Separator, secondary battery, and electrical apparatus

Abstract

Disclosed in the present application are a separator, a secondary battery, and an electrical apparatus. The separator comprises a substrate and a bonding coating distributed on at least one surface of the substrate; the bonding coating comprises organic coatings and connection bridges, the organic coatings being distributed on the surface of the substrate, two adjacent organic coatings being connected by means of one connection bridge, and the width of the connection bridges being less than the maximum size of the organic coatings in the width direction of the connection bridges. The separator of the present application ensures an electrolyte to undergo continuous diffusion and wetting on the surface of the coating, thereby effectively improving the wettability of the electrolyte; the organic coatings are distributed on the surface of the substrate at equal intervals, resulting in small blockage of the substrate; after coating, the air permeability value of the separator increases slightly, and the obstruction to the transmission of lithium ions is low, which help to reduce the internal resistance of batteries and improve the bonding force between the separator and electrode sheets, thereby reducing the conditions of displacement or misalignment between positive and negative electrode sheets in the production process of secondary batteries.

Description

Separator, secondary battery and electric device

[0001] The present application claims priority to the Chinese patent application No. 202411017933.1, filed on July 26, 2024, and entitled "Separator, secondary battery and electric device", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of secondary batteries, in particular to a separator, a secondary battery and an electric device. BACKGROUND

[0003] The separator mainly plays a role of isolating the positive and negative electrodes to prevent short circuit of the battery, and at the same time, conducts ions to make the electrochemical reaction proceed smoothly. The separator has an important influence on the cycle performance, rate performance and safety performance of the battery. With the continuous improvement of the energy density of the secondary battery, the performance requirements of the separator are also gradually improved.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] The purpose of the present application is to provide a separator, a secondary battery and an electric device, which guarantees the continuous diffusion and wetting of the electrolyte on the surface of the coating, effectively improves the wettability of the electrolyte, reduces the internal resistance of the separator, and improves the adhesion between the separator and the electrode sheet.

[0006] To achieve the above purpose, the first aspect of the present application provides a separator, comprising a substrate and an adhesive coating distributed on at least one surface of the substrate.

[0007] The adhesive coating comprises an organic coating and a connecting bridge, the organic coating is distributed on the surface of the substrate, and two adjacent organic coatings are connected by the connecting bridge.

[0008] The width of the connecting bridge is less than the maximum dimension of the organic coating in the width direction of the connecting bridge.

[0009] As an embodiment of the present application, the organic coating is in the form of a circular dot, and the width of the connecting bridge is less than the diameter of the circular dot.

[0010] As an embodiment of the present application, the diameter of the circular dot is 50 μm to 600 μm.

[0011] As an embodiment of the present application, the thickness of the organic coating is 1 μm to 20 μm.

[0012] As an embodiment of the present application, the width of the connecting bridge is 20 μm to 200 μm, and the length of the connecting bridge is 0.1 mm to 1 mm.

[0013] As an embodiment of the present application, the bonding coating covers 8% to 51% of the surface area of the substrate, and the area density of the bonding coating is 0.2 g / m 2 ~1.5 g / m 2 .

[0014] As an embodiment of the present application, the bonding coating comprises a polymer and a bonding agent, and the mass ratio of the polymer to the bonding agent is (3-9):1.

[0015] As an embodiment of the present application, the polymer comprises at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polymethacrylate, and an acrylic copolymer derivative; and / or

[0016] The bonding agent comprises at least one polar functional group in the molecular structure, and the polar functional group comprises at least one of C=O, -CN, -OH, -COOH, -COOLi, -COONa, -CONH-, and -NHCOO-.

[0017] A second aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and a separator between the positive electrode sheet and the negative electrode sheet, wherein the separator is the above-mentioned separator.

[0018] A third aspect of the present application provides an electrical device comprising the above-mentioned secondary battery.

[0019] The separator of the present application ensures that the electrolyte continuously diffuses and wets on the surface of the coating, effectively improves the wettability of the electrolyte, and the organic coating is distributed on the surface of the separator substrate, which has little plugging effect on the substrate, increases the air permeability of the coated separator little, and has little hindering effect on the transmission of lithium ions, which is conducive to reducing the internal resistance of the secondary battery, improving the long-term cycle performance of the battery, avoiding the problem of serious coating hole plugging caused by full coverage coating, effectively improving the ionic conductivity, reducing the internal resistance of the separator, improving the adhesion between the separator and the electrode sheet, and reducing the offset or misalignment between the positive and negative electrode sheets during the production process of the secondary battery. BRIEF DESCRIPTION OF DRAWINGS

[0020] FIG. 1 is a structural schematic diagram of the bonding coating of the present application. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme of the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0022] In the present application, the technical features described in an open manner include both a closed technical solution consisting of the listed features and an open technical solution including the listed features.

[0023] In the present application, if no special description is provided, the numerical range is considered to be continuous and includes the minimum value and the maximum value of the range and each value between the minimum value and the maximum value. Further, when the range refers to an integer, each integer between the minimum value and the maximum value of the range is included. In addition, when multiple ranges are provided to describe a feature or a characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein should be interpreted as including any and all sub-ranges subsumed therein.

[0024] In the present application, the specific dispersion and stirring treatment method is not particularly limited.

[0025] Unless otherwise specified, the components and raw materials used in the embodiments and comparative examples of the present application are commercially available raw materials or instruments, and the components and raw materials used in each parallel experiment are the same.

[0026] The embodiment of the present application provides a separator, which comprises a substrate and a bonding coating layer distributed on at least one surface of the substrate.

[0027] As shown in FIG. 1, the bonding coating layer 1 comprises an organic coating layer 2 and a connecting bridge 3, the organic coating layer is distributed on the surface of the substrate, and two adjacent organic coating layers are connected through the connecting bridge;

[0028] The width of the connecting bridge is less than the maximum dimension of the organic coating layer in the width direction of the connecting bridge.

[0029] The present application sets the organic coating layer on the substrate and connects the organic coating layer through the connecting bridge, the separator ensures the continuous diffusion and wetting of the electrolyte on the surface of the coating layer, effectively improves the electrolyte wettability, the organic coating layer is distributed on the surface of the separator substrate at equal intervals, the plugging of the substrate is small, the air permeability of the coated separator increases little, the transmission of lithium ions is hindered little, which is conducive to reducing the internal resistance of the secondary battery, improving the long-term cycle performance of the battery, avoiding the problem of serious coating hole plugging caused by full coverage coating, effectively improving the ionic conductivity, reducing the internal resistance of the separator, improving the adhesion between the separator and the pole piece, and reducing the offset or misalignment between the positive and negative pole pieces during the production process of the secondary battery.

[0030] The connecting bridge described in the present application effectively improves the air permeability and reduces the impedance, provides a fast flow channel for the electrolyte, and is conducive to the rapid infiltration of the electrolyte on the diaphragm, effectively improves the electrolyte infiltration speed, when the width of the connecting bridge is less than the maximum size of the organic coating in the width direction of the connecting bridge, the continuity of the infiltration can be ensured, and the air permeability is better, thereby effectively improving the air permeability of the coating and the liquid climbing speed.

[0031] In one embodiment, the organic coating is in the form of a circular dot, and the width of the connecting bridge is less than the diameter of the circular dot.

[0032] In one embodiment, the diameter of the circular dot is 50 μm to 600 μm, for example, it can be 50 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, or a range formed by any two of the above values, when the diameter of the circular dot is 50 μm to 600 μm, the air permeability of the coating is not affected, and the electrolyte infiltration speed is effectively improved, the internal resistance is reduced, and the adhesion between the diaphragm and the pole piece is improved.

[0033] In one embodiment, the thickness of the organic coating is 1 μm to 20 μm, for example, it can be 1 μm, 2 μm, 4 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 20 μm, or a range formed by any two of the above values, when the thickness of the adhesive coating is 1 to 20 μm, the transmission resistance of lithium ions is small, the air permeability, impedance, adhesion, and liquid climbing speed of the coating are improved.

[0034] In one embodiment, the width of the connecting bridge is 20 μm to 200 μm, for example, it can be 20 μm, 40 μm, 80 μm, 100 μm, 200 μm, or a range formed by any two of the above values, when the width of the connecting bridge is 20 μm to 200 μm, the continuity of the infiltration can be ensured, and the air permeability is better, thereby effectively improving the air permeability of the coating and the liquid climbing speed.

[0035] In one embodiment, the organic coating is distributed on the surface of the substrate at substantially equal intervals. The substantially equal intervals mean that the deviation of the interval of the organic coating on the surface of the substrate is within 20%.

[0036] In one embodiment, the length of the connecting bridge is 0.1mm-1mm, for example, 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1mm or any range between any two of the numbers. When the distance between the adhesive coatings is 0.1mm-1mm, the electrolyte infiltration speed is improved, the lithium ion transmission is less hindered, and the coating porosity, impedance, adhesion and wicking speed are improved.

[0037] In one embodiment, the adhesive coating covers 8%-51% of the surface area of the substrate, for example, 8%, 10%, 20%, 30%, 40%, 51% or any range between any two of the numbers.

[0038] In one embodiment, the areal density of the adhesive coating is 0.2g / m 2 -1.5g / m 2 , for example, 0.2g / m 2 , 0.4g / m 2 , 0.6g / m 2 , 0.8g / m 2 , 1g / m 2 , 1.2g / m 2 , 1.5g / m 2 or any range between any two of the numbers. In this application, the areal density of the adhesive coating refers to the weight of the adhesive coating per unit area on one side of the substrate.

[0039] In one embodiment, the areal density of the adhesive coating is 0.5-1.1g / m 2 .

[0040] In one embodiment, the adhesive coating includes a polymer and an adhesive, and the mass ratio of the polymer to the adhesive is (3-9):1, for example, 3:1, 4:1, 5:1, 6:1, 8:1, 9:1 or any range between any two of the numbers.

[0041] In one embodiment, the polymer includes at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polymethyl acrylate, and acrylate copolymer derivative.

[0042] In one embodiment, the binder molecule structure comprises at least one polar functional group, which includes at least one of C=O, -CN, -OH, -COOH, -COOLi, -COONa, -CONH-, -NHCOO-.

[0043] In one embodiment, the binder includes at least one of an acrylate copolymer, an acrylonitrile copolymer, polyvinyl alcohol, polyacrylic acid amide, and polyurethane.

[0044] In one embodiment, the substrate is a polymer substrate or a composite substrate composed of a polymer substrate and a heat-resistant coating layer, the polymer substrate includes at least one of a polyolefin substrate, a PET non-woven fabric substrate, a polyimide non-woven fabric substrate, and a PVDF porous substrate; and the heat-resistant coating layer includes at least one of an alumina heat-resistant coating layer, a boehmite heat-resistant coating layer, a silica heat-resistant coating layer, a cellulose fiber heat-resistant coating layer, a composite heat-resistant layer composed of cellulose fiber and alumina, a composite heat-resistant layer composed of cellulose fiber and boehmite, an aramid heat-resistant layer, a composite heat-resistant layer composed of aramid and alumina, a composite heat-resistant layer composed of aramid and boehmite, a polyimide heat-resistant layer, a composite heat-resistant layer composed of polyimide and alumina, a composite heat-resistant layer composed of polyimide and boehmite, a zirconia heat-resistant layer, an aluminum hydroxide heat-resistant layer, and a titanium dioxide heat-resistant layer.

[0045] In one embodiment, the substrate has a thickness of 4 μm to 20 μm, for example, 4 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 20 μm, or a range defined by any two of the above values.

[0046] In one embodiment, the polymer substrate has a porosity of 30% to 60%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or a range defined by any two of the above values.

[0047] One embodiment of the present application provides a secondary battery, which includes a positive electrode sheet, a negative electrode sheet, and a separator between the positive electrode sheet and the negative electrode sheet, the separator being the above-mentioned separator.

[0048] One embodiment of the present application provides an electric device, which includes the above-mentioned secondary battery.

[0049] More specifically, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector, the positive electrode material layer including a positive electrode active material.

[0050] Specifically, the positive active material can be selected from sodium-iron complex oxides, sodium-cobalt complex oxides, sodium-manganese complex oxides, sodium-nickel complex oxides, sodium-nickel-titanium complex oxides, sodium-nickel-manganese complex oxides, sodium-iron-manganese complex oxides, sodium-nickel-cobalt-manganese complex oxides, sodium-iron-phosphate compounds, sodium-manganese-phosphate compounds, sodium-cobalt-phosphate compounds, lithium-nickel-cobalt-manganese oxides, lithium-containing phosphates, and the like. However, the present application is not limited to these materials, and other conventional materials that can be used as positive active materials for batteries can also be used. These positive active materials can be used alone or in combination with two or more kinds.

[0051] In the present application, the type of the positive current collector is not particularly limited, and can be any material known to be suitable for use as a positive current collector. In one embodiment, the positive current collector includes metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, and the like, and carbon materials such as carbon cloth, carbon paper, and the like. In one embodiment, the positive current collector is a metal material. In one embodiment, the positive current collector is aluminum.

[0052] The form of the positive current collector is not particularly limited. When the positive current collector is a metal material, the form of the positive current collector can be a metal foil, a metal cylinder, a metal roll, a metal sheet, a metal foil, a metal expanded metal, a punched metal, a foamed metal, and the like. When the positive current collector is a carbon material, the form of the positive current collector can include, but is not limited to, a carbon sheet, a carbon film, a carbon cylinder, and the like.

[0053] In one embodiment, the positive active material layer further includes a conductive agent and a binder.

[0054] In one embodiment, the secondary battery further includes a negative electrode tab including a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, the negative active material layer including a negative active material.

[0055] In the present application, the negative current collector is not particularly limited, and can be any material known to be suitable for use as a negative current collector, such as a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a foamed nickel, a foamed copper, or a composite current collector, and the like.

[0056] In one embodiment, the negative active material can be at least one of natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O12, Li-Al alloy, and metallic lithium, and the like. 12

[0057] In one embodiment, the negative active material layer further includes a conductive agent and a binder.

[0058] ​In one embodiment, the type of the conductive agent is not limited, and any known conductive agent can be used.

[0059] In one embodiment, the conductive agent includes at least one of acetylene black, needle coke, carbon nanotube, graphene, and other carbon materials.

[0060] In one embodiment, the type of the binder in the positive electrode sheet and / or the negative electrode sheet is not limited, and any known binder can be used.

[0061] In one embodiment, the binder includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, cellulose nitrate, styrene butadiene rubber, nitrile rubber, fluoro rubber, isoprene rubber, polybutadiene rubber, ethylene-propylene rubber, polyvinylidene fluoride, polytetrafluoroethylene, and fluorinated polyvinylidene fluoride.

[0062] In the secondary battery mentioned in the present application, a separator is generally provided between the positive electrode and the negative electrode to prevent short circuit. The material and shape of the separator are not particularly limited as long as the effects of the present application are not significantly impaired.

[0063] In one embodiment, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The material of the above-mentioned separator can be used alone or in any combination.

[0064] In some embodiments, the secondary battery can include an outer package that can be used to package the above-mentioned electrode assembly and electrolyte.

[0065] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. can be listed.

[0066] In some embodiments, the type of the electrolyte is also not particularly limited. Among them, the electrolyte includes electrolyte salt and organic solvent, and the specific types of electrolyte salt and organic solvent are not particularly limited, and can be selected according to actual needs. The electrolyte can also include an additive, and the type of the additive is not particularly limited, which can be a film-forming additive for the positive electrode and / or the negative electrode, or an additive that can improve certain properties of the battery, such as an additive that improves the high or low temperature performance of the battery.

[0067] The shape of the secondary battery is not particularly limited in the present application, which can be cylindrical, square or any other shape.

[0068] Some embodiments of the present application provide a power consuming device comprising the secondary battery as described above as a power supply for the power consuming device.

[0069] For example, the power consuming device can include a mobile device (e.g., a mobile phone, a notebook computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0070] The present application is further illustrated below with specific examples:

[0071] Example 1

[0072] This example provides a separator, and a preparation method thereof includes the following steps:

[0073] Coating slurry preparation: 70 g of water and 1 g of acrylonitrile multi-copolymer (hereinafter referred to as LA133) were weighed and added to a planetary stirring tank, stirred at a speed of 500 rpm for 45 min, then stirred at a speed of 50 rpm for 45 min; 5 g of vinylidene fluoride-hexafluoropropylene copolymer (hereinafter referred to as PVdF-HFP) powder was added, stirred at a speed of 300 rpm for 15 min, stirred at a speed of 40 rpm for 15 min, then stirred at a speed of 1200 rpm for 25 min, then stirred at a speed of 50 rpm for 25 min, then 4 g of vinylidene fluoride-hexafluoropropylene copolymer powder was added, stirred at a speed of 350 rpm for 15 min, stirred at a speed of 35 rpm for 15 min, then stirred at a speed of 2000 rpm for 120 min, then stirred at a speed of 60 rpm for 120 min, and finally 20 g of water was added, stirred at a speed of 1500 rpm for 40 min, then stirred at a speed of 50 rpm for 40 min, to obtain a slurry, wherein the mass ratio of the polymer to the binder is 9:1.

[0074] Adhesive coating: a 7 μm polyethylene porous separator was selected as the substrate, and the porosity of the separator was 35%; a specially carved micro-concave roller was used to uniformly coat the slurry on one side surface of the porous substrate. The concave roller was carved with a specially designed pattern, and the pattern size was: the diameter of the circular mesh hole was 300 μm, the mesh hole depth was 5 μm, the width size of the connecting bridge between the circular mesh holes was 20 μm, and the length of the connecting bridge was 0.5 mm. The coated separator passed through an oven at 75°C at a speed of 80 m / min, and was wound to obtain a separator.

[0075] Example 2

[0076] The difference between Example 2 and Example 1 is that the diameter of the circular mesh hole of the concave roller in Example 2 is adjusted to 50 μm, thereby changing the diameter of the circular point.

[0077] Example 3

[0078] Example 3 differs from Example 1 in that Example 3 changes the diameter of the circular dots by adjusting the gravure roll circular cell diameter to 600 pm.

[0079] Example 4

[0080] Example 4 differs from Example 1 in that Example 4 changes the diameter of the circular dots by adjusting the gravure roll circular cell diameter to 30 pm.

[0081] Example 5

[0082] Example 5 differs from Example 1 in that Example 5 changes the diameter of the circular dots by adjusting the gravure roll circular cell diameter to 650 pm.

[0083] Example 6

[0084] Example 6 differs from Example 1 in that Example 6 changes the length of the connecting bridges by adjusting the gravure roll circular cell connecting bridge length to 1 mm.

[0085] Example 7

[0086] Example 7 differs from Example 1 in that Example 7 changes the length of the connecting bridges by adjusting the gravure roll circular cell connecting bridge length to 0.1 mm.

[0087] Example 8

[0088] Example 8 differs from Example 1 in that Example 8 changes the thickness of the organic coating by adjusting the gravure roll circular cell depth to 1 pm.

[0089] Example 9

[0090] Example 9 differs from Example 1 in that Example 9 changes the thickness of the organic coating by adjusting the gravure roll circular cell depth to 20 pm.

[0091] Example 10

[0092] Example 10 differs from Example 1 in that Example 10 changes the width of the connecting bridges by adjusting the gravure roll circular cell connecting bridge width dimension to 10 pm.

[0093] Example 11

[0094] Example 11 differs from Example 1 in that Example 11 changes the width of the connecting bridges by adjusting the gravure roll circular cell connecting bridge width dimension to 100 pm.

[0095] Example 12

[0096] Example 12 is different from Example 1 in that the connecting bridge width between the circular cells of the gravure roll is adjusted to 200 pm in Example 12.

[0097] Example 13

[0098] Example 13 is different from Example 1 in that the amount of polymer used in the preparation process is adjusted to adjust the mass ratio of polymer: binder in Example 13, and the others are the same.

[0099] Coating slurry preparation: 70 g of water and 2.5 g of acrylonitrile multi-copolymer (LA133) were weighed and added to a planetary stirring tank, stirred at 500 rpm for 45 min, then stirred at 50 rpm for 45 min; 5 g of vinylidene fluoride-hexafluoropropylene copolymer powder was added, stirred at 300 rpm for 15 min, stirred at 40 rpm for 15 min, then stirred at 1200 rpm for 25 min, then stirred at 50 rpm for 25 min, then 2.5 g of vinylidene fluoride-hexafluoropropylene copolymer powder was added, stirred at 350 rpm for 15 min, stirred at 35 rpm for 15 min, then stirred at 2000 rpm for 120 min, then stirred at 60 rpm for 120 min, and finally 20 g of water was added, stirred at 1500 rpm for 40 min, then stirred at 50 rpm for 40 min, to obtain a slurry, wherein the mass ratio of polymer: binder is 3: 1.

[0100] Example 14

[0101] Example 14 is different from Example 1 in that equal amounts of polyvinylidene fluoride (hereinafter referred to as PVDF) are used to replace vinylidene fluoride-hexafluoropropylene copolymer, and the others are the same.

[0102] Example 15

[0103] Example 15 is different from Example 1 in that equal amounts of polymethacrylate (hereinafter referred to as PMMA) are used to replace vinylidene fluoride-hexafluoropropylene copolymer, and the others are the same.

[0104] Example 16

[0105] Example 16 is different from Example 1 in that equal amounts of polyvinyl alcohol (hereinafter referred to as PVA) are used to replace acrylonitrile multi-copolymer, and the others are the same.

[0106] Comparative Example 1

[0107] Comparative Example 1 differs from Example 1 in that Comparative Example 1 uses a conventional full coverage micro-embossed roll coating with a thickness of 5 μm.

[0108] Comparative Example 2

[0109] Comparative Example 2 differs from Example 1 in that Comparative Example 2 does not contain connecting bridges.

[0110] Comparative Example 3

[0111] Comparative Example 3 differs from Example 1 in that Comparative Example 3 changes the diameter of the circular dots by adjusting the circular mesh cell diameter of the gravure roll to 20 μm.

[0112] The corresponding parameters of Examples 1-16 and Comparative Examples 1-3 are shown in Table 1.

[0113] Table 1

[0114] Performance Test

[0115] The separators prepared in the examples and comparative examples were subjected to separator adhesion tests, air permeability tests, impedance tests, and liquid climbing speed tests. The specific test conditions are as follows:

[0116] (1) Separator adhesion: the separator was laminated with a positive electrode sheet (ternary NCM positive electrode sheet) and a negative electrode sheet (artificial graphite negative electrode sheet), respectively (when the coating is only coated on one side of the substrate, the coating side faces the positive electrode during the test of the adhesion between the separator and the positive electrode, and the coating side faces the negative electrode during the test of the adhesion between the separator and the negative electrode), and then hot-pressed, with the hot-pressing parameters being as follows: pressure 3 MPa, temperature 90 °C, time 15 s; the positive or negative electrode sheet + separator unit after hot-pressing was cut into a 50 mm wide sample, and the separator and the electrode sheet on the sample were subjected to 180° peeling test using an electronic tensile testing machine to obtain the adhesion between the separator and the electrode sheet.

[0117] (2) Air permeability: tested using a Gurley air permeability tester. Specifically, the time required for 100 cc of air to completely permeate the separator under a certain pressure difference was recorded, which was the air permeability value of the separator. The higher the air permeability value, the worse the air permeability.

[0118] (3) Membrane impedance: the symmetrical battery was assembled with the structure of first copper foil + blue glue + membrane + second copper foil (the coating 2 of the membrane was fixed to face the second copper foil assembly), a circular hole with a diameter of 12 mm (actual effective area through which lithium ions can pass) was punched in the center of the blue glue; the number of layers of the membrane was designed to be 1, 2, 3, and 4, respectively, and 3 parallel samples of each layer of the membrane were prepared, and after drying, the symmetrical battery was packaged; the impedance of the symmetrical battery was tested by using an electrochemical workstation, and the test frequency was 3 MHz-200 mHz; the impedance values obtained by testing the symmetrical battery of the 1, 2, 3, and 4 layers of the membrane were linearly fitted, and the slope of the straight line was defined as the membrane impedance.

[0119] (4) Membrane liquid climbing speed: the membrane was cut into a long strip of 100x15mm, and the long strip of the membrane was fixed in an electrolyte tank with consistent height (the lithium salt in the electrolyte was LiPF6, the concentration was 1mol / L, and the electrolyte solvent was a mixed solvent of EC, EMC and DEC, wherein the mass ratio of EC, EMC and DEC was 1:1:1), and the distance climbed by the electrolyte within 30s was recorded. The distance climbed by the electrolyte was used to represent the liquid climbing speed of the membrane.

[0120] The test results are shown in Table 2.

[0121] Table 2

[0122] As can be seen from Table 2, the membrane described in the application ensures that the electrolyte continuously diffuses and wets on the surface of the coating, effectively improves the wettability of the electrolyte, the organic coating is distributed on the surface of the membrane substrate at equal intervals, the plugging of the substrate is small, the air permeability value of the coated membrane increases very small, the transmission of lithium ions is hindered, which is conducive to reducing the internal resistance of the secondary battery, improving the long-term cycle performance of the battery, avoiding the problem of serious coating hole plugging caused by full coverage coating, effectively improving the ionic conductivity, reducing the internal resistance of the membrane, improving the adhesion between the membrane and the pole piece, so that the positive and negative pole pieces will not be offset or misaligned during the production process of the secondary battery.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A separator comprising a substrate and a binding coating layer distributed on at least one surface of the substrate; the binding coating layer comprises an organic coating layer distributed on the surface of the substrate, and a connecting bridge connecting two adjacent organic coating layers; the width of the connecting bridge is less than the maximum dimension of the organic coating layer in the width direction of the connecting bridge.

2. The septum of claim 1, wherein, the organic coating layer is in the form of a circular dot, and the width of the connecting bridge is less than the diameter of the circular dot.

3. The septum of claim 2, wherein, the diameter of the circular dot is 30 μm to 650 μm.

4. The septum of claim 3, wherein, the diameter of the circular dot is 50 μm to 600 μm.

5. The septum of claim 1, wherein, the thickness of the organic coating layer is 1 μm to 20 μm.

6. The septum of claim 1, wherein, the organic coating layer is distributed on the surface of the substrate at substantially equal intervals.

7. The septum of claim 1, wherein, the width of the connecting bridge is 20 μm to 200 μm, and the length of the connecting bridge is 0.1 mm to 1 mm.

8. The septum of claim 1, wherein, The adhesive coating covers 8% to 51% of the surface area of the substrate, and the area density of the adhesive coating is 0.2 g / m 2 ~ 1.5 g / m 2 .

9. The septum of claim 8, wherein, The areal density of the adhesive coating is 0.5 g / m 2 ~ 1.1 g / m 2 .

10. The septum of claim 1, wherein, the binding coating layer comprises a polymer and a binding agent, and the mass ratio of the polymer to the binding agent is (3 to 9) :

1.

11. The septum of claim 10, wherein, the polymer comprises at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polymethacrylate, and acrylic copolymer derivative; and / or the binding agent comprises at least one polar functional group in the molecular structure, and the polar functional group comprises at least one of C=O, -CN, -OH, -COOH, -COOLi, -COONa, -CONH-, and -NHCOO-.

12. The septum of claim 10, wherein, the binding agent comprises at least one of acrylic copolymer, acrylonitrile copolymer, polyvinyl alcohol, polyacrylamide, and polyurethane.

13. The septum of claim 1, wherein, the substrate is a polymer substrate or a composite substrate composed of a polymer substrate and a heat-resistant coating layer.

14. The septum of claim 13, wherein, the polymer substrate comprises at least one of a polyolefin substrate, a PET non-woven fabric substrate, a polyimide non-woven fabric substrate, and a PVDF porous substrate.

15. The septum of claim 13, wherein, the heat-resistant coating layer comprises at least one of an alumina heat-resistant coating layer, a boehmite heat-resistant coating layer, a silica heat-resistant coating layer, a cellulose fiber heat-resistant coating layer, a composite heat-resistant layer composed of cellulose fiber and alumina, a composite heat-resistant layer composed of cellulose fiber and boehmite, an aramid heat-resistant layer, a composite heat-resistant layer composed of aramid and alumina, a composite heat-resistant layer composed of aramid and boehmite, a polyimide heat-resistant layer, a composite heat-resistant layer composed of polyimide and alumina, a composite heat-resistant layer composed of polyimide and boehmite, a zirconia heat-resistant layer, an aluminum hydroxide heat-resistant layer, and a titanium dioxide heat-resistant layer.

16. The septum of claim 13, wherein, the thickness of the substrate is 4 μm to 20 μm.

17. The septum of claim 13, wherein, the porosity of the polymer substrate is 30% to 60%. 18.A secondary battery comprising a positive electrode sheet, a negative electrode sheet, and a separator between the positive electrode sheet and the negative electrode sheet, wherein the separator is the separator according to any one of claims 1 to 17. 19.An electric device comprising the secondary battery according to claim 18.

20. The powered device of claim 19, wherein, the electric device is selected from mobile devices, electric vehicles, electric trains, ships, satellites, and energy storage systems.

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