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

Abstract

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 provided on at least one surface of the porous substrate. The porous coating includes a polymer. The thickness covariance of the separator is from 0.01 to 0.02. The separator provided by the present application has good thickness consistency, which is beneficial to improving the encapsulation performance of the electrochemical device, and the obtained electronic device has a long service life and good performance in use.

Description

Technical Field

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

[0002] Lithium-ion batteries have the advantages of large energy storage density, high open-circuit voltage, low self-discharge rate, long cycle life, good safety, etc., and are now widely used as power sources in electronic products such as cameras, mobile phones, drones, laptop computers, and smart watches.

[0003] As the application range of lithium-ion batteries continues to expand, the market has put forward higher requirements for lithium-ion batteries. As one of the important components in lithium-ion batteries, the separator will directly affect the performance of lithium-ion batteries. At present, the coatings on the surface of the separator in batteries for light power are mostly prepared by spraying methods, but the obtained separators have poor thickness consistency, thus affecting the packaging performance of lithium-ion batteries. Summary of the Invention

[0004] The purpose of the present application is to provide a separator, an electrochemical device including the separator, and an electronic device, so as to improve the thickness consistency of the separator in the electrochemical device, and further improve the packaging performance 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, but the electrochemical device of the present application is not limited to lithium-ion batteries.

[0006] The first aspect of the present application provides a separator. The separator includes a porous substrate and a porous coating provided on at least one surface of the porous substrate. The porous coating includes a polymer, and the coefficient of variation (COV) of the thickness of the separator is 0.01 to 0.02. 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 surface of the porous substrate refers to the two surfaces opposite to each other along its own thickness direction. It can be understood that the porous coating can be provided on all or part of the surface of the porous substrate, as long as the purpose of the present application can be achieved. The thickness COV of the separator obtained in the present application is within the above range. 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 packaging performance of the electrochemical device. For example, for an electrochemical device containing 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 the tab and winding excellent rate well-known in the art, and the above-mentioned thickness COV is the thickness COV well-known in the prior art. It can be understood that both the porous substrate (with a pore size of 10 nm to 80 nm) and the porous coating (polymer coating) have a pore structure.

[0007] At present, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) is widely used in the coating of diaphragms. Without a ceramic coating, the mass percentage content of hexafluoropropylene (HFP) in PVDF-HFP is usually greater than 50%. In order to improve the kinetic performance of electrochemical devices, ethylene methyl carbonate (EMC) and dimethyl carbonate (DMC) are usually added to the electrolyte. However, at high temperatures (such as temperatures greater than or equal to 80 °C), EMC and DMC will dissolve PVDF-HFP, causing the diaphragm to gel, thereby affecting the encapsulation performance of the electrochemical device. In addition, the high price of PVDF-HFP also increases the cost of the diaphragm. Based on the above problems, while improving the thickness uniformity of the diaphragm, the present application further selects the polymer in the porous coating to improve the gelling phenomenon of the diaphragm. The above-mentioned ceramic coating refers to the ceramic coating known in the art, and the present application does not limit it.

[0008] In an embodiment of the present application, based on the mass of the porous coating, the mass percentage of the polymer is 76.5% to 92.5%, and the swelling degree of the polymer in the test electrolyte is 40% to 170%. The test electrolyte is composed of an organic solvent and lithium hexafluorophosphate. The organic solvent is a mixture of ethylene carbonate (EC), propylene carbonate (PC), and DMC in a mass ratio of 7:2:1, and the concentration of lithium hexafluorophosphate is 1 mol / L. The swelling degree of the polymer in the test electrolyte within the above range can improve the gel phenomenon of the separator. Specifically, when the mass percentage of the polymer is too low (e.g., less than 76.5%) or the swelling degree of the polymer in the test electrolyte is too small (e.g., less than 40%), the adhesion between the porous substrate and the porous coating will be affected, such as the adhesion force and / or the adhesion area, etc. When the mass percentage of the polymer is too high (e.g., higher than 92.5%) or the swelling degree of the polymer in the test electrolyte is too large (e.g., greater than 170%), the polymer is likely to block the pore structure of the porous substrate and affect the lithium ion transport, and even cause lithium deposition and black spot phenomena in the electrochemical device. By regulating the mass percentage of the polymer and the swelling degree within the above range, for example, the mass percentage of the polymer can be 76.5%, 78%, 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 92.5% or any range therebetween, and the swelling degree of the polymer in the test electrolyte can be 40%, 50%, 60%, 70%, 80%, 90%, 100%, 110%, 120%, 130%, 140%, 150%, 160%, 170% or any range therebetween, the adhesion between the porous substrate and the porous coating is guaranteed, and the gel phenomenon of the separator is also improved, which is beneficial to improving the encapsulation performance of the electrochemical device and does not affect the lithium ion transport performance in the electrochemical device. In the present application, the above swelling degree is the swelling degree well known in the art.

[0009] In an embodiment of the present application, the polymer includes at least one of polyacrylamide, polyolefins with 19 to 35 carbon atoms in the monomer, polyvinylidene fluoride, PVDF-HFP with a mass percentage of HFP less than 5%, homopolymers formed by the following compounds, or copolymers formed by any two of the following compounds: 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, n-butyl acrylate, cyclohexyl acrylate, octyl acrylate, vinyl acrylate, methyl vinyl acrylate, isopentyl acrylate. Preferably, the polymer includes at least one of polyvinylidene fluoride, PVDF-HFP with a mass percentage of HFP less than 5%, or copolymers formed by styrene and one of the following compounds: butadiene, methyl methacrylate, acrylonitrile, acrylic acid, methacrylic acid, isobutyl acrylate, isobutyl methacrylate, butyl acrylate, butyl methacrylate, isooctyl acrylate, isooctyl methacrylate, methyl acrylate, glycidyl methacrylate, n-butyl acrylate, cyclohexyl acrylate, octyl acrylate, vinyl acrylate, methyl vinyl acrylate, isopentyl acrylate.

[0010] The above polymers 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 adhesive force, 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 polymers 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 infiltrate 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 have a relatively low price, which is beneficial to controlling the cost of the separator.

[0011] In one 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, blocking the pore structures of the porous substrate and the porous coating, affecting the transport of lithium ions and causing lithium plating 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. By adjusting the Tg of the polymer within the above range, 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. On the basis of improving the thickness uniformity and gel phenomenon of the separator, it will not affect other properties of the electrochemical device, such as the lithium ion transport performance and the structural stability of the electrochemical device, etc.

[0012] In one embodiment of the present application, the Dv50 of the polymer is 5 μm to 10 μm. When the Dv50 of the polymer is too small (e.g., less than 5 μm) or too large (e.g., greater than 10 μm), it will affect the thickness uniformity of the porous coating, and thus affect the thickness uniformity of the separator. By adjusting the Dv50 of the polymer within the above range, for example, the Dv50 of the polymer can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or any range therebetween, which is beneficial to improving the thickness uniformity of the separator, and thus improving the encapsulation performance of the electrochemical device. The present application has no particular limitation on the particle size distribution of the polymer, as long as the purpose of the present application can be achieved. Specifically, when the particle size distribution of the polymer is too narrow, the cost of the polymer increases. When the particle size distribution of the polymer is too wide, it will affect the thickness uniformity of the porous coating, and thus affect the thickness uniformity of the separator. Exemplarily, in the present application, the difference between Dv90 and Dv10 is used to characterize the particle size distribution of the polymer. Preferably, 10 μm ≤ Dv90 - Dv10 ≤ 15 μm.

[0013] In one embodiment of the present application, at 85 °C, after the polymer is immersed in the test electrolyte for 2 h, the viscosity of the test electrolyte is less than or equal to 10000 mPa·s. Preferably, the viscosity is greater than or equal to 1 mPa·s and less than or equal to 10000 mPa·s. This shows that the polymer has good electrolyte resistance, so that the separator is not easily prone to gel phenomenon, which is beneficial to improving the encapsulation performance of the electrochemical device.

[0014] In an embodiment of the present application, the sphericity of the polymer is greater than or equal to 0.7 and less than 1. When the sphericity of the polymer is too small (e.g., less than 0.7), the polymer dissolves in the pore structure in the porous substrate, affecting the transport of lithium ions. 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 thickness uniformity and gel phenomenon of the separator, it will not affect the lithium ion transport performance in the electrochemical device, such as kinetic performance. In the present application, the above sphericity is the sphericity known in the prior art.

[0015] In an embodiment of the present application, the porous coating further includes an auxiliary binder, a thickener and a wetting agent. Based on the mass of the porous coating, the mass percentage content of the auxiliary binder is 4% to 17.5%, the mass percentage content of the thickener is 0.5% to 1%, and the mass percentage content of the wetting agent is 3% to 5%. By regulating the mass percentage contents of the auxiliary binder, the thickener and the wetting agent within the above range, for example, the mass percentage content of the auxiliary binder can be 4%, 5%, 10%, 15%, 17.5% or any range therebetween, the mass percentage content of the thickener can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or any range therebetween, and the mass percentage content of the wetting agent can be 3%, 3.5%, 4%, 4.5%, 5% or any range therebetween, the obtained separator has good thickness uniformity, and its gel phenomenon is improved. The present application has no particular limitation on the auxiliary binder, the thickener and the wetting agent, as long as the purpose 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 thickener 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 alkyl naphthalene sulfonates, sodium dodecylbenzenesulfonate or polyoxyethylene fatty alcohol ethers.

[0016] In an embodiment of the present application, the separator is hot-pressed at 85 °C under a pressure of 1 MPa for 1 h, and the thickness compression amount of the separator is 80% to 95%. When the thickness compression amount of the separator is too small (e.g., less than 80%), the thickness of the obtained separator is likely to be too thick, the thickness of the electrochemical device increases, which will affect the volumetric energy density of the electrochemical device. When the thickness compression amount of the separator is too large (e.g., greater than 95%), it will affect the structure of the separator itself. By regulating the thickness compression amount of the separator within the above range, for example, the thickness compression amount of the separator is 80%, 85%, 90%, 95% or any range therebetween, on the basis of improving the thickness uniformity and gel phenomenon of the separator, it will not affect the volumetric energy density of the electrochemical device.

[0017] In an embodiment of the present application, the water droplet contact angle of the porous coating is 60° to 90°. By adjusting the water droplet contact angle of the porous coating within the above range, for example, the water droplet contact angle of the porous coating can be 60°, 61°, 70°, 75°, 80°, 85°, 90° or any range therebetween, it shows that the separator has good wettability and can be fully wetted by the electrolyte. In the present application, the above water droplet contact angle is the water droplet contact angle known in the prior art.

[0018] In an 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 (for example, 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 (for example, greater than 0.4 g / m 2 ), it will affect the lithium ion transport. By adjusting 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 thickness uniformity and gel phenomenon of the separator, it will not affect the lithium ion transport performance in the electrochemical device.

[0019] In an embodiment of the present application, the thickness ratio of the porous coating to the porous substrate is 1:2 to 1:5, and the thickness of the porous substrate is 8 μm to 40 μm. By adjusting the thickness ratio of the porous coating to the porous substrate and the thickness of the porous substrate within the above range, for example, the thickness ratio of the porous coating to the porous substrate can be 1:2, 1:3, 1:4, 1:5 or any range therebetween, and the thickness of the porous substrate can be 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm or any range therebetween, on the basis of improving the thickness uniformity and gel phenomenon of the separator, it can avoid the overall thickness of the separator being too thick and affecting the energy density of the electrochemical device. Among them, the thickness of the porous coating only needs to meet the above thickness ratio of the porous coating to the porous substrate and the thickness range of the porous substrate, for example, the thickness of the porous coating can be 5 μm to 20 μm.

[0020] In an embodiment of 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 with 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, thus 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 consistency of the porous coating will be affected, thus affecting the thickness consistency 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.

[0021] In an embodiment of the present application, the separator satisfies at least one of the following characteristics: (a) the air permeability of the separator is 60 s / 100 ml to 300 s / 100 ml; (b) the porosity of the separator is 30% to 55%; (c) the pore size of the porous substrate is 10 nm to 60 nm; (d) the thermal shrinkage rate of the separator in the longitudinal direction and the width direction at 130 °C is less than or equal to 10%. When the separator satisfies at least one of the above characteristics (a)-(d), it is beneficial to improve the encapsulation performance of the electrochemical device without affecting other properties of the electrochemical device, such as the lithium ion transport performance and safety performance of the electrochemical device.

[0022] In an embodiment of the present application, the air permeability of the separator is 60 s / 100 ml to 300 s / 100 ml. By controlling the air permeability of the separator within the above range, for example, the air permeability of the separator can be 60 s / 100 ml, 100 s / 100 ml, 150 s / 100 ml, 200 s / 100 ml, 250 s / 100 ml, 300 s / 100 ml or any range therebetween. On the basis of improving the thickness consistency and gel phenomenon of the separator, the separator also has appropriate air permeability, which is beneficial to improving the encapsulation performance of the electrochemical device and enabling the electrochemical device to have good kinetic performance (such as rate performance).

[0023] In an embodiment of the present application, the porosity of the separator is 30% to 55%. By controlling the porosity of the separator within the above range, for example, the porosity of the separator can be 30%, 35%, 40%, 45%, 50%, 55% or any range therebetween. On the basis of improving the thickness uniformity and gelling phenomenon of the separator, the separator can still meet the normal transmission of lithium ions in the electrochemical device. At the same time, the separator also has good structural stability, which is beneficial to improving the encapsulation performance of the electrochemical device without affecting the lithium ion transmission performance and safety performance of the electrochemical device. Among them, the porosity of the porous substrate and the porous coating in the separator can meet the porosity of the above separator. For example, the porosity of the porous substrate can be 20% to 60%, and the porosity of the porous coating can be 40% to 70%.

[0024] In an embodiment of the present application, the pore diameter of the porous substrate is 10 nm to 80 nm. By controlling the pore diameter of the porous substrate within the above range, for example, the pore diameter of the porous substrate can be 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm or any range therebetween. On the basis of improving the thickness uniformity and gelling phenomenon of the separator, it can meet the normal transmission of lithium ions in the electrochemical device, which is beneficial to improving the encapsulation performance of the electrochemical device without affecting the lithium ion transmission performance of the electrochemical device.

[0025] In an embodiment of the present application, at 130 °C, the thermal shrinkage rate of the separator in the longitudinal direction and the thermal shrinkage rate in the width direction are both less than or equal to 10%. Preferably, the thermal shrinkage rates are both greater than 0% and less than or equal to 10%. For example, the thermal shrinkage rate in the longitudinal direction and the thermal shrinkage rate in the width direction are each independently 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any range therebetween, indicating that the separator has good thermal stability. This is beneficial to improving the encapsulation performance of the electrochemical device, and the electrochemical device also has good safety performance.

[0026] The present application does not particularly limit the preparation method of the separator, as long as the purpose of the present application can be achieved. For example, the preparation method of the separator can include but is not limited to the following steps: adding the substances used in the porous coating (such as polymers, binders, thickeners, and wetting agents, etc.) into a solvent and mixing evenly to obtain a porous coating slurry, and 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 solvent, as long as the purpose of the present application can be achieved. For example, the solvent can 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 coating method, as long as the purpose of the present application can be achieved. For example, the microgravure coating method, etc.

[0027] The second aspect of the present application provides an electrochemical device, which includes the separator in any of the above embodiments. The above separator has good thickness consistency and is not prone to the phenomenon of separator gelation, thus being beneficial to improving the encapsulation performance of the electrochemical device.

[0028] In one embodiment of the present application, the electrochemical device 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 65%), the high-temperature performance of the electrochemical device will be affected. By adjusting 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 encapsulation performance of the electrochemical device, it is beneficial to improve the high-temperature performance of the electrochemical device.

[0029] In one embodiment of the present application, the carboxylic acid ester includes at least one of 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, butyl propionate, pentyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate or ethyl pivalate. The above carboxylic acid ester is not likely to react with the above separator, which is beneficial to inhibiting the gelation phenomenon of the separator, thereby improving the encapsulation performance of the electrochemical device.

[0030] In the present application, the electrolyte may further include other non-aqueous solvents. There is no particular limitation on the other non-aqueous solvents in the present application, as long as the purpose of the present application can be achieved. For example, it may include at least one of carbonate compounds, ether compounds, or other organic solvents. The above-mentioned carbonate compounds may include at least one of linear carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The above-mentioned linear carbonate compounds may include at least one of DMC, diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or ethyl methyl carbonate (EMC). The above-mentioned other cyclic carbonates may include at least one of EC, 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-mentioned 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-mentioned 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-mentioned other non-aqueous solvents is 5% to 80%, such as 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any range therebetween.

[0031] In the present application, the electrolyte may further include a lithium salt. There is no particular limitation on the lithium salt in the present application, as long as the purpose of the present application can be achieved. For example, the lithium salt may include at least one of lithium hexafluorophosphate, LiAsF6, LiClO4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, or LiSiF6, and preferably LiPF6.

[0032] 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 a 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.

[0033] 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, etc.

[0034] 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.

[0035] 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 fibers, 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 fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or nanofibers. The above metal materials may include, but are not limited to, metal powders and / or metal fibers. 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.

[0036] 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-mentioned conductive agent and the above-mentioned binder.

[0037] 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 composite current collectors, 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.

[0038] 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 insert / extract lithium ions, lithium metal, a lithium metal alloy, a material that can dope / dedope lithium, or a transition metal oxide.

[0039] The material that can reversibly insert / extract lithium ions may include, but is not limited to, carbon materials, which 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 among 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 / dedope 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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: lithium metal secondary batteries, lithium ion secondary batteries (lithium ion batteries), lithium polymer secondary batteries, or lithium ion polymer secondary batteries, etc.

[0044] 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, separator, and 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 electrolyte into the packaging bag and sealing it to obtain the electrochemical device; or stacking the positive electrode, separator, and 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 electrolyte into the packaging bag and sealing it to obtain the electrochemical device. In addition, an overcurrent protection element, a guide plate, etc. may also be placed in the packaging bag as needed to prevent the pressure inside the electrochemical device from rising and overcharging and discharging.

[0045] The third aspect of the present application provides an electronic device including the electrochemical device in any of the above embodiments. The electrochemical device provided by the present application has good packaging performance, so that the electronic device provided by the present application has a long service life and good performance.

[0046] 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, laptop computers, pen input computers, mobile computers, e-book readers, mobile phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, hand-held cleaners, portable CD players, mini discs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium ion capacitors, etc.

[0047] 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 provided on at least one surface of the porous substrate. The porous coating includes a polymer. The coefficient of variation (COV) of the thickness of the separator is from 0.01 to 0.02. The separator provided by the present application has good thickness consistency, which is beneficial to improving the packaging 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. The obtained electronic device has a long service life and good performance in use. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application, and those of ordinary skill in the art can also obtain other embodiments according to these drawings.

[0049] Figure 1 Schematic cross-sectional structure diagram of the separator in an embodiment of the present application;

[0050] Figure 2 Schematic cross-sectional structure diagram of the separator in another embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] In order to make the object, technical solution and advantages of the present application clearer, the following further details the present application with reference to the drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. All other technical solutions obtained by those of ordinary skill in the art based on the embodiments in the present application belong to the scope of protection of the present application.

[0052] It should be noted that in the specific implementation manner of the present application, a lithium-ion battery is taken as an example of the electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to the lithium-ion battery.

[0053] As Figure 1 shown, the separator 30 includes a porous substrate 31 and a porous coating 32 provided on one surface of the porous substrate 31 along its thickness direction. It can be understood that the porous coating 32 can also be provided on both surfaces of the porous substrate 31 along its thickness direction (as Figure 2 shown).

[0054] Hereinafter, examples and comparative examples are given to more specifically illustrate the implementation manners 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.

[0055] Testing methods and equipment:

[0056] Testing of the Tg of the polymer:

[0057] The Tg of the polymer was tested using a differential scanning calorimeter.

[0058] Testing of the viscosity of the electrolyte:

[0059] The polymer was immersed in the test electrolyte at 85 °C for 2 h, and then the viscosity of the electrolyte was measured using a rotational viscometer. Among them, the mass ratio of the polymer to the test electrolyte was 1:20. The test electrolyte was composed of an organic solvent and lithium hexafluorophosphate. The organic solvent was a mixture of EC, PC, and DMC in a mass ratio of 7:2:1, and the concentration of lithium hexafluorophosphate was 1 mol / L.

[0060] Testing of the swelling degree of the polymer:

[0061] The polymer was added to water to obtain an emulsion with a solid content of 30 wt%. The emulsion was coated on a glass substrate and dried at 85 °C to obtain a polymer film. A polymer film with a mass of m1 was placed in the test electrolyte and immersed at 85 °C for 6 h. The mass of the polymer film at this time was recorded as m2. The swelling degree of the polymer = (m2 - m1) / m1 × 100%. Each example or comparative example was tested 3 times, and the average value was taken as the final swelling degree of the polymer. Among them, the test electrolyte was the same as that in the electrolyte viscosity test.

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

[0063] Refer to the national standard GB / T 19077-2016 (《Laser diffraction method for particle size distribution》), and use a laser particle size analyzer (such as Malvern Master Size 3000) to measure.

[0064] In this application, Dv10 refers to the particle size corresponding to when the cumulative volume distribution percentage of the measured polymer reaches 10%; Dv50 refers to the particle size corresponding to when the cumulative volume distribution percentage of the measured polymer reaches 50%; Dv90 refers to the particle size corresponding to when the cumulative volume distribution percentage of the measured polymer reaches 90%.

[0065] Testing of the thickness compression amount of the separator:

[0066] Ten separators were stacked together, and the thickness at this time was recorded as D1. After hot pressing at 85 °C under a pressure of 1 MPa for 1 h, the thickness before and after hot pressing was measured and recorded as D2. The thickness compression amount = (D1 - D2) / D1 × 100%.

[0067] Testing of the gas permeability of the separator:

[0068] The air permeability of the separator was tested using an air permeability tester, where the volume of the air column of the air permeability tester was 100 cm 3 , the test area of the separator was 6.45 cm 2 . During the test, the separator was kept absolutely flat, and the test was repeated 3 times. The average value was taken as the final air permeability value.

[0069] Test of the separator porosity:

[0070] The porosity of the separator was tested using the gas displacement method. Porosity = (V - V0) / V × 100%, where the pore volume was V - V0, V0 was the true volume of the separator, and V was the total volume of the separator. The test equipment was a fully automatic true density tester (AccuPycⅡ1340), and the test gas was helium.

[0071] Test of the thermal shrinkage rate of the separator:

[0072] The separator was obtained by disassembling a lithium-ion battery. The separator was laminated along the length direction (MD direction) to obtain three layers of separators with the upper edges aligned in the length direction. A die with a size of 72.5 mm × 54.2 mm was used. Among them, the edge with a length of 72.5 mm of the die was placed parallel to the length direction of the separator, and three separator samples were obtained by punching with a stamping machine. The size X1 in the width direction (TD direction) and the size Z1 in the length direction of the separator samples were measured. The separator samples were laminated in the way that each was separated by a piece of white paper (the size of the white paper was A6, 105 mm × 148 mm). The laminated separator samples were placed in a steel plate. The oven temperature was set to 135 °C. After the oven reached the set temperature, the separator samples were put into the oven together with the steel plate and baked for 1 h. After baking, the samples were taken out and left to stand at room temperature for 10 min. The sizes in the length direction and width direction of the baked separator samples with the same number were measured respectively. The average size of each sample in the width direction was recorded as X2, and the average size of each sample in the length direction was recorded as Z2. If the edge shrinkage of the sample was uneven, the position with the maximum shrinkage was taken as the standard. Among them, the length direction and width direction of the separator were the length direction and width direction commonly used in the art.

[0073] The thermal shrinkage rate in the width direction = (X1 - X2) / X1 × 100%,

[0074] The thermal shrinkage rate in the length direction = (Z1 - Z2) / Z1 × 100%.

[0075] Test of the water contact angle of the porous coating:

[0076] The test was carried out using a water contact angle tester.

[0077] Thickness test:

[0078] (1) Test of the thickness range and COV of the separator: Along the length direction of the separator, measure 1 point every 5 mm with a micrometer, and a total of 30 points are measured. 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.

[0079] (2) Test of the thickness of the lithium-ion battery: Along the length direction of the lithium-ion battery, measure 1 point every 5 mm with a micrometer, and a total of 10 points are measured. Take the final average value as the thickness of the lithium-ion battery.

[0080] Test of the wet pressing adhesion force:

[0081] 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 force between the separator and the positive electrode according to the national standard GB / T 2792-1998 (Test Method for 180° Peel Strength of Pressure-Sensitive Adhesive Tapes).

[0082] Judgment of the gel phenomenon:

[0083] 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".

[0084] Judgment of the degree of lithium deposition:

[0085] 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 10 charge-discharge cycles, charge it at a constant current of 1C to 4.45V again, and 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 of less than 5%, and take pictures to record the state of the negative electrode plate.

[0086] Judge the degree of lithium deposition of the lithium-ion battery according to the following criteria:

[0087] No lithium deposition: There is no lithium deposition on the surface of the negative electrode plate;

[0088] Slight lithium deposition: The area of lithium deposition on the surface of the negative electrode plate is less than 10%;

[0089] Moderate lithium deposition: The area of lithium deposition on the surface of the negative electrode plate is 10% to 30%;

[0090] Severe lithium plating: The lithium deposition area on the surface of the negative electrode tab is greater than 30%.

[0091] Test of winding excellent rate:

[0092] Use a winding device to continuously produce 1000 lithium-ion batteries, and count the number of scrapped lithium-ion batteries caused by pole ear misalignment; winding excellent rate = (1 - number of scrapped batteries due to pole ear misalignment / 1000) × 100%. Among them, when the pole ear misalignment is severe and welding cannot be carried out, it is determined as pole ear misalignment.

[0093] Storage performance at 80°C:

[0094] Let the lithium-ion battery stand still in an environment of 25°C for 30 min, then charge it at a constant current of 0.2C to 4.2V, then charge it at a constant voltage of 4.2V to 0.05C, stand still for 30 min, and then discharge it at a rate of 0.5C to 2.8V, and record the appearance size of the lithium-ion battery at this time; then place the fully charged battery in an oven at about 80°C for storage for about 7 days, and record the appearance size of the lithium-ion battery.

[0095] Judge the storage performance of the lithium-ion battery according to the following deformation criteria:

[0096] No deformation: The thickness change rate of the lithium-ion battery is less than 3%;

[0097] Slight deformation: The thickness change rate of the lithium-ion battery is 3% to 10%;

[0098] Deformation: The thickness change rate of the lithium-ion battery is greater than 10%.

[0099] Example 1-1

[0100] <Preparation of the positive electrode>

[0101] Mix the positive electrode active material LiCoO2, the conductive agent conductive carbon black, and the binder polyvinylidene fluoride in a mass ratio of 96:2:2, add N-methylpyrrolidone (NMP), and stir evenly under the action of a vacuum mixer to obtain a positive electrode slurry, where the solid content of the positive electrode slurry is 70 wt%. Coat the positive electrode slurry evenly on one surface of a positive electrode current collector aluminum foil with a thickness of 12 μm, dry the aluminum foil at 120°C for 1 h to obtain a positive electrode with a positive electrode material layer coated on one side. Repeat the above steps 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, dry it under vacuum conditions at 120°C for 1 h to obtain a positive electrode with a specification of 74 mm × 867 mm.

[0102] <Preparation of the negative electrode>

[0103] The graphite as the negative electrode active material, styrene-butadiene rubber as the binder, and sodium carboxymethyl cellulose are mixed at a mass ratio of 97.4:1.4:1.2, and deionized water is added. After being stirred evenly under the action of a vacuum mixer, a negative electrode slurry is obtained, where the solid content of the negative electrode slurry is 75 wt%. The negative electrode slurry 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.

[0104] <Preparation of electrolyte>

[0105] 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.

[0106] <Preparation of separator>

[0107] Cyclohexyl methacrylate and isobutyl acrylate are mixed at a mass ratio of 5:95 to obtain an auxiliary binder. The polymer styrene-2-ethylhexyl acrylate copolymer, the auxiliary binder, the thickener sodium carboxymethyl cellulose, and the wetting agent polyoxyethylene fatty alcohol ether are mixed at a mass ratio of 90:6.5:0.5:3, and after adding water, they are stirred evenly to obtain a porous coating slurry with a solid content of 10 wt%. The porous coating slurry is evenly coated on one surface of a porous substrate with a thickness of 16 μm by the microgravure coating method, and then dried at 45 °C to obtain a separator with a porous coating coated on one side. The above steps are repeated to obtain a separator with a porous coating coated on both sides. Among them, the Dv50 of the polymer is 8 μm, the sphericity is 0.8, the Tg is 50 °C, the mass ratio of styrene to 2-ethylhexyl acrylate in the styrene-2-ethylhexyl acrylate copolymer is 7:3, the material of the porous substrate is polypropylene with a weight average molecular weight of 500000, the pore diameter of the porous substrate is 30 nm, the thickness of the porous substrate is 16 μm, the surface density of the porous coating is 0.2 g / m 2 , and the thickness ratio of the porous coating to the porous substrate is 1:3.

[0108] <Preparation of lithium-ion battery>

[0109] Stack the positive electrode, separator, and negative electrode prepared above in sequence, with the separator placed in the middle of the positive electrode and the negative electrode to play an isolation role, and wind them to obtain an electrode assembly. Place the electrode assembly in an aluminum-plastic film packaging bag, inject the electrolyte after drying, and obtain a lithium-ion battery through processes such as vacuum packaging, standing, formation, degassing, and trimming.

[0110] Examples 1-2 to Examples 1-10

[0111] Except for adjusting the relevant parameters according to Table 1, the rest are the same as Example 1-1.

[0112] Examples 2-1 to Examples 2-3

[0113] Except for adjusting the relevant parameters according to Table 2, the rest are the same as Example 1-1.

[0114] Examples 3-1 to Examples 3-4

[0115] Except for adjusting the relevant parameters according to Table 3, the rest are the same as Example 1-1.

[0116] Examples 4-1 to Examples 4-8

[0117] Except for adjusting the relevant parameters according to Table 4, the rest are the same as Example 1-1.

[0118] Examples 5-1 to Examples 5-6

[0119] Except for adding carboxylic acid ester according to Table 5 when preparing the organic solvent in the <Preparation of Electrolyte> step and adjusting the relevant parameters according to Table 5, the rest are the same as Example 1-1.

[0120] Comparative Example 1

[0121] Except for replacing the polymer with PVDF-HFP with a mass percentage of HFP of 10% in the <Preparation of Separator>, the rest are the same as Example 1-1.

[0122] The relevant preparation parameters and performance parameters of each example and comparative example are shown in Tables 1 to 5.

[0123] Table 1

[0124]

[0125]

[0126] Note: In the styrene-ethylhexyl acrylate copolymer (7:3) of Example 1 in Table 1, "7:3" indicates the mass ratio of styrene to ethylhexyl acrylate in the styrene-ethylhexyl acrylate copolymer. The same applies to the descriptions of the other examples.

[0127] As can be seen from Examples 1-1 to 1-10 and Comparative Example 1, when the thickness COV of the separator is within the scope of the present application, the winding excellence rate of the lithium-ion battery is improved, that is, the packaging performance of the lithium-ion battery is improved.

[0128] The properties of the polymer and the separator usually affect the performance of the lithium-ion battery. As can be seen from Examples 1-1 to 1-10, when the polymer is within the scope of the present application, the gel phenomenon of the separator is improved, and the obtained lithium-ion battery has good packaging performance and the lithium deposition phenomenon is also improved.

[0129] Table 2

[0130]

[0131] The mass percentage contents of the polymer, the auxiliary binder, the thickener and the wetting agent in the porous coating usually affect the performance of the separator and the lithium-ion battery. As can be seen from Example 1-1 and Examples 2-1 to 2-3, when the mass percentage contents of the polymer, the auxiliary binder, the thickener and the wetting agent in the porous coating are within the scope of the present application, the obtained separator also has good thickness uniformity, electrolyte resistance and thermal stability, the gel phenomenon of the separator is improved, and the obtained lithium-ion battery has good packaging performance and the lithium deposition phenomenon is also improved.

[0132] Table 3

[0133]

[0134] The Dv50 and sphericity of the polymer usually affect the performance of the separator and the lithium-ion battery. As can be seen from Example 1-1 and Examples 3-1 to 3-4, when the Dv50 and sphericity of the polymer are within the scope of the present application, the obtained separator also has good thickness uniformity, and its gel phenomenon is improved, so that the obtained lithium-ion battery has good packaging performance and the lithium deposition phenomenon is also improved.

[0135] Table 4

[0136]

[0137] The thickness of the porous substrate, the thickness ratio of the porous coating to the porous substrate, the areal density of the porous coating, the pore size of the porous substrate, and the weight-average molecular weight of polypropylene generally affect the performance of the separator and the lithium-ion battery. It can be seen from Examples 1-1, 4-1 to 4-8 that when the thickness of the porous substrate, the thickness ratio of the porous coating to the porous substrate, the areal density of the porous coating, the pore size of the porous substrate, and the weight-average molecular weight of polypropylene are within the scope of the present application, the obtained separator has good thickness uniformity, appropriate water droplet contact angle and thermal stability, and its gel phenomenon is improved, so that the obtained lithium-ion battery has good encapsulation performance and the lithium plating phenomenon is also improved.

[0138] Table 5

[0139]

[0140] The components in the electrolyte generally affect the performance of the lithium-ion battery. Referring to Table 5, it can be seen from Examples 1-1, 5-1 to 5-6 that when the electrolyte contains carboxylic esters and their types and mass percentage contents are within the scope of the present application, the encapsulation performance and high-temperature storage performance of the lithium-ion battery can be further improved.

[0141] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the scope of protection of the present application.

Claims

1. A separator, which comprises a porous substrate and a porous coating disposed on at least one surface of the porous substrate, the porous coating comprising a polymer, the thickness covariance of the separator being 0.01 to 0.02; the glass transition temperature of the polymer being 40 °C to 65 °C; The polymer comprises at least one of polyvinylidene fluoride, a polyvinylidene fluoride - hexafluoropropylene copolymer with a mass percentage of hexafluoropropylene less than 5%, or a copolymer of styrene and one of the following compounds: butadiene, methyl methacrylate, acrylonitrile, acrylic acid, methacrylic acid, isobutyl acrylate, isobutyl methacrylate, butyl acrylate, butyl methacrylate, isooctyl acrylate, isooctyl methacrylate, methyl acrylate, glycidyl methacrylate, n - butyl acrylate, cyclohexyl acrylate, octyl acrylate, vinyl acrylate, methyl vinyl acrylate, isopentyl acrylate; Based on the mass of the porous coating, the mass percentage of the polymer is 76.5% to 92.5%; The sphericity of the polymer is greater than or equal to 0.7 and less than 1; The thickness ratio of the porous coating to the porous substrate is 1:2 to 1:5, and the thickness of the porous substrate is 8 μm to 40 μm.

2. The separator according to claim 1, wherein, The swelling degree of the polymer in the test electrolyte is 40% to 170%, the test electrolyte is composed of an organic solvent and lithium hexafluorophosphate, the organic solvent is a mixture of ethylene carbonate, propylene carbonate and dimethyl carbonate in a mass ratio of 7:2:1, and the concentration of lithium hexafluorophosphate is 1 mol / L.

3. The diaphragm according to claim 1, wherein, The Dv50 of the polymer is 5 μm to 10 μm.

4. The diaphragm according to claim 1, wherein, At 85 °C, after the polymer is immersed in the test electrolyte for 2 h, the viscosity of the test electrolyte is less than or equal to 10000 mPa·s, the test electrolyte is composed of an organic solvent and lithium hexafluorophosphate, the organic solvent is a mixture of ethylene carbonate, propylene carbonate and dimethyl carbonate in a mass ratio of 7:2:1, and the concentration of lithium hexafluorophosphate is 1 mol / L.

5. The separator according to claim 1, wherein, The porous coating further comprises an auxiliary binder, a thickener and a wetting agent. Based on the mass of the porous coating, the mass percentage of the auxiliary binder is 4% to 17.5%, the mass percentage of the thickener is 0.5% to 1%, and the mass percentage of the wetting agent is 3% to 5%.

6. The separator according to claim 1, wherein, The separator is hot - pressed at 85 °C under a pressure of 1 MPa for 1 h, and the thickness compression amount of the separator is 80% to 95%.

7. The separator according to claim 1, wherein, The water droplet contact angle of the porous coating is 60° to 90°.

8. The separator according to claim 1, wherein, 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 material of the porous substrate comprises polypropylene with a weight - average molecular weight of 100000 to 1000000.

10. The separator according to claim 1, which satisfies at least one of the following characteristics: (a) The air permeability of the separator is 60 s / 100 ml to 300 s / 100 ml; (b) The porosity of the separator is 30% to 55%; (c) The pore diameter of the porous substrate is 10 nm to 80 nm; (d) At 130 °C, the thermal shrinkage rate in the longitudinal direction and the thermal shrinkage rate in the width direction of the separator are both less than or equal to 10%.

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

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

13. The electrochemical device according to claim 12, wherein, The carboxylic acid ester comprises at least one of 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, butyl propionate, pentyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate or ethyl pivalate.

14. An electronic device, which comprises the electrochemical device according to any one of claims 11 to 13.

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