specifically 20, 30, 40, 55, 67, 86, 92, 100, 120, 150 or any range between any two of the above values, preferably 40-100; the length of the region is 3470 μm, and the width is 2600 μm. At this time, the secondary battery cycle can not only reduce the probability of the generation of the interface purple lithium precipitation phenomenon, but also improve its own high-temperature cycle performance.

[0048] It should be noted that the shape of the point-shaped adhesive is not particularly limited in the present application. Since the three-dimensional shape of the point-shaped adhesive is not intuitive, the shape of the point-shaped adhesive is described in terms of the projected shape of the point-shaped adhesive in the region. Specifically, the projected shape of the point-shaped adhesive in the region 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 projected shape of the point-shaped adhesive in the region is a circular ring shape, in some embodiments of the present application, the projected 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 point-shaped adhesive in the present application is also relative to the projected shape of the point-shaped adhesive in the region, which refers to the distance between the two most distant points in the projected shape. Specifically, when the projected shape of the point-shaped adhesive is a circular shape, the "longest diameter" refers to the diameter of the circle; when the projected shape is a circular ring shape, the "longest diameter" refers to the major radius of the circular ring; when the projected shape is an elliptical shape, the "longest diameter" refers to the length of the major axis of the ellipse; and when the projected shape is a square or rectangular shape, the "longest diameter" refers to the length of the diagonal of the square or rectangular shape.

[0049] In some embodiments of the present application, in order to further improve the kinetic performance of the diaphragm, the distance between two adjacent point-shaped adhesives in the same adhesive layer of the diaphragm is 20 μm to 1000 μm, preferably 150 nm to 400 nm. In the present application, the "distance between two adjacent adhesion points" refers to the distance between the projections of two adjacent adhesion points, which is the distance between the closest parts of the two projections.

[0050] The present application does not have a particular limitation on the distribution of the adhesion points in the region. In actual production, the adhesion points in the region are generally uniform and regular based on the need for preparation process, that is, the distance between two adjacent adhesion points in the region is basically the same, and the projections of the adhesion points in the region can form a pattern similar to a rectangle or a square. As an example, in the present embodiment, the adhesion points in the region are uniformly distributed, and the projections of the adhesion points can be arranged in a pattern similar to a rectangle. In addition, in the specific embodiments of the present application, since each adhesion point has more than one adjacent point, and the arrangement of the adhesion points in the present embodiment is relatively regular, the "distance between two adjacent adhesion points" refers to the average distance, and the specific algorithm is: average distance = sum of distances between all adjacent adhesion points in the region / number of adhesion points in the region.

[0051] In some embodiments of the present application, in order to further improve the surface adhesion of the diaphragm and make the diaphragm less likely to deform, the projected area of all adhesion points in any region of the adhesive layer in the region generally accounts for 20% to 60% of the total area of the region, preferably 20% to 35%.

[0052] 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, 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.

[0053] 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, or 1≤D2 / D1≤2.

[0054] In addition, the flow guide layer and the adhesive layer in the separator are generally prepared by coating. The coating equipment is selected from one of gravure, microgravure, screen printing, and extrusion coating. In order to more conveniently control the line or point shape of the adhesive, as well as the thickness, width and spacing between adjacent line-shaped adhesives of the line-shaped adhesive, and the number, spacing and size of the point-shaped adhesive, as an example, the screen printing coating method is used to prepare the flow guide layer and the adhesive layer in the specific embodiments of the present application. When this method is used, the line or point shape of the adhesive can be changed by replacing the screen printing plate of different types, and the structural parameters of the line-shaped adhesive or the point-shaped adhesive can be changed by changing the mesh of the screen printing plate.

[0055] In some embodiments of the present application, the adhesive layer comprises, by weight fraction, a first aqueous polymer; wherein the polymerized monomers of the first aqueous polymer comprise at least two of butadiene, methyl acrylate, methyl methacrylate, styrene, butyl methacrylate, isooctyl acrylate, ethylene, propylene or vinylidene fluoride. The first aqueous polymer itself also has good adhesion, and the main chain and the side chain of the first aqueous polymer can also be additionally grafted with an adhesive, which is conducive to improving the adhesion of the adhesive layer. For example, the first (or second) aqueous polymer can be grafted with acrylic acid, methyl methacrylate, butyl acrylate, octyl acrylate, isooctyl acrylate, butadiene or acrylonitrile, etc.

[0056] 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 include 85% to 95% inorganic particles and 5% to 15% inorganic layer binder, wherein the inorganic particles include at least one of alumina, 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 inorganic layer binder includes polyacrylate.

[0057] 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 electrolyte transport rate of the flow guide layer in the secondary battery in the present application is greater than the electrolyte transport rate of the adhesive layer. The electrolyte transport rate of the adhesive layer is 5 mm / min to 40 mm / min, and the electrolyte transport rate of the flow guide layer is 15 mm / min to 60 mm / min.

[0058] Electrolyte

[0059] The electrolyte can play a role in transporting lithium ions and electrons, ensuring the formation of a path inside the electrochemical device. There are also schemes for reducing 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.

[0060] 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 ethylene glycol diethyl cyan ether and lithium tetrafluoroborate; (2) the electrolyte includes adiponitrile and fluorobenzene. For example, the electrolyte includes ethylene glycol diethyl cyan ether and lithium tetrafluoroborate, and the mass content ratio of ethylene glycol diethyl cyan ether and lithium tetrafluoroborate is 10 to 150 based on the total mass of the electrolyte; more preferably, the ratio of the two is 30 to 75. Alternatively, the electrolyte includes adiponitrile and fluorobenzene, and the sum of the mass content of adiponitrile and the mass content of fluorobenzene is 4.5% to 10% based on the total mass of the electrolyte.

[0061] Positive electrode

[0062] In the present application, the positive electrode needs to be arranged on the surface of the flow guide layer, and the edge of the positive electrode is provided with a tab, and the tab is located on the extension line of at least part of the linear adhesive, so that the electrolyte at both ends of the battery cell can be transported to the main body of the battery cell, prolonging the cycle performance of the battery cell and reducing the risk of lithium precipitation at the end.

[0063] In addition, the positive electrode in the present application 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. The "positive electrode active material layer disposed on at least one surface of the positive electrode current collector" means that 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 object of the present application can be achieved. In addition, in the present application, "the edge of the positive electrode is provided with a tab" means that the edge of the positive electrode current collector is provided with a tab.

[0064] 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 + , and other alkali metal ions to ensure that the electrochemical device can be normally charged and discharged. 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, and a ternary material, which includes, but is not limited to, at least one of LiNi x Co y Mn z O2, LiNi x Co y Al z O2, and the like, and the content of Ni, Co, Mn, Al, and the like 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 0.04 O2, 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, and the like.

[0065] 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, or the like.

[0066] 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).

[0067] In the positive electrode, the type of positive electrode current collector is not particularly limited, and it can be any known material 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 and carbon paper. 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 aid or a conductive coating, or the like. The conductive aid includes, but is not limited to, carbon and noble metals such as gold, platinum, and silver. The conductive coating can be a mixture layer of inorganic oxides, conductive agents, and positive electrode binders.

[0068] 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 the positive electrode active material layer on the positive electrode current collector, thereby obtaining the 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-methylpyrrolidone (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 pressure-bonded to the positive electrode current collector.

[0069] Negative electrode

[0070] 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.

[0071] 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.

[0072] 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.

[0073] In some embodiments of the present application, the negative electrode active material layer can also contain a negative electrode binder and a thickening agent, and the present application does not have a particular limitation on the type of the negative electrode binder and the thickening agent as long as the purpose of the present application can be achieved. For example, the negative electrode 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 electrode slurry can include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose.

[0074] In the negative electrode, the material of the negative electrode current collector includes, but is not limited to, a copper foil, an aluminum foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, or a polymer substrate coated with a conductive metal, and the present application is not particularly limited. 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.

[0075] In addition, in the present application, the thickness of the negative electrode current collector and the negative electrode 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 electrode current collector is 4 μm to 12 μm, and the thickness of the single-sided negative electrode active material layer is 30 μm to 160 μm.

[0076] In addition, similar to the preparation of the positive electrode, in the preparation of the negative electrode, either the negative electrode slurry can be configured, then the negative electrode slurry is coated on the negative electrode current collector and dried, thereby forming a negative electrode active material layer on the negative electrode current collector, so as to obtain the negative electrode; or the components in the negative electrode active material layer can be dry-mixed to form a sheet, then the obtained sheet is crimped to the negative electrode current collector to form a negative electrode active material layer, thereby obtaining the negative electrode. The solvent in the negative electrode slurry includes any one of an aqueous solvent, an organic solvent, etc. The aqueous solvent includes, but is not limited to, a mixed solvent of alcohol and water, or water, etc. The organic solvent includes, but is not limited to, aliphatic hydrocarbons such as hexane, aromatic hydrocarbons such as benzene, toluene, xylene, methylnaphthalene, heterocyclic compounds such as quinoline and pyridine, ketones such as acetone, methyl ethyl ketone, and cyclohexanone, esters such as methyl acetate and methyl acrylate, amines such as diethylene triamine and N,N-dimethyl aminopropylamine, ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF), amides such as N-methyl pyrrolidone (NMP), dimethyl formamide, and dimethyl acetamide, and aprotic polar solvents such as hexamethyl phosphoramide and dimethyl sulfoxide. In addition, in some other embodiments, in the case of using an aqueous solvent, a thickening agent and a styrene-butadiene rubber (SBR) emulsion are also 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 their salts, etc.

[0077] 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-disc players, 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.

[0078] Embodiments

[0079] The following embodiments and comparative examples are described with respect to lithium-ion secondary batteries to more specifically illustrate the embodiments of the electrochemical device of the present application. Those skilled in the art will appreciate that the preparation methods described in the present application are merely examples, and any other suitable preparation method is within the scope of the present application.

[0080] Test methods and apparatus:

[0081] Electrolyte transport rate test:

[0082] 1. Cut the separator sample into a 15 mm wide and 100 mm long sample for standby;

[0083] 2. Fix both ends of the sample, and suspend the middle position. Drop 1 ml of electrolyte to the middle position of the sample (as shown in FIG. 1) using a 1 ml syringe;

[0084] 3. Time for 1 min, test the distance of electrolyte diffusion along the length direction of the sample, repeat three times for each sample, and take the average value.

[0085] Adhesion point number detection:

[0086] At any position on the surface of the separator, select an area with a length of 3470 pm and a width of 2600 pm. Using a CCD (Charge-coupled Device) electronic microscope of the model VHX5000 of Keyence, observe and record the image information of the area after magnification of 100 times. FIG. 2 is a CCD image of Example 3-4. The counting method of the adhesion points in the area is as follows:

[0087] The adhesion points incompletely displayed in the area are not counted in the total number if less than 50% of the entire adhesion point in the selected area, and equal to or greater than 50% are counted as one adhesion point.

[0088] Adhesion force test:

[0089] The adhesion between the separator and the positive electrode or negative electrode is tested according to the national standard GB / T 2790-1995, i.e., the 180° peeling test standard. The separator and the positive electrode or negative electrode are cut into 54.2 mm x 72.5 mm samples, the separator and the positive electrode or negative electrode are compounded, and hot pressing is performed using a hot press. The hot pressing conditions are: temperature 85°C, pressure 1Mpa, and hot pressing time 85s (seconds). The compounded sample is cut into 15 mm x 54.2 mm strips, and the adhesion between the separator and the positive electrode or negative electrode is tested according to the 180° peeling test standard.

[0090] High-temperature cycle performance test:

[0091] The secondary battery is 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 is discharged at 0.2C to 3V, then rested for 5 minutes, and the initial discharge capacity C0 of the secondary battery is measured.

[0092] Then charging and discharging are performed, where one charge and one discharge are counted as one cycle, and 800 cycles are performed. The discharge capacity C1 of the secondary battery after 800 cycles is measured. The charging process is: (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) rest for 5 minutes; (7) 0.5C constant current charging to 4.53V, constant voltage charging to 0.05C. The discharge process is: 0.7C constant current discharging to 3.0V.

[0093] Capacity retention rate after 800 cycles at 45°C = C1 / C0 x 100%.

[0094] The higher the capacity retention rate, the better the high-temperature cycle performance of the secondary battery.

[0095] Low-temperature performance test:

[0096] Step 1: In an environment of 25°C, the first charge and discharge of the formed secondary battery is performed. When discharging, discharge at 0.2C constant current to 3V, then rest the discharged secondary battery for 5 minutes, then charge at 0.5C constant current to 4.53V, then constant voltage charge to 0.02C, and rest for 60 minutes.

[0097] 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°C. Rest for 5 minutes.

[0098] Step 3: The secondary battery is placed in 10℃, 0℃, -10℃, -20℃ environment in turn for discharging, and the discharge is carried out at 0.2C constant current to 2.5V, and the final discharge capacity of the secondary battery under each temperature condition is recorded in turn. Before each discharge, the secondary battery is charged in a 25℃ environment, and the charging is carried out at a charging rate of 0.5C to 4.53V first, and then to 0.02C.

[0099] Step 4: The final discharge capacity of the secondary battery under the condition of -20℃ is selected, and the low-temperature capacity retention rate of the secondary battery under the condition of -20℃ is calculated by using the following expression:

[0100] The low-temperature capacity retention rate = (-20℃ condition of the final discharge capacity of the secondary battery / 25℃ condition of the discharge capacity of the first cycle of the secondary battery) x 100%.

[0101] The greater the low-temperature capacity retention rate, the better the low-temperature performance of the secondary battery.

[0102] Example 1-1

[0103] Preparation of the separator

[0104] Inorganic particles boehmite with a Dv50 of 1 µm and polyacrylate are mixed 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%, and then the obtained inorganic coating slurry is uniformly coated on one side of the base film layer made of polyethylene (PE) by micro-concave coating method, and dried in an oven to obtain an inorganic ceramic layer.

[0105] 90g of the second aqueous polymer particles (with a weight average molecular weight of 600,000 and the polymerized monomers being styrene and butyl methacrylate in a molar ratio of 1:1) are added to a stirrer, 10g of sodium carboxymethyl cellulose is added, stirred and mixed uniformly, 5g of wetting agent dimethyl silicone is added, and then deionized water is added for stirring, and the viscosity of the slurry is adjusted to 2000mPa·s~5000mPa·s, and the solid content is 5%, to obtain the flow guide layer slurry. Then the above-mentioned binding layer slurry is uniformly coated on the surface of the base film layer by screen printing, and the coating weight is 0.5g / m 2 , and then dried in an oven to form a flow guide layer.

[0106] Preparation of the negative electrode

[0107] The negative 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, and then deionized water was added as a solvent to prepare a negative electrode slurry with a solid content of 70%. The negative electrode slurry was then uniformly stirred in a vacuum mixer. 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 cold-pressed to obtain a negative electrode tab with a 150-µm-thick negative active material layer on one surface. The above coating step was then repeated on the other surface of the negative electrode tab to obtain a negative electrode tab coated with a negative active material layer on both surfaces. The negative electrode tab was cut into a 74 mm x 867 mm size and had its tabs welded.

[0108] <Manufacture of a positive electrode>

[0109] The positive active material lithium cobaltate, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 94:3:3, and then N-methyl pyrrolidone (NMP) was added as a solvent to prepare a positive electrode slurry with a solid content of 75%. The positive electrode slurry was then uniformly stirred in a vacuum mixer. 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 cold-pressed to obtain a positive electrode tab with a 100-µm-thick positive active material layer on one surface. The above step was then repeated on the other surface of the positive electrode tab to obtain a positive electrode tab coated with a positive active material layer on both surfaces. The positive electrode tab was cut into a 74 mm x 867 mm size and had its tabs welded.

[0110] <Manufacture of an electrolyte>

[0111] The non-aqueous organic solvents ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC) were mixed in a mass ratio of 20:30:20:28:2 in an environment with a water content of less than 10 ppm, and then lithium hexafluorophosphate (LiPF6) was added to the non-aqueous organic solvents to dissolve and mix uniformly, thereby obtaining an electrolyte. The mass content of LiPF6 was 8% based on the total mass of the electrolyte.

[0112] <Manufacture of a secondary battery>

[0113] The above-prepared positive electrode, separator, and negative electrode were sequentially stacked with the positive electrode in contact with the flow guide layer and the negative electrode in contact with the adhesive layer, and with the tabs of the positive electrode located on the extension line of at least part of the linear adhesive. The electrode assembly was then obtained by winding. The electrode assembly was placed in an aluminum-plastic film packaging bag, and was dehydrated at 80°C. The electrolyte was injected, and the secondary battery was obtained by vacuum packaging, standing, formation, shaping, and other processes.

[0114] Examples 1-2 to 1-15

[0115] Except for adjusting the thickness D2, width W2, and the interval between adjacent linear adhesives according to Table 1, the rest is basically the same as Example 1-1.

[0116] Comparative Example 1 to Comparative Example 4

[0117] Except for adjusting the thickness D2, width W2, and the interval between adjacent linear adhesives according to Table 1, the rest is basically the same as Example 1-1.

[0118] Table 1

[0119]

[0120] Note: D2 in Table 1 is the thickness of the linear adhesive, W2 is the width of the linear adhesive, the unit of electrolyte transmission rate is mm / min, the unit of adhesive force is N / m, and the same applies to Tables 2 to 4. In Comparative Example 4, the surface of the base film layer is completely covered by the linear adhesive, so the sum of the projected area of the linear adhesive on the base film layer accounts for 100% of the area of the base film layer.

[0121] Example 2-1 to Example 2-6

[0122] Except for replacing the type of second water-based polymer particles according to Table 2, the rest is basically the same as Example 1-10.

[0123] Table 2

[0124]

[0125] Example 3-1

[0126] Except for preparing the separator according to the following method and adjusting the relevant parameters of the adhesive layer, the rest of the steps are basically the same as Example 1-10:

[0127] Preparation of the separator

[0128] 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.

[0129] 90 g of first water-based polymer particles (weight average molecular weight of 600,000, polymerized monomers are butadiene and methyl acrylate at 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 for stirring, the viscosity of the slurry was adjusted to 2000 mPa·s~5000 mPa·s, and the solid content was 5%, to obtain a bonding layer slurry. Then the above bonding layer slurry was uniformly coated on the surface of the inorganic ceramic layer by micro-concave coating method, the coating weight was 0.5 g / m 2 , and then drying was completed in an oven to form a bonding layer.

[0130] 90 g of second water-based polymer particles (weight average molecular weight of 600,000, polymerized monomers are styrene and butyl methacrylate at 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 for stirring, the viscosity of the slurry was adjusted to 2000 mPa·s~5000 mPa·s, and the solid content was 5%, to obtain a flow layer slurry. Then the above bonding layer slurry was uniformly coated on the surface of the base film layer by silk screen printing method, the coating weight was 0.5 g / m 2 , and then drying was completed in an oven to form a flow layer.

[0131] Examples 3-2~3-21

[0132] Except that the preparation parameters of the electrolyte were adjusted according to Table 3, the rest was basically the same as Example 4-1.

[0133] Table 3

[0134]

[0135] Example 4-1

[0136] Except that the electrolyte was prepared according to the following method, the rest of the steps were basically the same as Example 1-10:

[0137] <Preparation of electrolyte>

[0138] In an argon atmosphere glove box with water content less than 10 ppm, non-aqueous organic solvents EC, DEC, PC, PP, VC were mixed according to a mass ratio of 20:30:20:28:2 to prepare a base solvent, then LiPF6, ethylene glycol dicyan ether, lithium tetrafluoroborate were added to form an electrolyte. Based on the total mass of the electrolyte, the mass content of LiPF6 was 8%, the mass content of ethylene glycol dicyan ether and lithium tetrafluoroborate was shown in Table 4, and the rest was the base solvent.

[0139] Examples 4-2~4-6

[0140] The rest of the steps are basically the same as those in Example 4-1, except that the relevant preparation parameters of the electrolyte are adjusted according to Table 4.

[0141] Example 4-7

[0142] The rest of the steps are basically the same as those in Example 1-10, except that the electrolyte is prepared according to the following method:

[0143] Preparation of electrolyte

[0144] In an argon glove box with a water content of 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 prepare a base solvent, and then lithium salt lithium hexafluorophosphate (LiPF6), adiponitrile, and fluorobenzene are added to form an electrolyte. Based on the total mass of the electrolyte, the mass content of LiPF6 is 8%, the mass content of adiponitrile and fluorobenzene is shown in Table 4, and the rest is the base solvent.

[0145] Examples 4-8 to 4-16

[0146] The rest of the steps are basically the same as those in Example 4-8, except that the relevant preparation parameters of the electrolyte are adjusted according to Table 4.

[0147] Table 4

[0148]

[0149] Note: The content of each component of the electrolyte in Table 4 omits "%".

[0150] As can be seen from the examples and comparative examples in Tables 1 to 4, when the separator of the application is used in a secondary battery, the high-temperature cycle performance of the secondary battery can be effectively improved. In particular, when the separator of the application contains an adhesive layer, the high-temperature cycle performance of the secondary battery can be further improved. In particular, when ethylene glycol dicyan ether and lithium tetrafluoroborate are added to the electrolyte, or adiponitrile and chlorobenzene are added, the low-temperature performance of the secondary battery can also be improved.

[0151] It should be noted that in this document, the terms "comprising", "including", or any other variant thereof are intended to cover non-exclusive inclusions, so that a process, method, or article including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or inherent to such a process, method, or article.

[0152] Each embodiment in the specification is described in a related manner, and the same or similar parts between each embodiment can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0153] The above merely provides preferred embodiments of the present application, and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A diaphragm, characterized by It comprises a base film layer, one surface of which is provided with an inorganic ceramic layer, and the other surface is provided with linear binders, which constitute a flow guide layer; the thickness of each linear binder is D2, the width is W2, 1 μm≤D2≤5 μm, 20 μm≤W2≤400 μm.

2. The separator according to claim 1, characterized in that It satisfies at least one of the following conditions: (1) the linear binders are parallel to each other; (2) the sum of the projection areas of all the linear binders on the base film layer accounts for 10% to 30% of the area of the base film layer; (3) 2 μm≤D2≤4 μm; (4) 150 μm≤W2≤250 μm; (5) the distance between adjacent linear binders is 50 μm to 500 μm.

3. The separator of claim 1, wherein The surface of the inorganic ceramic layer away from the base film layer is provided with point binders, and all the point binders constitute a bonding layer, the longest diameter of each point binder is 20 μm to 500 μm, and there are 30 to 150 point binders in any area of the surface of the bonding layer, the length of the area is 3470 μm, and the width is 2600 μm.

4. The diaphragm of claim 3, wherein The thickness of the bonding layer is D1, and the diaphragm satisfies at least one of the following conditions: (1) the distance between adjacent two point binders is 20 μm to 1000 μm; (2) the projection area of all the point binders in any area accounts for 20% to 60% of the total area of the area; (3) 0.2 μm≤D1≤4 μm; (4) 1≤D2 / D1≤2.

5. The diaphragm of claim 3, wherein The projection shape of the point binder 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 3 or 4, wherein The bonding layer comprises a first aqueous polymer, and the monomers of the first aqueous polymer comprise at least two of butadiene, methyl acrylate, methyl methacrylate, styrene, butyl methacrylate, isooctyl acrylate, ethylene, propylene or vinylidene fluoride.

7. The separator according to any one of claims 1 to 5, wherein All the linear binders constitute a flow guide layer, and the flow guide layer comprises a second aqueous polymer, and the monomers of the second aqueous polymer comprise at least two of styrene, butyl methacrylate, propylene, vinylidene fluoride or hexafluoropropylene.

8. The septum of claim 2, wherein, The distance between adjacent linear binders is 110 μm to 360 μm.

9. A secondary battery characterized by comprising: It comprises an electrolyte and an electric core, the electric core is sequentially stacked with a positive electrode, a diaphragm according to any one of claims 1 to 8 and a negative electrode along its thickness direction, the positive electrode is arranged on the surface of the flow guide layer; the edge of the positive electrode is also provided with a tab, and the tab is located on the extension line of at least part of the linear binder.

10. The secondary battery according to claim 9, characterized by The surface of the inorganic ceramic layer away from the base film layer is provided with point binders, and all the point binders constitute a bonding layer, the electrolyte transmission rate of the flow guide layer is greater than the electrolyte transmission rate of the bonding layer.

11. The secondary battery according to claim 10, characterized by The electrolyte transmission rate of the bonding layer is 5 mm / min to 40 mm / min, and the electrolyte transmission rate of the flow guide layer is 15 mm / min to 60 mm / min.

12. The secondary battery according to claim 9, characterized by The electrolyte comprises ethylene glycol dicyanide and lithium tetrafluoroborate; and / or, The electrolyte comprises adiponitrile and fluorobenzene.

13. The secondary battery according to claim 12, characterized by The electrolyte comprises ethylene glycol dicyanoether and lithium tetrafluoroborate, and the ratio of the mass content of the ethylene glycol dicyanoether to the mass content of the lithium tetrafluoroborate is 10-150 based on the total mass of the electrolyte.

14. The secondary battery according to claim 13, characterized by The ratio of the mass content of the ethylene glycol dicyanoether to the mass content of the lithium tetrafluoroborate is 30-75.

15. The secondary battery according to claim 12, characterized by The electrolyte comprises adiponitrile and fluorobenzene, and the sum of the mass content of the adiponitrile and the mass content of the fluorobenzene is 4.5%-10% based on the total mass of the electrolyte.

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