Diaphragm and battery

Abstract

The invention provides a diaphragm and a battery, the diaphragm comprises a base material layer and a coating layer located on one side surface or two side surfaces of the base material layer, the coating layer comprises a first coating layer and a second coating layer, the first coating layer comprises first particles with the component of an organic compound, and the second coating layer comprises second particles with the component of an organic compound. The unit molecular structure of the organic compound comprises at least one of a carbon-carbon double bond, a phosphorus-oxygen double bond, a carbon-nitrogen double bond, a carbon-sulfur double bond and a carbon-oxygen double bond; the second coating is of a porous structure formed by taking a fluorine-containing polymer as a continuous phase, through holes are formed in the surface of the second coating, and in the 100 [mu] m * 100 [mu] m area of the surface of the second coating, the orthographic projection area of the through holes on the base material layer and / or the first coating accounts for 10%-90% of the surface area of the diaphragm. According to the diaphragm and the battery, the stability of the CEI membrane at high temperature can be improved, the rupture of the CEI membrane is reduced or even avoided, and the high-temperature intermittent cycle capacity retention rate and the recovery capacity retention rate after high-temperature storage of the battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a diaphragm and a battery comprising the diaphragm. Background Art

[0002] Lithium-ion batteries, due to their high energy density, long cycle life, lack of memory effect, and environmental friendliness, have been widely used in smartphones, tablets, smart wearables, power tools, and electric vehicles. To meet consumer demand, a direct strategy for improving battery energy density is to increase the charge cutoff voltage of lithium batteries. However, due to the characteristics of the positive electrode active materials, after exceeding the platform voltage, the positive electrode active particles are extremely unstable after delithiation. This is especially true under high-temperature testing conditions, where the reaction is exacerbated and the active particle structure is prone to collapse, thus affecting various test performances. Therefore, the stability of the positive electrode active particles under high voltage has become a major challenge in the development of high-energy-density lithium-ion batteries. Summary of the Invention

[0003] Research has found that in high temperature environments, the electrolyte interface (CEI) on the surface of the positive electrode material of lithium-ion batteries is prone to rupture, and after rupture, it will be unable to prevent the electrolyte from interacting with highly active ions (such as Co 4+ 、Fe 3+ 、Mn 2+ 、Ni 3+ 、Al 3+ 、Ti 4+ ), which triggers continuous side reactions and deteriorates the interface performance between the diaphragm and the positive electrode, thereby accelerating the cracks and structural collapse of the positive electrode active particles, and reducing the high-temperature intermittent cycle capacity retention rate of the lithium-ion battery and the recovery capacity retention rate after high-temperature storage.

[0004] To address the technical problem of lithium-ion batteries experiencing high-temperature conditions, where the electrolyte interface (CEI) on the surface of the positive electrode material is prone to rupture, resulting in deteriorated interfacial properties between the separator and the positive electrode sheet, the present invention provides a separator and a battery incorporating the separator. The separator of the present invention is capable of dissociating organic matter containing electron-deficient groups that participate in the formation of the CEI film. The CEI film formed with the participation of the organic matter containing electron-deficient groups exhibits excellent high-temperature resistance, improving the stability of the CEI film at high temperatures, reducing or even preventing CEI film rupture, and enhancing the interfacial properties between the separator and the positive electrode sheet, thereby improving the battery's high-temperature intermittent cycling capacity retention and the recovery capacity retention after high-temperature storage.

[0005] The first aspect of the present invention provides a diaphragm, which includes a substrate layer and a coating located on one side or both sides of the substrate layer, the coating including a first coating and a second coating, the first coating being located on the surface of the substrate layer, and the second coating being located on the surface of the first coating, the first coating including first particles, the components of the first particles being organic compounds, the unit molecular structure of the organic compounds including one or more of carbon-carbon double bonds, phosphorus-oxygen double bonds, carbon-nitrogen double bonds, carbon-sulfur double bonds and carbon-oxygen double bonds; the second coating is a porous structure formed by a fluoropolymer as a continuous phase, the surface of the second coating including through holes, and in an area of ​​100 μm×100 μm on the surface of the second coating, the orthographic projection area of ​​the through holes on the substrate layer and / or the first coating accounts for 10%-90% of the surface area of ​​the diaphragm.

[0006] The second aspect of the present invention provides a battery, which includes a positive electrode sheet and the separator described in the first aspect of the present invention, the positive electrode sheet includes a positive electrode collector and a positive electrode active layer located on one side or both sides of the positive electrode collector, and the coating corresponds to the positive electrode active layer.

[0007] Through the above technical solution, the present invention has at least the following advantages compared with the prior art: The present invention provides a coating including a first coating and a second coating on one or both sides of the substrate layer of the diaphragm, wherein the first coating includes first particles, and the organic compound component of the first particles contains electron-deficient groups (such as carbon-carbon double bonds, phosphorus-oxygen double bonds, carbon-nitrogen double bonds, carbon-sulfur double bonds, and carbon-oxygen double bonds). The first particles can dissolve at high temperatures to produce organic matter containing electron-deficient groups. The organic matter containing electron-deficient groups can diffuse directly or through the through holes on the surface of the second coating to the interface between the diaphragm and the positive electrode sheet, and participate in the film-forming reaction of the CEI film. The participation of the organic matter containing electron-deficient groups can effectively enhance the high-temperature performance of the CEI film, reduce or even avoid damage to the CEI, improve the interface performance between the diaphragm and the positive electrode under high-temperature conditions, reduce interface impedance, and improve the high-temperature intermittent cycle capacity retention rate and the recovery capacity retention rate after high-temperature storage of the battery. At the same time, the diaphragm of the present invention also controls the proportion of the orthographic projection area of ​​the through-holes in the second coating layer on the substrate layer and / or the first coating layer in the surface area of ​​the diaphragm, thereby facilitating the rapid and directionally diffused diffusion of the organic matter containing the electron-deficient group from the first coating layer of the diaphragm to the interface of the positive electrode sheet through the through-holes, thereby creating favorable conditions for the organic matter containing the electron-deficient group to participate in the formation of the CEI film, improving the uniformity of the CEI film, and also limiting its excessive diffusion in the electrolyte outside the interface, thereby avoiding its influence on other battery properties.

[0008] Other features and advantages of the present invention will be described in detail in the following detailed description.

[0009] 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

[0010] Figure 1 This is one of the schematic cross-sectional views of the diaphragm of the present invention.

[0011] Figure 2 This is the second schematic cross-sectional view of the diaphragm of the present invention.

[0012] Figure 3 This is the third schematic cross-sectional view of the diaphragm of the present invention.

[0013] Figure 4 Schematic diagram of the cross section of the positive electrode sheet of the present invention.

[0014] Figure 5 Schematic diagram of the positive electrode sheet of the present invention. DETAILED DESCRIPTION

[0015] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention. In this article, unless otherwise specified, data ranges include endpoints.

[0016] It should be noted that the numerical expressions such as "first" and "second" in the present invention are only used to distinguish different substances or usage methods, and do not represent a difference in order.

[0017] A first aspect of the present invention provides a diaphragm, comprising a substrate layer and a coating located on one or both surfaces of the substrate layer, the coating comprising a first coating and a second coating, the first coating being located on the surface of the substrate layer, the second coating being located on the surface of the first coating, the first coating comprising first particles, the first particles being composed of an organic compound, the unit molecular structure of the organic compound comprising one or more of a carbon-carbon double bond, a phosphorus-oxygen double bond, a carbon-nitrogen double bond, a carbon-sulfur double bond, and a carbon-oxygen double bond; the second coating being a porous structure formed of a fluoropolymer as a continuous phase, the surface of the second coating comprising through-holes, and in an area of ​​100 μm × 100 μm on the surface of the second coating, the orthographic projection area of ​​the through-holes on the substrate layer and / or the first coating accounts for 10% to 90% of the surface area of ​​the diaphragm, for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or within a range consisting of any two of the above values.

[0018] In the present invention, Figure 1 、 Figure 2 and Figure 3 As shown, the diaphragm 4 includes a substrate layer 3 and a substrate layer on one side (such as Figure 1 and Figure 2 as shown) or both sides (as shown Figure 3 The coating comprises a first coating 1 and a second coating 2, wherein the first coating is located on the surface of the substrate layer, and the second coating is located on the surface of the first coating.

[0019] A coating including a first coating and a second coating is coated on one or both sides of the substrate layer of the diaphragm, the first coating including first particles, the first particles being composed of organic compounds, the unit molecular structure of which includes carbon-carbon double bonds, phosphorus-oxygen double bonds, carbon-nitrogen double bonds, carbon-sulfur double bonds, and carbon-oxygen double bond electron-deficient groups. When the battery is in a high temperature state, the first particles in the first coating can dissolve and dissociate to form organic matter containing carbon-carbon double bonds, phosphorus-oxygen double bonds, carbon-nitrogen double bonds, carbon-sulfur double bonds, or carbon-oxygen double bond electron-deficient groups. These organic matter containing electron-deficient groups rapidly diffuse to the interface between the diaphragm and the positive electrode sheet, and participate in the CEI film-forming reaction, so that the CEI film has excellent high-temperature resistance and is not prone to rupture, thereby continuously and effectively isolating the electrolyte from contact with the surface of the highly active positive electrode sheet, inhibiting the occurrence of side reactions, improving the interface performance between the diaphragm and the positive electrode sheet, and reducing the interface impedance. The second coating is a porous structure formed by a fluoropolymer as a continuous phase, and the surface of the second coating includes through-holes. At the same time, the proportion of the orthographic projection area of ​​the through-holes on the substrate layer and / or the first coating in the surface area of ​​the diaphragm in an area of ​​100 μm×100 μm on the surface of the second coating is controlled to be within the above range. When the second coating is present on the surface of the first coating, it is convenient for the organic matter containing electron-deficient groups to diffuse rapidly and directionally from the first coating of the diaphragm to the interface of the positive electrode sheet through the through-holes, creating favorable conditions for the organic matter containing electron-deficient groups to participate in the formation of the CEI film, and it can also limit its excessive diffusion in the electrolyte outside the interface, thereby avoiding its impact on other battery properties. When the proportion of the through-holes is less than the above range, the diffusion channel is reduced, which is not conducive to the diffusion of the organic matter containing electron-deficient groups to the interface between the diaphragm and the positive electrode sheet. When the proportion of the through-holes is greater than the above range, it is not conducive to the adhesion between the diaphragm and the electrode sheet, and the interface performance between the diaphragm and the electrode sheet is reduced. The diaphragm of the present invention can help improve the heat resistance of the CEI membrane, reduce the risk of CEI membrane damage at high temperatures, improve the high-temperature intermittent cycle capacity retention rate of the battery, reduce the irreversible capacity loss during high-temperature storage of the battery, and improve the recovery capacity retention rate after high-temperature storage.

[0020] It can be understood that in the present invention, the first particles in the first coating can dissolve and dissociate to form organic matter containing carbon-carbon double bonds, phosphorus-oxygen double bonds, carbon-nitrogen double bonds, carbon-sulfur double bonds or carbon-oxygen double bonds electron-deficient groups. The organic matter does not exist alone in the form of a group, and the organic matter can be one or more of an organic compound, a monomer, and an ion.

[0021] In the present invention, the dissolution of the first particles does not mean that the particle state of all the first particles disappears or that all the particles of the first particles are completely dissolved, but that the particle state of a single first particle disappears completely or partially. It can also be the dissolution of some groups in a single first particle, and the particle state of a single first particle can be retained completely.

[0022] In the present invention, the through hole refers to a hole extending from one side of the second coating layer to the other side of the second coating layer in the thickness direction of the separator. It is understood that in a surface SEM image of the separator, the first coating layer and / or the substrate layer can be seen through the through hole.

[0023] In the present invention, the proportion of the orthographic projection area of ​​the through holes on the substrate layer and / or the first coating layer in the surface area of ​​the diaphragm in an area of ​​100 μm×100 μm on the surface of the second coating layer can be measured by scanning electron microscopy (SEM). Specifically, a surface micrograph of the diaphragm is obtained using an SEM, and an area of ​​100 μm×100 μm on the surface of the second coating layer is randomly selected as an analysis area. This area is divided into 400×400 uniform squares (it can be understood that the above-mentioned analysis area is also the area of ​​the diaphragm surface, and therefore the number of squares on the diaphragm surface is Y=400×400). If the coverage area of ​​the through holes in the square exceeds half of the square area, it indicates that the square is occupied by the through holes; otherwise, it indicates that the square is not occupied by the through holes. By counting the number of squares occupied by the through holes, the total number of squares occupied by the through holes is recorded as X, and the area proportion is (X / Y)×100%. The above operation is repeated 5 times, and the average of the 5 times is taken as the final measurement result.

[0024] By providing first particles containing electron-deficient groups in the separator and controlling the coverage of through-holes that facilitate the diffusion of organic matter containing electron-deficient groups, the high-temperature resistance of the CEI membrane can be improved compared to existing technologies, reducing or even preventing CEI membrane damage, and improving the battery's high-temperature intermittent cycling capacity retention and the recovery capacity retention after high-temperature storage. To further enhance this effect, one or more of these technical features can be further optimized.

[0025] In some embodiments, in an area of ​​100 μm×100 μm on the surface of the second coating layer, the orthographic projection area of ​​the through hole on the substrate layer and / or the first coating layer accounts for 20%-80% of the surface area of ​​the diaphragm.

[0026] In some embodiments, the coating layer includes the first coating layer and the second coating layer. It can be understood that the structure of the diaphragm is that the first coating layer is located on one side or both sides of the substrate layer, and the second coating layer is located on the surface of the first coating layer (e.g. Figure 1 、 Figure 2 and Figure 3 As shown), the first coating includes first particles, the components of which include elemental nitrogen, elemental sulfur and elemental phosphorus, and the second coating includes a fluorine-containing polymer, and the second coating includes elemental fluorine.

[0027] In some embodiments, the coating comprises a first coating and a second coating, and on the surface of the coating away from the substrate layer, the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur, and elemental phosphorus is (0.25-3):1, for example, 0.25:1, 0.5:1, 0.75:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, or within a range formed by any two of the above values. The weight of elemental fluorine refers to the weight of all fluorine elements exposed on the surface of the coating, and the sum of the weights of elemental nitrogen, elemental sulfur, and elemental phosphorus refers to the total weight of the three elements exposed on the surface of the coating. It is understood that since the surface of the second coating includes a through hole, and the through hole can expose the first coating and / or the substrate layer, therefore, when the coating comprises both the first coating and the second coating, the surface of the coating can include the surface of the second coating and the surface of the first coating. On the surface of the coating away from the substrate layer, the elements exposed on the surface of the coating can include one or more of elemental nitrogen, elemental sulfur, and elemental phosphorus as well as elemental fluorine. When the element exposed on the surface of the coating away from the substrate layer includes one of elemental nitrogen, elemental sulfur and elemental phosphorus, the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus refers to the weight of the one element (i.e., one of elemental nitrogen, elemental sulfur and elemental phosphorus); when the surface of the coating away from the substrate layer includes multiple elements of elemental nitrogen, elemental sulfur and elemental phosphorus, the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus refers to the sum of the weights of multiple elements (multiple elements of elemental nitrogen, elemental sulfur and elemental phosphorus).

[0028] Specifically, when the coating contains a large number of through holes, the elements exposed on the coating surface should include not only the elements of the second coating but also the elements exposed through the pores of the second coating, so that the element content exposed on the coating surface can reflect the overall comprehensive performance of the coating and the interface performance between the diaphragm and the electrode.

[0029] By controlling the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur, and elemental phosphorus on the surface of the first coating layer and the second coating layer away from the substrate layer within the above range, on the one hand, the carbon-carbon double bond, phosphorus-oxygen double bond, carbon-nitrogen double bond, carbon-sulfur double bond, or carbon-oxygen double bond electron-deficient group and the fluorine element can be further promoted to act together on the CEI film, thereby improving the high-temperature performance of the CEI film and improving the interface performance between the separator and the positive electrode sheet. On the other hand, the electron-withdrawing property between the double bonds formed by elemental fluorine and one or more of elemental nitrogen, elemental sulfur, and elemental phosphorus (for example, one or more of carbon-carbon double bonds, phosphorus-oxygen double bonds, carbon-nitrogen double bonds, carbon-sulfur double bonds, and carbon-oxygen double bonds) can be utilized to improve the adhesion between the first coating layer and the second coating layer under high temperature conditions, improve the interface performance between the separator and the electrode sheet under high temperature conditions, and improve the structural stability of the separator, thereby avoiding separation of the first coating layer and the second coating layer, and preventing excessive interfacial impedance during high-temperature intermittent cycling, thereby affecting the high-temperature intermittent cycling capacity retention rate.

[0030] In some embodiments, the coating includes the first coating and the second coating, and on the surface of the coating away from the substrate layer, the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus is (0.35-2):1.

[0031] In the present invention, the coating includes the first coating and the second coating. On the surface of the coating away from the substrate layer, the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus can be measured by an energy dispersive X-ray spectrometer (EDS). Specifically, the coating surface is first cleaned and dried with a solvent, and the system is calibrated using a standard sample containing elemental fluorine, elemental nitrogen, elemental sulfur and elemental phosphorus. Under a scanning electron microscope (SEM), an EDS surface scanning analysis is performed on the surface of the coating away from the substrate layer to obtain the weight a1 of elemental fluorine and the sum of the weights b1 of elemental nitrogen, elemental sulfur and elemental phosphorus, and the ratio a1:b1 of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus is calculated.

[0032] In some embodiments, the thickness of the first coating is 0.2 μm-5 μm, for example, 0.2 μm, 1 μm, 1.5 μm, 1.8 μm, 2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.5 μm, 3.8 μm, 4 μm, 4.5 μm, 5 μm, or a range formed by any two of the above values.

[0033] In some embodiments, the weight percentage of the first particles in the first coating is 90%-99%, for example, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or within a range formed by any two of the above values.

[0034] In some embodiments, the median particle size Dv50 of the first particles is 0.05μm-5μm, for example, 0.05μm, 0.08μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm or within the range of any two of the above values. The median particle size of the first particles is controlled within the above range to improve the softness of the first coating, thereby improving the fit between the diaphragm and the electrode, maintaining the integrity of the electrode structure, and improving the cycle performance of the battery at room temperature. At the same time, the bonding strength between the first coating and the substrate layer and the second coating is enhanced, the structural stability of the diaphragm is maintained, the cycle interface impedance between the diaphragm and the electrode is reduced, and the cycle performance of the battery at room temperature is improved.

[0035] In the present invention, the median particle size Dv50 of the first particles refers to the particle size corresponding to the cumulative volume particle size distribution percentage of the first particles, arranged in ascending order of particle size, reaching 50%. The median particle size Dv50 of the first particles can be measured using a Malvern Mastersizer 3000 laser particle size analyzer.

[0036] In some embodiments, the specific surface area of ​​the first particles is 4 m 2 / g-35m 2 / g, for example, 4m 2 / g, 6m² / g, 8m 2 / g、10m 2 / g、12m 2 / g、14m 2 / g、16m 2 / g、18m 2 / g, 20m 2 / g、30m 2 / g、35m 2 / g or is within the range formed by any two of the above values. When the specific surface area of ​​the first particles is controlled to be within the above range, the contact area between the first particles and the electrolyte is large, and the dissolution rate is accelerated. At high temperatures, the surface atoms of the first particles are more likely to generate organic matter containing electron-deficient groups, so that the organic matter containing electron-deficient groups participates in the construction of the CEI membrane faster and more, forming a more high-temperature resistant electrolyte membrane (CEI membrane), avoiding damage to the diaphragm, and improving the high-temperature intermittent cycle capacity retention rate of the battery and the recovery capacity retention rate after high-temperature storage.

[0037] In some embodiments, in the unit structure of the organic compound, the sum of the number of carbon-carbon double bonds, phosphorus-oxygen double bonds, carbon-nitrogen double bonds, carbon-sulfur double bonds and carbon-oxygen double bonds is 3-12, for example, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or in the range formed by any two of the above values.

[0038] The number of carbon-carbon double bonds, phosphorus-oxygen double bonds, carbon-nitrogen double bonds, carbon-sulfur double bonds, and carbon-oxygen double bonds in the unit structure of the organic compound is controlled within the above range. On the one hand, this can ensure the rigidity of the chemical structure of the organic compound, thereby improving the rigidity of the first particle and maintaining the structural stability of the first coating. On the other hand, containing an appropriate amount of electron-deficient groups can promote the participation of the dissociated organic matter in the CEI film-forming reaction, thereby improving the stability of the film formation. If the number of electron-deficient groups is too small, the particle rigidity is insufficient and the coating structure stability deteriorates. If the number of electron-deficient groups is too large, the chemical oxidation resistance of the particles deteriorates, causing the first coating to be easily oxidized, increasing the side reaction of the electrolyte and causing gas generation after high-temperature storage.

[0039] In some embodiments, the organic compound includes 1,3,5-triazine-2,4,6-triamine, melamine polyphosphate, melamine hydrobromide, melamine polyphosphate, symmetrical triaminotriazine, 2-(4-bromophenyl)-4,6-dimethyl-1,3,5-triazine, 2,4-diamino-6-dimethylamino-1,3,5-triazine, cyanuric chloride, melamine thiocyanate, melamine cyanurate, 2-amino-4,6-methoxy-1,3,5-triazine, 1-(4,6-diamino-1,3,5-triazine-2-yl)guanidine, uracil, cytosine, 5- One or more of azacytosine, indole-3-propionic acid, N4-methylcytosine, 1-phenyl-3-methyl-5-pyrazolone, formaldehyde polymelamine hydrochloride, 2,4,6-triphenyl-1,3,5-triazine, 2-quinolinesulfonic acid and 2-quinolinesulfonate, 2,4,6-tris(2-pyridyl)triazine, tris(tribromophenoxy)triazine, dithiourea, 2,4-dimercapto-5,6-diaminopyrimidine, 4,6-dimethyl-2-mercaptopyrimidine, 1,3,4-thiadiazole-2-thione salt, coumarin-3-sulfonate, and 3-methyl-1-phenyl-2-phosphacyclopentene 1-oxide.

[0040] In some embodiments, the first coating layer includes an adhesive, and the weight proportion of the adhesive in the first coating layer is 1%-10%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or within the range of any two of the above values.

[0041] In some embodiments, the adhesive includes polyvinyl alcohol, styrene-butadiene rubber, ethylene-vinyl acetate copolymer, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polymethyl methacrylate, polybutyl methacrylate, styrene acrylic latex, polyacrylonitrile, polyethyl acrylate, polyvinyl acetate, polyacrylate, polyurethane polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene or one or more copolymer systems derived from the above polymers.

[0042] In some embodiments, the thickness of the second coating is 0.5 μm-5 μm, for example, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.5 μm, 3.8 μm, 4 μm, 4.5 μm, 5 μm, or a range formed by any two of the above values.

[0043] In some embodiments, the weight percentage of the fluoropolymer in the second coating is 70%-100%, for example, 70%, 72%, 75%, 78%, 80%, 83%, 85%, 88%, 90%, 92%, 95%, 98%, 100% or within the range of any two of the above values.

[0044] In some embodiments, the components of the second coating further include one or more of aluminum oxide, boehmite, magnesium hydroxide, magnesium oxide, boron nitride, aluminum nitride, and silicon oxide. In the second coating, the weight proportion of one or more of aluminum oxide, boehmite, magnesium hydroxide, magnesium oxide, boron nitride, aluminum nitride, and silicon oxide is 0%-30%, for example, 0%, 2%, 5%, 7%, 10%, 12%, 15%, 18%, 20%, 25%, 28%, 30%, 35% or within the range of any two of the above values.

[0045] In some embodiments, the fluorine-containing polymer includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

[0046] In some embodiments, the ratio of the thickness of the first coating layer to the thickness of the second coating layer is 0.4-3, for example, 0.4, 0.8, 1.2, 1.6, 2, 2.4, 2.8, 3 or within the range of any two of the above values. Controlling the ratio of the thickness of the first coating layer to the thickness of the second coating layer within the above range can shorten the path of the organic matter containing electron-deficient groups generated by the dissolution of the first particles in the electrolyte under high temperature conditions to diffuse through the second coating layer to the positive electrode sheet, thereby ensuring that the organic matter containing electron-deficient groups can smoothly pass through the second coating layer and reach the positive electrode sheet side to participate in the film-forming reaction of the CEI film.

[0047] In some embodiments, the coating is located on one side of the substrate layer, and the other side of the substrate layer includes a third coating (e.g. Figure 1 and Figure 2 shown).

[0048] In some embodiments, the third coating layer is the same as the second coating layer, and the surface of the third coating layer includes through holes (such as Figure 1 It should be understood that the same herein means that the components and structures of the coatings are the same, but the thicknesses of the coatings may be the same or different.

[0049] In some embodiments, the third coating layer is different from the second coating layer in that the surface of the third coating layer does not include through holes (e.g., Figure 2 (as shown in 6).

[0050] In some embodiments, the third coating includes a first polymer and filler particles. Based on the total mass of the polymer coating, the mass proportion of the first polymer is 20%-70%, for example, 20%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or within the range of any two of the above values, and the mass proportion of the filler particles is 30%-80%, for example, 30%, 40%, 50%, 60%, 70%, 80% or within the range of any two of the above values.

[0051] In some embodiments, the first polymer comprises one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyhexafluoropropylene, fluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, nitrile rubber, poly(p-phenylene terephthalamide), poly(m-phenylene isophthalamide), and copolymer systems derived from the foregoing polymers.

[0052] In some embodiments, the filler particles include boehmite, aluminum oxide, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, cerium oxide, zirconium titanate, barium titanate, magnesium fluoride, 1,3,5-triazine-2,4,6-triamine, melamine thiocyanate, melamine cyanurate, symmetrical triaminotriazine, 2-(4-bromophenyl)-4,6-dimethylbenzene, 1,3,5-triazine-2,4,6-triamine ... One or more of 1,3,5-triazine, 1-(4,6-diamino-1,3,5-triazine-2-yl)guanidine, 2,4-diamino-6-dimethylamino-1,3,5-triazine, cyanuric chloride, 2,4,6-tris(2-pyridyl)triazine, 2,4,6-triphenyl-1,3,5-triazine, tris(tribromophenoxy)triazine, 2-amino-4,6-methoxy-1,3,5-triazine, uracil and cytosine.

[0053] In some embodiments, the porosity of the substrate layer is 25%-70%, for example, 25%, 30%, 35%, 37%, 40%, 45%, 47%, 50%, 53%, 55%, 60%, 62%, 65%, 70% or within a range formed by any two of the above values.

[0054] In some embodiments, the thickness of the substrate layer is 2 μm-10 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or a range formed by any two of the above values.

[0055] In some embodiments, the substrate layer comprises one or more of polyolefin, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl chloride, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyethylene terephthalate, polybutylene terephthalate, poly(p-phenylene terephthalamide), poly(m-phenylene isophthalamide), and derivatives of the foregoing polymers.

[0056] In some embodiments, in an environment of 85° C., a membrane weighing 1.5 g is immersed in a first solution with a volume of 5 mL for 2 h, and the permeability increment of the membrane is 20 sec / 100 cc-400 sec / 100 cc, for example, 20 sec / 100 cc, 40 sec / 100 cc, 60 sec / 100 cc, 80 sec / 100 cc, 100 sec / 100 cc, 120 sec / 100 cc, 140 sec / 100 cc, 160 sec / 100 cc, 180 sec / 100 cc, 200 sec / 100 cc, 220 sec / 100 cc, 250 sec / 100 cc, 260 sec / 100 cc, 300 sec / 100 cc, 320 sec / 100 cc, 340 sec / 100 cc. cc, 380sec / 100cc, 400sec / 100cc or within the range formed by any two of the above values, and the first solution soaked with the diaphragm is a soaking solution, in which the sum of the weight proportions of elemental nitrogen, elemental sulfur and elemental phosphorus is 500ppm-20000ppm, for example, 500ppm, 1000ppm, 2500ppm, 5000ppm, 6000ppm, 8000ppm, 10000ppm, 12000ppm, 15000ppm, 18000ppm, 20000ppm or within the range formed by any two of the above values, wherein the first solution is composed of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate, and the weight ratio of the dimethyl carbonate, the ethylene carbonate and the ethyl methyl carbonate is 1:1:1.

[0057] When the diaphragm is tested using the above method, the incremental permeability of the diaphragm is controlled at 20sec / 100cc-400sec / 100cc, which can ensure that lithium ions pass through the diaphragm normally and maintain the charge and discharge capacity of the battery. In addition, the sum of the weight proportions of elemental nitrogen, elemental sulfur and elemental phosphorus in the immersion solution in which the diaphragm is soaked is controlled to be 500ppm-20000ppm, which can ensure that the first particles in the first coating of the diaphragm dissociate at high temperature to produce sufficient organic matter containing carbon-carbon double bonds, phosphorus-oxygen double bonds, carbon-nitrogen double bonds, carbon-sulfur double bonds or carbon-oxygen double bonds with electron-deficient groups, which effectively participate in CEI film formation and enhance the heat resistance of the CEI film.

[0058] In the present invention, the incremental air permeability of the diaphragm is measured by the following method: specifically, three pieces of diaphragms weighing 1.5 g are cut at a longitudinal interval of 150 mm, the diaphragms are placed in a permeability meter for air permeability testing, and the average value of the three test results is taken as the air permeability A of the diaphragm before immersion, in units of sec / 100 cc; in an environment of 85°C, the three diaphragms weighing 1.5 g are soaked in a first solution with a volume of 5 mL for 2 hours, the diaphragm is taken out, placed on filter paper to absorb the residual liquid, the surface of the diaphragm is purged with nitrogen until it is completely dry, the diaphragm is placed in a permeability meter for air permeability testing, and the average value of the three test results is taken as the air permeability B of the diaphragm after immersion, in units of sec / 100 cc; the incremental air permeability of the diaphragm is calculated by formula BA, in units of sec / 100 cc.

[0059] In the present invention, the sum of the weight proportions of elemental nitrogen, elemental sulfur and elemental phosphorus in the soaking solution is measured by the following method: take 2 mL of the soaking solution, weigh its weight as M1, dilute it to 20 mL with ultrapure water, use ICP-MS to detect the element concentration in the solution (detection wavelengths are: elemental nitrogen is 174.27 nm, elemental sulfur is 180.73 nm, and elemental phosphorus is 178.22 nm), and calculate the proportion according to the formula: the sum of the weight proportions of elemental nitrogen, elemental sulfur and elemental phosphorus = [(C N +C S +C P )×(20 / 2) / M1], the unit is μg / g (ppm), where C N is the elemental nitrogen concentration in μg / mL, C S is the elemental sulfur concentration in μg / mL, C Pis the concentration of elemental phosphorus, expressed in μg / mL. It should be noted that the soaking solution may include one or more of elemental nitrogen, elemental sulfur and elemental phosphorus. When the soaking solution includes one of elemental nitrogen, elemental sulfur and elemental phosphorus, the sum of the weight proportions of the elemental nitrogen, elemental sulfur and elemental phosphorus refers to the weight proportion of the one element (i.e., one of elemental nitrogen, elemental sulfur and elemental phosphorus); when the soaking solution includes multiple elements of elemental nitrogen, elemental sulfur and elemental phosphorus, the sum of the weights of the elemental nitrogen, elemental sulfur and elemental phosphorus refers to the sum of the weights of multiple elements (multiple elements of elemental nitrogen, elemental sulfur and elemental phosphorus).

[0060] The second aspect of the present invention provides a battery, which includes a positive electrode sheet and the separator described in the first aspect of the present invention, the positive electrode sheet includes a positive electrode collector and a positive electrode active layer located on one side or both sides of the positive electrode collector, and the coating corresponds to the positive electrode active layer.

[0061] In the present invention, "the coating corresponds to the positive electrode active layer" means that when the coating is located on one surface of the substrate layer, the positive electrode active layer corresponds to the coated side of the separator, and the negative electrode active layer corresponds to the other side of the separator; when the coating is located on both surfaces of the substrate layer, the positive electrode active layer corresponds to either coated side of the separator, and the negative electrode active layer corresponds to the other side of the separator. In this case, the organic matter containing electron-deficient groups produced by the dissolution of the first particles at high temperature can quickly diffuse to the positive electrode sheet through the through-pores of the second coating, participate in the film-forming reaction of the CEI film, enhance the high-temperature resistance of the CEI film, and improve the interfacial stability between the separator and the positive electrode sheet, thereby improving the battery's high-temperature intermittent cycle capacity retention rate and the recovery capacity retention rate after high-temperature storage.

[0062] In some embodiments, as Figure 4 As shown, in the thickness direction K of the positive electrode sheet 5, the positive electrode sheet includes a first surface 52 and a second surface 53, the first surface corresponds to the coating, and the first surface includes a plurality of pits 51. The battery satisfies the following relationship: 0.005≤V1 / D1≤10 (V1 / D1 is, for example, 0.005, 0.01, 0.03, 0.05, 0.08, 0.1, 0.3, 0.5, 1, 1.3, 1.5, 1.8, 2, 3, 4, 5, 6, 7, 8, 9, 10 or is within the range of any two of the above values), wherein D1 is the Dv10 of the first particle, in μm, and V1 is the average volume of the pits, in mm 3The study found that by setting regular pits on the first surface of the positive electrode sheet corresponding to the coating, the electrolyte retention capacity of the positive electrode active layer can be enhanced, thereby increasing the dissolution amount of organic matter containing electron-deficient groups in the first particles in the coating of the diaphragm corresponding to the positive electrode side, and the smaller the particle size of the first particles, the more organic matter containing electron-deficient groups dissolved from the first particles on the positive electrode side. However, if the pit volume is too large, the particle size of the first particles is too small, and the dissolution amount of organic matter containing electron-deficient groups is too large, the gap between the diaphragm and the positive electrode sheet will be too large, increasing the occurrence of diaphragm. The risk of delamination between the diaphragm and the positive electrode sheet. Therefore, when the Dv10 of the first particle and the average volume of the pit are controlled so that the battery satisfies the above relationship, the electrolyte retention capacity of the positive electrode active layer can be expanded, and the dissolution amount of organic matter containing electron-deficient groups in the first particle on the positive electrode side can be increased. At the same time, it can also avoid the delamination of the diaphragm and the positive electrode sheet due to excessive dissolution, ensure the appropriate gap between the diaphragm and the positive electrode sheet, avoid the increase of interface impedance, and improve the battery's high-temperature intermittent cycle capacity retention rate and the recovery capacity retention rate after high-temperature storage.

[0063] In some embodiments, the battery satisfies the following relationship: 0.05≤V1 / D1≤5.

[0064] In some embodiments, the Dv10 of the first particles is 0.01 μm-0.5 μm, for example, 0.01 μm, 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.34 μm, 0.4 μm, 0.43 μm, 0.46 μm, 0.5 μm, or a range formed by any two of the above values.

[0065] In the present invention, the Dv10 of the first particles refers to the particle size corresponding to the 10% cumulative volume particle size distribution percentage of the first particles, arranged in ascending order of particle size. In the present invention, the particle size Dv10 of the first particles can be measured using a Malvern Mastersizer 3000 laser particle size analyzer.

[0066] In some embodiments, the average volume V1 of the pits is 0.001 mm 3 -0.15mm 3 , for example 0.001mm 3 , 0.005mm 3 , 0.01mm 3 , 0.015mm 3 , 0.02mm 3 , 0.025mm 3 , 0.03mm 3 , 0.035mm 3 , 0.04mm 3, 0.045mm 3 , 0.05mm 3 , 0.1mm 3 , 0.13mm 3 , 0.15mm 3 Or within the range formed by any two of the above values.

[0067] In some embodiments, the volume of the pit is measured by the following method: using a 3D optical profilometer to scan the surface of the positive electrode sheet, when the pit has a regular geometric shape (such as a cylinder, cone, cube, etc.), obtaining parameters such as the depth, diameter or side length of the pit, and obtaining the volume of the pit according to the volume calculation formula of the specific geometric shape; when the pit has an irregular geometric shape, depicting a circle connected to the orthographic projection of the irregular pit on the first surface, and measuring its diameter d, combined with the depth h of the irregular pit, according to the formula π(d / 2) 2 h calculates the volume of the irregular pits, and calculates the average value of the volumes of 100 pits, which is the average volume of the pits.

[0068] In some embodiments, at least a portion of the first surface is recessed toward the second surface to form a plurality of pits, and a plurality of protrusions are correspondingly provided on the second surface.

[0069] According to a specific embodiment, V1 is 0.001-0.15, D1 is 0.01-0.5, and the battery satisfies the following relationship: 0.005≤V1 / D1≤10.

[0070] According to a specific embodiment, V1 is 0.001-0.15, D1 is 0.01-0.5, and the battery satisfies the following relationship: 0.05≤V1 / D1≤5.

[0071] In some embodiments, the average depth of the pits is 2 μm-30 μm, for example, 2 μm, 6 μm, 10 μm, 14 μm, 18 μm, 20 μm, 24 μm, 26 μm, 30 μm, or a range formed by any two of the above values.

[0072] In some embodiments, the average depth of the pits is 3 μm-20 μm.

[0073] In the present invention, the depth of the pit is the vertical distance from the lowest point of the pit bottom to the plane where the first surface is located along the thickness direction K (e.g. Figure 4 As shown in b), the depths of 100 pits are counted and the average value is calculated, which is the average depth of the pits.

[0074] In some embodiments, the average spacing between adjacent pits is 100 μm-500 μm, for example, 100 μm, 120 μm, 150 μm, 180 μm, 200 μm, 230 μm, 250 μm, 280 μm, 300 μm, 350 μm, 380 μm, 400 μm, 430 μm, 450 μm, 500 μm or within a range formed by any two of the above values.

[0075] In the present invention, the spacing between adjacent pits refers to the shortest distance between the edge lines of two adjacent pits (e.g. Figure 4 As shown in a in FIG), the distances between 100 groups of adjacent pits are counted and the average value is calculated, which is the average distance between adjacent pits.

[0076] In some embodiments, as Figure 5 As shown, the shape of the orthographic projection of the pit on the first surface is a regular shape (for example, a circle 511, an ellipse 512, a diamond 513, a rectangle 514, a square 515, etc.) or an irregular shape (for example, an island 516).

[0077] In some embodiments, the positive electrode active layer includes a positive electrode active material, a positive electrode conductor, and a positive electrode binder.

[0078] In some embodiments, the positive electrode active material includes at least one of lithium nickelate, lithium titanate, lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganate.

[0079] In some embodiments, the positive electrode active material includes lithium cobalt oxide.

[0080] In some embodiments, the positive electrode conductive agent includes at least one of conductive carbon black, carbon nanotubes, conductive graphite, and graphene.

[0081] In some embodiments, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), acrylic acid-modified PVDF, polyacrylate polymers, acrylic polymers, polytetrafluoroethylene, polyacrylonitrile, polyimide, styrene-butadiene rubber, and styrene-acrylic rubber.

[0082] In some embodiments, the battery includes a negative electrode sheet, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer located on one side or both sides of the negative electrode current collector, the negative electrode active layer includes a negative electrode active material, a negative electrode conductor and a negative electrode binder, the negative electrode active material includes a silicon-based material, and the silicon-based material includes at least one of elemental silicon, silicon oxides (such as SiOx / C), silicon-carbon composites (such as Si / C), silicon-nitrogen composites, and silicon alloys.

[0083] The present invention will be described in detail below through examples. The examples described in the present invention are only some examples of the present invention, not all examples. All other examples obtained by persons of ordinary skill in the art based on the examples of the present invention without creative work are within the scope of protection of the present invention.

[0084] Example 1 (1) Preparation of positive electrode sheet Lithium cobalt oxide, binder polyvinylidene fluoride (PVDF 500), and conductive material (conductive carbon black: carbon nanotubes = 2:1) are mixed in N-methylpyrrolidone (NMP) solvent in a weight ratio of 96:2:2, and continuously stirred in a stirrer to form a uniform, flowing positive electrode slurry. Subsequently, the positive electrode slurry is coated on both sides of an aluminum foil with a thickness of 10μm, and placed in a 120℃ vacuum oven to dry for 6 hours. After rolling and slitting, a positive electrode sheet is obtained. The depth and density of the pits on the first surface of the positive electrode sheet are then controlled by a protruding roller to obtain a positive electrode sheet with regular pits, wherein the average volume of the pits is 0.4mm 3 (ie, V1 is 0.05), the average depth of the pits is 12 μm, the average spacing between adjacent pits is 263 μm, and the shape of the orthographic projection of the pits on the first surface is circular.

[0085] (2) Preparation of negative electrode sheet Graphite, silicon-carbon composite (Dv50 = 7μm), conductive material (carbon black: carbon nanotubes = 1:1), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber were mixed in an aqueous solvent at a weight ratio of 92:6:1:0.5:0.5. This mixture was continuously stirred in a blender to form a uniform, fluid negative electrode slurry. The slurry was then coated on both sides of a 10μm-thick current collector copper foil and dried in a 120°C vacuum oven for 6 hours. The resulting negative electrode sheets were then rolled and slit.

[0086] (3) Preparation of electrolyte In an argon-filled glove box (moisture <1ppm, oxygen <1ppm), ethylene carbonate, propylene carbonate, propyl propionate, and ethyl propionate were mixed in a mass ratio of 15:15:50:20 to form a uniform solvent. Then, 16wt% LiPF6, 3wt% 1,3,6-hexanetricarbonitrile, and 19wt% fluoroethylene carbonate were slowly added. After stirring, the desired lithium-ion battery electrolyte was obtained.

[0087] (4) Preparation of diaphragm 96 parts by weight of melamine cyanurate (first particles) and 4 parts by weight of polymethyl methacrylate (binder) were mixed in water and stirred thoroughly to obtain a mixed slurry with a solid content of 25%. The mixed slurry was coated on one surface of the substrate layer by a gravure roller and dried in a multi-section oven at 60°C to form a first coating layer. The thickness of the first coating layer was 2 μm. In the first coating layer, the sum of the number of carbon-carbon double bonds, phosphorus-oxygen double bonds, carbon-nitrogen double bonds, carbon-sulfur double bonds and carbon-oxygen double bonds in the unit structure of the organic compound (melamine cyanurate) was 6. The median particle size Dv50 of the first particles was 0.8 μm, and the specific surface area of ​​the first particles was 9.4 m 2 / g; PVDF (fluoropolymer) was dissolved in a solvent DMAC and stirred thoroughly to obtain a solution, which was then coated on the surface of the first coating layer and the other side surface of the substrate layer by a gravure roller, and then extracted in a water tank and dried at 60°C to form a second coating layer on the surface of the first coating layer, and a third coating layer was formed on the other side surface of the substrate layer. The second coating layer and the third coating layer were porous structures formed by a continuous phase of polyvinylidene fluoride (PVDF), and the weight proportion of the fluoropolymer (i.e., polyvinylidene fluoride) in the second coating layer and the third coating layer was 100%. The surfaces of the second coating layer and the third coating layer included through holes. The thickness of the second coating layer and the third coating layer was 1 μm, and the ratio of the thickness of the first coating layer to the thickness of the second coating layer was 2. In the area of ​​100μm×100μm on the surface of the second coating, the orthographic projection area of ​​the through holes on the substrate layer and / or the first coating accounts for 57.3% of the surface area of ​​the diaphragm. The coating includes a first coating and a second coating. On the surface of the coating away from the substrate layer, the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus is 0.68:1. In an environment of 85°C, a diaphragm weighing 1.5g is immersed in a first solution with a volume of 5mL for 2h. The permeability value increase of the diaphragm is 36sec / 100cc, and the first solution soaked with the diaphragm is the immersion solution. In the immersion solution, the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus is 2530ppm.

[0088] (5) Preparation of lithium-ion batteries The positive electrode sheet, separator, and negative electrode sheet prepared above are wound to prepare a bare battery cell; the bare battery cell is then placed in an aluminum-plastic film, and the prepared electrolyte is injected into the dried bare battery cell. After vacuum packaging, room temperature standing, high-temperature formation and other processes, the desired lithium-ion battery is obtained, wherein the separator coating corresponds to the positive electrode active layer, and the battery satisfies V1 / D1=0.05 / 0.14=0.4.

[0089] Example 2 group This set of examples is used to illustrate the effects produced when the composition of the first particles is changed.

[0090] Example 2-1 This embodiment is carried out with reference to Example 1, except that the component of the first particle is uracil, and in the unit structure of the organic compound, the sum of the numbers of carbon-carbon double bonds, phosphorus-oxygen double bonds, carbon-nitrogen double bonds, carbon-sulfur double bonds, and carbon-oxygen double bonds is 3. On the surface of the coating away from the substrate layer, the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur, and elemental phosphorus is 0.41:1. In an environment of 85°C, a diaphragm weighing 1.5 g is immersed in a first solution with a volume of 5 mL for 2 h. The permeability value increase of the diaphragm is 44 sec / 100 cc, and the first solution soaked with the diaphragm is an immersion solution. In the immersion solution, the sum of the weight proportions of elemental nitrogen, elemental sulfur, and elemental phosphorus is 8432 ppm.

[0091] Example 2-2 This embodiment is carried out with reference to Example 1, except that the component of the first particle is 3-methyl-1-phenyl-2-phosphacyclopentene 1-oxide, and in the unit structure of the organic compound, the sum of the number of carbon-carbon double bonds, phosphorus-oxygen double bonds, carbon-nitrogen double bonds, carbon-sulfur double bonds, and carbon-oxygen double bonds is 5. On the surface of the coating away from the substrate layer, the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur, and elemental phosphorus is 0.27:1. In an environment of 85°C, a diaphragm weighing 1.5 g is immersed in a first solution with a volume of 5 mL for 2 h. The permeability value increase of the diaphragm is 39 sec / 100 cc, and the first solution soaked with the diaphragm is the soaking solution. In the soaking solution, the sum of the weight proportions of elemental nitrogen, elemental sulfur, and elemental phosphorus is 1955 ppm.

[0092] Example 2-3 This embodiment is carried out with reference to Example 1, except that the component of the first particle is melamine thiocyanate, and in the unit structure of the organic compound, the sum of the numbers of carbon-carbon double bonds, phosphorus-oxygen double bonds, carbon-nitrogen double bonds, carbon-sulfur double bonds, and carbon-oxygen double bonds is 3. On the surface of the coating away from the substrate layer, the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur, and elemental phosphorus is 1.2:1. In an environment of 85°C, a diaphragm weighing 1.5 g is immersed in a first solution with a volume of 5 mL for 2 h. The permeability value increase of the diaphragm is 52 sec / 100 cc, and the first solution soaked with the diaphragm is an immersion solution. In the immersion solution, the sum of the weight proportions of elemental nitrogen, elemental sulfur, and elemental phosphorus is 3558 ppm.

[0093] Examples 2-4 This embodiment is carried out with reference to Example 1, except that the component of the first particle is 2,4-dimercapto-5,6-diaminopyrimidine, and in the unit structure of the organic compound, the sum of the number of carbon-carbon double bonds, phosphorus-oxygen double bonds, carbon-nitrogen double bonds, carbon-sulfur double bonds, and carbon-oxygen double bonds is 3. On the surface of the coating away from the substrate layer, the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur, and elemental phosphorus is 1.06:1. In an environment of 85°C, a membrane weighing 1.5 g is immersed in a first solution with a volume of 5 mL for 2 h. The permeability value increase of the membrane is 61 sec / 100 cc, and the first solution soaked with the membrane is a soaking solution. In the soaking solution, the sum of the weight proportions of elemental nitrogen, elemental sulfur, and elemental phosphorus is 3648 ppm.

[0094] Example 3 group This set of examples is used to illustrate the effects produced when the median particle size Dv50 of the first particles and / or the specific surface area of ​​the first particles are changed.

[0095] This example group was carried out with reference to Example 1, except that the median particle size Dv50 of the first particles and / or the specific surface area of ​​the first particles were changed, as shown in Table 1 for details.

[0096] Table 1 Example 4 Group This set of embodiments is used to illustrate the impact when the proportion of the orthographic projection area of ​​the through hole on the substrate layer and / or the first coating layer in the diaphragm surface area changes in the area of ​​the second coating layer of 100 μm×100 μm.

[0097] Example 4-1 This embodiment is carried out with reference to embodiment 1, except that, in the area of ​​100 μm×100 μm of the second coating, the orthographic projection area of ​​the through hole on the substrate layer and / or the first coating accounts for 10.6% of the surface area of ​​the diaphragm, and on the surface of the coating away from the substrate layer, the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus is 2.85:1. In an environment of 85°C, a diaphragm weighing 1.5 g is immersed in a first solution with a volume of 5 mL for 2 h, and the permeability value increase of the diaphragm is 396 sec / 100 cc. The first solution soaked with the diaphragm is an immersion solution, and the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus in the immersion solution is 325 ppm.

[0098] Example 4-2 This embodiment is carried out with reference to embodiment 1, except that, in the area of ​​100 μm×100 μm of the second coating, the orthographic projection area of ​​the through hole on the substrate layer and / or the first coating accounts for 20.8% of the surface area of ​​the diaphragm, and on the surface of the coating away from the substrate layer, the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus is 1.18:1. In an environment of 85°C, a diaphragm weighing 1.5 g is immersed in a first solution with a volume of 5 mL for 2 h, and the permeability value increase of the diaphragm is 356 sec / 100 cc. The first solution soaked with the diaphragm is the immersion solution, and the sum of the weight proportions of elemental nitrogen, elemental sulfur and elemental phosphorus in the immersion solution is 1773 ppm.

[0099] Example 4-3 This embodiment is carried out with reference to embodiment 1, except that, in the area of ​​100 μm×100 μm of the second coating, the orthographic projection area of ​​the through hole on the substrate layer and / or the first coating accounts for 79.3% of the surface area of ​​the diaphragm, and on the surface of the coating away from the substrate layer, the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus is 0.58:1. In an environment of 85°C, a diaphragm weighing 1.5 g is immersed in a first solution with a volume of 5 mL for 2 h, and the permeability value increase of the diaphragm is 39 sec / 100 cc. The first solution soaked with the diaphragm is the immersion solution, and the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus in the immersion solution is 8546 ppm.

[0100] Example 4-4 This embodiment is carried out with reference to embodiment 1, except that, in the area of ​​100 μm×100 μm of the second coating, the orthographic projection area of ​​the through hole on the substrate layer and / or the first coating accounts for 89.2% of the surface area of ​​the diaphragm, and on the surface of the coating away from the substrate layer, the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus is 0.54:1. In an environment of 85°C, a diaphragm weighing 1.5 g is immersed in a first solution with a volume of 5 mL for 2 h, and the permeability value increase of the diaphragm is 32 sec / 100 cc. The first solution soaked with the diaphragm is the immersion solution, and the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus in the immersion solution is 12054 ppm.

[0101] Example 5 Group This set of examples is used to illustrate the effects produced when the ratio of the thickness of the first coating layer to the thickness of the second coating layer is changed.

[0102] This embodiment group was carried out with reference to embodiment 1, except that the ratio of the thickness of the first coating layer to the thickness of the second coating layer was changed by changing the thickness of the first coating layer and / or the thickness of the second coating layer, as shown in Table 2.

[0103] Table 2 “*” indicates the same as Example 1 Example 6 This set of embodiments is used to illustrate the impact when V1 / D1 changes.

[0104] This embodiment group was carried out with reference to the embodiment 1, except that V1 / D1 was changed by changing the particle size Dv10 (D1) of the first particles and / or the average volume (V1) of the positive electrode pits, as shown in Table 3 for details.

[0105] Table 3 Example 7 This example is carried out with reference to Example 1, except that the weight proportion of the first particles in the first coating is 98%, the thickness of the first coating is 3 μm, the thickness of the second coating is 0.5 μm, the ratio of the thickness of the first coating to the thickness of the second coating is 6, and on the surface of the coating away from the substrate layer, the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus is 0.15:1. In an environment of 85°C, a membrane weighing 1.5 g is immersed in a first solution with a volume of 5 mL for 2 h, and the permeability value increase of the membrane is 12 sec / 100 cc. The first solution soaked with the membrane is the soaking solution, and in the soaking solution, the sum of the weight proportions of elemental nitrogen, elemental sulfur and elemental phosphorus is 18445 ppm.

[0106] Example 8 This embodiment is carried out with reference to embodiment 1, except that the weight proportion of the first particles in the first coating is 90.2%, the proportion of the orthographic projection area of ​​the through holes on the substrate layer and / or the first coating in the area of ​​100 μm×100 μm of the second coating in the surface area of ​​the diaphragm is 10.1%, and the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus on the surface of the coating away from the substrate layer is 2.2:1. In an environment of 85°C, a diaphragm weighing 1.5 g is immersed in a first solution with a volume of 5 mL for 2 h, and the permeability value increase of the diaphragm is 410 sec / 100 cc, and the first solution soaked with the diaphragm is the immersion solution. In the immersion solution, the sum of the weight proportions of elemental nitrogen, elemental sulfur and elemental phosphorus is 653 ppm.

[0107] Example 9 This embodiment is carried out with reference to embodiment 1, except that the weight proportion of the first particles in the first coating is 98%, the orthographic projection area of ​​the through holes on the substrate layer and / or the first coating in the area of ​​100 μm×100 μm of the second coating accounts for 89.5% of the surface area of ​​the diaphragm, and on the surface of the coating away from the substrate layer, the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus is 0.12:1. In an environment of 85°C, a diaphragm weighing 1.5 g is immersed in a first solution with a volume of 5 mL for 2 h, and the air permeability value increase of the diaphragm is 27 sec / 100 cc. The first solution soaked with the diaphragm is the immersion solution, and the sum of the weight proportions of elemental nitrogen, elemental sulfur and elemental phosphorus in the immersion solution is 23109 ppm.

[0108] Comparative Example 1 This embodiment group is carried out with reference to Example 1, except that the component of the first particle is aluminum oxide, and in an environment of 85°C, a diaphragm weighing 1.5 g is immersed in a first solution with a volume of 5 mL for 2 hours, and the permeability value increase of the diaphragm is 135 sec / 100 cc, and the first solution soaked with the diaphragm is an immersion solution, and in the immersion solution, the sum of the weight proportions of elemental nitrogen, elemental sulfur and elemental phosphorus is 0 ppm.

[0109] Comparative Example 2 This embodiment group was carried out with reference to Example 1, except that the surface of the second coating did not include through holes. In an environment of 85°C, a diaphragm weighing 1.5 g was immersed in a first solution with a volume of 5 mL for 2 h. The permeability value of the diaphragm increased by 532 sec / 100 cc, and the first solution soaked with the diaphragm was an immersion solution. In the immersion solution, the sum of the weight proportions of elemental nitrogen, elemental sulfur and elemental phosphorus was 105 ppm.

[0110] Comparative Example 3 This embodiment group was carried out with reference to Example 1, except that, in the area of ​​100 μm×100 μm of the second coating, the orthographic projection area of ​​the through hole on the substrate layer and / or the first coating accounted for 9.3% of the surface area of ​​the diaphragm, and on the surface of the coating away from the substrate layer, the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus was 2.88:1. In an environment of 85°C, a diaphragm weighing 1.5 g was immersed in a first solution with a volume of 5 mL for 2 h, and the permeability value increase of the diaphragm was 326 sec / 100 cc. The first solution soaked with the diaphragm was an immersion solution, and the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus in the immersion solution was 640 ppm.

[0111] Comparative Example 4 This embodiment group was carried out with reference to Example 1, except that, in the area of ​​100 μm×100 μm of the second coating, the orthographic projection area of ​​the through hole on the substrate layer and / or the first coating accounted for 94.7% of the surface area of ​​the diaphragm, and on the surface of the coating away from the substrate layer, the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus was 0.07:1. In an environment of 85°C, a diaphragm weighing 1.5 g was immersed in a first solution with a volume of 5 mL for 2 h, and the permeability value of the diaphragm increased by 17 sec / 100 cc. The first solution soaked with the diaphragm was the immersion solution, and the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus in the immersion solution was 25300 ppm.

[0112] Comparative Example 5 This embodiment group was carried out with reference to Example 1, except that the second coating was a porous structure formed by a continuous phase of polyacrylonitrile (fluorine-free), and on the surface of the coating away from the substrate layer, the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur, and elemental phosphorus was 0. In an environment of 85°C, a diaphragm weighing 1.5 g was immersed in a first solution with a volume of 5 mL for 2 h, and the permeability value increase of the diaphragm was 118 sec / 100 cc. The first solution soaked with the diaphragm was the soaking solution, and the sum of the weight proportions of elemental nitrogen, elemental sulfur, and elemental phosphorus in the soaking solution was 3520 ppm.

[0113] Comparative Example 6 This embodiment group is carried out with reference to Example 1, except that the coating located on the surface of one side of the substrate layer includes only the first coating, and the third coating is located on the surface of the other side of the substrate layer. On the surface of the coating away from the substrate layer, the ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur and elemental phosphorus is 0. In an environment of 85°C, a diaphragm weighing 1.5g is immersed in a first solution with a volume of 5mL for 2h, and the permeability value increase of the diaphragm is 85sec / 100cc. The first solution soaked with the diaphragm is the soaking solution. In the soaking solution, the sum of the weight proportions of elemental nitrogen, elemental sulfur and elemental phosphorus is 35300ppm.

[0114] Test Case The batteries prepared in the examples and comparative examples were subjected to the following performance tests. The test results are shown in Table 4: (1) Normal temperature cycle capacity retention rate / % (600 cycles in an environment of 25℃±2℃): At 25°C ± 2°C, charge the battery at a constant current of 1C to a maximum voltage of 4.53V, then continue constant voltage charging to 0.05C, rest for 5 minutes, then discharge at a constant current of 0.7C to 3V, rest for 5 minutes, and record the initial discharge capacity as C0. Cycle mode: charge at a constant current of 1C to a maximum voltage of 4.53V, then continue constant voltage charging to 0.05C, rest for 5 minutes, then discharge at a constant current of 0.7C to 3V. After 600 cycles, record the discharge capacity as C1. Room temperature cycle capacity retention rate (C1 / C0) × 100%.

[0115] (2) High temperature intermittent cycle capacity retention rate / % (intermittent cycle for 91 days in 45℃±2℃ environment): Initial capacity Q1 test: The battery is left at rest in an environment of 25℃±3℃ for 10 minutes. Then, it is discharged at a constant current of 0.2C to a cutoff voltage of 3V and left at rest for another 10 minutes. Next, it is charged at a constant current of 0.8C to full charge, then switched to constant voltage charging to a current cutoff of 0.05C and left at rest for 10 minutes. Then, it is discharged again at a constant current of 0.2C to 3V. The discharge capacity at this time is recorded as the initial capacity Q1. Intermittent discharge and charge at 45℃±2℃: The battery is allowed to stand in a 45℃±2℃ environment for 10 minutes; then discharged at a constant current of 0.5C to a cut-off voltage of 3V; then allowed to stand for 10 minutes; and charged at a constant current of 0.7C to a fully charged state. The total test time for the above standing, discharging, standing, and charging steps is controlled to be 24 hours; Final capacity Q2 test: The intermittent discharge and charge steps at 45℃±2℃ are regarded as one cycle, and the cycle is carried out for a total of 91 days. After the cycle is completed, the battery is moved to a 25℃±5℃ environment. After the sample returns to room temperature, the initial capacity Q1 test steps are repeated. The discharge capacity obtained by the test is the final capacity Q2, and (Q2 / Q1)×100% is the final cycle capacity retention rate.

[0116] (2) High temperature storage recovery capacity retention rate / % (stored in 85℃±2℃ environment for 6 hours): Initial capacity Q3 test: Place the battery in a 25℃±2℃ environment and let it rest for 10 minutes; then discharge it at 0.5C to a lower voltage of 3V and let it rest for another 10 minutes; then charge it at a constant current of 0.7C to full charge, switch to constant voltage charging to a current cutoff of 0.05C, and let it rest for another 10 minutes; then discharge it again at a constant current of 0.5C to a lower voltage of 3V, and record the discharge capacity at this time as the initial capacity Q3; Test the state before storage: After completing the initial capacity test, let it stand for 10 minutes, charge it at a constant current of 0.7C to full charge, then switch to constant voltage charging until the current reaches 0.05C; let the fully charged battery stand at 25℃±2℃ for 2 hours; Recovery capacity Q4 test: Place the battery in a constant temperature box at 85℃±2℃ and store it for 6 hours. After storage, take out the sample and let it stand at 25℃±2℃ for 2 hours to allow the battery to return to room temperature. After the sample returns to room temperature, repeat the initial capacity Q3 test steps mentioned above. The discharge capacity obtained from the test is the recovery capacity Q4, and (Q4 / Q3)×100% is the recovery capacity retention rate.

[0117] Table 4 By comparing the test results of the comparative example and the embodiment in Table 4, it can be seen that the room temperature cycle capacity retention rate, high temperature intermittent cycle capacity retention rate and high temperature storage recovery capacity retention rate of the embodiment battery are all significantly improved. This shows that by arranging the first particles containing electron-deficient groups in the diaphragm and controlling the coverage rate of the through holes that facilitate the diffusion of organic matter containing electron-deficient groups, the high temperature resistance of the CEI membrane is effectively improved, and the damage of the CEI membrane is reduced or even avoided, thereby significantly improving the room temperature cycle capacity retention rate, high temperature intermittent cycle capacity retention rate and recovery capacity retention rate after high temperature storage of the battery.

[0118] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention 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 in the present invention and fall within the scope of protection of the present invention.

Claims

1. A diaphragm, characterized in that: The diaphragm includes a substrate layer and a coating located on one or both sides of the substrate layer, the coating including a first coating and a second coating, the first coating being located on the surface of the substrate layer, the second coating being located on the surface of the first coating, the first coating including first particles, the first particles being composed of organic compounds, the unit molecular structure of the organic compounds including one or more of carbon-carbon double bonds, phosphorus-oxygen double bonds, carbon-nitrogen double bonds, carbon-sulfur double bonds, and carbon-oxygen double bonds; the second coating is a porous structure formed with a fluoropolymer as a continuous phase, the surface of the second coating including through holes, and in an area of ​​100 μm×100 μm on the surface of the second coating, the orthographic projection area of ​​the through holes on the substrate layer and / or the first coating accounts for 10%-90% of the surface area of ​​the diaphragm.

2. The diaphragm according to claim 1, wherein The coating comprises the first coating and the second coating, and on a surface of the coating away from the substrate layer, a ratio of the weight of elemental fluorine to the sum of the weights of elemental nitrogen, elemental sulfur, and elemental phosphorus is (0.25-3):1; And / or, in the unit structure of the organic compound, the sum of the numbers of carbon-carbon double bonds, phosphorus-oxygen double bonds, carbon-nitrogen double bonds, carbon-sulfur double bonds and carbon-oxygen double bonds is 3-12.

3. The diaphragm according to claim 1, wherein The organic compounds include 1,3,5-triazine-2,4,6-triamine, melamine polyphosphate, melamine hydrobromide, melamine polyphosphate, symmetrical triaminotriazine, 2-(4-bromophenyl)-4,6-dimethyl-1,3,5-triazine, 2,4-diamino-6-dimethylamino-1,3,5-triazine, cyanuric chloride, melamine thiocyanate, melamine cyanurate, 2-amino-4,6-methoxy-1,3,5-triazine, 1-(4,6-diamino-1,3,5-triazin-2-yl)guanidine, uracil, cytosine, 5-azacytosine , indole-3-propionic acid, N4-methylcytosine, 1-phenyl-3-methyl-5-pyrazolone, formaldehyde polymelamine hydrochloride, 2,4,6-triphenyl-1,3,5-triazine, 2-quinolinesulfonic acid and 2-quinolinesulfonate, 2,4,6-tris(2-pyridyl)triazine, tris(tribromophenoxy)triazine, dithiourea, 2,4-dimercapto-5,6-diaminopyrimidine, 4,6-dimethyl-2-mercaptopyrimidine, 1,3,4-thiadiazole-2-thione salt, coumarin-3-sulfonate, 3-methyl-1-phenyl-2-phosphacyclopentene 1-oxide; And / or, the fluorine-containing polymer includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin. The diaphragm according to claim 1 , wherein: The ratio of the thickness of the first coating layer to the thickness of the second coating layer is 0.4-3; and / or, the thickness of the first coating layer is 0.2 μm-5 μm; and / or, the thickness of the second coating layer is 0.5 μm-5 μm; and / or, the weight proportion of the first particles in the first coating layer is 90%-99%; And / or, the weight proportion of the fluorine-containing polymer in the second coating layer is 70%-100%; and / or, the median particle size Dv50 of the first particles is 0.05 μm-5 μm; And / or, the specific surface area of ​​the first particles is 4m 2 / g-35m 2 / g. The diaphragm according to claim 1 , wherein One side surface of the substrate layer includes the coating layer, and the other side surface of the substrate layer includes a third coating layer; and / or, the porosity of the substrate layer is 25%-70%; and / or, the thickness of the substrate layer is 2 μm-10 μm; And / or, the components of the substrate layer include one or more of polyolefin, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl chloride, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyethylene terephthalate, polybutylene terephthalate, poly(p-phenylene terephthalamide), poly(m-phenylene isophthalamide) and derivatives of the above polymers.

6. The diaphragm according to any one of claims 1 to 5, wherein In an environment of 85°C, the diaphragm weighing 1.5g is soaked in a first solution with a volume of 5mL for 2h, the air permeability value increment of the diaphragm is 20 sec / 100cc-400sec / 100cc, and the first solution soaked with the diaphragm is a soaking solution, in which the sum of the weight proportions of elemental nitrogen, elemental sulfur and elemental phosphorus is 500ppm-20000ppm, wherein the first solution is composed of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate, and the weight ratio of the dimethyl carbonate, the ethylene carbonate and the ethyl methyl carbonate is 1:1:

1.

7. A battery, characterized in that: The battery comprises a positive electrode sheet and the separator described in claims 1 to 6. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer located on one side or both sides of the positive electrode current collector. The coating corresponds to the positive electrode active layer.

8. The battery according to claim 7, wherein In the thickness direction of the positive electrode sheet, the positive electrode sheet includes a first surface and a second surface, the first surface corresponds to the coating, the first surface includes a plurality of pits, and the battery satisfies the following relationship: 0.005≤V1 / D1≤10, wherein D1 is the Dv10 of the first particle, in μm, and V1 is the average volume of the pits, in mm 3 .

9. The battery according to claim 8, wherein: The battery satisfies the following relationship: 0.05≤V1 / D1≤5, and / or, the average volume V1 of the pits is 0.001 mm 3 -0.15mm 3 ; and / or, the Dv10 of the first particles is 0.01 μm-0.5 μm; And / or, at least a portion of the first surface is recessed toward the second surface to form a plurality of pits, and a plurality of protrusions are correspondingly provided on the second surface.

10. The battery according to claim 8, wherein The average depth of the pits is 2 μm-30 μm; and / or, the average spacing between adjacent pits is 100 μm-500 μm; And / or, the shape of the orthographic projection of the pit on the first surface includes one or more of a circle, an ellipse, a diamond, a rectangle, a square and an island.

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