Diaphragm, electrochemical device comprising diaphragm and electronic device

Abstract

The present application provides a diaphragm, an electrochemical device comprising the same, and an electronic device, the diaphragm comprising a porous base material and a porous coating layer disposed on at least one surface of the porous base material, the porous coating layer comprising a polymer, and the thickness covariance of the diaphragm being 0.01 to 0.02. The diaphragm provided by the invention has good thickness consistency, so that the packaging performance of an electrochemical device is improved, and the obtained electronic device has relatively long service life and good use performance.

Description

[0001] This application is a divisional application with application number 202280006061.1, application date March 31, 2022, and invention name “A diaphragm, an electrochemical device and an electronic device comprising the diaphragm”. Technical Field

[0002] The present application relates to the field of electrochemical technology, and in particular to a diaphragm, an electrochemical device comprising the diaphragm, and an electronic device. Background Art

[0003] Lithium-ion batteries have the advantages of high energy storage density, high open-circuit voltage, low self-discharge rate, long cycle life and good safety. They are now widely used as power sources in electronic products such as cameras, mobile phones, drones, laptops and smart watches.

[0004] As the use of lithium-ion batteries continues to expand, the market is placing higher demands on them. As a key component in lithium-ion batteries, the separator directly impacts their performance. Currently, the surface coating of separators used in lightweight power batteries is mostly produced using a spray coating method. However, the resulting separator thickness is poorly consistent, which in turn affects the packaging performance of lithium-ion batteries. Summary of the Invention

[0005] The purpose of the present application is to provide a diaphragm, an electrochemical device and an electronic device comprising the diaphragm, so as to improve the thickness consistency of the diaphragm in the electrochemical device, thereby improving the packaging performance of the electrochemical device.

[0006] It should be noted that, in the invention content of the present application, a lithium-ion battery is used as an example of an electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to a lithium-ion battery.

[0007] The first aspect of the present application provides a kind of diaphragm, diaphragm comprises a porous substrate and a porous coating arranged on at least one surface of the porous substrate, the porous coating comprises a polymer, and the thickness covariance (COV) of the diaphragm is 0.01 to 0.02. Specifically, a porous coating is provided on one surface of the porous substrate, or a porous coating is provided on both surfaces of the porous substrate, wherein the surface of the porous substrate refers to two surfaces relative to each other along its thickness direction. It is understood that the porous coating can be provided in the entire region or a partial region of the porous substrate surface, as long as the purpose of the present application can be achieved. The thickness COV of the diaphragm obtained in the present application is within the above range, for example, the thickness COV of the diaphragm can be 0.01, 0.012, 0.014, 0.016, 0.018, 0.02 or any range therebetween, indicating that the diaphragm has good thickness consistency, which is conducive to improving the packaging performance of the electrochemical device, for example, for an electrochemical device containing multiple poles, the winding rate of the electrochemical device can be improved. In this application, the tabs and winding ratios mentioned above are those known in the art, and the thickness COV mentioned above is those known in the art. It is understood that both the porous substrate (pore diameter 10 nm to 80 nm) and the porous coating (polymer coating) have a porous structure.

[0008] At present, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) is widely used in the coating of diaphragm, wherein in the absence of ceramic coating, the mass percentage of hexafluoropropylene (HFP) in PVDF-HFP is generally greater than 50%. In order to improve the kinetic performance of electrochemical devices, ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) are usually added to the electrolyte, but at high temperatures (for example, a temperature greater than or equal to 80 ° C), EMC and DMC dissolve PVDF-HFP, causing the diaphragm to produce a gel phenomenon, thereby affecting the packaging performance of the electrochemical device. In addition, PVDF-HFP is relatively expensive, which also leads to an increase in the cost of the diaphragm. Based on the above problems, the present application further selects the polymer in the porous coating while improving the consistency of the thickness of the diaphragm, so as to improve the gel phenomenon of the diaphragm. The above-mentioned ceramic coating refers to a ceramic coating known in the art, and this application is not limited thereto.

[0009] In one 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%, the swelling degree of the polymer in the test electrolyte is 40% to 170%, and the test electrolyte is composed of an organic solvent and lithium hexafluorophosphate, the organic solvent is ethylene carbonate (EC), propylene carbonate (PC) and DMC mixed 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 can improve the gelation phenomenon of the diaphragm within the above range. Specifically, when the mass percentage of the polymer is too low (for example, less than 76.5%) or the swelling degree of the polymer in the test electrolyte is too small (for example, less than 40%), it will affect the adhesion between the porous substrate and the porous coating, such as bonding force and / or bonding area. When the mass percentage of the polymer is too high (for example, higher than 92.5%) or the polymer swelling rate in the test electrolyte is too large (for example, greater than 170%), the polymer can easily clog the pore structure of the porous substrate and affect the transmission of lithium ions, and even cause lithium deposition and black spots in the electrochemical device. By regulating the mass percentage and swelling degree of the polymer 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 gelation phenomenon of the diaphragm is also improved, thereby improving the packaging performance of the electrochemical device and not affecting the transport performance of lithium ions in the electrochemical device. In the present application, the above swelling degree is a swelling degree well known in the art.

[0010] In one embodiment of the present application, the polymer includes polyacrylamide, a polyolefin having a monomer carbon number of 19 to 35, polyvinylidene fluoride, PVDF-HFP having a mass percentage of HFP less than 5%, a homopolymer formed by the following compounds, or at least one of a copolymer 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, epoxy methyl methacrylate, n-butyl acrylate, cyclohexyl acrylate, octyl acrylate, vinyl acrylate, methyl vinyl acrylate, and isopentyl acrylate. Preferably, the polymer includes at least one of polyvinylidene fluoride, PVDF-HFP with a mass percentage of HFP less than 5%, or a copolymer 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, epoxy methyl methacrylate, n-butyl acrylate, cyclohexyl acrylate, octyl acrylate, vinyl acrylate, methyl vinyl acrylate, and isopentyl acrylate.

[0011] The above-mentioned polymer has good thermal stability and electrolyte resistance, and the cross-linked structure it has makes it randomly distributed in the porous coating, and the bonding force is high, so that the bonding between the porous substrate and the porous coating is guaranteed, and the gelation phenomenon of the diaphragm is also improved, and then the packaging performance of the electrochemical device is improved. In addition, the diaphragm comprising the above-mentioned polymer also has good bonding between it and the positive pole and the negative pole, and can suppress the deformation problem caused by the expansion of the negative pole, and then improve the structural stability of the electrochemical device. Especially for polymers containing polar functional groups such as carboxyl or hydroxyl, it can improve the affinity of the electrolyte to fully infiltrate the diaphragm, and improve the bonding between the diaphragm and the positive pole, the diaphragm and the negative pole, on the basis of improving the diaphragm gelation phenomenon, it is more conducive to improving the structural stability of the electrochemical device. In addition, the above-mentioned polymer price is relatively low, which is conducive to controlling the cost of the diaphragm.

[0012] 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 (for example, below 40°C), during the post-treatment of the diaphragm (for example, a drying treatment), it is easy for the porous substrate and the porous coating to adhere to each other and block the pore structure of the porous substrate and the porous coating, affecting the transmission of lithium ions and causing the electrochemical device to produce lithium precipitation. When the Tg of the polymer is too high (for example, above 65°C), it will affect the adhesion between the porous substrate and the porous coating, so that the electrochemical device is at risk of deformation due to insufficient adhesion. By regulating 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, while improving the thickness consistency and gelation of the diaphragm, it will not affect other properties of the electrochemical device, such as the transmission performance of lithium ions and the structural stability of the electrochemical device.

[0013] 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 (for example, less than 5 μm) or too large (for example, greater than 10 μm), the thickness consistency of the porous coating will be affected, thereby affecting the thickness consistency of the diaphragm. By regulating 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 conducive to improving the thickness consistency of the diaphragm, thereby improving the packaging performance of the electrochemical device. The present application has no particular restrictions 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 polymer cost is increased. When the particle size distribution of the polymer is too wide, the thickness consistency of the porous coating will be affected, thereby affecting the thickness consistency of the diaphragm. For example, in the present application, the particle size distribution of the polymer is characterized by the difference between Dv90 and Dv10, preferably, 10 μm ≤ Dv90 - Dv10 ≤ 15 μm.

[0014] In one embodiment of the present application, after the polymer is immersed in a test electrolyte for 2 hours at 85°C, the viscosity of the test electrolyte is less than or equal to 10,000 mPa·s. Preferably, the viscosity is greater than or equal to 1 mPa·s and less than or equal to 10,000 mPa·s. This indicates that the polymer has good electrolyte resistance, and thus the separator is less likely to gel, which is beneficial for improving the packaging performance of the electrochemical device.

[0015] In one 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 (for example, less than 0.7), the polymer dissolves in the pore structure covering 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, while improving the thickness consistency and gel phenomenon of the diaphragm, it will not affect the transport performance of lithium ions in the electrochemical device, such as kinetic performance. In the present application, the above sphericity is the sphericity known in the prior art.

[0016] In one embodiment of the present application, the porous coating further comprises an auxiliary binder, a thickener and a wetting agent, and 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%. By regulating the mass percentages of the auxiliary binder, the thickener and the wetting agent within the above ranges, for example, the mass percentage of the auxiliary binder can be 4%, 5%, 10%, 15%, 17.5% or any range therebetween, the mass percentage of the thickener 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, the resulting diaphragm has good thickness consistency and its gelation phenomenon is improved. The present application has no particular restrictions on the auxiliary binder, thickener and wetting agent, as long as the purpose of the present application can be achieved. For example, the auxiliary binder may include but is not limited to at least one of cyclohexyl methacrylate, isobutyl acrylate or methyl methacrylate, the thickener may include but is not limited to at least one of sodium carboxymethyl cellulose, alginic acid or gelatin, and the wetting agent may include but is not limited to at least one of alkyl naphthalene sulfonate, sodium dodecylbenzene sulfonate or polyoxyethylene fatty alcohol ether.

[0017] In one embodiment of the present application, the diaphragm is hot-pressed at 85°C with a pressure of 1 MPa for 1 hour, and the thickness compression of the diaphragm is 80% to 95%. When the thickness compression of the diaphragm is too small (for example, less than 80%), the thickness of the obtained diaphragm tends to be thicker, and the thickness of the electrochemical device increases, which will affect the volume energy density of the electrochemical device. When the thickness compression of the diaphragm is too large (for example, greater than 95%), it will affect the structure of the diaphragm itself. By regulating the thickness compression of the diaphragm within the above range, for example, the thickness compression of the diaphragm is 80%, 85%, 90%, 95% or any range therebetween, while improving the thickness consistency and gel phenomenon of the diaphragm, the volume energy density of the electrochemical device will not be affected.

[0018] In one embodiment of the present application, the water droplet contact angle of the porous coating is 60° to 90°. By regulating 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, indicating 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.

[0019] In one embodiment of the present application, the surface density of the porous coating is 0.1 g / m 2 Up to 0.4g / m 2 When the surface density of the porous coating is too small (e.g. less than 0.1 g / m 2 ), which will affect the adhesion between the porous substrate and the porous coating. When the surface density of the porous coating is too large (for example, greater than 0.4 g / m 2 ), which will affect the transmission of lithium ions. By adjusting the surface density of the porous coating within the scope of this application, for example, the surface density of the porous coating can be 0.1g / m 2 , 0.15g / m 2 , 0.2g / m 2 , 0.25g / m 2 , 0.3g / m 2 , 0.35g / m 2 , 0.4g / m 2 Or any range therebetween, on the basis of improving the thickness consistency and gel phenomenon of the separator, it will not affect the lithium ion transport performance in the electrochemical device.

[0020] In one embodiment of the present application, the thickness ratio of the porous coating layer to the porous substrate is 1:2 to 1:5, and the thickness of the porous substrate is 8 μm to 40 μm. By regulating the thickness ratio of the porous coating layer to the porous substrate and the thickness of the porous substrate within the above range, for example, the thickness ratio of the porous coating layer 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 consistency and gelation of the diaphragm, so as to avoid the thickness of the entire diaphragm being too thick and affecting the energy density of the electrochemical device. Among them, the thickness of the porous coating layer only needs to meet the thickness ratio of the porous coating layer to the porous substrate and the thickness range of the porous substrate. For example, the thickness of the porous coating layer can be 5 μm to 20 μm.

[0021] In one embodiment of the present application, the material of porous substrate may include but is not limited to at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Preferably, the material of 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 porous substrate and porous coating will be affected, thereby affecting the packaging performance of electrochemical device. When the weight average molecular weight of polypropylene is too large (e.g., greater than 1,000,000), the thickness consistency of porous coating will be affected, thereby affecting the thickness consistency of diaphragm and the packaging performance of electrochemical device. By regulating and controlling the weight average molecular weight of the polypropylene in 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 packaging performance of electrochemical device can be effectively improved.

[0022] In one embodiment of the present application, the separator satisfies at least one of the following characteristics: (a) the air permeability of the separator is 60s / 100ml to 300s / 100ml; (b) the porosity of the separator is 30% to 55%; (c) the pore size of the porous substrate is 10nm to 60nm; (d) the thermal shrinkage rate of the separator along its own length direction and the thermal shrinkage rate in the width direction at 130°C are both 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 packaging performance of the electrochemical device without affecting other properties of the electrochemical device, such as the lithium ion transmission performance and safety performance of the electrochemical device.

[0023] In one embodiment of the present application, the air permeability of the diaphragm is 60s / 100ml to 300s / 100ml. By regulating the air permeability of the diaphragm within the above range, for example, the air permeability of the diaphragm can be 60s / 100ml, 100s / 100ml, 150s / 100ml, 200s / 100ml, 250s / 100ml, 300s / 100ml or any range therebetween, on the basis of improving the thickness consistency and gel phenomenon of the diaphragm, the diaphragm also has a suitable air permeability, which is beneficial to improving the packaging performance of the electrochemical device and making the electrochemical device have good kinetic performance (such as rate performance).

[0024] In one embodiment of the present application, the porosity of the diaphragm is 30% to 55%. By regulating the porosity of the diaphragm within the above range, for example, the porosity of the diaphragm can be 30%, 35%, 40%, 45%, 50%, 55% or any range therebetween. On the basis of improving the thickness consistency and gelation of the diaphragm, the diaphragm can also meet the normal transmission of lithium ions in the electrochemical device. At the same time, the diaphragm also has good structural stability, which is beneficial to improve the packaging 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 porosity of the porous coating in the diaphragm can meet the porosity of the above-mentioned diaphragm. 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%.

[0025] In one embodiment of the present application, the pore size of the porous substrate is 10 nm to 80 nm. By regulating the pore size of the porous substrate within the above range, for example, the pore size 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, while improving the thickness consistency and gel phenomenon of the diaphragm, it can meet the normal transmission of lithium ions in the electrochemical device, thereby improving the packaging performance of the electrochemical device without affecting the lithium ion transmission performance of the electrochemical device.

[0026] In one embodiment of the present application, the separator has a heat shrinkage rate in both its longitudinal direction and width direction at 130°C of less than or equal to 10%. Preferably, the heat shrinkage rate is greater than 0% and less than or equal to 10%. For example, the heat shrinkage rate in the longitudinal direction and the heat 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 for improving the packaging performance of the electrochemical device while also providing good safety performance for the electrochemical device.

[0027] The present application has no particular restrictions on the preparation method of the diaphragm, as long as the purpose of the present application can be achieved, for example, the preparation method of the diaphragm may include but is not limited to the following steps: the substance used in the porous coating (such as polymer, binder, thickener and wetting agent, etc.) is added to a solvent and mixed to obtain a porous coating slurry, and then the porous coating slurry is applied to the surface of the porous substrate, and the diaphragm is obtained by drying. Wherein, the present application has no particular restrictions on the above-mentioned 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 has no particular restrictions on the method for the above-mentioned coating, as long as the purpose of the present application can be achieved, such as micro-concave roller coating method, etc.

[0028] The second aspect of the present application provides an electrochemical device comprising the separator according to any one of the above embodiments. The separator has good thickness consistency and is not prone to separator gelation, thereby improving the packaging performance of the electrochemical device.

[0029] In one embodiment of the present application, the electrochemical device includes an electrolyte, the electrolyte includes a carboxylate, and the mass percentage of the carboxylate is 10% to 65% based on the mass of the electrolyte. When the mass percentage of the carboxylate is too high (for example, greater than 65%), the high temperature performance of the electrochemical device will be affected. By regulating the mass percentage of the carboxylate within the above range, for example, the mass percentage of the carboxylate can be 10%, 20%, 30%, 40%, 50%, 60%, 65% or any range therebetween, it is beneficial to improve the high temperature performance of the electrochemical device on the basis of improving the packaging performance of the electrochemical device.

[0030] 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-mentioned carboxylic acid ester is not easy to react with the above-mentioned diaphragm, which is beneficial to suppressing the gelation phenomenon of the diaphragm, thereby improving the packaging performance of the electrochemical device.

[0031] In the present application, the electrolyte may also include other non-aqueous solvents. The present application has no particular restrictions on other non-aqueous solvents, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to at least one of a carbonate compound, an ether compound or other organic solvents. The above-mentioned carbonate compound may include but is not limited to at least one of a linear carbonate compound, a cyclic carbonate compound or a fluorinated carbonate compound. The above-mentioned linear carbonate compound may include but is not limited to 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 but are not limited to at least one of EC, PC, butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluorinated carbonate compound may include, but is not limited to, 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 trifluoromethylethylene carbonate. The above-mentioned ether compound may include, but is not limited to, 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 other organic solvents may include, but are not limited to, 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 a phosphate ester. The weight percentage of the other non-aqueous solvents is 5% to 80% based on the weight of the electrolyte, for example, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any range therebetween.

[0032] In the present application, the electrolyte may also include lithium salts. There is no particular limitation on the lithium salts in the present application as long as the purpose of the present application can be achieved. For example, the lithium salts may include but are not limited to at least one of lithium hexafluorophosphate, LiAsF6, LiClO4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3 or LiSiF6, preferably LiPF6.

[0033] 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 can 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 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.

[0034] In this application, the positive electrode material layer includes positive electrode active materials. There is no particular limitation on the positive electrode active materials in this application, as long as the purpose of this application can be achieved. For example, it can 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 can include at least one of nickel, manganese, cobalt, or iron. Specifically, the positive electrode active materials can include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(Ni a1 Co [[ID=�]] 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), LiC ol-y2 Mn y2 O2 (0 < y2 < 1), LiNi l-y3 Mn y3 O2 (0 < y3 < 1), Li(Ni​​​​​​​​​​​​​​​​​​​​​

[0035] The positive electrode material layer may also include a binder. The present application has no particular limitation on the binder as long as the purpose of the present application can be achieved. For example, it may include but is not limited to polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or at least one of nylon.

[0036] In the present application, the positive electrode material layer may further include a conductive agent, and the present application has no particular restrictions on the conductive agent, as long as the purpose of the present 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-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers, and specifically, the metal may include but are not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole.

[0037] 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. The present application does not particularly limit the composition of the conductive layer, and it may be a conductive layer commonly used in the art, for example, including but not limited to the above-mentioned conductive agent and the above-mentioned binder.

[0038] In the present application, the above-mentioned 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. The present application has no special restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it can include but is not limited to copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or composite current collector, etc. In the present application, there is no special restriction on the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved, for example, the thickness is 4μm to 12μm. In the present application, the negative electrode material layer can be arranged on one surface in the thickness direction of the negative electrode current collector, or on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or a partial area of ​​the negative electrode current collector. The present application has no special restrictions, as long as the purpose of the present application can be achieved.

[0039] In the present 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 the present application can be achieved. For example, it may include, but is not limited to, at least one of a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / de-doping lithium, or a transition metal oxide.

[0040] The material capable of reversibly intercalating / deintercalating 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) in an amorphous, plate-shaped, flake-shaped, spherical, or fibrous form. The amorphous carbon may include, but is not limited to, at least one of soft carbon, hard carbon, mesophase pitch carbonization product, 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 capable of doping / de-doping 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.

[0041] In the present application, the negative electrode material layer may further include a conductive agent. The present application places no particular limitation on the conductive agent as long as the object of the present application can be achieved. For example, it may include, but is not limited to, at least one of the above-mentioned conductive agents.

[0042] In the present application, the negative electrode material layer may further include a binder. The present application places no particular limitation on the binder as long as the object of the present application can be achieved. For example, it may include, but is not limited to, at least one of the above-mentioned binders.

[0043] Optionally, the negative electrode may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. The present application has no particular limitation on the composition of the conductive layer, which may be a conductive layer commonly used in the art, and may include but is not limited to the above-mentioned conductive agent and the above-mentioned binder.

[0044] The electrochemical device of the present application is not particularly limited and may include any device that generates 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.

[0045] The preparation process of an electrochemical device is well known to those skilled in the art and is not particularly limited in this 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 winding, folding, and other operations as needed to obtain a wound electrode assembly, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag, and sealing the bag to obtain an electrochemical device; or stacking the positive electrode, separator, and negative electrode in sequence, and then securing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag, and sealing the bag to obtain an electrochemical device. In addition, overcurrent protection components, guide plates, etc. may also be placed in the packaging bag as needed to prevent pressure rise and overcharging and discharging inside the electrochemical device.

[0046] The third aspect of the present application provides an electronic device, which includes the electrochemical device according to any one of the above embodiments. The electrochemical device provided by the present application has good packaging performance, so the electronic device provided by the present application has a long service life and good performance.

[0047] The electronic device of the present application is not particularly limited and can be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0048] The present application provides a diaphragm, an electrochemical device, and an electronic device including the diaphragm. The diaphragm comprises a porous substrate and a porous coating disposed on at least one surface of the porous substrate. The porous coating comprises a polymer. The thickness COV of the diaphragm is 0.01 to 0.02. The diaphragm provided herein has good thickness consistency, which is beneficial for improving the packaging performance of the electrochemical device. For example, for an electrochemical device containing multiple tabs, it can improve the winding efficiency of the electrochemical device. The resulting electronic device has a long service life and good performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0050] Figure 1 A schematic diagram of the cross-sectional structure of a diaphragm in one embodiment of the present application;

[0051] Figure 2 This is a schematic diagram of the cross-sectional structure of a diaphragm in another embodiment of the present application. DETAILED DESCRIPTION

[0052] To make the objectives, technical solutions, and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and examples. It is apparent that the described embodiments are only a portion of the embodiments of this application, rather than all of them. All other technical solutions derived by those of ordinary skill in the art based on the embodiments in this application fall within the scope of protection of this application.

[0053] It should be noted that in the specific embodiments of the present application, a lithium-ion battery is used as an example of an electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to a lithium-ion battery.

[0054] like Figure 1 As 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 is understood that the porous coating 32 can also be provided on both surfaces of the porous substrate 31 along its thickness direction (e.g., Figure 2 shown).

[0055] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0056] Test methods and equipment:

[0057] Polymer Tg test:

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

[0059] Test for electrolyte viscosity:

[0060] The polymer was immersed in the test electrolyte at 85°C for 2 hours, and the viscosity of the electrolyte was measured using a rotational viscometer. The mass ratio of polymer to test electrolyte was 1:20. The test electrolyte consisted of an organic solvent and lithium hexafluorophosphate (LiFP). The organic solvent was a mixture of EC, PC, and DMC in a mass ratio of 7:2:1, and the concentration of LiFP was 1 mol / L.

[0061] Test of polymer swelling degree:

[0062] A 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 immersed in a test electrolyte at 85°C for 6 hours. The mass of the polymer film at this time was recorded as m2. The polymer swelling degree = (m2 - m1) / m1 × 100%. Each example or comparative example was tested three times, and the average value was taken as the final polymer swelling degree. The test electrolyte was the same as that used in the electrolyte viscosity test.

[0063] Polymer particle size test:

[0064] The particle size distribution was determined using a laser particle size analyzer (such as Malvern Master Size 3000) in accordance with the national standard GB / T 19077-2016 (Particle Size Distribution by Laser Diffraction Method).

[0065] 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%; and Dv90 refers to the particle size corresponding to when the cumulative volume distribution percentage of the measured polymer reaches 90%.

[0066] Diaphragm thickness compression test:

[0067] Stack 10 diaphragms together and record the thickness at this time as D1. After hot pressing at 85°C with a pressure of 1 MPa for 1 hour, test the thickness before and after hot pressing and record the thickness at this time as D2. Thickness compression = (D1-D2) / D1×100%.

[0068] Diaphragm air permeability test:

[0069] The air permeability of the membrane was tested using an air permeability meter, where the air column volume of the air permeability meter was 100 cm 3 , the diaphragm test area is 6.45cm 2 During the test, keep the diaphragm absolutely flat, repeat the test 3 times, and take the average value as the final air permeability value.

[0070] Diaphragm porosity test:

[0071] The porosity of the diaphragm was measured using the gas displacement method: porosity = (V - V0) / V × 100%, where the pore volume is V - V0, where V0 is the true volume of the diaphragm and V is the total volume of the diaphragm. The test was performed using a fully automatic true density tester (AccuPyc II 1340) and helium as the test gas.

[0072] Diaphragm thermal shrinkage test:

[0073] Lithium-ion batteries were disassembled to obtain separators. The separators were stacked along the longitudinal direction (MD) to produce three separator layers with aligned longitudinal edges. A 72.5 mm × 54.2 mm die was used, with the 72.5 mm edge of the die placed parallel to the longitudinal direction of the separator. Three separator samples were punched out using a punch press. The separator samples were measured for their width (TD) dimension (X1) and length (Z1). Separator samples were stacked, each separated by a sheet of white paper (A6 size, 105 mm × 148 mm). The stacked separator samples were placed on a steel plate and set to 135°C. After reaching the set temperature, the separators were placed in the oven along with the steel plate and baked for 1 hour. After baking, the samples were removed and allowed to rest at room temperature for 10 minutes. The baked length and width dimensions of the separators with the same number were measured. The average width dimension of each sample was recorded as X2, and the average length dimension of each sample was recorded as Z2. If the sample edge shrinks unevenly, the maximum shrinkage position shall be used as the standard. The length direction and width direction of the diaphragm are the length direction and width direction commonly used in the art.

[0074] Thermal shrinkage in the width direction = (X1-X2) / X1×100%,

[0075] Thermal shrinkage in the longitudinal direction = (Z1-Z2) / Z1×100%.

[0076] Test of water drop contact angle of porous coating:

[0077] The test was carried out using a water drop contact angle tester.

[0078] Thickness test:

[0079] (1) Diaphragm Thickness Range and COV Testing: Measure 30 points along the length of the diaphragm at 5mm intervals using a micrometer. The thickness range and COV are calculated. The thickness range and COV are known in the art and can be calculated using methods known in the art.

[0080] (2) Test of lithium-ion battery thickness: Use a micrometer to measure one point every 5 mm along the length direction of the lithium-ion battery, and test a total of 10 points. The final average value is taken as the thickness of the lithium-ion battery.

[0081] Wet pressure adhesion test:

[0082] The fully charged lithium-ion battery was disassembled to obtain the composite part of the separator and the positive electrode. The composite part was cut into 15 mm × 54.2 mm strip samples. The adhesion between the separator and the positive electrode was tested according to the national standard GB / T 2792-1998 (Test method for 180° peel strength of pressure-sensitive adhesive tapes).

[0083] Judgment of gel phenomenon:

[0084] After discharge, the lithium-ion batteries in each example and comparative example were disassembled and inspected for the presence of a gel-like substance inside the lithium-ion battery. If a gel-like substance was present, the separator was considered to have gelled, and this was scored as "yes." If no gel-like substance was present, the separator was considered to have not gelled, and this was scored as "no."

[0085] Determination of lithium precipitation degree:

[0086] Place the lithium-ion battery in a 0°C thermostat and let it rest for 60 minutes to reach a constant temperature. Once the battery reaches a constant temperature, charge it at 0°C at a constant current of 1C to 4.45V. Then, charge it at a constant voltage of 4.45V to 0.025C. Let it rest for 5 minutes, and then discharge it at a constant current of 1C to 3.0V. This constitutes one charge-discharge cycle. After 10 cycles, charge it at a constant current of 1C to 4.45V, and then charge it at a constant voltage of 4.45V to 0.025C. This completes a fully charged battery that has undergone 10 cycles. Disassemble the battery in a dry room with a humidity of less than 5%, and photograph the condition of the negative electrode.

[0087] The degree of lithium plating of lithium-ion batteries is determined according to the following standards:

[0088] No lithium deposition: no lithium deposition on the surface of the negative electrode;

[0089] Slight lithium deposition: The lithium deposition area on the surface of the negative electrode is less than 10%;

[0090] Moderate lithium deposition: The lithium deposition area on the surface of the negative electrode is 10% to 30%;

[0091] Severe lithium deposition: The lithium deposition area on the surface of the negative electrode is greater than 30%.

[0092] Winding quality test:

[0093] Use a winding machine to continuously produce 1,000 lithium-ion batteries and count the number of lithium-ion batteries that were scrapped due to tab misalignment. Winding quality rate = (1 - number of scrapped tab misalignment batteries / 1,000) × 100%. Tab misalignment is considered when the tab misalignment is so severe that welding is impossible.

[0094] 80℃ storage performance:

[0095] The lithium-ion battery was placed in a 25°C environment for 30 minutes, then charged to 4.2V at a constant current rate of 0.2C, then charged to 0.05C at a constant voltage rate of 4.2V, placed in a 30-minute environment, and then discharged to 2.8V at a rate of 0.5C. The external dimensions of the lithium-ion battery at this time were recorded. The fully charged battery was then placed in an oven at approximately 80°C for approximately 7 days, and the external dimensions of the lithium-ion battery were recorded.

[0096] The storage performance of lithium-ion batteries is judged according to the following deformation standards:

[0097] No deformation: The thickness change rate of lithium-ion batteries is less than 3%;

[0098] Slight deformation: The thickness change rate of lithium-ion batteries is 3% to 10%;

[0099] Deformation: The thickness change rate of lithium-ion batteries is greater than 10%.

[0100] Example 1-1

[0101] <Preparation of Positive Electrode>

[0102] The positive electrode active material LiCoO2, the conductive agent conductive carbon black, and the binder polyvinylidene fluoride were mixed in a mass ratio of 96:2:2. N-methylpyrrolidone (NMP) was added and stirred evenly in a vacuum mixer to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was evenly coated on one surface of a 12 μm thick positive electrode current collector aluminum foil. The aluminum foil was dried at 120°C for 1 hour to obtain a positive electrode coated on one side with a positive electrode material layer. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode coated on both sides with a positive electrode material layer. After cold pressing, cutting, and slitting, the cathode was dried under vacuum at 120°C for 1 hour to obtain a positive electrode with a size of 74 mm x 867 mm.

[0103] <Preparation of Negative Electrode>

[0104] The negative electrode active material graphite, the binder styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed in a mass ratio of 97.4:1.4:1.2, deionized water was added, and the mixture was stirred uniformly in a vacuum mixer to obtain a negative electrode slurry with a solids content of 75 wt%. The negative electrode slurry was evenly coated on one surface of a 12 μm thick copper foil for the negative electrode current collector. The foil was then dried at 120°C to obtain a negative electrode coated on one side with a 130 μm thick negative electrode material layer. The above steps were repeated on the other surface of the aluminum foil to obtain a negative electrode coated on both sides. The negative electrode was then cold pressed, cut, and slit, and then dried under vacuum at 120°C for 1 hour to obtain a negative electrode measuring 78 mm x 875 mm.

[0105] <Preparation of Electrolyte>

[0106] In an argon atmosphere glove box with a water content of <10 ppm, EC, PC, and DMC were mixed in a mass ratio of 3:2.5:4.5 to obtain an organic solvent. Lithium hexafluorophosphate (LIPF) was then added to the organic solvent to obtain an electrolyte solution. The concentration of the lithium salt was 1 mol / L.

[0107] <Preparation of Separator>

[0108] Cyclohexyl methacrylate and isobutyl acrylate were mixed in a mass ratio of 5:95 to obtain an auxiliary binder. 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. After adding water, the mixture was stirred evenly to obtain a porous coating slurry with a solid content of 10 wt%. The porous coating slurry was evenly coated on one surface of a porous substrate with a thickness of 16 μm using a micro-concave roller coating method, and then dried at 45 ° C to obtain a diaphragm coated with a porous coating on one side. The above steps were repeated to obtain a diaphragm coated with a porous coating on both sides. The polymer has a Dv50 of 8 μm, a sphericity of 0.8, and a Tg of 50°C. The mass ratio of styrene to isooctyl acrylate in the styrene-isooctyl acrylate copolymer is 7:3. The porous substrate is made of polypropylene with a weight-average molecular weight of 500,000. The pore size of the porous substrate is 30 nm, the thickness of the porous substrate is 16 μm, and the surface density of the porous coating is 0.2 g / m 2 , the thickness ratio of the porous coating and the porous substrate is 1:3.

[0109] <Preparation of lithium-ion batteries>

[0110] The prepared positive electrode, separator, and negative electrode are stacked in order, with the separator positioned between the positive and negative electrodes to provide isolation, and then wound to form an electrode assembly. The electrode assembly is then placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. The lithium-ion battery is then produced through vacuum packaging, resting, formation, degassing, and trimming.

[0111] Example 1-2 to Example 1-10

[0112] Except for adjusting the relevant parameters according to Table 1, the rest is the same as Example 1-1.

[0113] Example 2-1 to Example 2-3

[0114] Except for adjusting the relevant parameters according to Table 2, the rest is the same as Example 1-1.

[0115] Example 3-1 to Example 3-4

[0116] Except for adjusting the relevant parameters according to Table 3, the rest is the same as Example 1-1.

[0117] Example 4-1 to Example 4-8

[0118] Except for adjusting the relevant parameters according to Table 4, the rest is the same as Example 1-1.

[0119] Example 5-1 to Example 5-6

[0120] Except that carboxylic acid ester was added according to Table 5 and relevant parameters were adjusted according to Table 5 when preparing the organic solvent in the step of <Preparation of Electrolyte>, the rest was the same as Example 1-1.

[0121] Comparative Example 1

[0122] The process was the same as that of Example 1-1 except that the polymer was replaced with PVDF-HFP having an HFP content of 10% by mass in the process of <Preparation of Separator>.

[0123] The relevant preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 5.

[0124] Table 1

[0125]

[0126]

[0127] Note: The “7:3” in the styrene-isooctyl acrylate copolymer (7:3) of Example 1 in Table 1 indicates that the mass ratio of styrene to isooctyl acrylate in the styrene-isooctyl acrylate copolymer is 7:3. The same applies to the other examples.

[0128] It can be seen from Examples 1-1 to 1-10 and Comparative Example 1 that when the thickness COV of the separator is within the range of the present application, the winding efficiency of the lithium-ion battery is improved, that is, the packaging performance of the lithium-ion battery is improved.

[0129] The properties of polymers and diaphragms usually affect the performance of lithium-ion batteries. It can be seen from Examples 1-1 to 1-10 that when the polymer is within the scope of this application, the gelation phenomenon of the diaphragm is improved, and the obtained lithium-ion battery has good packaging performance and its lithium plating phenomenon is also improved.

[0130] Table 2

[0131]

[0132] The mass percentages of polymers, auxiliary binders, thickeners and wetting agents in the porous coating usually affect the performance of the diaphragm and the lithium-ion battery. It can be seen from Examples 1-1, 2-1 and 2-3 that when the mass percentages of polymers, auxiliary binders, thickeners and wetting agents in the porous coating are within the range of this application, the obtained diaphragm also has good thickness consistency, electrolyte resistance and thermal stability, the gelation phenomenon of the diaphragm is improved, and the obtained lithium-ion battery has good packaging performance and its lithium precipitation phenomenon is also improved.

[0133] Table 3

[0134]

[0135]

[0136] The Dv50 and sphericity of the polymer usually affect the performance of the separator and the lithium-ion battery. It can be seen from Examples 1-1, 3-1 and 3-4 that when the Dv50 and sphericity of the polymer are within the scope of this application, the obtained separator also has good thickness consistency and its gelation phenomenon is improved, so that the obtained lithium-ion battery has good packaging performance and its lithium plating phenomenon is also improved.

[0137] Table 4

[0138]

[0139] The thickness of the porous substrate, the thickness ratio of the porous coating and the porous substrate, the surface density of the porous coating, the pore size of the porous substrate, and the weight-average molecular weight of the polypropylene usually affect the performance of the diaphragm and the lithium-ion battery. It can be seen from Examples 1-1 and 4-1 to 4-8 that when the thickness of the porous substrate, the thickness ratio of the porous coating and the porous substrate, the surface density of the porous coating, the pore size of the porous substrate, and the weight-average molecular weight of the polypropylene are within the scope of this application, the obtained diaphragm has good thickness consistency, a suitable water droplet contact angle and thermal stability, and its gelation phenomenon is improved, so that the obtained lithium-ion battery has good packaging performance and its lithium precipitation phenomenon is also improved.

[0140] Table 5

[0141]

[0142] The components in the electrolyte usually affect the performance of the lithium-ion battery. Referring to Table 5, it can be seen from Examples 1-1, 5-1 and 5-6 that when the electrolyte contains carboxylic acid esters and their type and mass percentage are within the range of this application, the packaging performance and high-temperature storage performance of the lithium-ion battery can be further improved.

[0143] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A separator comprising a porous substrate and a porous coating disposed on at least one surface of the porous substrate, wherein the porous coating comprises a polymer, the separator having a thickness covariance of 0.01 to 0.02, and a thickness ratio of the porous coating to the porous substrate of 1:2 to 1:

5.

2. The diaphragm according to claim 1, wherein Based on the mass of the porous coating, the mass percentage of the polymer is 76.5% to 92.5%, the swelling degree of the polymer in the test electrolyte is 40% to 170%, and 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 the lithium hexafluorophosphate is 1 mol / L.

3. The diaphragm according to claim 1, wherein The thickness covariance of the diaphragm is 0.013 to 0.

018. The diaphragm according to claim 1 , wherein: The polymer includes polyacrylamide, polyolefin having a monomer carbon atom number of 19 to 35, polyvinylidene fluoride, a polyvinylidene fluoride-hexafluoropropylene copolymer having a mass percentage of hexafluoropropylene of less than 5%, a homopolymer formed by the following compounds, or at least one copolymer 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, epoxy methyl methacrylate, n-butyl acrylate, cyclohexyl acrylate, octyl acrylate, vinyl acrylate, methyl vinyl acrylate, and isopentyl acrylate. The diaphragm according to claim 1 , wherein The polymer includes 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, epoxy methyl methacrylate, n-butyl acrylate, cyclohexyl acrylate, octyl acrylate, vinyl acrylate, methyl vinyl acrylate, and isopentyl acrylate. The diaphragm according to claim 1 , wherein: The polymer has a glass transition temperature of 40°C to 65°C.

7. The diaphragm according to claim 1, wherein The polymer has a Dv50 of 5 μm to 10 μm.

8. The diaphragm according to claim 1, wherein At 85° C., after the polymer is immersed in a test electrolyte for 2 hours, the viscosity of the test electrolyte is less than or equal to 10,000 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 the lithium hexafluorophosphate is 1 mol / L.

9. The diaphragm according to claim 1, wherein The polymer has a sphericity greater than or equal to 0.7 and less than 1.

10. The diaphragm 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%.

11. The diaphragm according to claim 1, wherein The separator was hot-pressed at 85° C. with a pressure of 1 MPa for 1 hour, and the thickness of the separator was compressed by 80% to 95%.

12. The diaphragm according to claim 1, wherein The porous coating layer has a water drop contact angle of 60° to 90°.

13. The diaphragm according to claim 1, wherein The surface density of the porous coating is 0.1 g / m 2 Up to 0.4g / m 2 .

14. The diaphragm according to claim 1, wherein The porous substrate has a thickness of 8 μm to 40 μm.

15. The diaphragm according to claim 1, wherein The material of the porous substrate includes polypropylene having a weight average molecular weight of 100,000 to 1,000,000.

16. The diaphragm according to claim 1, which satisfies at least one of the following characteristics: (a) the air permeability of the diaphragm is 60s / 100ml to 300s / 100ml; (b) the porosity of the separator is 30% to 55%; (c) the pore size of the porous substrate is 10 nm to 80 nm; (d) The separator has a heat shrinkage rate in both its longitudinal direction and width direction at 130° C. that is less than or equal to 10%. 17 . An electrochemical device comprising the separator according to claim 1 . 18 . The electrochemical device according to claim 17 , comprising an electrolyte, wherein the electrolyte comprises a carboxylate ester, and the mass percentage of the carboxylate ester is 10% to 65% based on the mass of the electrolyte.

19. The electrochemical device according to claim 18, wherein 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.

20. An electronic device comprising the electrochemical device according to any one of claims 17 to 19.

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