A separator, an electrochemical device comprising the separator, and an electronic device

Abstract

A separator, an electrochemical device and an electronic device comprising the separator. The separator (30) includes a porous substrate (31) and a porous coating (32) provided on at least one surface of the porous substrate (31). The porous coating (32) includes a polymer, and the polymer includes polymer particles. In a 130 μm × 100 μm area on the surface of the porous coating (32), the number of polymer particles with a maximum diameter between 5 μm and 14 μm is 100 to 180. The large-sized polymer particles in the separator can increase the interface gap at the corners of the electrochemical device. In this way, during the charge and discharge cycles of the electrochemical device, the electrolyte at the corner interface can be well infiltrated, effectively improving the corner purple spot / black spot problem of the electrochemical device.

Description

Technical Field

[0001] The present application relates to the field of electrochemistry technology, and particularly relates to a separator, an electrochemical device including the separator, and an electronic device. Background Art

[0002] Electrochemical devices, such as batteries, are widely used in fields such as wearable devices, smart phones, drones, laptop computers, etc. due to their advantages of high working voltage, high energy density, environmental friendliness, and stable cycling. With the development of modern information technology and the expansion of the application of electrochemical devices, the comprehensive performance requirements for batteries are getting higher and higher.

[0003] As an important component in the battery, the separator is crucial for the comprehensive performance of the battery. However, when the existing separator is applied to the battery, the interface gap at the corner of the battery is small. During the charge and discharge cycle of the battery, the electrolyte is difficult to infiltrate at the corner due to extrusion, resulting in the problem of purple / black spots at the corner. Summary of the Invention

[0004] The present application provides a separator, an electrochemical device including the separator, and an electronic device to improve the problem of purple / black spots at the corner of the electrochemical device.

[0005] It should be noted that in the summary of the invention of the present application, a lithium-ion battery is used as an example of the electrochemical device to explain the present application. However, the electrochemical device of the present application is not limited to lithium-ion batteries.

[0006] In the first aspect of the present application, a separator is provided. The separator includes a porous substrate and a porous coating disposed on at least one surface of the porous substrate. The porous coating includes a polymer, and the polymer includes polymer particles. In a 130 μm × 100 μm area on the surface of the porous coating, the number of polymer particles with a maximum diameter between 5 μm and 14 μm is 100 to 180.

[0007] The separator of this application is observed by a scanning electron microscope (SEM) at a magnification of 500 times. In a region of 130 μm × 100 μm (i.e., the region observable by one eyepiece), the number of polymer particles with a maximum diameter between 5 μm and 14 μm is 100 to 180. By controlling the number of polymer particles with a maximum diameter between 5 μm and 14 μm within the above range, the large-particle-size (maximum diameter between 5 μm and 14 μm) polymers in the separator play a role in creating gaps for corner buffering in the electrochemical device, increasing the corner interface gap of the electrochemical device. In this way, during the charge-discharge cycle of the electrochemical device, the electrolyte at the corner interface can be well infiltrated. Thus, the problem of purple / black spots at the corners of the electrochemical device is effectively improved. Moreover, compared with the conventionally sized polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) commonly used in the prior art, the large-particle-size polymers used in this application have a lower softening point and are more likely to play a bonding role in the electrochemical device, increasing the bonding force between the separator and the positive or negative electrode and suppressing the deformation problem of the electrochemical device caused by negative electrode swelling. The purple or black spots in this application are the purple or black spots known in the art.

[0008] The porous coating of this application is provided on at least one surface of the porous substrate. Specifically, a porous coating is provided on one surface of the porous substrate, or porous coatings are provided on both surfaces of the porous substrate. Herein, the surfaces of the porous substrate refer to the two surfaces opposite to each other along its thickness direction. Those skilled in the art should understand that the porous coating can be provided on all or part of the surface of the porous substrate as long as the purpose of this application can be achieved. Both the porous substrate and the porous coating of this application have a pore structure. For example, the pore diameter of the porous substrate is 10 nm to 60 nm, and the porosity of the porous coating is 30% to 55%.

[0009] This application has no particular limitation on the thickness of the porous substrate and the porous coating as long as the purpose of this application can be achieved. For example, the thickness ratio of the porous coating to the porous substrate is 1:2 to 1:5, the thickness of the porous substrate is 12 μm to 40 μm, and the thickness of the porous coating can be 5 μm to 20 μm. In this application, the thickness of the porous coating refers to the thickness of a single-layer porous coating on any surface of the porous substrate.

[0010] In the present application, the material of the porous substrate may include, but is not limited to, at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Preferably, the material of the porous substrate includes polypropylene having a weight average molecular weight of 100,000 to 1,000,000. When the weight average molecular weight of polypropylene is too small (e.g., less than 100,000), the adhesion between the porous substrate and the porous coating will be affected, thereby affecting the encapsulation performance of the electrochemical device. When the weight average molecular weight of polypropylene is too large (e.g., greater than 1,000,000), the thickness uniformity of the porous coating will be affected, thereby affecting the thickness uniformity of the separator and the encapsulation performance of the electrochemical device. By controlling the weight average molecular weight of polypropylene in the porous substrate material within the above range, for example, the weight average molecular weight of polypropylene can be 100,000, 200,000, 400,000, 600,000, 800,000, 1,000,000 or any range therebetween, the encapsulation performance of the electrochemical device can be effectively improved.

[0011] In one embodiment of the present application, within a 130 μm × 100 μm area on the surface of the porous coating, the number of polymer particles with a maximum diameter less than 5 μm is 10 to 40, and the number of polymer particles with a maximum diameter greater than 14 μm is 0 to 10. By controlling the number of polymer particles with a maximum diameter less than 5 μm and the number of polymer particles with a maximum diameter greater than 14 μm within the above range, in any 130 μm × 100 μm area on the surface of the porous coating, the maximum diameter of most polymer particles is between 5 μm and 14 μm. When the particle size distribution of the polymer particles in the porous coating is in the above state, while maintaining the adhesion force, the particle size of the polymer particles is generally larger, and the large-particle-size polymers in the separator can play a role in creating gaps for buffering at the corners of the electrochemical device, increasing the corner interface gap of the electrochemical device. In this way, during the charge and discharge cycle of the electrochemical device using the separator containing the above porous coating, the electrolyte at the corner interface can be well infiltrated. Thus, the problem of corner purple / black spots of the electrochemical device is effectively improved.

[0012] In an embodiment of the present application, the particle size of the polymer particles satisfies: 1 μm ≤ Dv10 ≤ 3 μm, 4 μm ≤ Dv50 ≤ 8 μm, 7 μm ≤ Dv90 ≤ 20 μm. For example, Dv10 can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm or any range therebetween, Dv50 can be 4 μm, 5 μm, 6 μm, 7 μm, 8 μm or any range therebetween, Dv90 can be 7 μm, 9 μm, 12 μm, 15 μm, 17 μm, 20 μm or any range therebetween. Using a polymer with the above particle size is more conducive to improving the thickness uniformity of the separator, and further improving the encapsulation performance of the electrochemical device. At the same time, when the particle size of the polymer is within the above range, it is more conducive to making the maximum diameter of most polymer particles between 5 μm and 14 μm in any 130 μm × 100 μm area on the surface of the porous coating. When the particle size distribution of the polymer particles in the porous coating is in the above state, while maintaining the adhesion, the particle size of the polymer particles is generally large, and the large-particle-size polymers in the separator can play a role in creating gaps at the corners of the electrochemical device, increasing the corner interface gap of the electrochemical device. In this way, during the charge and discharge cycle of the electrochemical device using the separator containing the above porous coating, the electrolyte at the corner interface can be well infiltrated. Thus, the problem of purple / black spots at the corners of the electrochemical device is effectively improved. In the present application, Dv10 represents the particle size at which, in the particle size distribution based on volume, starting from the small particle size side, the cumulative volume reaches 10%. Dv50 represents the particle size at which, in the particle size distribution based on volume, starting from the small particle size side, the cumulative volume reaches 50%. Dv90 represents the particle size at which, in the particle size distribution based on volume, starting from the small particle size side, the cumulative volume reaches 90%.

[0013] In an embodiment of the present application, the components of the polymer include at least one of polyvinylidene fluoride, polyacrylate, styrene-butadiene rubber, polyacrylamide or polyolefin; the polyacrylate is polymerized from at least one of the following monomers: styrene, butadiene, methyl methacrylate, acrylonitrile, acrylic acid, methacrylic acid, isobutyl acrylate, isobutyl methacrylate, butyl acrylate, butyl methacrylate, isooctyl acrylate, isooctyl methacrylate, methyl acrylate, glycidyl methacrylate; the monomers constituting the polyolefin are C 19 to C 35Olefins. Preferably, the components of the polymer include at least one of polyvinylidene fluoride, polystyrene-isobutyl acrylate, polystyrene-iso-octyl acrylate, or styrene-butadiene rubber. In this application, polyvinylidene fluoride includes polyvinylidene fluoride homopolymer and PVDF-HFP, and the mass content of hexafluoropropylene (HFP) in PVDF-HFP is greater than 0% and less than or equal to 5%. The polymers of the above components have good thermal stability and electrolyte resistance. The cross-linked structure they possess makes them randomly distributed in the porous coating, and they have a relatively high adhesion, ensuring the adhesion between the porous substrate and the porous coating, improving the gel phenomenon of the separator, and further improving the encapsulation performance of the electrochemical device. In addition, the separator containing the above polymer also has good adhesion with the positive electrode and the negative electrode, which can inhibit the deformation problem caused by the swelling of the negative electrode, and further improve the structural stability of the electrochemical device. Especially for polymers containing polar functional groups such as carboxyl or hydroxyl groups, they can improve the affinity of the electrolyte to fully wet the separator, and improve the adhesion between the separator and the positive electrode, and between the separator and the negative electrode. On the basis of improving the gel phenomenon of the separator, it is more conducive to improving the structural stability of the electrochemical device. In addition, the above polymers are of low price, which is beneficial to controlling the cost of the separator.

[0014] In an embodiment of the present application, the porous coating further includes an auxiliary binder, a wetting agent, and a thickening agent; based on the mass of the porous coating, the mass percentage of the polymer is 76.5% to 92.5%, the mass percentage of the auxiliary binder is 4% to 20%, the mass percentage of the wetting agent is 3% to 5%, and the mass content of the thickening agent is 0.5% to 1%. Preferably, the mass percentage of the polymer is 80% to 90%, the mass percentage of the auxiliary binder is 5% to 10%, the mass percentage of the wetting agent is 3%, and the mass content of the thickening agent is 0.5%. For example, the mass of the polymer can be 76.5%, 78%, 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 92.5% or any range therebetween, the mass percentage of the auxiliary binder can be 4%, 5%, 10%, 15%, 17.5% or any range therebetween, the mass percentage of the thickening agent can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or any range therebetween, and the mass percentage of the wetting agent can be 3%, 3.5%, 4%, 4.5%, 5% or any range therebetween. If the mass percentage of the polymer is too low (e.g., less than 76.5%), it will affect the adhesion between the porous substrate and the porous coating, such as the adhesion force and / or the adhesion area, etc.; if the mass percentage of the polymer is too high (e.g., higher than 92.5%), the polymer is likely to block the pore structure of the porous substrate and affect the transport of lithium ions, and even cause lithium deposition and corner purple / black spot phenomena in the electrochemical device. By controlling the mass percentages of the polymer, auxiliary binder, wetting agent, and thickening agent in the porous coating within the above ranges, the obtained separator has good thickness uniformity, and the large-particle-size polymer in the separator increases the interface gap at the corners of the electrochemical device. In this way, during the charge and discharge cycles of the electrochemical device, the electrolyte at the corner interface can be well infiltrated, effectively improving the corner purple / black spot problem of the electrochemical device. The present application places no particular restrictions on the auxiliary binder, thickening agent, and wetting agent, as long as the objectives of the present application can be achieved. For example, the auxiliary binder can include, but is not limited to, at least one of cyclohexyl methacrylate, isobutyl acrylate, or methyl methacrylate, the thickening agent can include, but is not limited to, at least one of sodium carboxymethyl cellulose, alginic acid, or gelatin, and the wetting agent can include, but is not limited to, at least one of alkylnaphthalene sulfonate, sodium dodecylbenzenesulfonate, or polyoxyethylene fatty alcohol ether.

[0015] In an embodiment of the present application, the glass transition temperature (Tg) of the polymer is 40°C to 65°C. When the Tg of the polymer is too low (e.g., below 40°C), during the post-treatment of the separator (e.g., drying treatment), it is easy for adhesion to occur between the porous substrate and the porous coating, clogging the pore structures of the porous substrate and the porous coating, affecting the transport of lithium ions, and resulting in lithium deposition and corner purple / black spot phenomena in the electrochemical device. When the Tg of the polymer is too high (e.g., above 65°C), it will affect the adhesion between the porous substrate and the porous coating, making the electrochemical device at risk of deformation due to insufficient adhesion. For example, the Tg of the polymer can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or any range therebetween. By regulating the Tg of the polymer within the above range, on the basis of improving the corner purple / black spot problem of the electrochemical device, other performances of the electrochemical device will not be affected, such as the transport performance of lithium ions and the structural stability of the electrochemical device, etc.

[0016] In an embodiment of the present application, the swelling degree of the polymer is 50% to 150%. When the swelling degree of the polymer is too small (e.g., less than 50%), it will affect the adhesion between the porous substrate and the porous coating, such as the adhesion force and / or adhesion area, etc. When the swelling degree of the polymer in the test electrolyte is too large (e.g., greater than 150%), the polymer is likely to clog the pore structure of the porous substrate, affecting the transport of lithium ions, and even resulting in lithium deposition and black spot phenomena in the electrochemical device. By regulating the swelling degree of the polymer within the above range, for example, the swelling degree of the polymer can be 50%, 60%, 70%, 80%, 90%, 100%, 110%, 120%, 130%, 140%, 150% or any range therebetween, the adhesion between the porous substrate and the porous coating is ensured, and the gel phenomenon of the separator is also improved, thus being beneficial to improving the corner purple / black spot problem of the electrochemical device. In the present application, the above swelling degree is the swelling degree well-known in the art.

[0017] In an embodiment of the present application, the sphericity of the polymer is greater than or equal to 0.7 and less than 1.0. When the sphericity of the polymer is too small (e.g., less than 0.7), the polymer dissolves in the pore structures covering the porous substrate, affecting the transport of lithium ions and resulting in lithium deposition and corner purple / black spot phenomena in the electrochemical device. By regulating the sphericity of the polymer within the above range, for example, the sphericity of the polymer can be 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.99 or any range therebetween, on the basis of improving the corner purple / black spot problem of the electrochemical device, the transport performance of lithium ions in the electrochemical device will not be affected either, such as the kinetic performance. In the present application, the above sphericity is the sphericity known in the prior art.

[0018] In one embodiment of the present application, the adhesion of the porous coating is from 2 N / m to 6 N / m. When the adhesion of the porous coating is too low (e.g., less than 2 N / m), the electrochemical device is prone to deformation in the later stage of the charge-discharge cycle. When the adhesion of the porous coating is too high (e.g., greater than 6 N / m), problems such as corner purple / black spots are likely to occur in the main area outside the corner area of the electrochemical device due to poor electrolyte infiltration. Controlling the adhesion of the porous coating within the above range is more conducive to improving the problems of corner purple / black spots and deformation in the later stage of the cycle of the electrochemical device. In the present application, the adhesion of the porous coating is the wet pressing adhesion.

[0019] In one embodiment of the present application, the water contact angle of the porous coating is from 60° to 90°. By controlling the water contact angle of the porous coating within the above range, for example, the water contact angle of the porous coating can be 60°, 61°, 70°, 75°, 80°, 85°, 90° or any range therebetween, indicating that the separator has good wettability and can be fully infiltrated by the electrolyte. In the present application, the above water contact angle is the water contact angle known in the prior art.

[0020] In one embodiment of the present application, the areal density of the porous coating is 0.1 g / m 2 to 0.4 g / m 2 . When the areal density of the porous coating is too small (e.g., less than 0.1 g / m 2 ), it will affect the adhesion between the porous substrate and the porous coating. When the areal density of the porous coating is too large (e.g., greater than 0.4 g / m 2 ), it will affect the lithium ion transport and cause lithium deposition and corner purple / black spot phenomena in the electrochemical device. By controlling the areal density of the porous coating within the range of the present application, for example, the areal density of the porous coating can be 0.1 g / m 2 , 0.15 g / m 2 , 0.2 g / m 2 , 0.25 g / m 2 , 0.3 g / m 2 , 0.35 g / m 2 , 0.4 g / m 2 or any range therebetween, on the basis of improving the problem of corner purple / black spots of the electrochemical device, it will not affect the lithium ion transport performance in the electrochemical device.

[0021] In an embodiment of the present application, the thickness covariance (COV) value of the separator is from 0.01 to 0.02. For example, the thickness COV of the separator can be 0.01, 0.012, 0.014, 0.016, 0.018, 0.02 or any range therebetween, indicating that the separator has good thickness consistency, which is beneficial to improving the encapsulation performance of the electrochemical device. For example, for an electrochemical device with multiple tabs, the winding excellent rate of the electrochemical device can be improved. In the present application, the above-mentioned tab and winding excellent rate are both well-known tabs and winding excellent rates in the art, and the above thickness COV is the well-known thickness COV in the prior art.

[0022] In an embodiment of the present application, the thickness difference value of the separator is from 0 μm to 3.3 μm; for example, the thickness difference of the separator can be 0 μm, 1 μm, 2 μm, 3 μm, 3.1 μm, 3.2 μm, 3.3 μm or any range therebetween, indicating that the separator has good thickness consistency, which is beneficial to improving the encapsulation performance of the electrochemical device. For example, for an electrochemical device with multiple tabs, the winding excellent rate of the electrochemical device can be improved.

[0023] In an embodiment of the present application, the ionic resistance of the separator is from 0.5 Ω to 1.5 Ω. For example, the ionic resistance of the separator can be 0.5 Ω, 0.7 Ω, 0.9 Ω, 1.1 Ω, 1.3 Ω, 1.5 Ω or any range therebetween. When the ionic resistance of the separator is too small (e.g., less than 0.5 Ω), the ionic transport rate of the separator is relatively fast, and the electrochemical device is prone to heat generation, affecting the safety performance of the electrochemical device. When the ionic resistance of the separator is too large (e.g., greater than 1.5 Ω), the electrochemical device is more likely to have purple / black spot problems. Controlling the ionic resistance of the separator within the above range is more conducive to improving the purple / black spot problems at the corners of the electrochemical device.

[0024] The present application does not particularly limit the preparation method of the separator, as long as the object of the present application can be achieved. For example, the preparation method of the separator may include, but is not limited to, the following steps: adding the substances used in the porous coating (such as polymers, binders, wetting agents, thickeners, etc.) into a solvent and mixing evenly to obtain a porous coating slurry, then coating the porous coating slurry on the surface of the porous substrate, and drying to obtain the separator. Among them, the present application does not particularly limit the above-mentioned solvent, as long as the object of the present application can be achieved. For example, the solvent may include, but is not limited to, at least one of water, ethanol, N-methylpyrrolidone (NMP), or dimethylacetamide. The present application does not particularly limit the above-mentioned coating method, as long as the object of the present application can be achieved. For example, the rotary spraying method and the microgravure coating method, etc., and the microgravure coating method is preferred. The adoption of the microgravure coating method is more conducive to improving the corner purple spot / black spot problem of the electrochemical device. At the same time, the separator prepared by the microgravure coating method has better thickness consistency. At the same time, due to the further selection of the substances used in the porous coating in the present application, the separator is also more resistant to electrolytes and high temperatures, thus being more conducive to solving the gel problem of the high-temperature sprayed separator, and the production cost is also lower.

[0025] The second aspect of the present application provides an electrochemical device, which includes the separator in any of the above embodiments.

[0026] In an embodiment of the present application, the electrochemical device further includes an electrolyte, and the electrolyte includes a carboxylic acid ester; based on the mass of the electrolyte, the mass percentage content of the carboxylic acid ester is 10% to 65%. When the mass percentage content of the carboxylic acid ester is too high (for example, higher than 60%), it will affect the high-temperature performance of the electrochemical device. By controlling the mass percentage content of the carboxylic acid ester within the above range, for example, the mass percentage content of the carboxylic acid ester can be 10%, 20%, 30%, 40%, 50%, 60%, 65%, or any range therebetween. On the basis of improving the corner purple spot / black spot problem of the electrochemical device, it is beneficial to improve the high-temperature performance of the electrochemical device.

[0027] In an embodiment of the present application, the carboxylic acid ester includes at least one of butyl propionate, amyl propionate, γ-butyrolactone, γ-valerolactone, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate, or ethyl pivalate. The above-mentioned carboxylic acid esters are not likely to react with the above-mentioned separator, which is beneficial to inhibiting the gel phenomenon of the separator, thereby improving the encapsulation performance of the electrochemical device, and the setting of large-particle-size polymers effectively improves the corner purple spot / black spot problem of the electrochemical device.

[0028] In this application, the electrolyte may further include other non-aqueous solvents. There are no particular limitations on the other non-aqueous solvents in this application, as long as the objectives of this application can be achieved. For example, it may include at least one of carbonate compounds, ether compounds, or other organic solvents. The above carbonate compounds may include at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The above chain carbonate compounds may include at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or ethyl methyl carbonate (EMC). The above other cyclic carbonates may include at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinylene ethylene carbonate (VEC). The fluorinated carbonate compounds may include at least one of 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, or trifluoromethyl ethylene carbonate. The above ether compounds may include at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxane, 1,4-dioxane, or 1,3-dioxolane. The above other organic solvents may include at least one of ethyl vinyl sulfone, methyl isopropyl sulfone, isopropyl sec-butyl sulfone, sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or phosphate esters. Based on the mass of the electrolyte, the mass percentage content of the above other non-aqueous solvents is 5% to 80%, such as 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any range therebetween.

[0029] In this application, the electrolyte may further include a lithium salt. There are no particular limitations on the lithium salt in this application, as long as the objectives of this application can be achieved. For example, the lithium salt may include at least one of lithium hexafluorophosphate (LiPF6), LiAsF6, LiClO4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, or LiSiF6, and preferably LiPF6.

[0030] In this application, the above-mentioned positive electrode is the positive electrode in an electrochemical device. The positive electrode generally includes a positive electrode current collector and a positive electrode material layer. In this application, there is no particular limitation on the positive electrode current collector, as long as the purpose of this application can be achieved. For example, it may include, but is not limited to, aluminum foil, aluminum alloy foil, or composite current collector, etc. In this application, there is no particular limitation on the thickness of the positive electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness is 8 μm to 12 μm. In this application, the positive electrode material layer can be disposed on one surface in the thickness direction of the positive electrode current collector, or can be disposed on both surfaces in the thickness direction of the positive electrode current collector. It should be noted that the "surface" here can be the entire area of the positive electrode current collector, or can be a partial area of the positive electrode current collector. There is no particular limitation in this application, as long as the purpose of this application can be achieved.

[0031] In this application, the positive electrode material layer includes a positive electrode active material. There is no particular limitation on the positive electrode active material in this application, as long as the purpose of this application can be achieved. For example, it may include, but is not limited to, at least one of composite oxides, sulfides, selenides, or halides of lithium or transition metal elements. There is no particular limitation on the above-mentioned transition metal elements in this application, as long as the purpose of this application can be achieved. For example, it may include at least one of nickel, manganese, cobalt, or iron. Specifically, the positive electrode active material may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(Ni a1 Co b1 Mn c1 )O2 (0 < a1 < 1, 0 < b1 < 1, 0 < c1 < 1, a1 + b1 + c1 = 1), LiMn2O4LiNi 1-y1 Co y1 O2 (0 < y1 < 1), LiCo l-y2 Mn y2 O2 (0 < y2 < 1), LiNi l-y3 Mn y3 O2 (0 < y3 < 1), Li(Ni a2 Mn b2 Co c2 )O4 (0 < a2 < 2, 0 < b2 < 2, 0 < c2 < 2, a2 + b2 + c2 = 2), LiMn 2-z1 Ni z1 O4 (0 < z1 < 2), LiMn 2-z2 Co z2 O4 (0 < z2 < 2), Li(Ni a3 Co b3 Al c3 )O2 (0 < a3 < 1, 0 < b3 < 1, 0 < c3 < 1, a3 + b3 + c3 = 1), LiCoPO4 or LiFePO4, or at least one of them.

[0032] The positive electrode material layer may further include a binder. There is no particular limitation on the binder in this application, as long as the purpose of this application can be achieved. For example, it may include, but is not limited to, at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0033] In this application, the positive electrode material layer may further include a conductive agent. There is no particular limitation on the conductive agent in this application, as long as the purpose of this application can be achieved. For example, it may include, but is not limited to, at least one of natural graphite, artificial graphite, conductive carbon black (SuperP), carbon nanotubes (CNTs), carbon fiber, flake graphite, Ketjen black, graphene, metal materials, or conductive polymers. The above carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above carbon fiber may include, but is not limited to, vapor-grown carbon fiber (VGCF) and / or nanofiber. The above metal materials may include, but are not limited to, metal powder and / or metal fiber. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole.

[0034] Optionally, the positive electrode may further include a conductive layer, which is located between the positive electrode current collector and the positive electrode material layer. There is no particular limitation on the composition of the conductive layer in this application. It may be a commonly used conductive layer in the art. For example, it may include, but is not limited to, the above conductive agent and the above binder.

[0035] In this application, the above negative electrode is the negative electrode in the electrochemical device. The negative electrode generally includes a negative electrode current collector and a negative electrode material layer. There is no particular limitation on the negative electrode current collector in this application, as long as the purpose of this application can be achieved. For example, it may include, but is not limited to, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector, etc. In this application, there is no particular limitation on the thickness of the current collector of the negative electrode, as long as the purpose of this application can be achieved. For example, the thickness is 4 μm to 12 μm. In this application, the negative electrode material layer may be disposed on one surface in the thickness direction of the negative electrode current collector, or may be disposed on both surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here may be the entire area of the negative electrode current collector or a partial area of the negative electrode current collector. There is no particular limitation in this application, as long as the purpose of this application can be achieved.

[0036] In this application, the negative electrode material layer includes a negative electrode active material. The negative electrode active material is not particularly limited as long as the object of this application can be achieved. For example, it may include, but is not limited to, at least one of a material that can reversibly intercalate / deintercalate lithium ions, lithium metal, a lithium metal alloy, a material that can dope / de-dope lithium, or a transition metal oxide.

[0037] The material that can reversibly intercalate / deintercalate lithium ions may include, but is not limited to, carbon materials. The carbon materials include crystalline carbon and / or amorphous carbon. The crystalline carbon may include, but is not limited to, natural graphite, artificial graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase carbon microbeads, mesophase pitch, or high-temperature calcined carbon (such as petroleum coke or coke derived from coal tar pitch) that is amorphous or in the form of plates, flakes, spheres, or fibers. The amorphous carbon may include, but is not limited to, at least one of soft carbon, hard carbon, mesophase pitch carbonization products, or calcined coke. The lithium metal alloy includes lithium and at least one metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, or Sn. The material that can dope / de-dope lithium may include, but is not limited to, Si, SiO x (0 < x ≤ 2), Si / C composite, Si-Q alloy (where Q includes at least one of alkali metals, alkaline earth metals, Group 13 to Group 16 elements, transition elements, and rare earth elements, but is not Si), Sn, SnO2, Sn-C composite, Sn-R (where R includes at least one of alkali metals, alkaline earth metals, Group 13 to Group 16 elements, transition elements, and rare earth elements, but is not Sn), etc. Q and R each independently include at least one of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, or Po. The transition metal oxide may include, but is not limited to, vanadium oxide and / or lithium vanadium oxide.

[0038] In this application, a conductive agent may also be included in the negative electrode material layer. The conductive agent in this application is not particularly limited as long as the object of this application can be achieved. For example, it may include, but is not limited to, at least one of the above conductive agents.

[0039] In this application, a binder may also be included in the negative electrode material layer. The binder in this application is not particularly limited as long as the object of this application can be achieved. For example, it may include, but is not limited to, at least one of the above binders.

[0040] Optionally, the negative electrode may further include a conductive layer located between the negative electrode current collector and the negative electrode material layer. The present application places no particular limitation on the composition of the conductive layer, which may be a commonly used conductive layer in the art and may include, but is not limited to, the above-mentioned conductive agent and the above-mentioned binder.

[0041] The electrochemical device of the present application is not particularly limited and may include any device that undergoes an electrochemical reaction. In some embodiments, the electrochemical device may include, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery, etc.

[0042] The preparation process of the electrochemical device is well-known to those skilled in the art and is not particularly limited in the present application. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, the separator, and the negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain the electrochemical device; or stacking the positive electrode, the separator, and the negative electrode in sequence, and then fixing the four corners of the entire laminated structure with tape to obtain a laminated electrode assembly, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain the electrochemical device. In addition, an overcurrent protection element, a guide plate, etc. may be placed in the packaging bag as needed to prevent the pressure inside the electrochemical device from rising and overcharging and discharging.

[0043] The third aspect of the present application provides an electronic device including the electrochemical device in any of the above embodiments. The electronic device of the present application is not particularly limited and may be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a minidisc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flash, a camera, a large household battery, and a lithium ion capacitor, etc.

[0044] The present application provides a separator, an electrochemical device and an electronic device comprising the separator. The separator includes a porous substrate and a porous coating disposed on at least one surface of the porous substrate. The porous coating includes a polymer, and the polymer includes polymer particles. In a 130 μm × 100 μm area on the surface of the porous coating, the number of polymer particles with a maximum diameter between 5 μm and 14 μm is 100 to 180. The large-sized polymers in the separator provided by the above solution can play a role in creating gaps at the corners for buffering, increasing the interface gap at the corners of the electrochemical device. In this way, during the charge and discharge cycles of the electrochemical device, the electrolyte at the corner interface can be well infiltrated, effectively improving the purple spot / black spot problem at the corners of the electrochemical device. Moreover, compared with the prior art, the large-sized polymer particles used in the present application have a lower softening point and are more likely to play a bonding role in the electrochemical device, increasing the bonding force between the separator and the positive electrode or the negative electrode, and suppressing the deformation problem of the electrochemical device caused by the swelling of the negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the embodiments of the present application and the prior art, the following briefly introduces the drawings required for use in the embodiments and the prior art. Obviously, the drawings described below are only some embodiments of the present application, and those of ordinary skill in the art can also obtain other drawings based on these drawings.

[0046] Figure 1 Schematic cross-sectional structure diagram of the separator in an embodiment of the present application;

[0047] Figure 2 Schematic cross-sectional structure diagram of the separator in another embodiment of the present application;

[0048] Figure 3 SEM photographs of polymer particles on the surface of the porous coating in Examples 1-3 of the present application;

[0049] Figure 4 SEM photograph of polymer particles on the surface of the porous coating in Comparative Example 1 of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] In order to make the objectives, technical solutions and advantages of the present application clearer, the following further elaborates on the present application with reference to the accompanying drawings and by way of examples. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application fall within the scope of protection of the present application.

[0051] It should be noted that in the specific embodiments of the present application, a lithium-ion battery is used as an example of the electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to lithium-ion batteries.

[0052] As shown Figure 1 in FIG. 1, the separator 30 includes a porous substrate 31 and a porous coating 32 provided on one surface of the porous substrate 31 in the thickness direction thereof. It can be understood that the porous coating 32 can also be provided on both surfaces of the porous substrate 31 in the thickness direction thereof (as shown Figure 2 in FIG. 2).

[0053] Hereinafter, examples and comparative examples will be given to more specifically illustrate the embodiments of the present application. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0054] Testing methods and equipment:

[0055] Measurement of the number of polymer particles in a 130 μm × 100 μm area on the surface of the porous coating:

[0056] The separator coated with the porous coating is cut into 10 mm × 10 mm samples, and then the samples are placed under SEM and observed at a magnification of 500 times. Five arbitrary 130 μm × 100 μm areas (i.e., the areas that can be observed under one eyepiece) are selected in the field of view, and the numbers of polymer particles with a maximum diameter less than 5 μm, a maximum diameter between 5 μm and 14 μm, and a maximum diameter greater than 14 μm in the selected areas are respectively recorded, and then the average values are respectively taken, which are respectively the numbers of polymer particles with a maximum diameter less than 5 μm, a maximum diameter between 5 μm and 14 μm, and a maximum diameter greater than 14 μm in a 130 μm × 100 μm area of the porous coating.

[0057] Measurement of the Tg of the polymer:

[0058] The Tg of the polymer is measured using a differential scanning calorimeter.

[0059] Measurement of the swelling degree of the polymer:

[0060] The polymer is added to water to obtain an emulsion with a solid content of 30 wt%. The emulsion is coated on a glass substrate and dried at 85°C to obtain a polymer film. A polymer film with a mass of m1 is placed in a test electrolyte and soaked at 85°C for 6 h, and the mass of the polymer film at this time is recorded as m2. The swelling degree of the polymer = (m2 - m1) / m1 × 100%. Each example or comparative example is tested 3 times, and the average value is taken as the final swelling degree of the polymer.

[0061] The test electrolyte is composed of an organic solvent and lithium hexafluorophosphate. The organic solvent is a mixture of EC, PC, and DMC in a mass ratio of 7:2:1, and the concentration of lithium hexafluorophosphate is 1 mol / L.

[0062] Testing of the particle size of polymer particles:

[0063] Referring to the national standard GB / T 19077-2016 (Method of Laser Diffraction for Particle Size Distribution), use a laser particle size analyzer (such as Malvern Master Size 3000) to measure Dv10, Dv50, and Dv90.

[0064] Testing of the water contact angle of the porous coating:

[0065] The test is carried out using a water contact angle tester.

[0066] Thickness testing:

[0067] Testing of the thickness range and COV of the separator: Measure 1 point every 5 mm along the length direction of the separator using a micrometer, with a total of 30 points tested, and then calculate the thickness range and COV of the separator. Among them, the thickness range and COV are the thickness range and COV known in the prior art, and can be calculated according to the methods known in the prior art.

[0068] Testing of the wet pressing adhesion:

[0069] Fully charge and disassemble the lithium-ion battery to obtain the part where the separator is combined with the positive electrode. Cut the combined part into strip samples of 15 mm×54.2 mm, and test the adhesion between the porous coating of the separator and the positive electrode (positive electrode material layer) according to the national standard GB / T 2792-1998 (Test Method for 180° Peel Strength of Pressure-Sensitive Adhesive Tapes).

[0070] Judgment of gel phenomenon:

[0071] After discharging the lithium-ion batteries in each example and comparative example, disassemble them and observe whether there is a gel-like substance inside the lithium-ion battery. If there is a gel-like substance, the separator shows a gel phenomenon and is recorded as "yes"; if there is no gel-like substance, the separator does not show a gel phenomenon and is recorded as "no".

[0072] Judgment of lithium plating degree:

[0073] Place the lithium-ion battery in a constant temperature oven at 0°C and let it stand for 60 min to make the lithium-ion battery reach a constant temperature. Charge the lithium-ion battery that has reached a constant temperature at a constant current of 1C to 4.45V at 0°C, then charge it at a constant voltage of 4.45V to 0.025C, let it stand for 5 min, and then discharge it at a constant current of 1C to 3.0V; this is one charge-discharge cycle. After 10 charge-discharge cycles, charge it at a constant current of 1C to 4.45V again, and then charge it at a constant voltage of 4.45V to 0.025C to obtain a fully charged battery after 10 cycles. Disassemble the battery in a dry room with a humidity less than 5%, and take pictures to record the state of the negative electrode plate.

[0074] Judge the degree of lithium plating in lithium-ion batteries according to the following criteria:

[0075] No lithium plating: There is no lithium deposition on the surface of the negative electrode sheet;

[0076] Slight lithium plating: The lithium deposition area on the surface of the negative electrode sheet is less than 10%;

[0077] Moderate lithium plating: The lithium deposition area on the surface of the negative electrode sheet is 10% to 30%;

[0078] Severe lithium plating: The lithium deposition area on the surface of the negative electrode sheet is greater than 30%.

[0079] Test for purple / black spots:

[0080] Place the lithium-ion battery in a constant temperature oven at 0°C and let it stand for 60 minutes to make the lithium-ion battery reach a constant temperature. Charge the lithium-ion battery that has reached a constant temperature at a constant current of 1C to 4.45V at 0°C, then charge it at a constant voltage of 4.45V to 0.025C, let it stand for 5 minutes, and then discharge it at a constant current of 1C to 3.0V; this is one charge-discharge cycle. After 500 charge-discharge cycles, charge it at a constant current of 1C to 4.45V again, and then charge it at a constant voltage of 4.45V to 0.025C to obtain a fully charged battery after 500 cycles. Disassemble the battery in a dry room with a humidity of less than 5%, and take pictures to record whether there are purple / black spots at the corner interface of the negative electrode sheet. If there are purple / black spots, it means that the lithium-ion battery has purple / black spots and is recorded as "yes"; if there are no purple / black spots, it means that the lithium-ion battery does not have purple / black spots and is recorded as "no".

[0081] Test for winding yield:

[0082] Use a winding device to continuously produce 1000 lithium-ion batteries, and count the number of lithium-ion batteries scrapped due to ear misalignment; Winding yield = (1 - number of ear misalignment scrapped / 1000) × 100%. Among them, when the misalignment is severe and welding cannot be performed, it is determined as ear misalignment.

[0083] Example 1-1

[0084] <Preparation of the positive electrode>

[0085] The positive electrode active material LiCoO2, the conductive agent conductive carbon black, and the binder polyvinylidene fluoride are mixed at a mass ratio of 96:2:2, N-methylpyrrolidone (NMP) is added, and they are stirred evenly under the action of a vacuum mixer to obtain a positive electrode paste, where the solid content of the positive electrode paste is 70 wt%. The positive electrode paste is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12 μm, and the aluminum foil is dried at 120 °C for 1 h to obtain a positive electrode with a positive electrode material layer coated on one side. The above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode with a positive electrode material layer coated on both sides. Then, after cold pressing, slicing, and slitting, it is dried under vacuum conditions at 120 °C for 1 h to obtain a positive electrode with a specification of 74 mm × 867 mm.

[0086] <Preparation of the negative electrode>

[0087] The negative electrode active material graphite, the binder styrene-butadiene rubber, and the negative electrode thickener sodium carboxymethyl cellulose are mixed at a mass ratio of 97.4:1.4:1.2, deionized water is added, and they are stirred evenly under the action of a vacuum mixer to obtain a negative electrode paste, where the solid content of the negative electrode paste is 75 wt%. The negative electrode paste is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 12 μm, and the copper foil is dried at 120 °C to obtain a negative electrode with a negative electrode material layer coated on one side and a coating thickness of 130 μm. The above steps are repeated on the other surface of the aluminum foil to obtain a negative electrode with a negative electrode material layer coated on both sides. Then, after cold pressing, slicing, and slitting, it is dried under vacuum conditions at 120 °C for 1 h to obtain a negative electrode with a specification of 78 mm × 875 mm.

[0088] <Preparation of the electrolyte>

[0089] In an argon atmosphere glove box with a water content < 10 ppm, EC, PC, and DMC are mixed at a mass ratio of 3:2.5:4.5 to obtain an organic solvent, and then lithium salt lithium hexafluorophosphate is added to the organic solvent to obtain an electrolyte. Among them, the concentration of the lithium salt is 1 mol / L.

[0090] <Preparation of the separator>

[0091] Cyclohexyl methacrylate and isobutyl acrylate were mixed in a mass ratio of 5:95 to obtain an auxiliary binder, and the polymer styrene-isooctyl acrylate copolymer, the auxiliary binder, the thickener sodium carboxymethyl cellulose and the wetting agent polyoxyethylene fatty alcohol ether were mixed in a mass ratio of 90:6.5:0.5:3, and stirred evenly after adding water to obtain a porous coating slurry with a solid content of 10wt%. The porous coating slurry was uniformly coated on one surface of a porous substrate with a thickness of 16μm by a micro-concave roller coating method, and then dried at 45°C to obtain a diaphragm coated with a porous coating on one side. Repeat the above steps to obtain a diaphragm coated with a porous coating on both sides. The polymer has a Dv10 of 2.5 μm, a Dv50 of 5 μm, a Dv90 of 9.5 μm, a sphericity of 0.8, a Tg of 50°C, a mass ratio of monomer styrene to isooctyl acrylate in the styrene-isooctyl acrylate copolymer of 9:1, a porous substrate material is polypropylene with a weight average molecular weight of 1,000,000, a pore size of the porous substrate of 30 nm, and a surface density of the porous coating of 0.2 g / m 2 , the thickness of the porous coating is 14 μm.

[0092] <Preparation of lithium-ion batteries>

[0093] The positive electrode, separator and negative electrode prepared above are stacked in order, with the separator placed between the positive electrode and the negative electrode to play a role of isolation, and then wound to obtain an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, and after drying, the electrolyte is injected, and a lithium-ion battery is obtained through vacuum packaging, standing, formation, degassing, trimming and other processes.

[0094] Example 1-2 to Example 1-9

[0095] Except for adjusting the relevant preparation parameters according to Table 1-1, the rest is the same as Example 1-1.

[0096] Example 2-1 to Example 2-6

[0097] Except for adjusting the relevant preparation parameters according to Table 2-1, the rest is the same as Example 1-3.

[0098] Example 3-1 to Example 3-4

[0099] Except for adjusting the relevant preparation parameters according to Table 3-1, the rest is the same as Example 1-3.

[0100] Example 4-1 to Example 4-3

[0101] Except for adjusting the relevant preparation parameters according to Table 4-1, the rest is the same as Example 1-3.

[0102] Example 5-1 to Example 5-6

[0103] Except that carboxylic acid ester is added according to Table 5 and relevant parameters are adjusted according to Table 5 when preparing the organic solvent in the step of <Preparation of Electrolyte>, the rest is the same as Example 1-1.

[0104] Comparative Example 1

[0105] The process was the same as Example 1-1 except that the polymer was replaced with PVDF-HFP and the content of HFP in PVDF-HFP was 15% in <Preparation of Separator>.

[0106] The relevant preparation parameters of each embodiment and comparative example are shown in Table 1-1 to Table 4-1 and Table 5, and the performance parameters are shown in Table 1-2 to Table 4-2 and Table 5.

[0107] Table 1-1

[0108]

[0109]

[0110] Note: The "mass ratio 9:1" in the styrene-isooctyl acrylate copolymer (mass ratio 9:1) of Example 1 means that the mass ratio of styrene monomer to isooctyl acrylate monomer in the styrene-isooctyl acrylate copolymer is 9:1, and the descriptions of the remaining embodiments and comparative examples are similar.

[0111] Table 1-2

[0112]

[0113] As shown in Table 1-1 and Table 1-2, it can be seen from Examples 1-1 to 1-9 and Comparative Example 1 that when the type of polymer is within the scope of this application, the prepared diaphragm has good thickness consistency, electrolyte resistance and thermal stability, and also has suitable ionic resistance, and the gel phenomenon of the diaphragm is improved. The lithium ion battery containing the diaphragm of this application is selected, and its lithium precipitation phenomenon and corner purple / black spot problems are effectively improved, and the lithium ion battery has better packaging performance and good winding rate.

[0114] Figure 3 SEM images of polymer particles of Examples 1-3 are shown. Figure 4The SEM photograph of the polymer particles of Comparative Example 1 is shown. In the SEM photographs of the polymer particles of Examples 1-3, the number of polymer particles with a maximum diameter less than 5 μm in any area of 130 μm × 100 μm on the porous coating surface is 33, the number of polymer particles with a maximum diameter between 5 μm and 14 μm is 162, and the number of polymer particles with a maximum diameter greater than 14 μm is 0. It can be seen that most of the polymer particles have a maximum diameter between 5 μm and 14 μm, indicating that the particle size of the polymer particles of the present application is relatively large. From Figure 3 It can also be seen that the polymer particles are relatively dispersed, and the clustering phenomenon is not obvious. In the SEM photograph of the polymer particles of Comparative Example 1, the particle sizes of the polymer particles are basically at the nanometer level, and obvious large-area clustering phenomena occur among the polymer particles due to their small particle sizes.

[0115] Table 2-1

[0116]

[0117] Table 2-2

[0118]

[0119] As can be seen from Table 2-1 and Table 2-2, the mass percentage contents of the polymer, auxiliary binder, thickener, and wetting agent in the porous coating usually affect the performance of the separator and the lithium-ion battery. From Examples 1-3, Examples 2-1 to Examples 2-6, it can be seen that when the mass percentage contents of the polymer, auxiliary binder, thickener, and wetting agent in the porous coating are within the scope of the present application, the prepared separator has good thickness consistency, electrolyte resistance, and thermal stability, and also has a suitable ionic resistance, and the gel phenomenon of the separator is improved. For a lithium-ion battery using the separator of the present application, the lithium plating phenomenon and the corner purple spot / black spot problems are effectively improved, and the lithium-ion battery has good encapsulation performance and winding excellent rate. In particular, when the polymer is styrene-2-ethylhexyl acrylate copolymer (mass ratio 7:3), the mass percentage content of the polymer is 90%, and the auxiliary binder is 6.5%, the ionic resistance of the separator is the lowest when the water contact angle of the porous coating is within the scope of the present application.

[0120] Table 3-1

[0121]

[0122] Table 3-2

[0123]

[0124] As can be seen from Table 3-1 and Table 3-2, the Tg and sphericity of the polymer usually affect the performance of the separator and the lithium-ion battery. From Examples 1-3, Examples 3-1 to 3-4, it can be seen that when the Tg and sphericity of the polymer are within the scope of this application, the prepared separator has good thickness consistency, electrolyte resistance performance and thermal stability, and also has appropriate ionic resistance, and the gel phenomenon of the separator is improved. For a lithium-ion battery using the separator of this application, the lithium plating phenomenon and the corner purple spot / black spot problem are effectively improved, and the lithium-ion battery has good encapsulation performance and winding excellent rate.

[0125] Table 4-1

[0126]

[0127] Table 4-2

[0128]

[0129] As can be seen from Table 4-1 and Table 4-2, the areal density of the porous coating usually affects the performance of the separator and the lithium-ion battery. From Examples 1-3, Examples 4-1 to 4-3, it can be seen that when the areal density of the porous coating is within the scope of this application, the prepared separator has good thickness consistency, electrolyte resistance performance and thermal stability, and also has appropriate ionic resistance, and the gel phenomenon of the separator is improved. For a lithium-ion battery using the separator of this application, the lithium plating phenomenon and the corner purple spot / black spot problem are effectively improved, and the lithium-ion battery has good encapsulation performance and winding excellent rate.

[0130] Table 5

[0131]

[0132] Note: The "\ " in Table 5 indicates that there is no corresponding parameter or substance.

[0133] As can be seen from Table 5, the components in the electrolyte usually affect the performance of the lithium-ion battery. From Examples 1-3, Examples 5-1 to 5-6, it can be seen that when the electrolyte contains carboxylic esters and the types and mass percentage contents of the carboxylic esters are within the scope of this application, for a lithium-ion battery using the electrolyte of this application, the lithium plating phenomenon and the corner purple spot / black spot problem are effectively improved, and the lithium-ion battery has good encapsulation performance.

[0134] The above are only the preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of this application shall be included within the scope of protection of this application.

Claims

1. A separator, which comprises a porous substrate and a porous coating provided on at least one surface of the porous substrate, the porous coating comprising a polymer, and the polymer comprising polymer particles; In a 130 μm × 100 μm area on the surface of the porous coating, the number of the polymer particles with the maximum diameter between 5 μm and 14 μm is 100 to 180; The swelling degree of the polymer is 50% to 110%, and the sphericity of the polymer is greater than or equal to 0.7 and less than 1.

0.

2. The diaphragm according to claim 1, wherein In a 130 μm × 100 μm area on the surface of the porous coating, the number of the polymer particles with the maximum diameter less than 5 μm is 10 to 40, and the number of the polymer particles with the maximum diameter greater than 14 μm is 0 to 10.

3. The diaphragm according to claim 1, wherein, The particle size of the polymer particles satisfies: 1 μm ≤ Dv10 ≤ 3 μm, 4 μm ≤ Dv50 ≤ 8 μm, 7 μm ≤ Dv90 ≤ 20 μm.

4. The diaphragm according to claim 1, wherein, The components of the polymer include at least one of polyvinylidene fluoride, polyacrylate, styrene-butadiene rubber, polyacrylamide or polyolefin; The polyacrylate is polymerized from at least one of the following monomers: styrene, butadiene, methyl methacrylate, acrylonitrile, acrylic acid, methacrylic acid, isobutyl acrylate, isobutyl methacrylate, butyl acrylate, butyl methacrylate, isooctyl acrylate, isooctyl methacrylate, methyl acrylate, glycidyl methacrylate; The monomers constituting the polyolefin are olefins having C 19 to C 35 .

5. The diaphragm according to claim 1, wherein, The components of the polymer include at least one of polyvinylidene fluoride, polystyrene-isobutyl acrylate, polystyrene-isooctyl acrylate or styrene-butadiene rubber.

6. The diaphragm according to claim 1, wherein, The porous coating further includes an auxiliary binder, a wetting agent and a thickening agent; Based on the mass of the porous coating, the mass percentage content of the polymer is 76.5% to 92.5%, the mass percentage content of the auxiliary binder is 4% to 20%, the mass percentage content of the wetting agent is 3% to 5%, and the mass content of the thickening agent is 0.5% to 1%.

7. The diaphragm according to claim 1, wherein, The glass transition temperature of the polymer is 40 °C to 65 °C.

8. The diaphragm according to claim 1, wherein, The porous coating satisfies at least one of the following characteristics: (i) The adhesion of the porous coating is 2 N / m to 6 N / m; (ii) The water droplet contact angle of the porous coating is 60° to 90°; (iii) The areal density of the porous coating is 0.1 g / m 2 to 0.4 g / m 2 .

9. The diaphragm according to claim 1, wherein, The separator satisfies at least one of the following characteristics: (1) The thickness covariance value of the separator is 0.01 to 0.02; (2) The thickness extreme difference of the separator is 0 μm to 3.3 μm; (3) The ionic resistance of the separator is 0.5 Ω to 1.5 Ω.

10. An electrochemical device, which comprises the separator according to any one of claims 1 to 9.

11. The electrochemical device according to claim 10, which further comprises an electrolyte, and the electrolyte comprises a carboxylic acid ester; Based on the mass of the electrolyte, the mass percentage content of the carboxylic acid ester is 10% to 65%.

12. The electrochemical device according to claim 11, wherein, The carboxylic acid esters include at least one of butyl propionate, amyl propionate, γ-butyrolactone, γ-valerolactone, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate or ethyl pivalate.

13. An electronic device, comprising the electrochemical device according to any one of claims 10 to 12.

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