Separator and electrochemical device

Abstract

The present invention relates to the technical field of electrochemical devices, and in particular to a separator and an electrochemical device. The separator comprises a carrier layer and a polymer layer located on one side surface or two side surfaces of the carrier layer; the polymer layer comprises a polymer A and a polymer B; the polymer A is a copolymer comprising a first monomer and a second monomer; the polymer B is a copolymer or homopolymer comprising a third monomer; and the ratio of the weight of the polymer A to the weight of the polymer B is (0.1-9):1. The separator has a low swelling degree in an electrolyte and high adhesion strength, and is durable and stable, thereby reducing the thickness swelling rate of a battery, and improving the cycle performance of the battery, particularly the long cycle performance.

Description

Diaphragms and electrochemical devices Technical Field

[0001] The present disclosure relates to the technical field of electrochemical devices, and in particular to a diaphragm and an electrochemical device. Background Art

[0002] Lithium-ion batteries offer advantages over other secondary batteries, such as high energy density, long cycle life, low self-discharge, and no memory effect. Consequently, they have been widely recognized and applied in the market since their introduction. Lithium-ion batteries are typically composed of positive and negative electrode materials, a separator, and an electrolyte. The separator acts as a barrier between the positive and negative electrode materials, preventing direct contact and electron transfer between them while allowing ions in the electrolyte to pass through the separator to the positive and negative electrodes.

[0003] Existing technologies typically enhance the performance of diaphragms by coating their surfaces. For example, an inorganic layer is applied to the diaphragm to improve thermal stability, while an organic adhesive layer is applied to the diaphragm to enhance adhesion between the diaphragm and the electrode. However, while existing organic adhesive layers swell slightly, their adhesion is weak. Alternatively, within lithium-ion batteries, they swell significantly due to the electrolyte, rapidly decreasing adhesion between the electrode and diaphragm interface. This results in a continuous weakening of the diaphragm-electrode adhesion after repeated charge and discharge cycles, impacting the long-term stability of the battery.

[0004] Therefore, there is an urgent need to invent a diaphragm that has better bonding properties, low swelling degree in the battery, and long-lasting and stable bonding force. Summary of the Invention

[0005] The present invention aims to overcome the existing problems of separators, such as low swelling in electrolyte but weak adhesion, or high swelling but a continuous decrease in adhesion between the separator and the electrode after repeated charge and discharge, which reduces the long-term stability of the battery. The present invention provides a separator and electrochemical device. The separator exhibits low swelling in electrolyte, strong, long-lasting, and stable adhesion, reducing the thickness expansion rate of the battery and improving its cycle performance, particularly long-term cycle performance.

[0006] Research has found that reducing the swelling degree of the diaphragm in the electrolyte, improving the adhesion of the diaphragm and its long-term stability can reduce the thickness expansion rate of the battery and improve the battery's cycle performance, especially long-cycle performance.

[0007] On the one hand, in order to reduce the degree of swelling of the diaphragm in the electrolyte and improve the adhesion of the diaphragm and its long-term stability, a diaphragm with a specific structure can be used to reduce the degree of swelling of the diaphragm in the electrolyte, while improving the adhesion of the diaphragm and making the strong adhesion lasting and stable.

[0008] On the other hand, in order to reduce the degree of swelling of the diaphragm in the electrolyte and improve the adhesion of the diaphragm and its long-term stability, a diaphragm with a coating of a specific surface density can be combined with an electrolyte with a specific component content to reduce the degree of swelling of the diaphragm in the electrolyte, while improving the adhesion of the diaphragm and making the strong adhesion lasting and stable.

[0009] In order to achieve the above-mentioned purpose of the invention, the first aspect of the present disclosure provides a separator for a lithium-ion battery, wherein the separator includes a carrier layer and a polymer layer located on one side or both sides of the carrier layer; the polymer layer includes polymer A and polymer B, wherein the polymer A is a copolymer including a first monomer and a second monomer, and the polymer B is a copolymer or homopolymer including a third monomer, and the ratio of the weight of the polymer A to the weight of the polymer B is (0.1-9):1.

[0010] A second aspect of the present disclosure provides an electrochemical device, which includes the separator according to the first aspect of the present disclosure.

[0011] A third aspect of the present disclosure provides an electrochemical device, which includes a diaphragm, an electrolyte, a positive electrode sheet, and a negative electrode sheet. The electrolyte includes ethyl propionate, and the weight content of the ethyl propionate is SC based on the total weight of the electrolyte; the diaphragm includes a carrier layer and a polymer layer located on one side or both sides of the carrier layer. The surface density of the polymer layer is CW, and the electrochemical device satisfies the following relationship: 0.4≤SC / CW≤6.

[0012] Through the above technical solution, the present disclosure has at least the following advantages compared with the prior art:

[0013] (1) The membrane disclosed herein has a low degree of swelling in the electrolyte;

[0014] (2) The membrane disclosed herein has strong bonding force and is durable and stable;

[0015] (3) The thickness expansion rate of the electrochemical device disclosed herein is low;

[0016] (4) The electrochemical device disclosed herein has good cycle performance, especially good long cycle performance.

[0017] Other features and advantages of the present disclosure will be described in detail in the following detailed description.

[0018] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG1 is a schematic diagram of a battery separator according to the present disclosure.

[0020] The reference numerals are as follows: 10 carrier layer, 11 substrate, 12 heat-resistant layer; 20 polymer layer, 21 polymer A, 22 polymer B. DETAILED DESCRIPTION

[0021] The following is a detailed description of the specific embodiments of the present disclosure. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure and are not intended to limit the present disclosure. In this article, unless otherwise specified, data ranges include endpoints.

[0022] It should be noted that the numerical expressions such as "first" and "second" in the present disclosure are only used to distinguish different substances or usage methods, and do not represent a difference in order.

[0023] In a first aspect of the present disclosure, a separator for a lithium-ion battery is provided, comprising a carrier layer and a polymer layer located on one or both sides of the carrier layer; the polymer layer comprises a polymer A and a polymer B, wherein the polymer A is a copolymer comprising a first monomer and a second monomer, and the polymer B is a copolymer or homopolymer comprising a third monomer, and the ratio of the weight of the polymer A to the weight of the polymer B is (0.1-9):1.

[0024] As shown in Figure 1, the diaphragm may include a carrier layer 10 and a polymer layer 20 located on one or both sides of the carrier layer 10. The diaphragm having the above-mentioned specific structure can not only improve the thermal stability of the diaphragm, ensure that the diaphragm has good heat resistance, but also improve the adhesion between the diaphragm and the electrode.

[0025] The polymer layer 20 may include a polymer A 21 and a polymer B 22 .

[0026] The degree of swelling of polymer A in the electrolyte is low, which can reduce the swelling of the polymer layer in the electrolyte. The ion conductivity of polymer B is good, which can improve the ion conductivity of the polymer layer. The polymer layer including polymer A and polymer B can not only have excellent adhesion between the diaphragm and the electrode, but also reduce the degree of swelling of the diaphragm in the electrolyte, improve the adhesion of the diaphragm and its long-term stability, and improve the ion conductivity of the diaphragm, thereby reducing the thickness expansion rate of the battery and improving the cycle performance of the battery.

[0027] The polymer A may be a copolymer including a first monomer and a second monomer.

[0028] The polymer B may be a copolymer or a homopolymer including a third monomer.

[0029] The weight ratio of the polymer A to the polymer B can be (0.1-9):1 (e.g., 0.1:1, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 6:1, 7:1, 8:1, 9:1).

[0030] The above-mentioned diaphragm with a specific structure can have lower swelling and higher ion conductivity by limiting the polymer A and polymer B in the polymer layer. The adhesion of the diaphragm can be improved and the stability can be sustained. By limiting the weight ratio of polymer A and polymer B in the polymer layer, the adhesion and ion conductivity of the diaphragm can be better adapted, thereby improving the comprehensive performance of the diaphragm. Therefore, the diaphragm with the above-mentioned specific structure can reduce the swelling degree of the diaphragm, improve the adhesion and long-term stability of the diaphragm, and provide the ion conductivity of the diaphragm.

[0031] In the present disclosure, the separator with the above-mentioned specific structure has been able to achieve lower swelling, stronger adhesion, and longer-term stability than the existing technology, thereby achieving a low thickness expansion rate and good cycle performance, especially good long-term cycle performance in the battery. To further improve the performance, one or more of the technical features can be further optimized.

[0032] In one embodiment, the weight ratio of polymer A to polymer B in the polymer layer is (0.25-1):1. When the weight ratio of polymer A to polymer B in the polymer layer is limited to the above-mentioned specific range, the adhesion and ion conductivity of the separator can be better adapted, thereby further improving the combined performance of the adhesion and ion conductivity of the separator.

[0033] In one example, the first monomer includes one or more of ethylene, propylene, and butene.

[0034] In one example, the second monomer includes one or more of methacrylic acid, acrylic acid, acrylic ester, styrene, butadiene, vinyl chloride, acrylonitrile, isoprene, ethylene oxide, propylene oxide, and vinyl acetate.

[0035] According to a specific embodiment, the acrylate includes esters of its homologues. For example, the acrylate includes at least one of methyl acrylate, ethyl acrylate, methyl 2-methacrylate, and ethyl 2-methacrylate. The second monomer type of polymer A can increase the adhesiveness of polymer A.

[0036] In one embodiment, the first monomer includes one or more of ethylene, propylene, and butene, and the second monomer includes one or more of methacrylic acid, acrylic acid, acrylic esters, styrene, butadiene, vinyl chloride, acrylonitrile, isoprene, ethylene oxide, propylene oxide, and vinyl acetate. The polymer A formed by the specific first and second monomers can reduce the swelling of the polymer layer and improve its adhesion, thereby improving the adhesion of the separator and making the adhesion of the separator durable and stable, thereby reducing the thickness expansion rate of the battery and improving the battery's cycle performance, especially long-term cycle performance.

[0037] According to a specific embodiment, in polymer A, the molar ratio of the first monomer to the second monomer is (0.5-99):1 (e.g., 0.5:1, 1:1, 5:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 99:1). When the molar ratio of the first monomer to the second monomer is limited to the above specific range, the swelling degree of the separator can be reduced and the adhesion of the separator can be improved.

[0038] In one example, in polymer A, the molar ratio of the first monomer to the second monomer is (5-90):1.

[0039] According to a specific embodiment, polymer A includes at least one of polyethylene-methacrylic acid copolymer, polyethylene-acrylic acid copolymer, polypropylene-acrylic acid copolymer, and polyethylene-styrene copolymer.

[0040] In one example, the third monomer includes one or more of vinylidene fluoride, hexafluoropropylene, tetrafluoroethylene, vinyl chloride, butadiene, and acrylonitrile.

[0041] According to a specific embodiment, polymer B includes at least one of polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-tetrafluoroethylene copolymer, polyvinylidene fluoride, and polyvinylidene fluoride-acrylic acid copolymer.

[0042] In one embodiment, the first monomer includes one or more of ethylene, propylene, and butene; the second monomer includes one or more of acrylate, styrene, butadiene, vinyl chloride, acrylonitrile, isoprene, ethylene oxide, propylene oxide, and vinyl acetate; and the third monomer includes one or more of vinylidene fluoride, hexafluoropropylene, tetrafluoroethylene, vinyl chloride, butadiene, and acrylonitrile. Because the selected first, second, and third monomers have strong similarities with the diaphragm substrate and the binder used in the electrode, the polymer layer in the diaphragm of the present disclosure has strong adhesion to the substrate layer, and at the same time has good compatibility with the binder in the electrode, thereby making the adhesion between the diaphragm and the electrode stronger and more stable.

[0043] According to a specific embodiment, the softening temperature of polymer A is 40°C to 90°C. Exemplary are any of 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C or any value between the range values ​​composed of any two of the above values. Limiting the softening temperature of polymer A to the above-mentioned specific range is beneficial to improving the adhesion of the polymer. When the softening temperature is too low (for example, below 40°C), the polymer will stick to itself and the roller during use, affecting the performance of the diaphragm; when the softening temperature is too high (for example, above 90°C), the polymer requires too high a temperature to achieve good adhesion, which will affect the solid electrolyte interface film (SEI film) and further affect the performance of electrochemical devices such as batteries.

[0044] In one embodiment, the softening temperature of polymer A is 50°C to 70°C.

[0045] According to a specific embodiment, the median particle size Dv50 of the primary particles of polymer A is 0.1 μm to 5 μm. Exemplary values ​​are any of 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, and 5 μm, or any value within a range consisting of any two of the above values. When the median particle size Dv50 of the primary particles of polymer A is limited to the above specific range, it is beneficial to improve the adhesion between the diaphragm and the electrode, and at the same time, the porosity of the diaphragm can be increased, providing storage space for the electrolyte, while preventing pore blockage and reducing the lithium ion conductivity of the diaphragm.

[0046] In one example, the median particle size Dv50 of the primary particles of polymer A is 0.5 μm to 3 μm.

[0047] According to a specific embodiment, the molecular weight of polymer A is 10W to 100W. Exemplary values ​​include 10W, 20W, 30W, 40W, 50W, 60W, 70W, 80W, 90W, and 100W, or any value within a range consisting of any two of these values. Limiting the molecular weight of polymer A to this specific range helps improve the adhesion of the polymer layer.

[0048] In one embodiment, the molecular weight of polymer A is 40W to 60W.

[0049] According to a specific embodiment, the melting point of polymer B is 125°C to 200°C. Exemplary are any of 125°C, 130°C, 133°C, 138°C, 140°C, 146°C, 150°C, 160°C, 162°C, 170°C, 180°C, 190°C, 200°C or any value between the range values ​​consisting of any two of the above values. When the melting point is too low (for example, below 130°C), the polymer will stick to itself and the roller during use, affecting the performance of the diaphragm; when the melting point is too high (for example, above 150°C), the polymer requires too high a temperature to achieve good adhesion, which will affect the solid electrolyte interface film (SEI film) and further affect the performance of electrochemical devices such as batteries. Preferably, the melting point of polymer B is 130°C to 155°C.

[0050] According to a specific embodiment, the median particle size Dv50 of the primary particles of polymer B is 0.1 μm to 1 μm, and is exemplified by any of 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, and 1 μm, or any value between the ranges consisting of any two of the above values. The median particle size Dv50 of the secondary particles formed by the agglomeration of polymer B is 1 μm to 10 μm, and is exemplified by any of 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm, or any value between the ranges consisting of any two of the above values. When the Dv50 of the primary particles of polymer B and the Dv50 of the secondary particles formed by the agglomeration of polymer B are limited to the above specific ranges, it is beneficial to improve the adhesion of the polymer layer.

[0051] In one example, the median particle size Dv50 of the primary particles of polymer B is 0.2 μm to 0.4 μm, and the median particle size Dv50 of the secondary particles formed by agglomeration of polymer B is 1.5 μm to 5 μm.

[0052] According to a specific embodiment, the crystallinity of polymer B is 35% to 55%. Exemplary values ​​include 35%, 38%, 40%, 42%, 45%, 46%, 48%, 50%, 52%, and 55%, or any value within a range consisting of any two of these values. Limiting the crystallinity of polymer B to this specific range helps improve the adhesion of the polymer layer.

[0053] In one embodiment, the crystallinity of polymer B is 40% to 50%.

[0054] According to a specific embodiment, the molecular weight of polymer B is 10W to 100W. Exemplary values ​​include 10W, 20W, 30W, 40W, 50W, 60W, 70W, 80W, 90W, and 100W, or any value within a range consisting of any two of these values. Limiting the molecular weight of polymer B to this specific range helps improve the adhesion of the polymer layer.

[0055] In one embodiment, the median particle size Dv50 of the primary particles of polymer A is greater than the median particle size Dv50 of the primary particles of polymer B. When the median particle size Dv50 of the primary particles of polymer A is greater than the median particle size Dv50 of the primary particles of polymer B, it is beneficial to improve the adhesion of the polymer layer.

[0056] In one embodiment, the ratio of the median particle size Dv50 of the secondary particles formed by agglomeration of polymer B to the median particle size Dv50 of the primary particles of polymer A is (1-10):1. Exemplary ratios include any of 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, and 10:1, or any range between any two of these values. Within this range, the adhesion of the polymer layer is improved.

[0057] In one example, the ratio of Dv50 of the secondary particles formed by agglomeration of polymer B to Dv50 of the primary particles of polymer A is (1-5):1.

[0058] According to a specific embodiment, when polymer A and polymer B simultaneously have the aforementioned suitable softening temperature and particle size, the adhesion between the polymer layer and the electrode and carrier layer can be improved, and the polymer layer can be formed with appropriate pores and surface density, so that the diaphragm still has good air permeability, ion conductivity and electrolyte wettability after undergoing processes such as hot pressing and forming during the battery manufacturing process.

[0059] According to a specific embodiment, based on the sum of the weights of the polymer A and the polymer B, the weight content of the polymer A is 10wt% to 60wt% (for example, 10wt%, 20wt%, 30wt%, 40wt%, 50wt%, 60wt% or any point within the range formed by any two of the aforementioned numerical values), and the weight content of the polymer B is 40wt% to 90wt% (for example, 40wt%, 50wt%, 60wt%, 70wt%, 80wt%, 90wt% or any point within the range formed by any two of the aforementioned numerical values). When the weight content of polymer A and the weight content of polymer B in the polymer A and polymer B are respectively limited to the above-mentioned specific ranges, the adhesion between the separator and the electrode can be improved, the separator has a low degree of swelling in the electrolyte, has long-term stable adhesion performance, and improves the long cycle performance and expansion performance of the battery.

[0060] In one embodiment, based on the sum of the weights of polymer A and polymer B, the weight content of polymer A is 20 wt% to 40 wt%, and the weight content of polymer B is 60 wt% to 80 wt%. When the weight content of polymer A and polymer B in the polymer layer is limited to the above specific ranges, the adhesion between the separator and the electrode is improved, and the degree of swelling of the separator in the electrolyte is reduced.

[0061] According to a specific embodiment, the polymer layer further includes an auxiliary agent, wherein the auxiliary agent includes at least one of a first thickener, a first wetting agent, and a first binder. When the polymer layer includes the auxiliary agent, the adhesion of the polymer layer can be increased, making the preparation of the separator easier.

[0062] According to a specific embodiment, based on the total weight of the polymer layer, the weight content of the sum of the polymer A and the polymer B is 75wt% to 97.9wt%, the weight content of the first thickener is 1wt% to 10wt%, the weight content of the first wetting agent is 0.1wt% to 5wt%, and the weight content of the first binder is 1wt% to 10wt%.

[0063] In one example, based on the total weight of the polymer layer, the weight content of the sum of the polymer A and the polymer B is 89wt% to 97.9wt%, the weight content of the first thickener is 1wt% to 5wt%, the weight content of the first wetting agent is 0.1wt% to 1wt%, and the weight content of the first binder is 1wt% to 5wt%.

[0064] According to a specific embodiment, the first thickener includes but is not limited to at least one of hydroxyethyl cellulose, methyl hydroxyethyl cellulose, sodium carboxymethyl cellulose (CMC-Na), polyacrylamide (PAM), polyethylene oxide (PEO) and sodium alginate.

[0065] According to a specific embodiment, the first wetting agent includes but is not limited to at least one of fluoroalkyl methoxy ether alcohol, fluoroalkyl ethoxy ether alcohol, dimethylsiloxane, alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether and fatty acid polyoxyethylene ether.

[0066] According to a specific embodiment, the first binder includes but is not limited to at least one of methacrylic acid, styrene-butadiene latex, styrene-acrylic latex, pure styrene latex, polymethyl methacrylate, polybutyl methacrylate, polyethyl acrylate, polyvinyl alcohol, ethylene-vinyl acetate copolymer, polyvinyl acetate and polyurethane.

[0067] In one embodiment, the surface density of the polymer layer is 0.1 g / m 2 ~1g / m 2 . Exemplarily 0.1 g / m 2 , 0.2g / m 2 , 0.3g / m 2 , 0.4g / m 2 , 0.5g / m 2 , 0.6g / m 2 , 0.7g / m 2 , 0.8g / m 2 , 0.9g / m 2 , 1g / m 2 Or any point value within the range of the above two values. When the surface density of the polymer layer is too low (for example, less than 0.1g / m 2 ) Insufficient amount of polymer A and / or polymer B can not provide sufficient adhesion, and the electrochemical device such as the battery becomes soft, which may easily lead to safety accidents; when the surface density of the polymer layer is too high (for example, higher than 1g / m 2 ) The coating amount of polymer A and / or polymer B is too high, which blocks the transmission channel of the electrolyte and is not conducive to the rate performance and cycle performance of electrochemical devices such as batteries.

[0068] In one embodiment, the surface density of the polymer layer is 0.2 g / m 2 ~0.6g / m 2 .

[0069] In the present disclosure, surface density refers to single-sided surface density. For example, the surface density of the polymer layer indicates that when the polymer layer is located on the surface of one side of the heat-resistant layer or the surface of one side of the substrate, the surface density of the polymer layer is the surface density of that side (i.e., the side with the polymer layer); when the polymer layer is located on the surfaces of both sides of the heat-resistant layer or the surfaces of the heat-resistant layer and the substrate layer, the surface densities of the polymer layers on both sides are the same, and the surface density of the polymer layer is the surface density of either side.

[0070] In one example, the polymer layer has a thickness of 0.3 μm to 6 μm (eg, 0.3 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm).

[0071] In one example, the thickness of the polymer layer is 0.5 μm to 2 μm.

[0072] In one embodiment, the carrier layer includes a substrate and a heat-resistant layer located on one or both surfaces of the substrate. The heat-resistant layer 12 can be located on one or both surfaces of the substrate 11; the polymer layer 20 can be located on the surface of the heat-resistant layer 12, or on the surface of the substrate 11, or on both surfaces of the heat-resistant layer 12 and the substrate 11. As shown in Figure 1, the heat-resistant layer 12 is located on one surface of the substrate 11, and the polymer layer 20 is located on both surfaces of the heat-resistant layer 12 and the substrate 11.

[0073] According to a specific embodiment, the heat-resistant layer includes inorganic particles and a second binder.

[0074] In one example, based on the total weight of the heat-resistant layer, the weight content of the inorganic particles is 60wt% to 99wt%; exemplified by 60wt%, 70wt%, 80wt%, 90wt%, 95wt%, 99wt% or any point within the range consisting of any two of the foregoing values.

[0075] In one embodiment, based on the total weight of the heat-resistant layer, the weight content of the inorganic particles is 89.6 wt % to 98.2 wt %.

[0076] In one example, based on the total weight of the heat-resistant layer, the weight content of the second binder is 1wt% to 40wt%; illustrative examples are 1wt%, 5wt%, 10wt%, 20wt%, 40wt% or any point within the range of any two of the aforementioned values.

[0077] In one embodiment, based on the total weight of the heat-resistant layer, the weight content of the second binder is 1.8 wt % to 10 wt %.

[0078] According to a specific embodiment, the inorganic particles are selected from one or more of alumina, boehmite, magnesium oxide, boron nitride and magnesium hydroxide.

[0079] According to a specific embodiment, the median particle size Dv50 of the inorganic particles is 0.1 μm to 5 μm, exemplified by 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or any point within the range consisting of any two of the aforementioned values.

[0080] According to a specific embodiment, the second binder includes butadiene styrene latex, styrene acrylic latex, pure styrene latex, polymethyl methacrylate, polybutyl methacrylate, polyethyl acrylate, polyvinyl alcohol, ethylene-vinyl acetate copolymer, polyvinyl acetate and polyurethane.

[0081] According to a specific embodiment, the heat-resistant layer further includes a second thickener and / or a second wetting agent.

[0082] According to a specific embodiment, based on the total weight of the heat-resistant layer, the weight content of the inorganic particles is 40wt% to 99wt%, the weight content of the second binder is 1wt% to 20wt%, the weight content of the second thickener is 0wt% to 20wt%, and the weight content of the second wetting agent is 0wt% to 20wt%. When the weight content of the second thickener in the heat-resistant layer is 0wt%, it indicates that the second thickener is not present. When the weight content of the second wetting agent in the heat-resistant layer is 0wt%, it indicates that the second wetting agent is not present.

[0083] According to a specific embodiment, the second thickener includes but is not limited to at least one of polymethylcellulose sodium, hydroxyethyl cellulose, methylhydroxyethyl cellulose, sodium carboxymethyl cellulose (CMC-Na), polyacrylamide (PAM), polyethylene oxide (PEO) and sodium alginate.

[0084] According to a specific embodiment, the second wetting agent includes but is not limited to at least one of fluoroalkyl methoxy ether alcohol, fluoroalkyl ethoxy ether alcohol, dimethylsiloxane, alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether and fatty acid polyoxyethylene ether.

[0085] According to a specific embodiment, the thickness of the heat-resistant layer is 0.5 μm to 5 μm, for example 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or any value within the range formed by any two of the aforementioned values.

[0086] According to a specific embodiment, the thickness of the substrate is 3 μm to 20 μm, for example, 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, 18 μm, 20 μm, or any value within the range formed by any two of the aforementioned values.

[0087] According to a specific embodiment, the substrate is selected from at least one of polyethylene, polypropylene, a composite material of polyethylene and polypropylene, polyamide, polyimide, polyethylene terephthalate, polybutylene terephthalate, polystyrene and aramid.

[0088] According to a specific embodiment, the porosity of the substrate is 30% to 60% (e.g., 30%, 35%, 40%, 45%, 50%, 55%, 60%).

[0089] In one example, the porosity of the substrate is 35% to 55%.

[0090] According to a specific embodiment, the air permeability of the substrate is 30s / 100mL to 200s / 100mL (for example, 30s / 100mL, 50s / 100mL, 60s / 100mL, 80s / 100mL, 100s / 100mL, 120s / 100mL, 150s / 100mL, 170s / 100mL, 200s / 100mL).

[0091] In one embodiment, the air permeability of the substrate is 60 s / 100 mL to 160 s / 100 mL.

[0092] In this disclosure, the air permeability is defined in GB / T 36363-2018. The air permeability means that 100 mL of air passes through an area of ​​6.45 cm2 under a pressure of 1.21 kPa applied by the test instrument in a test temperature, humidity and normal pressure environment. 2 The time required for the spinning layer. The applied pressure of 1.21kPa is a constant pressure, and the 6.45cm 2 The area is fixed.

[0093] In one example, the porosity of the separator is 30% to 50% (eg, 30%, 35%, 40%, 45%, 50%).

[0094] In one example, the porosity of the separator is 35% to 45%.

[0095] In one example, the air permeability of the diaphragm is 100s / 100ml to 300s / 100ml (e.g., 100s / 100ml, 110s / 100ml, 120s / 100ml, 130s / 100ml, 140s / 100ml, 150s / 100ml, 180s / 100mL, 200s / 100mL, 220s / 100mL, 250s / 100mL, 280s / 100mL, 300s / 100mL).

[0096] In one embodiment, the air permeability of the membrane is 120s / 100ml to 250s / 100ml.

[0097] A second aspect of the present disclosure provides an electrochemical device, which includes the separator according to the first aspect of the present disclosure.

[0098] The materials of the electrochemical device except the diaphragm can be made according to the methods in the art, and can achieve the effect of reducing the thickness expansion rate and improving cycle performance, especially long cycle performance.

[0099] In one example, the electrochemical device includes an electrolyte, the electrolyte includes ethyl propionate, and the weight content of the ethyl propionate is SC based on the total weight of the electrolyte; the surface density of the polymer layer is CW, then the electrochemical device satisfies the following relationship: 0.4≤SC / CW≤6 (for example, 0.4, 0.5, 1, 2, 3, 4, 5, 6). When SC / CW is less than 0.4, the density of the polymer layer is too large, and polymer A and polymer B will adhere to the surface of the diaphragm. At the same time, due to the swelling effect of the polymer, it is easy to block the lithium ion transmission channel and reduce the lithium ion conductivity. At the same time, the content of ethyl propionate in the electrolyte is too low. At this time, the adhesion between the diaphragm and the electrode is excessive, and the thickness of the polymer layer is too large, which will increase the lithium ion transmission resistance. At the same time, the conductivity of the electrolyte is too low, which will further reduce the kinetic performance of the battery, thereby leading to deterioration of the cycle performance; when SC / CW is greater than 6, the density of the polymer layer is too small or the content of ethyl propionate in the electrolyte is too high, and the bonding sites of polymer A and polymer B with the electrode are reduced. At this time, the adhesion between the diaphragm and the electrode is too poor, resulting in poor interface in the later stage of the cycle and deterioration of the cycle performance.

[0100] In one example, 0.7≤SC / CW≤4.

[0101] In one embodiment, the surface density CW of the polymer layer is 0.1 g / m 2 ~1g / m 2 (For example, 0.1 g / m 2 , 0.2g / m 2 , 0.3g / m 2 , 0.4g / m 2, 0.5g / m 2 , 0.6g / m 2 , 0.7g / m 2 , 0.8g / m 2 , 0.9g / m 2 , 1g / m 2 ).

[0102] In one embodiment, the surface density CW of the polymer layer is 0.2 g / m 2 ~0.6g / m 2 .

[0103] In one embodiment, based on the total weight of the electrolyte, the weight content SC of the ethyl propionate is 5 wt% to 70 wt% (for example, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 30 wt%, 35 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%).

[0104] In one embodiment, based on the total weight of the electrolyte, the weight content SC of the ethyl propionate is 30 wt % to 60 wt %.

[0105] In one example, the electrolyte solution includes an electrolyte salt, an organic solvent, and an additive.

[0106] In one example, the electrolyte salt includes lithium hexafluorophosphate (LiPF6), lithium nitrate, lithium difluorooxalatoborate, lithium perchlorate, lithium difluorophosphate, lithium tetrafluoroborate, bisoxalatoborate, lithium bisdifluorosulfonyl imide, and lithium bistrifluoromethylsulfonyl imide.

[0107] In one example, the organic solvent includes one or more of ethyl propionate, ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate.

[0108] In one example, the additive includes one or more of tris(trimethylsilyl)phosphite, tris(trimethylsilyl)borate, 1,3-propane sultone (PS), vinylene carbonate, and fluoroethylene carbonate (FEC).

[0109] According to a specific embodiment, based on the total weight of the electrolyte, the weight content of the electrolyte salt is 8wt% to 22wt% (for example, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 22wt%), the weight content of the organic solvent is 73wt% to 91.5wt% (for example, 73wt%, 75wt%, 78wt%, 80wt%, 82wt%, 85wt%, 88wt%, 90wt%, 91.5wt%), and the weight content of the additive is 0.5wt% to 5wt% (for example, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%).

[0110] In one example, based on the total weight of the electrolyte, the weight content of the electrolyte salt is 13 wt % to 19 wt %, the weight content of the organic solvent is 77 wt % to 86 wt %, and the weight content of the additive is 1 wt % to 4 wt %.

[0111] In one example, the electrochemical device includes a negative electrode sheet and a positive electrode sheet.

[0112] In one example, the separator is disposed between the positive electrode sheet and the negative electrode sheet.

[0113] In one example, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on one or both sides of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, a conductive agent, and a third binder.

[0114] In one example, based on the total weight of the positive electrode active material layer, the weight content of the positive electrode active material is 80wt% to 99.8wt% (for example, 80wt%, 85wt%, 90wt%, 95wt%, 99.8wt%), the weight content of the conductive agent is 0.1wt% to 10wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 7wt%, 10wt%), and the weight content of the third binder is 0.1wt% to 10wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 7wt%, 10wt%).

[0115] In one example, based on the total weight of the positive electrode active material layer, the weight content of the positive electrode active material is 90wt% to 99.6wt%, the weight content of the conductive agent is 0.2wt% to 5wt%, and the weight content of the third binder is 0.2wt% to 5wt%.

[0116] In one example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on one or both sides of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material, a conductive agent, and a fourth binder.

[0117] In one example, based on the total weight of the negative electrode active material layer, the weight content of the negative electrode active material is 80wt% to 99.7wt% (for example, 80wt%, 85wt%, 90wt%, 95wt%, 99.7wt%), the weight content of the conductive agent is 0.1wt% to 10wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 7wt%, 10wt%), and the weight content of the fourth binder is 0.1wt% to 10wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 7wt%, 10wt%).

[0118] In one example, based on the total weight of the negative electrode active material layer, the weight content of the negative electrode active material is 85wt% to 99.4wt%, the weight content of the conductive agent is 0.2wt% to 5wt%, and the weight content of the fourth binder is 0.2wt% to 5wt%.

[0119] In one example, the conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, metal powder, and carbon fiber.

[0120] In one embodiment, the thickener is selected from at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and carboxymethyl cellulose.

[0121] In one example, the third binder is selected from at least one of polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), polytetrafluoroethylene, and polyethylene oxide.

[0122] In one example, the fourth binder is selected from at least one of polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), polytetrafluoroethylene, and polyethylene oxide.

[0123] In one example, the negative electrode active material includes a carbon-based negative electrode material and / or a silicon-based negative electrode material.

[0124] In one example, the carbon-based negative electrode material includes at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon, and soft carbon.

[0125] In one embodiment, the silicon-based negative electrode material is selected from at least one of a silicon-oxygen negative electrode material and a silicon-carbon negative electrode material, such as Si, SiC, SiOx(0 <x<2)。

[0126] In one embodiment, the positive electrode active material is selected from one or more of transition metal lithium oxide, lithium iron phosphate, and lithium manganate; the chemical formula of transition metal lithium oxide is Li 1+x Ni y Co z M (1-y-z) O2, wherein -0.1≤x≤1, 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; wherein M is one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

[0127] In one embodiment, the positive electrode active material is lithium cobalt oxide.

[0128] Since the electrochemical device of the present disclosure includes the separator of the present disclosure, the electrochemical device has a low thickness expansion rate and good cycle performance, especially good long-cycle performance.

[0129] A third aspect of the present disclosure provides an electrochemical device, which includes a diaphragm, an electrolyte, a positive electrode sheet, and a negative electrode sheet, wherein the electrolyte includes ethyl propionate, and the weight content of the ethyl propionate is SC based on the total weight of the electrolyte; the diaphragm includes a carrier layer and a polymer layer located on one side or both sides of the carrier layer, and the surface density of the polymer layer is CW, then the electrochemical device satisfies the following relationship: 0.4≤SC / CW≤6 (for example, 0.4, 0.1, 0.5, 1, 2, 3, 4, 5, 6). When SC / CW is less than 0.4, the density of the polymer layer is too large, and the content of ethyl propionate in the electrolyte is too low. At this time, the adhesion between the diaphragm and the electrode is excessive, and the thickness of the polymer layer is too large, which will increase the resistance to lithium ion transmission. At the same time, the conductivity of the electrolyte is too low, which will further reduce the kinetic performance of the battery, thereby causing the cycle performance to deteriorate; when SC / CW is greater than 6, the density of the polymer layer is too small, and the content of ethyl propionate in the electrolyte is too high. At this time, the adhesion between the diaphragm and the electrode is too poor, resulting in a deterioration of the interface in the later stage of the cycle and deterioration of the cycle performance.

[0130] In one example, 0.7≤SC / CW≤4.

[0131] In one embodiment, based on the total weight of the electrolyte, the weight content SC of the ethyl propionate is 5 wt% to 70 wt% (for example, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 30 wt%, 35 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%).

[0132] In one embodiment, based on the total weight of the electrolyte, the weight content SC of the ethyl propionate is 30 wt % to 60 wt %.

[0133] In one embodiment, the surface density CW of the polymer layer is 0.1 g / m 2 ~1g / m 2 (For example, 0.1 g / m 2 , 0.2g / m 2 , 0.3g / m 2 , 0.4g / m 2 , 0.5g / m 2 , 0.6g / m 2 , 0.7g / m 2 , 0.8g / m 2 , 0.9g / m 2 , 1g / m 2 ).

[0134] In one embodiment, the surface density CW of the polymer layer is 0.2 g / m 2 ~0.6g / m 2 .

[0135] In one example, the electrochemical device is a battery, such as a lithium-ion battery.

[0136] In one embodiment, after the electrochemical device is cycled for 800T at 25°C, the bonding force between the separator and the positive electrode sheet is ≥5 N / m.

[0137] In one embodiment, after the electrochemical device is cycled for 800T at 25°C, the bonding force between the separator and the negative electrode sheet is ≥5 N / m.

[0138] In one example, the electrochemical device has a capacity retention rate of ≥89.5% after cycling for 800T at 25°C.

[0139] In one example, the electrochemical device has a thickness expansion rate of ≤8.5% after 800T cycles at 25°C.

[0140] In one example, the separator is disposed between the positive electrode sheet and the negative electrode sheet.

[0141] In one example, the electrochemical device is a battery, such as a lithium-ion battery.

[0142] In one example, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on one or both sides of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a fifth binder.

[0143] In one example, based on the total weight of the positive electrode active material layer, the weight content of the positive electrode active material is 80wt% to 99.8wt% (for example, 80wt%, 85wt%, 90wt%, 95wt%, 99.8wt%), the weight content of the conductive agent is 0.1wt% to 10wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 7wt%, 10wt%), and the weight content of the fifth binder is 0.1wt% to 10wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 7wt%, 10wt%).

[0144] In one example, based on the total weight of the positive electrode active material layer, the weight content of the positive electrode active material is 90wt% to 99.6wt%, the weight content of the conductive agent is 0.2wt% to 5wt%, and the weight content of the fifth binder is 0.2wt% to 5wt%.

[0145] In one example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on one or both sides of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, a conductive agent, and a sixth binder.

[0146] In one example, based on the total weight of the negative electrode active material layer, the weight content of the negative electrode active material is 80wt% to 99.7wt% (for example, 80wt%, 85wt%, 90wt%, 95wt%, 99.7wt%), the weight content of the conductive agent is 0.1wt% to 10wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 7wt%, 10wt%), and the weight content of the sixth binder is 0.1wt% to 10wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 7wt%, 10wt%).

[0147] In one example, based on the total weight of the negative electrode active material layer, the weight content of the negative electrode active material is 85wt% to 99.4wt%, the weight content of the conductive agent is 0.2wt% to 5wt%, and the weight content of the sixth binder is 0.2wt% to 5wt%.

[0148] In one example, the conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, metal powder, and carbon fiber.

[0149] In one embodiment, the thickener is selected from at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and carboxymethyl cellulose.

[0150] In one example, the fifth binder is selected from at least one of polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), polytetrafluoroethylene, and polyethylene oxide.

[0151] In one example, the sixth binder is selected from at least one of polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), polytetrafluoroethylene, and polyethylene oxide.

[0152] In one example, the negative electrode active material includes a carbon-based negative electrode material and / or a silicon-based negative electrode material.

[0153] In one example, the carbon-based negative electrode material includes at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon, and soft carbon.

[0154] In one embodiment, the silicon-based negative electrode material is selected from at least one of a silicon-oxygen negative electrode material and a silicon-carbon negative electrode material, such as Si, SiC, SiOx(0 <x<2)。

[0155] In one embodiment, the positive electrode active material is selected from one or more of transition metal lithium oxide, lithium iron phosphate, and lithium manganate; the chemical formula of transition metal lithium oxide is Li 1+x Ni y Co z M (1-y-z) O2, wherein -0.1≤x≤1, 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; wherein M is one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

[0156] In one embodiment, the positive electrode active material is lithium cobalt oxide.

[0157] The present disclosure discloses a diaphragm and an electrochemical device. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve it. It is particularly important to point out that all similar replacements and modifications are obvious to those skilled in the art and are considered to be included in this disclosure. The methods and applications of the present disclosure have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of this disclosure to implement and apply the technology of the present disclosure.

[0158] The reagents, instruments, and materials used in this disclosure can all be obtained through commercial channels.

[0159] The present disclosure is further described below with reference to the following embodiments:

[0160] Example 1 Battery and its preparation method

[0161] (1) Battery structure

[0162] The battery includes a positive electrode, a negative electrode, a separator and an electrolyte.

[0163] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on both sides of the positive electrode current collector;

[0164] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on both sides of the negative electrode current collector;

[0165] As shown in FIG1 , the diaphragm includes a carrier layer 10 and polymer layers 20 located on both sides of the carrier layer 10 , wherein the polymer layers 20 include polymer A 21 and polymer B 22 ; the carrier layer 10 includes a substrate 11 and a heat-resistant layer 12 located on one side of the substrate.

[0166] (2) Battery Preparation Method

[0167] (1) Preparation of diaphragm

[0168] 30 wt% of polymer A (polyethylene-methacrylic acid copolymer), 62 wt% of polymer B (polyvinylidene fluoride-hexafluoropropylene copolymer), 4 wt% of thickener (sodium carboxymethyl cellulose), 0.5 wt% of wetting agent (dimethylsiloxane), and 3.5 wt% of binder (polymethyl methacrylate) were added to deionized water at a solid content of 10%, and stirred at a stirring speed of 1500 rpm for 60 min to obtain a polymer slurry.

[0169] A 2 μm thick aluminum oxide layer (i.e., a heat-resistant layer composed of 92 wt% aluminum oxide, 4 wt% polymethyl methacrylate, and 4 wt% sodium polymethylcellulose) is coated on one side of a 5 μm thick polyethylene substrate, and a 0.5 g / m2 polymer layer is coated on the other side of the polyethylene substrate and the surface of the aluminum oxide layer. After drying in an oven, a diaphragm as shown in FIG1 is obtained.

[0170] (2) Preparation of negative electrode sheet

[0171] The negative electrode active material (artificial graphite), conductive agent (conductive carbon black), fourth binder (styrene-butadiene rubber), and thickener (lithium carboxymethyl cellulose) are mixed in a mass ratio of 96%:1.5%:1.5%:1%, and deionized water is added as a solvent to prepare a negative electrode slurry; the negative electrode slurry is then coated on a copper foil, dried, rolled and cut, and punched to obtain a negative electrode sheet.

[0172] (3) Preparation of positive electrode

[0173] The positive electrode active material (lithium cobalt oxide) is added to a stirring tank with a conductive agent (conductive carbon black) and a third binder (polyvinylidene fluoride) in a mass ratio of 97.2:1.5:1.3, and NMP solvent is added. The mixture is fully stirred according to a known batching process to obtain a positive electrode slurry; the positive electrode slurry is then coated on an aluminum foil, dried, rolled and cut, and punched to obtain a positive electrode sheet.

[0174] (4) Preparation of electrolyte

[0175] In a glove box filled with argon (H2O <0.1ppm, O2 <0.1ppm), the organic solvents (50 parts by weight of ethyl propionate, 7 parts by weight of EC, 10 parts by weight of DMC, and 15 parts by weight of EMC) were mixed evenly, and then fully dried electrolyte salt (13 parts by weight of lithium hexafluorophosphate) was quickly added thereto. After dissolution, additives (2.5 parts by weight of PS and 2.5 parts by weight of FEC) were added and mixed evenly to obtain the desired electrolyte.

[0176] (5) Preparation of batteries

[0177] The positive electrode sheet of step (3), the separator of step (1), and the negative electrode sheet of step (2) are wound to obtain a bare cell without liquid injection (wherein the first surface of the polyethylene substrate is close to the negative electrode sheet, and the second surface of the polyethylene substrate opposite to the first surface is close to the positive electrode sheet); the bare cell is placed in an outer package, and the electrolyte of step (4) is injected into the dried bare cell. After vacuum packaging, static aging, formation, sorting and other processes, the desired battery is obtained.

[0178] Among them, SC is 50%, CW g / m 2 0.5g / m 2 , then SC / CW=50% / 0.5=1.

[0179] Example 2 group

[0180] This set of examples is used to illustrate the effects of changing the weight ratio of polymer A to polymer B.

[0181] This example group was carried out with reference to Example 1, except that the weight ratio of polymer A to polymer B was changed. For details, see Table 1-1 and Table 1-2.

[0182] Example 3 group

[0183] This group of examples is used to illustrate the effects produced when the molar ratio of the first monomer to the second monomer in polymer A is changed.

[0184] This example group was carried out with reference to Example 1, except that the molar ratio of the first monomer and the second monomer in polymer A was changed. For details, see Table 1-1 and Table 1-2.

[0185] Example 4 Group

[0186] This set of examples is used to illustrate the effects of varying the specific selection of polymer A.

[0187] This example group was carried out with reference to Example 1, except that the specific selection of polymer A was changed. For details, see Table 1-1 and Table 1-2.

[0188] Example 5 Group

[0189] This set of examples is used to illustrate the effects of varying the specific selection of polymer B.

[0190] This example group was carried out with reference to Example 1, except that the specific selection of polymer B was changed. For details, see Table 1-1 and Table 1-2.

[0191] Example 6

[0192] This set of examples is used to illustrate the effects produced when the crystallinity of polymer B is changed.

[0193] This example group was carried out with reference to Example 1, except that the crystallinity of polymer B was changed. For details, see Table 1-1 and Table 1-2.

[0194] Example 7 Group

[0195] This set of examples is used to illustrate the effects produced when the ratio of the median particle size Dv50 of the secondary particles formed by agglomeration of polymer B to the median particle size Dv50 of the primary particles of polymer A is changed.

[0196] This example group was carried out with reference to Example 1, except that the ratio of the median particle size Dv50 of the secondary particles formed by agglomeration of polymer B to the median particle size Dv50 of the primary particles of polymer A was changed. For details, see Table 1-1 and Table 1-2.

[0197] Example 8 Group

[0198] This set of examples is used to illustrate the effects produced when the areal density of the polymer layer is changed.

[0199] This example group was carried out with reference to Example 1, except that the surface density of the polymer layer was changed. For details, see Table 1-1 and Table 1-2.

[0200] Example 9 Group

[0201] This set of embodiments is used to illustrate the impact produced when SC / CW changes.

[0202] This embodiment group was carried out with reference to the embodiment 1, except that SC / CW was changed. For details, see Table 1-1 and Table 1-2.

[0203] Example 10 Group

[0204] Example 10a

[0205] The same process as in Example 1 was carried out, except that the polymer in the polymer layer was 100% polymer A.

[0206] The preparation method of the polymer slurry is as follows: 92 wt% of polymer A (polyethylene-methacrylic acid copolymer), 4 wt% of thickener (sodium carboxymethyl cellulose), 0.5 wt% of wetting agent (dimethylsiloxane), and 3.5 wt% of binder (polymethyl methacrylate) are added to deionized water at a solid content of 10%, and stirred at a stirring speed of 1500 rpm for 60 minutes to obtain a polymer slurry. For details, see Table 1-1 and Table 1-2.

[0207] Example 10b

[0208] The same process as in Example 1 was carried out, except that the polymer in the polymer layer was 100% polymer B.

[0209] The preparation method of the polymer slurry is as follows: 92 wt% of polymer B (polyvinylidene fluoride-hexafluoropropylene copolymer), 4 wt% of thickener (sodium carboxymethyl cellulose), 0.5 wt% of wetting agent (dimethylsiloxane), and 3.5 wt% of binder (polymethyl methacrylate) are added to deionized water at a solid content of 10%, and stirred at a stirring speed of 1500 rpm for 60 minutes to obtain a polymer slurry. For details, see Table 1-1 and Table 1-2.

[0210] Example 10c

[0211] The same process as in Example 1 was carried out, except that the polymer in the polymer layer was 100% PVDF.

[0212] The preparation method of the polymer slurry is as follows: 92 wt% of PVDF, 4 wt% of a thickener (sodium carboxymethyl cellulose), 0.5 wt% of a wetting agent (dimethylsiloxane), and 3.5 wt% of a binder (polymethyl methacrylate) are added to deionized water at a solid content of 10%, and stirred at a stirring speed of 1500 rpm for 60 minutes to obtain a polymer slurry. For details, see Table 1-1 and Table 1-2.

[0213] Example 10d

[0214] The same procedure was followed as in Example 1, except that the weight ratio of polymer A to polymer B was 0.01:1. For details, see Table 1-1 and Table 1-2.

[0215] Example 10e

[0216] The same procedure was followed as in Example 1, except that the weight ratio of polymer A to polymer B was 9.5:1. For details, see Table 1-1 and Table 1-2.

[0217] Comparative Example 1

[0218] The same procedure was followed as in Example 10a, except that SC was adjusted to 5%, and SC / CW was 0.1. For details, see Table 1-1 and Table 1-2.

[0219] Comparative Example 2

[0220] The same procedure was followed as in Example 10b, except that SC was adjusted to 5%, and SC / CW was 0.1. For details, see Table 1-1 and Table 1-2.

[0221] Comparative Example 3

[0222] The same procedure was followed as in Example 10c, except that SC was adjusted to 5%, and SC / CW was 0.1. For details, see Table 1-1 and Table 1-2.

[0223] Comparative Example 4

[0224] The same procedure was followed as in Example 10d, except that SC was adjusted to 5%, and SC / CW was 0.1. For details, see Table 1-1 and Table 1-2.

[0225] Comparative Example 5

[0226] The same procedure was followed as in Example 10e, except that SC was adjusted to 5%, and SC / CW was 0.1. For details, see Table 1-1 and Table 1-2.

[0227] Table 1-1

[0228] Table 1-2 * indicates the same as Example 1; - indicates non-existent; E indicates the molar ratio of the first monomer to the second monomer; F indicates the weight content of polymer A based on the sum of the weights of polymer A and polymer B; G indicates the weight content of polymer B based on the sum of the weights of polymer A and polymer B; H indicates the ratio of the weight of polymer A to the weight of polymer B; M indicates the ratio of the median particle size Dv50 of the secondary particles formed by agglomeration of polymer B to the median particle size Dv50 of the primary particles of polymer A.

[0229] Battery performance test

[0230] The test methods and equipment used for comparison between the above embodiments and comparative examples are as follows:

[0231] (1) Adhesion test between the diaphragm polymer layer and the electrode plate:

[0232] The batteries obtained in the above embodiments and comparative examples were cycled for 800T and then removed from the stage, placed in an environment of (25±2)°C, and allowed to stand for 2 to 3 hours. The batteries were charged at a constant current of 0.7C with a cutoff current of 0.05C. When the battery terminal voltage reached the charge limit voltage (the charge limit voltage was 4.5V), constant voltage charging was switched until the charging current ≤ the cutoff current. Charging was stopped and left for 5 minutes. The fully charged (100% SOC) batteries were dissected, and the national standard GB / T 2790-1995, that is, the 180° peel test standard was used to test the adhesion between the diaphragm and the positive electrode sheet or the negative electrode sheet. The diaphragm and the positive electrode sheet or the negative electrode sheet were cut into 15mm×54.2mm strips, and the adhesion between the diaphragm and the positive electrode sheet or the negative electrode sheet was tested according to the 180° peel test standard.

[0233] (2) 25℃ cycle test

[0234] The batteries obtained in the above examples and comparative examples were placed in a (25±2)°C environment and left to stand for 2-3 hours. When the battery body reached (25±2)°C, the battery was charged at a constant current of 1C to a charge limit voltage of 4.5V, and then changed to constant voltage charging until the charging current ≤ the cutoff current of 0.05C. After the battery was fully charged (100% SOC), it was left for 5 minutes and then discharged at a constant current of 1C to a cutoff voltage of 3.0V. The highest discharge capacity of the first three cycles was recorded as the initial capacity Q. When the number of cycles reached 800, the discharge capacity Q1 of the last cycle of the battery was recorded.

[0235] Capacity retention rate (%) = Q1 / Q×100%.

[0236] Expansion rate test: Use a 600g flat plate thickness gauge to test the thickness of the battery, which is recorded as PPG thickness;

[0237] The initial thickness of the battery is recorded as P. When the number of cycles reaches 800, the thickness of the test battery is P1, and the thickness expansion rate (%) = P1 / P×100%.

[0238] The comparative tests of the embodiments and comparative examples are recorded in Table 2.

[0239] Table 2

[0240] As can be seen from Table 2, it can be seen from the comparative examples and the examples that the bonding force between the diaphragm of the example and the positive electrode sheet is improved, the bonding force between the diaphragm and the negative electrode sheet is improved, the capacity retention rate of the electrochemical device made of the diaphragm of the example is significantly improved, and the thickness expansion rate is reduced, indicating that the diaphragm disclosed in the present invention and the electrochemical device including the diaphragm, by designing a diaphragm with a specific structure, improve the cycle stability of the electrochemical device, especially the long cycle performance, and reduce the thickness expansion rate of the electrochemical device.

[0241] The preferred embodiments of the present disclosure are described in detail above, but the present disclosure is not limited thereto. Within the technical concept of the present disclosure, various simple variations of the technical solution of the present disclosure may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed by the present disclosure and fall within the scope of protection of the present disclosure.

Claims

1. A separator for a lithium ion battery, characterized in that: The diaphragm includes a carrier layer and a polymer layer located on one side or both sides of the carrier layer; the polymer layer includes polymer A and polymer B, the polymer A is a copolymer including a first monomer and a second monomer, the polymer B is a copolymer or homopolymer including a third monomer, and the ratio of the weight of the polymer A to the weight of the polymer B is (0.1-9):

1.

2. The diaphragm according to claim 1, wherein The first monomer includes one or more of ethylene, propylene and butene; and / or, the second monomer comprises one or more of methacrylic acid, acrylic acid, acrylic ester, styrene, butadiene, vinyl chloride, acrylonitrile, isoprene, ethylene oxide, propylene oxide and vinyl acetate; and / or, the third monomer includes one or more of vinylidene fluoride, hexafluoropropylene, tetrafluoroethylene, vinyl chloride, butadiene and acrylonitrile; And / or, in the polymer layer, the ratio of the weight of the polymer A to the weight of the polymer B is (0.25-1):1; And / or, in polymer A, the molar ratio of the first monomer to the second monomer is (0.5-99):1, preferably (5-90):

1.

3. The diaphragm according to claim 1 or 2, wherein: The softening temperature of the polymer A is 40°C to 90°C; and / or, the median particle size Dv50 of the primary particles of the polymer A is 0.1 μm to 5 μm; And / or, the molecular weight of the polymer A is 10W to 100W.

4. The diaphragm according to any one of claims 1 to 3, wherein: The melting point of the polymer B is 125°C to 200°C; And / or, the crystallinity of the polymer B is 35% to 55%; And / or, the molecular weight of the polymer B is 10W to 100W; And / or, the median particle size Dv50 of the primary particles of the polymer B is 0.1 μm to 1 μm, and the median particle size Dv50 of the secondary particles formed by agglomeration of the polymer B is 1 μm to 10 μm.

5. The diaphragm according to any one of claims 1 to 4, wherein The median particle size Dv50 of the primary particles of the polymer A is greater than the median particle size Dv50 of the primary particles of the polymer B; and / or, the ratio of the median particle size Dv50 of the secondary particles formed by agglomeration of the polymer B to the median particle size Dv50 of the primary particles of the polymer A is (1-10):1; And / or, based on the sum of the weights of the polymer A and the polymer B, the weight content of the polymer A is 10wt% to 60wt%, and the weight content of the polymer B is 40wt% to 90wt%.

6. The diaphragm according to any one of claims 1 to 5, wherein: The surface density of the polymer layer is 0.1 g / m 2 ~1g / m 2 ; And / or, the polymer layer has a thickness of 0.3 μm to 6 μm.

7. The diaphragm according to any one of claims 1 to 6, wherein: The carrier layer includes a substrate and a heat-resistant layer located on one or both sides of the substrate, wherein the heat-resistant layer includes inorganic particles and a second binder; Preferably, the inorganic particles are selected from one or more of alumina, boehmite, magnesium oxide, boron nitride and magnesium hydroxide; Preferably, the second binder includes butadiene styrene latex, styrene acrylic latex, pure benzene latex, polymethyl methacrylate, polybutyl methacrylate, polyethyl acrylate, polyvinyl alcohol, ethylene-vinyl acetate copolymer, polyvinyl acetate and polyurethane.

8. The diaphragm according to claim 7, wherein: The thickness of the heat-resistant layer is 0.5 μm to 5 μm; and / or, the median particle size Dv50 of the inorganic particles is 0.1 μm to 5 μm; And / or, based on the total weight of the heat-resistant layer, the weight content of the inorganic particles is 60wt% to 99wt%, and the weight content of the second binder is 1wt% to 40wt%.

9. The diaphragm according to claim 7 or 8, wherein: The thickness of the substrate is 3 μm to 20 μm; and / or, the porosity of the substrate is 30% to 60%; And / or, the air permeability of the substrate is 30s / 100ml to 200s / 100ml; and / or, the porosity of the diaphragm is 30% to 50%; And / or, the air permeability of the diaphragm is 100s / 100ml to 300s / 100ml.

10. An electrochemical device, characterized in that: The electrochemical device comprises the separator according to any one of claims 1 to 9.

11. The electrochemical device according to claim 10, wherein: The electrochemical device includes an electrolyte, the electrolyte includes ethyl propionate, and the weight content of the ethyl propionate is SC based on the total weight of the electrolyte; the surface density of the polymer layer is CW, and the electrochemical device satisfies the following relationship: 0.4≤SC / CW≤6.

12. The electrochemical device according to claim 11, wherein The surface density CW of the polymer layer is 0.1 g / m 2 ~1g / m 2 ; And / or, based on the total weight of the electrolyte, the weight content SC of the ethyl propionate is 5wt% to 70wt%.

13. An electrochemical device, characterized in that: The electrochemical device includes a diaphragm, an electrolyte, a positive electrode sheet and a negative electrode sheet; the electrolyte includes ethyl propionate, and the weight content of the ethyl propionate is SC based on the total weight of the electrolyte; the diaphragm includes a carrier layer and a polymer layer located on one side or both sides of the carrier layer, and the surface density of the polymer layer is CW, then the electrochemical device satisfies the following relationship: 0.4≤SC / CW≤6.

14. The electrochemical device according to claim 13, wherein: The surface density CW of the polymer layer is 0.1 g / m 2 ~1g / m 2 ; And / or, based on the total weight of the electrolyte, the weight content SC of the ethyl propionate is 5wt% to 70wt%.

15. The electrochemical device according to claim 13 or 14, wherein: The electrochemical device comprises a positive electrode sheet and a negative electrode sheet, and after the electrochemical device is cycled for 800T at 25°C, the bonding force between the separator and the positive electrode sheet is ≥5N / m; and / or, after the electrochemical device is cycled for 800T at 25°C, the bonding force between the separator and the negative electrode sheet is ≥5N / m; And / or, the electrochemical device has a capacity retention rate of ≥89.5% when cycled for 800T at 25°C; And / or, the electrochemical device has a thickness expansion ratio of ≤8.5% after 800T cycles at 25°C.

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