Separator and electrochemical and electronic devices including said separator

Abstract

The present invention provides a separator and an electrochemical device and an electronic device including the separator, the separator including a substrate and a first coating layer provided on at least one surface of the substrate, the first coating layer including a first polymer, and the number of particles of the first polymer having a maximum length of 10 μm to 30 μm within any 250 μm×200 μm area on the surface of the first coating layer is 10 to 30. The separator of the present invention has excellent interfacial bonding performance, improves the structural stability of a lithium ion battery, and provides the lithium ion battery with better charge / discharge characteristics, particularly rate characteristics and cycle characteristics under low temperature conditions.

Description

[Technical Field]

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to separators and electrochemical and electronic devices comprising said separators. [Background technology]

[0002] The separator is one of the key inner layer components in lithium-ion batteries. Separator performance determines the battery's interfacial structure and internal resistance, directly affecting battery characteristics such as capacity, cycle life, and safety. Therefore, a high-performance separator plays a crucial role in improving the overall performance of the battery. The separator's primary function is to isolate the battery's positive and negative electrodes, preventing contact and short-circuiting between the two electrodes, while also allowing electrolyte ions to pass through. Conventional lithium-ion battery separators are typically coated separators, but these separators are unable to simultaneously meet the requirements of high adhesion and high dynamic performance. Therefore, a need exists for a coated separator that can achieve both these properties.

[0003] Furthermore, with the rapid development of applications of lithium ion batteries in fields such as consumer devices, people have higher requirements for the charge-discharge cycle characteristics of lithium ion batteries, and especially under low temperature conditions, the actual charge-discharge characteristics of lithium ion batteries are far smaller than the designed values, which limits the further applications of lithium ion batteries. Summary of the Invention

[0004] The object of the present invention is to provide a separator, and an electrochemical device and an electronic device including the separator, thereby improving the rate performance and cycle performance of a lithium ion battery, particularly the rate performance and cycle performance under low temperature conditions. Specific technical solutions are as follows.

[0005] In the present invention, a lithium ion battery is used as an example of an electrochemical device, but the electrochemical device of the present invention is not limited to a lithium ion battery.

[0006] A first aspect of the present invention provides a separator comprising a substrate and a first coating layer provided on at least one surface of the substrate, wherein the first coating layer comprises a first polymer, and the number of particles of the first polymer having a maximum length of 10 μm to 30 μm is 10 to 30, preferably 20 to 30, within any 250 μm x 200 μm area on the surface of the first coating layer.

[0007] When the separator of the present invention is observed at 500x magnification using a scanning electron microscope (SEM), the number of first polymer particles having a maximum length of 10 μm to 30 μm is 10 to 30 in any 250 μm × 200 μm area (i.e., an area observable with a single eyepiece). Without being limited to any theory, by controlling the number of first polymer particles having a maximum length of 10 μm to 30 μm within the above range, a discrete dot-like distribution can be formed in the first coating layer, which provides a path for the transport of the electrolyte and further improves the properties of the lithium-ion battery, particularly its low-temperature properties.

[0008] The first coating layer of the present invention is provided on at least one surface of the separator substrate, for example, the first coating layer may be provided on one surface of the separator substrate or on both surfaces of the separator substrate. The positive electrode of the present invention may specifically refer to a positive electrode piece, and the negative electrode may specifically refer to a negative electrode piece.

[0009] In one embodiment of the present invention, the separator's air permeability P is 500 sec / 100 mL to 10,000 sec / 100 mL, preferably 1,000 sec / 100 mL to 5,000 sec / 100 mL. If the separator's air permeability P is too high (e.g., higher than 10,000 sec / 100 mL), the internal resistance of the lithium-ion battery increases, affecting the battery's rate discharge characteristics, particularly at low temperatures. If the separator's air permeability P is too low (e.g., lower than 500 sec / 100 mL), the separator's breathability is good, but the corresponding cell (lithium-ion battery) tends to have low hardness and become a soft cell. By controlling the air permeability P of the separator of the present invention within the above range, the rate characteristics of the lithium-ion battery, particularly at low temperatures, can be improved, and the cell hardness can be further improved.

[0010] In one embodiment of the present invention, the areal density W1 of the coating of the first coating layer of the separator is 0.4 g / m 2 ~2g / m 2 and preferably, the surface density W1 of the coating of the first coating layer is 0.4 g / m 2 ~1g / m 2 Without being limited to any theory, it is believed that if the areal density W1 of the coating of the first coating layer is too low (e.g., 0.4 g / m 2 If the surface density W1 of the first coating layer is too high (for example, 2 g / m 2 If the surface density W1 of the first coating layer of the present invention is controlled within the above range, excellent interfacial adhesion can be achieved between the separator and the electrode pieces, and the impact on the energy density of the lithium-ion battery is minimal.

[0011] In one embodiment of the present invention, the porosity K of the separator is 30% to 65%. Without being limited to any theory, if the porosity K of the separator is too low (e.g., lower than 30%), the electrolyte will not easily infiltrate the separator, affecting the separator's ion transport capacity. If the porosity K of the separator is too high (e.g., higher than 65%), the separator will become sparse, reducing its strength and affecting its penetration resistance. By controlling the porosity K of the separator of the present invention within the above range, the separator can have excellent ion transport capacity and strength.

[0012] In one embodiment of the present invention, the separator further includes a heat-resistant layer, which is disposed between the substrate and the first coating layer. The heat-resistant layer includes inorganic particles, and the Dv50 of the inorganic particles is 0.5 μm to 35 μm, preferably 5 μm to 35 μm. By disposing the heat-resistant layer between the substrate and the first coating layer, the strength and heat resistance of the separator can be further improved. It is undesirable for the particle size of the inorganic particles to be too large or too small. If the particle size of the inorganic particles is too large (e.g., larger than 35 μm), it is difficult to achieve a thin coating design for the heat-resistant layer, which affects the energy density of the lithium-ion battery. If the particle size of the inorganic particles is too small (e.g., smaller than 0.5 μm), the pores where the inorganic particles are deposited become small, which affects ion transport and the dynamic performance of the lithium-ion battery. By controlling the Dv50 of the inorganic particles within the above range, the separator can have a high energy density and excellent dynamic performance. The present invention does not particularly limit the thickness of the heat-resistant layer, and may be, for example, 0.6 μm to 40 μm, as long as the heat-resistant layer satisfies the requirements of the present invention.

[0013] In the present invention, the inorganic particles in the heat-resistant layer are not particularly limited as long as the object of the present invention can be achieved, and the inorganic particles include at least one of boehmite, magnesium hydroxide, alumina, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, boron nitride, and aluminum nitride.

[0014] In one embodiment of the present invention, the ratio of the separator's air permeability P to the surface density W1 of the first coating layer satisfies P / W1 = 500 to 6500. Without being limited by any theory, if the ratio of the separator's air permeability P to the surface density W1 of the first coating layer is too low (e.g., P / W1 less than 500), the separator's air permeability is low, indicating a low surface density of the first coating layer, which results in poor adhesion at the interface between the separator and the pole piece, affecting the hardness of the lithium-ion battery and making the cell more likely to be soft. If the ratio of the separator's air permeability P to the surface density W1 of the first coating layer is too high (e.g., P / W1 greater than 6500), the separator's air permeability is high, indicating poor breathability, and indicating a high surface density of the first coating layer, which increases the internal resistance of the lithium-ion battery and affects the battery's rate characteristics, especially at low temperatures. By controlling the ratio of the separator air permeability P to the areal density W1 of the first coating layer within the above range, the lithium ion battery has excellent rate characteristics, particularly at low temperatures.

[0015] In one embodiment of the present invention, the porosity K of the separator and the surface density W1 of the first coating layer satisfy the relationship K / W1 = 0.15 to 1.4. Without being limited to any theory, if the ratio of the porosity K of the separator to the surface density W1 of the first coating layer is too low (e.g., K / W1 is less than 0.15), the porosity of the separator is low and the surface density of the first coating layer is high, making it difficult for the electrolyte to penetrate the separator and providing the separator with ion transport capabilities. If the ratio of the porosity K of the separator to the surface density W1 of the first coating layer is too high (e.g., K / W1 is greater than 1.4), the porosity of the separator is high and the surface density of the first coating layer is low, making the separator sparse, reducing its strength and affecting its penetration resistance. By controlling the ratio of the porosity K of the separator to the areal density W1 of the first coating layer within the above range, it is possible to impart excellent ion transport capacity and strength to the separator.

[0016] In one embodiment of the present invention, the first coating layer further comprises a first auxiliary binder, and the mass ratio of the first polymer to the first auxiliary binder is 2.5 to 18. Without being limited to any particular theory, if the mass ratio of the first polymer to the first auxiliary binder is too low (e.g., lower than 2.5), the content of the first polymer decreases, reducing the gaps created by the particulate first polymer, affecting the transport of electrolyte between the first coating layer interface and simultaneously affecting the adhesive strength between the first coating layer and the electrode strips. If the mass ratio of the first polymer to the first auxiliary binder is too high (e.g., higher than 18), the cohesive strength of the first coating layer decreases, and the adhesive strength of the first polymer decreases accordingly. By controlling the mass ratio of the first polymer to the first auxiliary binder within the above range, the adhesive strength between the first coating layer and the electrode strips can be improved.

[0017] In the present invention, the first auxiliary binder is not particularly limited as long as it satisfies the requirements of the present invention, and may include, for example, at least one of ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, maleic acid, acrylonitrile, and butadiene.

[0018] In one embodiment of the present invention, the separator further includes a second coating layer, and the first and second coating layers may be provided on both sides of the separator, respectively. The second coating layer includes a second polymer and a second auxiliary binder, and the mass ratio of the second polymer to the second auxiliary binder is 5 to 20. Without being limited to any theory, if the mass ratio of the second polymer to the second auxiliary binder is too low (e.g., lower than 5), the content of the second polymer decreases, affecting the binding strength between the second coating layer and the electrode pieces. If the mass ratio of the second polymer to the second auxiliary binder is too high (e.g., higher than 20), the cohesive strength of the second coating layer decreases, and the binding performance of the second coating layer decreases. By controlling the mass ratio of the second polymer to the second auxiliary binder within the above range, excellent binding strength can be achieved between the second coating layer and the electrode pieces.

[0019] In the present invention, one side of the separator having the first coating layer can be brought into contact with the positive electrode piece, and the other side of the separator having the second coating layer can be brought into contact with the negative electrode piece, thereby achieving good bonding between the separator and the positive electrode piece and the negative electrode piece, and achieving better electrolyte infiltration between the separator and the positive electrode piece, thereby improving the low-temperature performance of the lithium-ion battery. The separator of the present invention has lithium ion permeability and electron blocking properties.

[0020] In one embodiment of the present invention, when the first coating layer is provided facing the positive electrode, the adhesive strength is 4 N / m to 20 N / m, which indicates excellent adhesive performance between the first coating layer and the positive electrode piece.

[0021] In one embodiment of the present invention, when the second coating layer is provided facing the negative electrode, the adhesive strength is 4 N / m to 20 N / m, which indicates excellent adhesive performance between the second coating layer and the negative electrode piece.

[0022] In one embodiment of the present invention, the mass percentage of the first polymer is 85% to 95% and the mass percentage of the first auxiliary binder is 5% to 15% relative to the total mass of the first coating layer. By controlling the contents of the first polymer and the first auxiliary binder within the above ranges, it is possible to obtain a first polymer with excellent adhesive properties, which provides high binding strength between the first coating layer and the positive electrode and improves the performance of the lithium-ion battery at low temperatures.

[0023] In one embodiment of the present invention, the softening point of the first polymer is 90°C to 150°C, preferably 110°C to 150°C. Without being limited to any theory, if the softening point of the first polymer is too high (e.g., higher than 150°C), the first polymer is difficult to soften when heated, resulting in a small bonded area and affecting the bonding strength between the first coating layer and the electrode strips. If the softening point of the first polymer is too low (e.g., lower than 90°C), the first polymer softens and tends to clog the pores of the coating layer / separator, affecting the dynamic performance of the lithium-ion battery. By controlling the softening point of the first polymer of the present invention within the above range, the first polymer can have excellent bonding properties and improve the bonding strength between the first coating layer and the electrode strips. The term "softening point" refers to the temperature at which a substance softens. The Dv50 of the first polymer is 3 μm to 16 μm. Without being limited by any theory, if the Dv50 of the first polymer is too small (for example, smaller than 3 μm), the interfacial gap between the separator and the electrode pieces is too small, resulting in a decrease in the ability to transport the electrolyte solution. If the Dv50 of the first polymer is too large (for example, larger than 16 μm), the gaps created by the particulate first polymer are too large, which also affects the binding ability between the separator and the electrode pieces. By controlling the Dv50 of the first polymer of the present invention within the above range, a first polymer with excellent binding properties can be obtained.

[0024] In one embodiment of the present invention, the surface density W2 of the coating in the second coating layer of the separator is 0.1 g / m 2 ~1g / m 2 Without being limited to any theory, it is believed that if the surface density W2 of the coating of the second coating layer is too low (e.g., 0.1 g / m 2 If the surface density W2 of the second coating layer is too high (for example, 1 g / m 2If the surface density W2 of the second coating layer of the present invention is controlled within the above range, excellent interfacial bonding performance can be achieved between the separator and the electrode pieces, and the effect on the rate performance of the lithium-ion battery is minimal.

[0025] In one embodiment of the present invention, the mass percentage of the second polymer is 88% to 92.5% and the mass percentage of the second auxiliary binder is 7.5% to 12% relative to the total mass of the second coating layer. By controlling the contents of the second polymer and the second auxiliary binder within the above ranges, a second coating layer having excellent adhesive properties can be obtained, and a strong binding strength can be achieved between the second coating layer and the negative electrode, thereby improving the performance of the lithium-ion battery at low temperatures.

[0026] In one embodiment of the invention, the first polymer comprises at least one of homopolymers and copolymers of vinylidene fluoride, hexafluoropropylene, ethylene, propylene, vinyl chloride, chloropropylene, acrylic acid, acrylates, styrene, butadiene, and acrylonitrile.

[0027] In the present invention, the second polymer is not particularly limited as long as it satisfies the requirements of the present invention. For example, the second polymer may contain at least one of ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, maleic acid, acrylonitrile, and butadiene. In one embodiment of the present invention, the Dv50 of the second polymer is 0.2 μm to 8 μm. By controlling the Dv50 of the second polymer within the above range, a second polymer with excellent binding properties can be obtained. In the present invention, the second auxiliary binder is not particularly limited as long as it satisfies the requirements of the present invention. For example, the second auxiliary binder may contain at least one of sodium carboxymethyl cellulose and dimethyl siloxane.

[0028] The method for preparing the first polymer of the present invention is not particularly limited, and any preparation method known to those skilled in the art can be used. For example, the first polymer can be produced by the following preparation method.

[0029] The reactor is evacuated and the oxygen gas is replaced with nitrogen gas. Then, deionized water, vinylidene fluoride (VDF), a perfluoroalkyl carboxylate emulsifier, and isopropanol chain transfer agent are added to the reactor with a stirrer until the reactor pressure reaches approximately 3.5 MPa. The temperature is then raised to 50-70°C, and the stirrer speed is set to 70-100 r / min to initiate the polymerization reaction. At the same time, vinylidene fluoride monomer is continuously added to maintain the reactor pressure at 3.5 MPa. The reaction is stopped until the solids content of the emulsion in the reactor reaches 25-30%, at which point the unreacted monomer is recovered, and the polymer emulsion is discharged. After centrifugation, washing, and drying, the first polymer is obtained.

[0030] The present invention does not particularly limit the initiator as long as it can initiate the polymerization of the monomer, and may be, for example, diisopropylbenzene hydroperoxide. The present invention does not particularly limit the amounts of the monomer, deionized water, initiator, and chain transfer agent added as long as it ensures that the polymerization reaction of the added monomer occurs, and for example, the amount of deionized water is 5 to 10 times the mass of the monomer, the initiator accounts for 0.05% to 0.5% of the mass of the monomer, the emulsifier accounts for 0.1% to 1% of the mass of the monomer, and the chain transfer agent accounts for 3% to 7% of the mass of the monomer.

[0031] The present invention does not particularly limit the methods for preparing the first auxiliary binder, the second polymer, and the second auxiliary binder, and a general preparation method known to those skilled in the art may be used, selected depending on the type of monomer used, and may be, for example, a solution method, a slurry method, a gas phase method, or the like.

[0032] The cathode pieces of the present invention are not particularly limited as long as they achieve the objectives of the present invention. For example, the cathode pieces typically include a cathode current collector and a cathode active material layer. Here, the cathode current collector is not particularly limited and may be any cathode current collector known in the art, such as aluminum foil, aluminum alloy foil, or a composite current collector. The cathode active material layer includes a cathode active material. The cathode active material is not particularly limited and may be any cathode active material known in the art, such as at least one of nickel cobalt manganese oxide (811, 622, 523, 111), nickel cobalt lithium aluminate, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, lithium manganese iron phosphate, and lithium titanate.

[0033] The negative electrode piece of the present invention is not particularly limited as long as it achieves the objectives of the present invention. For example, the negative electrode piece typically includes a negative electrode current collector and a negative electrode active material layer. Here, the negative electrode current collector is not particularly limited and may be any negative electrode current collector known in the art, such as copper foil, aluminum foil, aluminum alloy foil, or a composite current collector. The negative electrode active material layer includes a negative electrode active material, which is not particularly limited and may be any negative electrode active material known in the art, such as at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, silicon, silicon carbon, and lithium titanate.

[0034] The substrate of the separator of the present invention may include, but is not limited to, one or more selected from polyethylene, polypropylene, polyethylene terephthalate, polyimide, and aramid. For example, the polyethylene may include at least one component selected from high-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene. In particular, polyethylene and polypropylene have excellent short-circuit prevention properties and can improve the stability of lithium-ion batteries through their shutdown effect.

[0035] The lithium-ion battery of the present invention further includes an electrolyte. The electrolyte may be one or more of a gel electrolyte, a solid electrolyte, and an electrolytic solution, and the electrolytic solution includes a lithium salt and a non-aqueous solvent. In some embodiments of the present invention, the lithium salt is one or more selected from the group consisting of LiPF, LiBF, LiAsF, LiClO, LiB(CH), LiCHSO, LiCFSO, LiN(SOCF), LiC(SOCF), LiSiF, LiBOB, and lithium difluoroborate. For example, LiPF may be used as the lithium salt because it provides high ionic conductivity and improves cycle characteristics. The non-aqueous solvent may be a carbonate ester compound, a carboxylic acid ester compound, an ether compound, another organic solvent, or a combination thereof. The carbonate ester compound may be a chain carbonate ester compound, a cyclic carbonate ester compound, a fluorocarbonate ester compound, or a combination thereof. Examples of the linear carbonate ester compound include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate ester compound include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof. Illustrative examples of fluorocarbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, and combinations thereof.Examples of the carboxylic acid ester compounds include methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, gamma-butyrolactone, decalactone, valerolactone, mevalonolactone, caprolactone, and combinations thereof. Examples of the ether compounds include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof. Examples of the other organic solvents include dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylmethylamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters, and combinations thereof.

[0036] A second aspect of the present invention provides an electrochemical device including the separator of any of the above embodiments, which has excellent low-temperature rate characteristics and low-temperature cycle characteristics.A third aspect of the present invention provides an electronic device including the electrochemical device according to any of the above embodiments of the present invention, which has excellent low-temperature rate characteristics and low-temperature cycle characteristics.

[0037] The electronic device of the present invention is not particularly limited and may be any known electronic device used in the prior art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a mobile phone, a portable facsimile machine, a portable copier, a portable printer, a stereo headset, a video recorder, an LCD television, a portable vacuum cleaner, a portable CD player, a minidisc, a walkie-talkie, an electronic notebook, a calculator, a memory card, a portable tape recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, an electric bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium ion capacitor.

[0038] The preparation process of an electrochemical device is well known to those skilled in the art and is not particularly limited in the present invention. For example, a lithium ion battery can be manufactured by stacking a positive electrode and a negative electrode with a separator interposed therebetween, wrapping or folding the stack as necessary to place the stack in a case, injecting an electrolyte into the case, and sealing the case. The separator used is the separator provided in the present invention. If necessary, an overcurrent protection element, lead plates, etc. may be provided in the case to prevent an internal pressure rise and overcharging / discharging of the lithium ion battery.

[0039] In the present invention, the term "air permeability" refers to the time required for 100 ml of air to pass through a separator, and a larger air permeability indicates a poorer air permeability of the separator, while a smaller air permeability indicates a better air permeability of the separator. The term "Dv50" refers to the particle size at which the cumulative distribution of particles is 50%, i.e., the volume content of particles smaller than this particle size accounts for 50% of all particles.

[0040] The present invention provides a separator, as well as an electrochemical device and an electronic device including the separator, the separator including a substrate and a first coating layer provided on at least one surface of the substrate, the first coating layer including a first polymer, and the number of particles of the first polymer having a maximum length of 10 μm to 30 μm within any 250 μm × 200 μm area on the surface of the first coating layer is 10 to 30. The separator of the present invention has excellent interfacial bonding performance, improves the structural stability of lithium ion batteries, and provides lithium ion batteries with better charge / discharge characteristics, particularly rate performance and cycle performance under low temperature conditions. [Brief explanation of the drawings]

[0041] In order to more clearly explain the technical solutions of the present invention and the prior art, the following will briefly describe the drawings used in the embodiments and the prior art. It is obvious that the following drawings are only some embodiments of the present invention. [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a separator according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of a separator according to the second embodiment of the present invention. [Figure 3] FIG. 3 is a schematic diagram showing the configuration of a separator according to a third embodiment of the present invention. [Figure 4] 4 is a schematic diagram showing the configuration of a separator according to a fourth embodiment of the present invention, in which 1. substrate, 2. first coating layer, 3. second coating layer, and 4. heat-resistant layer. DETAILED DESCRIPTION OF THE INVENTION

[0042] In order to clearly define the objectives, technical solutions, and advantages of the present invention, the present invention will be described in more detail below with reference to the drawings and examples. Obviously, the described examples are only some of the embodiments of the present invention, and not all of the embodiments. All other technical solutions obtained by those skilled in the art based on the embodiments of the present invention are within the protection scope of the present invention.

[0043] In the embodiments of the present invention, the present invention will be described using a lithium ion battery as an example of an electrochemical device, but the electrochemical device of the present invention is not limited to a lithium ion battery.

[0044] In one embodiment of the present invention, as shown in FIG. 1, the separator of the present invention includes a substrate 1 and a first coating layer 2 provided on one surface of the substrate 1.

[0045] In one embodiment of the present invention, as shown in FIG. 2, a first coating layer 2 is provided on one surface of a substrate 1, and a second coating layer 3 is provided on the other surface, and a heat-resistant layer 4 is further provided between the first coating layer 2 and the substrate 1.

[0046] In one embodiment of the present invention, as shown in FIG. 3, the separator includes a substrate 1, and a first coating layer 2 and a second coating layer 3 provided on two surfaces of the substrate 1, respectively.

[0047] In one embodiment of the present invention, as shown in FIG. 4, the separator includes a substrate 1 and first coating layers 2 provided on two surfaces of the substrate 1, respectively.

[0048] Example Hereinafter, the embodiments of the present invention will be described in more detail with reference to examples and comparative examples. Various tests and evaluations were carried out as follows. Unless otherwise specified, "parts" and "%" are by mass.

[0049] Measurement method and equipment: Measurement of the number of particles of the first polymer within a 250 μm × 200 μm area on the surface of the first coating layer: The separator coated with the first coating layer was cut into 10 mm x 10 mm samples, and the samples were placed under an SEM and observed at a magnification of 500x. Five 250 μm x 200 μm areas (i.e., areas that can be observed with one eyepiece) were randomly selected from the field of view, and the number of first polymer particles in the selected areas with a maximum length of 10 μm to 30 μm was recorded, and the average value was then taken, i.e., the number of first polymer particles in a unit area of ​​the first coating layer with a maximum length of 10 μm to 30 μm.

[0050] Measuring separator air permeability: After disassembly, the lithium-ion battery to be measured after discharge was removed and the separator was removed. The separator was immersed in N-methylpyrrolidone (NMP) for 30 minutes and then dried in a draft chamber at 25°C for 4 hours. After drying, the separator was removed and a measurement sample measuring 4cm x 4cm was prepared in an environment with a temperature of 25°C and humidity of less than 80%. The air permeability was measured directly using the Gurley test (100mL) using an air permeability tester. The unit of air permeability is seconds (sec), i.e., the time required for 100mL of air to pass through a separator with an area of ​​4cm x 4cm.

[0051] Separator porosity measurement: The separator sample was dried in a vacuum oven at 85°C for 2 hours, removed, and placed in a desiccator to cool before measurement. The separator was wrapped flat in A4 paper, spread flat on a blade, and pressed in a press to prepare the sample for measurement. First, the thickness of the sample was measured using a micrometer with an accuracy of 0.0001 mm, and the apparent volume V1 of the sample was calculated based on the surface area and thickness of the sample. Next, the true volume V2 of the sample was measured using a true density meter (model number AccuPycII), and the porosity = (V1 - V2) / V1 x 100% was obtained.

[0052] Measurement of Dv50 of inorganic particles, first polymer, and second polymer: The Dv50 of the inorganic particles, the first polymer, and the second polymer are each measured using a laser particle size distribution analyzer.

[0053] Measurement of adhesion between separator and electrode strip: The Chinese national standard GB / T 2790-1995 was used to measure the adhesive strength between the separator and the positive or negative electrode pieces using the 180° peel measurement standard. The separator and the positive or negative electrode pieces were cut into 54.2 mm × 72.5 mm samples, and the separator and the positive or negative electrode pieces were combined and hot-pressed in a hot press under the following hot-pressing conditions: temperature 85°C, pressure 1 MPa, and hot-pressing time 85 seconds. The combined samples were cut into 15 mm × 54.2 mm strips, and the adhesive strength between the separator and the positive or negative electrode pieces was measured using the 180° peel measurement standard.

[0054] Determination of the softening point of the first polymer: Using a general-purpose differential scanning calorimeter (DSC), 5 mg of each first polymer sample prepared in each example and comparative example was taken, heated to 150°C at a heating rate of 5°C / min, and DSC curves were collected. The softening points, i.e., softening temperatures, of the first polymers were determined from the obtained DSC curves.

[0055] Measurement of hardness of lithium-ion batteries: The hardness of the cell was measured using the three-point bending method. The cell was operated at 25°C, fully discharged to 3.0 V, and the tabs were insulated. The spacing between the lower support rods of the hardness test fixture on a universal testing machine (Instron-3365) was adjusted to 2 / 3 of the cell width. The cell was placed flat on the lower fixture, with the width perpendicular to the support rods. The upper pressing head of the fixture was adjusted to be perpendicular to the width and positioned at the center of the cell. The downward pressure was applied at a rate of 5 mm / min. The cell's deformation displacement was recorded when the upper pressing head began to contact the cell. When the displacement reached 1 mm, the corresponding resistance to deformation was taken as the cell's hardness. The lower supporting rod was arc-shaped and had a diameter of 10 mm, and the upper pressing head was arc-shaped and had a diameter of 10 mm.

[0056] Measuring the discharge rate of a lithium-ion battery: 2C discharge rate measurement: At 25°C, the formed lithium-ion battery was charged at a constant current of 0.2C up to 4.45V, then charged at a constant voltage until the current was 0.05C or less, and then allowed to stand for 30 minutes. It was then discharged at a constant current of 0.2C down to 3.0V, and the 0.2C rate discharge capacity of the lithium-ion battery was measured.

[0057] At 25°C, the lithium-ion battery was charged at a constant current of 0.2C up to 4.45V, then charged at a constant voltage until the current dropped to 0.05C or less, then allowed to stand for 30 minutes, and then discharged at a constant current of 2C down to 3.0V, and the 2C rate discharge capacity of the lithium-ion battery was measured.

[0058] 2C rate discharge capacity retention rate (%) of lithium-ion secondary battery = 2C rate discharge capacity / 0.2C rate discharge capacity × 100%.

[0059] Measurement of 0.2C discharge rate at -20°C: At 25°C, the formed lithium-ion battery was charged at a constant current of 0.2C up to 4.45V, then charged at a constant voltage until the current was 0.05C or less, and then allowed to stand for 30 minutes. It was then discharged at a constant current of 0.2C down to 3.0V, and the 0.2C rate discharge capacity of the lithium-ion battery at 25°C was measured.

[0060] At 25°C, the lithium-ion battery was charged at a constant current of 0.2C up to 4.45V, and then charged at a constant voltage until the current dropped to 0.05C or less. The cell was then placed in a -20°C environment, allowed to stand for 60 minutes, and then discharged at a constant current of 0.2C down to 3.0V. The 0.2C rate discharge capacity of the lithium-ion battery at -20°C was determined.

[0061] 0.2C rate discharge capacity retention rate (%) of lithium-ion secondary battery at -20°C = 0.2C rate discharge capacity at -20°C / 0.2C rate discharge capacity at 25°C × 100%.

[0062] Measurement of cycle characteristics of lithium-ion batteries: The first charge and discharge cycle was performed at 12°C. The battery was charged at a constant current and constant voltage at a charge current of 2C up to a maximum voltage of 4.45V, and then discharged at a constant current of 1C down to a final voltage of 3.0V. The discharge capacity of the first cycle was recorded. The above steps were repeated for 500 charge and discharge cycles, and the discharge capacity of the 500th cycle was recorded. Cycle capacity retention = (discharge capacity at the 500th cycle / discharge capacity at the first cycle) × 100%.

[0063] Example 1 <1-1. Preparation of first polymer> The reactor was evacuated and the oxygen gas was replaced with nitrogen gas. Then, deionized water, vinylidene fluoride (VDF), diisopropylbenzene hydroperoxide as an initiator, perfluoroalkyl carboxylate as an emulsifier, and isopropanol as a chain transfer agent were added into the reactor equipped with a stirrer until the pressure in the reactor reached 3.5 MPa. The deionized water was 7 times the mass of the vinylidene fluoride monomer, the initiator accounted for 0.2% of the mass of the vinylidene fluoride monomer, the emulsifier accounted for 0.5% of the mass of the vinylidene fluoride monomer, and the chain transfer agent accounted for 5% of the mass of the vinylidene fluoride monomer. The temperature was then raised to 60°C, the agitator speed was set to 80 r / min, and the polymerization reaction was initiated. At the same time, vinylidene fluoride monomer was continuously added to maintain the reactor pressure at 3.5 MPa. The reaction was stopped until the solid content of the emulsion in the reactor reached 25%, and the unreacted monomer was recovered. The polymer emulsion was then centrifuged, washed, and dried to obtain a first polymer. The softening point of the first polymer was 125°C, and the Dv50 was 12 μm.

[0064] <1-2. Preparation of separator> <1-2-1. Preparation of first coating layer> The prepared first polymer and first auxiliary binder (a copolymer formed by polymerizing, by mass percentage, 80% styrene, 10% isobutyl acrylate, and 10% acrylonitrile, with a Dv50 of 0.2 μm) were added to a mixer in a mass ratio of 90:10 and stirred uniformly. Deionized water was then added and stirred to adjust the viscosity of the slurry to 100 mPa·s and the solid content to 12%, yielding Slurry A. Slurry A was uniformly applied to one side of a 5 μm-thick PE separator substrate, with the areal density of the first coating layer being 1 g / m. 2 The mixture was dried in an oven to form a separator having the structure shown in FIG.

[0065] The produced separator was observed under SEM at 500x magnification, and within any 250 μm × 200 μm area (unit area) on the surface of the first coating layer, the number of particles of the first polymer with a maximum length of 10 μm to 30 μm was 10 (abbreviated as the number of particles in Table 1).

[0066] <1-3. Preparation of positive electrode pieces> The positive electrode active materials, lithium cobalt oxide, acetylene black, and polyvinylidene fluoride (PVDF), were mixed in a mass ratio of 94:3:3, and then N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solids content of 75%. The slurry was then uniformly mixed. The slurry was uniformly applied to one surface of a 12 μm thick aluminum foil, dried at 90°C, and cold-rolled to obtain a positive electrode piece with a positive electrode active material layer thickness of 100 μm. The above steps were then repeated on the other surface of the positive electrode piece, resulting in a positive electrode piece with a positive electrode active material layer applied to both sides. The positive electrode piece was cut into a size of 74 mm x 867 mm, tabs were welded, and it was prepared for the next step.

[0067] <1-4. Preparation of negative electrode pieces> The negative electrode active materials, artificial graphite, acetylene black, styrene 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 slurry with a solids content of 70%. The slurry was then uniformly mixed. The slurry was uniformly applied to one surface of an 8 μm-thick copper foil, dried at 110°C, and cold-rolled to obtain a negative electrode piece with a negative electrode active material layer coated on one side and a thickness of 150 μm. The above application step was then repeated on the other surface of the negative electrode piece, resulting in a negative electrode piece with a negative electrode active material layer coated on both sides. The negative electrode piece was cut into a size of 74 mm x 867 mm, and a tab was welded for further preparation.

[0068] <1-5. Preparation of electrolyte> In an environment with a water content of less than 10 ppm, 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, and then lithium hexafluorophosphate (LiPF6) was dissolved in the non-aqueous organic solvent and mixed uniformly to obtain an electrolyte solution. Here, the mass ratio of LiPF6 to the non-aqueous organic solvent was 8:92.

[0069] <1-6. Preparation of Lithium-ion Battery> The positive electrode, separator, and negative electrode pieces were stacked in this order, and the side of the separator bearing the first coating layer was brought into contact with the positive electrode piece and wound to obtain an electrode assembly. The electrode assembly was placed in an aluminum plastic film outer bag, and moisture was removed at 80°C. The prepared electrolyte solution was poured in, and the assembly was vacuum packaged, left to stand, formed, shaped, and other processes to obtain a lithium-ion battery.

[0070] Example 2 In <Preparation of separator>, the same procedure as in Example 1 was carried out, except that the solid content of slurry A was increased and the number of particles of the first polymer having a maximum length of 10 μm to 30 μm in any 250 μm × 200 μm area on the surface of the first coating layer was set to 15, as shown in Table 1.

[0071] Example 3 In <Preparation of separator>, the same procedure as in Example 1 was carried out, except that the solid content of slurry A was increased and the number of particles of the first polymer having a maximum length of 10 μm to 30 μm in any 250 μm × 200 μm area on the surface of the first coating layer was set to 20, as shown in Table 1.

[0072] Example 4 In <Preparation of separator>, the same procedure as in Example 1 was carried out, except that the solid content of slurry A was increased and the number of particles of the first polymer having a maximum length of 10 μm to 30 μm in any 250 μm × 200 μm area on the surface of the first coating layer was set to 26, as shown in Table 1.

[0073] Example 5 In <Preparation of separator>, the same procedure as in Example 1 was carried out, except that the solid content of slurry A was increased and the number of particles of the first polymer having a maximum length of 10 μm to 30 μm in any 250 μm × 200 μm area on the surface of the first coating layer was set to 30, as shown in Table 1.

[0074] Example 6 In <Preparation of separator>, a heat-resistant layer and a second coating layer were added, and the surface density of the coating of the first coating layer was set to 0.4 g / m as shown in Table 2-2. 2 The procedure was the same as in Example 1 except that the <Preparation of lithium ion battery> was different from that in Example 1.

[0075] <1-6. Preparation of separator> <1-6-1. Preparation of heat-resistant layer> Inorganic boehmite particles with a Dv50 of 2 μm and polyacrylate were mixed in a mass ratio of 90:10, and the mixture was uniformly dispersed in deionized water to form a heat-resistant layer slurry with a solid content of 50%. The resulting heat-resistant layer slurry was then uniformly coated on one side of the separator substrate using a microgravure coating method to obtain a heat-resistant layer with the corresponding thickness, which was then dried in an oven. Next, a first coating layer was prepared on the surface of the heat-resistant layer according to the <Preparation of the First Coating Layer> in Example 1.

[0076] <1-6-2. Preparation of second coating layer> A second polymer (a copolymer formed by polymerizing, by mass percentage, 80% styrene, 10% isobutyl acrylate, and 10% acrylonitrile, with a Dv50 of 0.2 μm) and a second auxiliary binder (a mixture formed by 5.5% sodium carboxymethyl cellulose and 94.5% dimethylsiloxane) were added to a mixer in a mass ratio of 91:9 and stirred uniformly. Deionized water was then added and stirred, adjusting the viscosity of the slurry to 100 mPa s and the solid content to 12%, yielding Slurry B. Slurry B was then uniformly applied to the other side of the separator substrate (i.e., the side of the separator not having the first coating layer), and the surface density of the second coating layer was 0.2 g / m. 2 The mixture was dried in an oven to form a separator having the structure shown in FIG.

[0077] The obtained separator was observed under SEM at 500x magnification, and it was found that within any 250 μm x 200 μm area (unit area) on the surface of the first coating layer, the number of particles of the first polymer with a maximum length of 10 μm to 30 μm was 25 (abbreviated as the number of particles in Table 1 and Table 2-2).

[0078] <Preparation of lithium-ion batteries> The positive electrode, separator, and negative electrode pieces were stacked in this order, with the separator's first coating layer contacting the positive electrode piece and the separator's second coating layer contacting the negative electrode piece, and then wound to obtain an electrode assembly. The electrode assembly was placed in an aluminum plastic film outer bag, and moisture was removed at 80°C. The prepared electrolyte was poured in, and the assembly was vacuum packaged, left to stand, formed, shaped, and other processes to obtain a lithium-ion battery.

[0079] Examples 7, 8, and 9 were the same as Example 6, except that in <Preparation of separator>, the surface density of the coating of the first coating layer was adjusted as shown in Table 2-2.

[0080] Examples 10, 11, and 12 were similar to Example 7, except that in <Preparation of first polymer>, a first polymer was prepared in a manner similar to (1-1) Preparation of first polymer in Example 1, and the Dv50 of the first polymer was adjusted as shown in Table 2-2.

[0081] Examples 13, 14, 15, and 16 were similar to Example 7, except that in <Preparation of First Polymer>, a first polymer was prepared in a manner similar to (1-1) Preparation of First Polymer in Example 1, and the softening point of the first polymer was adjusted as shown in Table 2-2.

[0082] Examples 17, 18, 19, 20, and 21 were the same as Example 7, except that in <Preparation of the first coating layer>, the first auxiliary binder component and content were adjusted as shown in Table 2-1.

[0083] Examples 22, 23, 24, 25, 26, and 27 were similar to Example 7, except that a first polymer was prepared in a manner similar to that of (1-1) Preparation of First Polymer in Example 1, and the components and contents of the first polymer were adjusted as shown in Table 2-1.

[0084] Examples 28, 29, 30, 31, 32, and 33 were the same as Example 7, except that in <Preparation of heat-resistant layer>, the components and Dv50 of the inorganic particles were adjusted as shown in Table 2-2.

[0085] Examples 34 and 35 were the same as Example 7, except that in <Preparation of second coating layer>, the components and contents of the second polymer and second auxiliary binder were adjusted as shown in Table 2-1.

[0086] Examples 36, 37, 38, 39, and 40 were the same as Example 7, except that in <Preparation of second coating layer>, the Dv50 of the second polymer was adjusted as shown in Table 2-2.

[0087] Examples 41, 42, and 43 were the same as Example 7, except that in <Preparation of second coating layer>, the surface density of the coating of the second coating layer was adjusted as shown in Table 2-2.

[0088] Example 44 was the same as Example 7, except that in <Preparation of First Coating Layer>, the second coating layer was not provided on the surface of the separator.

[0089] Example 45 was the same as Example 7, except that in <Preparation of First Coating Layer>, no heat-resistant layer was provided between the first coating layer and the separator substrate.

[0090] Example 46 <Preparation of separator> was the same as in Example 7, except that the solid content of slurry A was reduced and the number of particles of the first polymer having a maximum length of 10 μm to 30 μm in any 250 μm × 200 μm area on the surface of the first coating layer was set to 10 as shown in Table 2-2.

[0091] Example 47 In <Preparation of separator>, the same procedure as in Example 7 was carried out, except that the solid content of slurry A was increased and the number of particles of the first polymer having a maximum length of 10 μm to 30 μm in any 250 μm × 200 μm area on the surface of the first coating layer was set to 30, as shown in Table 2-2.

[0092] Comparative Example 1 In <Preparation of separator>, the first polymer was prepared in a manner similar to that of (1-1) Preparation of the first polymer in Example 1, and the first polymer was a copolymer formed by polymerizing 80% styrene, 10% isobutyl acrylate, and 10% acrylonitrile, on a mass percentage basis; the first auxiliary binder was a mixture consisting of 5.5% sodium carboxymethyl cellulose and 94.5% dimethyl siloxane, on a mass percentage basis; the mass ratio of the first polymer to the second polymer was 91:9; and the number of particles of the first polymer having a maximum length of 10 μm to 30 μm in any 250 μm × 200 μm area on the surface of the first coating layer was set to 0, except that the same procedure was followed as in Example 1.

[0093] Comparative Example 2 In <Preparation of separator>, the same procedure as in Example 1 was carried out, except that the solid content of slurry A was increased and the number of particles of the first polymer having a maximum length of 10 μm to 30 μm in any 250 μm x 200 μm area on the surface of the first coating layer was set to 34.

[0094] Comparative Example 3 In <Preparation of separator>, the same procedure as in Example 1 was carried out, except that the solid content of slurry A was reduced and the number of particles of the first polymer having a maximum length of 10 μm to 30 μm in any 250 μm × 200 μm area on the surface of the first coating layer was set to 6.

[0095] Comparative Example 4 In <Preparation of separator>, a first polymer was prepared in a manner similar to that of (1-1) Preparation of the first polymer in Example 1, and the first polymer was a copolymer formed by polymerizing 80% styrene, 10% isobutyl acrylate, and 10% acrylonitrile, on a mass percentage basis. The first auxiliary binder was a mixture consisting of 5.5% sodium carboxymethyl cellulose and 94.5% dimethyl siloxane, on a mass percentage basis. The mass ratio of the first polymer to the second polymer was 91:9. As shown in Table 2-2, the number of particles of the first polymer having a maximum length of 10 μm to 30 μm in any 250 μm × 200 μm area on the surface of the first coating layer was 0, which was the same as in Example 7.

[0096] Comparative Example 5 <Preparation of separator> was the same as in Example 7, except that the solid content of slurry A was increased and the number of particles of the first polymer having a maximum length of 10 μm to 30 μm in any 250 μm × 200 μm area on the surface of the first coating layer was set to 34, as shown in Table 2-2.

[0097] Comparative Example 6 <Preparation of separator> was the same as in Example 7, except that the solid content of slurry A was increased and the number of particles of the first polymer having a maximum length of 10 μm to 30 μm in any 250 μm × 200 μm area on the surface of the first coating layer was set to 6, as shown in Table 2-2.

[0098] The preparation parameters and measurement results for each of the Examples and Comparative Examples are shown in Tables 1, 2-1 and 2-2.

[0099] [Table 1]

[0100] [Table 2-1(A)] [Table 2-1(B)] [Table 2-1(C)]

[0101] [Table 2-2(A)] [Table 2-2(B)] [Table 2-2(C)]

[0102] As can be seen from Examples 1 to 5, Comparative Examples 1 to 3, and Examples 6 to 47, and Comparative Examples 4 to 6, by controlling the number of first polymer particles in the first coating layer whose maximum length is between 10 μm and 30 μm within the range of the present invention, the room temperature rate characteristics, low temperature rate characteristics, and low-temperature cycle characteristics of the lithium-ion battery can be significantly improved without significantly affecting the hardness of the lithium-ion battery. When the first coating layer does not contain the first polymer of the present invention (the number of polymer particles whose maximum length is between 10 μm and 30 μm is zero, e.g., Comparative Examples 1 and 4), the room temperature rate characteristics, low temperature rate characteristics, and low-temperature cycle characteristics of the lithium-ion battery are all poor. When the number of first polymer particles whose maximum length is between 10 μm and 30 μm is too high or too low (e.g., Comparative Examples 2, 3, 5, and 6), it is difficult to improve the room temperature rate characteristics, low-temperature rate characteristics, and low-temperature cycle characteristics of the lithium-ion battery.

[0103] The surface density of the coating of the first coating layer also generally affects the characteristics of lithium ion batteries, and as can be seen from Examples 6 to 9, if the surface density of the coating of the first coating layer is within the range of the present invention, a lithium ion battery with excellent battery hardness, rate characteristics at room temperature, rate characteristics at low temperatures, and low-temperature cycle characteristics can be obtained.

[0104] The Dv50 of the first polymer also generally affects the characteristics of a lithium ion battery, and as can be seen from Examples 10 to 12, if the Dv50 of the first polymer is within the range of the present invention, a lithium ion battery excellent in battery hardness, room temperature rate characteristics, low temperature rate characteristics, and low temperature cycle characteristics can be obtained.

[0105] The softening point of the first polymer also generally affects the characteristics of a lithium ion battery, and as can be seen from Examples 13 to 16, if the softening point of the first polymer is within the range of the present invention, a lithium ion battery excellent in battery hardness, rate characteristics at room temperature, rate characteristics at low temperatures, and low-temperature cycle characteristics can be obtained.

[0106] The components and content of the first auxiliary binder also generally affect the characteristics of lithium ion batteries, and as can be seen from Examples 17 to 21, if the components and content of the first auxiliary binder are within the ranges of the present invention, a lithium ion battery with excellent battery hardness, room temperature rate characteristics, low temperature rate characteristics, and low temperature cycle characteristics can be obtained.

[0107] The components and content of the first polymer also generally affect the characteristics of lithium ion batteries, and as can be seen from Examples 22 to 27, if the components and content of the first polymer are within the ranges of the present invention, a lithium ion battery excellent in battery hardness, room temperature rate characteristics, low temperature rate characteristics, and low temperature cycle characteristics can be obtained.

[0108] The components and Dv50 of the inorganic particles in the heat-resistant layer also generally affect the characteristics of lithium-ion batteries, and as can be seen from Examples 28 to 33, if the components and Dv50 of the inorganic particles in the heat-resistant layer are within the ranges of the present invention, a lithium-ion battery with excellent battery hardness, room-temperature rate characteristics, low-temperature rate characteristics, and low-temperature cycle characteristics can be obtained.

[0109] The components and content of the second polymer, the components and content of the second auxiliary binder, the Dv50 of the second polymer, and the surface density of the second coating layer generally affect the characteristics of lithium-ion batteries, and as can be seen from Examples 34 to 43, by keeping the components and content of the second polymer, the components and content of the second auxiliary binder, the Dv50 of the second polymer, and the surface density of the second coating layer within the ranges of the present invention, a lithium-ion battery with excellent battery hardness, room temperature rate characteristics, low temperature rate characteristics, and low temperature cycle characteristics can be obtained.

[0110] As can be seen from Examples 7, 44, and 45, by providing a heat-resistant layer and a second coating layer on the separator, the hardness, room temperature rate characteristics, low temperature rate characteristics, and low temperature cycle characteristics of the lithium ion battery can be further improved.

[0111] The above are preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A separator, a substrate and a first coating layer provided on at least one surface of the substrate; the first coating layer comprises a first polymer and a first auxiliary binder, and the number of particles of the first polymer having a maximum length of 10 μm to 30 μm is 10 to 30 within any 250 μm x 200 μm area on the surface of the first coating layer; The first polymer has a Dv50 of 3 μm to 16 μm, the first auxiliary binder comprises at least one of homopolymers and copolymers of ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, maleic acid, acrylonitrile, and butadiene; the first polymer comprises at least one of a homopolymer and a copolymer of vinylidene fluoride, hexafluoropropylene, ethylene, propylene, vinyl chloride, and chloropropylene; A separator, wherein the mass percentage of the first polymer is 85% to 95% and the mass percentage of the first auxiliary binder is 5% to 15% relative to the total mass of the first coating layer.

2. The separator according to claim 1, wherein the separator has an air permeability P of 500 sec / 100 mL to 10,000 sec / 100 mL.

3. The surface density W1 of the first coating layer of the separator is 0.4 g / m ２ ~2g / m ２ The separator according to claim 1 ,

4. The separator according to claim 1, wherein the porosity K of the separator is 30% to 65%.

5. 2. The separator according to claim 1, further comprising a heat-resistant layer, the heat-resistant layer being provided between the substrate and the first coating layer, the heat-resistant layer containing inorganic particles, and the particle diameter Dv50 of the inorganic particles being 0.5 μm to 35 μm.

6. 6. The separator of claim 5, wherein the inorganic particles include at least one of boehmite, magnesium hydroxide, alumina, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, boron nitride, and aluminum nitride.

7. 2. The separator according to claim 1, wherein the air permeability P of the separator and the areal density W1 of the first coating layer satisfy P / W1=500 to 6500.

8. 2. The separator according to claim 1, wherein the porosity K of the separator and the areal density W1 of the first coating layer satisfy K / W1=0.15 to 1.

4.

9. the separator further comprises a second coating layer, the first coating layer and the second coating layer being respectively provided on both sides of the separator, the second coating layer comprising a second polymer and a second auxiliary binder, and a ratio of the mass of the second polymer to the mass of the second auxiliary binder being 5 to 20; the second polymer comprises at least one of homopolymers and copolymers of ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, maleic acid, acrylonitrile, and butadiene; 10. The separator of claim 1, wherein the second auxiliary binder comprises at least one of sodium carboxymethyl cellulose and dimethyl siloxane.

10. 2. The separator according to claim 1, wherein the adhesive strength of the first coating layer when provided facing the positive electrode is 4 N / m to 20 N / m.

11. 10. The separator according to claim 9, wherein the adhesive strength of the second coating layer when provided facing the negative electrode is 4 N / m to 20 N / m.

12. 2. The separator according to claim 1, wherein the softening point of the first polymer is 90°C to 150°C.

13. The surface density W2 of the coating in the second coating layer of the separator is 0.1 g / m ２ ~1g / m ２ The separator according to claim 1 ,

14. 10. The separator according to claim 9, wherein, relative to the total mass of the second coating layer, a mass percentage of the second polymer is 88% to 92.5%, and a mass percentage of the second auxiliary binder is 7.5% to 12%.

15. 10. The separator according to claim 9, wherein the second polymer has a Dv50 of 0.2 μm to 8 μm.

16. The separator is a) the number of particles of the first polymer having a maximum length of 10 μm to 30 μm is 20 to 30 within any 250 μm × 200 μm area on the surface of the first coating layer; b) The surface density W1 of the coating of the first coating layer of the separator is 0.4 g / m ２ ~1g / m ２ And, c) the separator has an air permeability P of 1000 sec / 100 mL to 5000 sec / 100 mL; d) the separator further includes a heat-resistant layer, the heat-resistant layer being provided between the substrate and the first coating layer, the heat-resistant layer including inorganic particles, and the particle diameter Dv50 of the inorganic particles being 5 μm to 35 μm; The separator according to claim 1 , wherein at least one of the following is satisfied:

17. An electrochemical device comprising the separator according to any one of claims 1 to 16.

18. 20. An electronic device comprising the electrochemical device of claim 17.

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