Separator and secondary battery

Abstract

The present application relates to the technical field of batteries, and discloses a separator and a secondary battery. In the separator of the present application, an organic coating containing inorganic particles is provided on an organic substrate. By controlling the size distribution of the inorganic particles and regulating the relationship between the size of the inorganic particles in the coating and the coating thickness, the overall adhesion of the coating can be effectively improved, and the separator has good dimensional stability at different temperatures, good electrolyte wettability, and high ion transport efficiency. When the separator is applied to the secondary battery, long cycle life and high safety can be achieved.

Description

A separator and a secondary battery

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411964458.9, filed with the Chinese Patent Office on December 30, 2024, entitled "A Diaphragm and a Secondary Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, specifically to a separator and a secondary battery. Background Technology

[0004] The separator is a crucial component of a secondary battery, primarily located between the positive and negative electrodes, enabling reversible ion transport through electrolyte wetting. However, existing separators mainly fall into two categories: unprocessed organic separators, which suffer from low thermal stability, significant dimensional variations at different temperatures, poor electrolyte wettability, and insufficient mechanical strength; and modified separators with additional coatings on an organic substrate. Modifications such as ceramic coatings significantly improve dimensional stability, mechanical strength, and electrolyte wettability. However, these modified separators exhibit reduced ion transport efficiency, and the coating adhesion gradually decreases with the back-and-forth ion transport and the slow contraction / expansion of the electrodes, leading to detachment. This not only affects the stability of the SEI (Solid Electrolyte Interface) membrane and / or CEI (Chemical-Electrochemical Interface) membrane of the electrode active material, but also results in decreased cycle performance and even safety issues. Summary of the Invention

[0005] The purpose of this application is to overcome the shortcomings of the existing technology and provide a separator. The separator has an organic coating containing inorganic particles on an organic substrate. By controlling the size distribution of the inorganic particles and adjusting the relationship between the size of the inorganic particles and the thickness of the coating, the adhesion of the overall coating can be effectively improved. At the same time, the separator has good dimensional stability at different temperatures, good wettability to electrolyte, and high ion transport efficiency. When applied to secondary batteries, it can achieve long cycle life and high safety.

[0006] To achieve the above objectives, in a first aspect of this application, a diaphragm is provided, comprising an organic substrate layer and an organic coating;

[0007] The organic coating contains inorganic particles, and the organic coating satisfies: Dv90 / H≥5;

[0008] Where D v90 μm is the particle size corresponding to the cumulative volume distribution percentage of the inorganic particles reaching 90%, and D v90 =3~120μm; Hμm is the thickness of the organic coating.

[0009] As a preferred embodiment of this application, the D v90 / H = 5~55.

[0010] As a preferred embodiment of this application, the D v90 =10~120μm.

[0011] In a preferred embodiment of this application, H = 0.5~5μm.

[0012] In a preferred embodiment of this application, the organic coating is provided on both sides of the organic substrate layer, and the sum of the areal densities of the organic coatings on both sides is 1.3 to 1.65 g / m². 2 The surface density of a substance refers to its mass per unit area. The phrase "the sum of the surface densities of the organic coatings on both sides" refers to the sum of the surface densities of the organic coatings on both sides of the organic substrate layer.

[0013] In a preferred embodiment of this application, the inorganic particles in the organic coating have a mass content of 10-50%.

[0014] As a preferred embodiment of this application, the organic coating comprises an organic polymer, which includes at least one of polyvinyl alcohol formaldehyde, aromatic amide, polyvinylidene fluoride, polyvinylidene fluoride copolymer, polyamide, polyimide, polyacrylonitrile, polyethylene oxide, polyurethane, polyphenylene ether, acrylate copolymer, and polymethyl methacrylate. Polyvinylidene fluoride-based copolymers are a class of fluoropolymers (such as PVDF-HFP copolymers) formed by copolymerizing polyvinylidene fluoride (PVDF) as the main chain with other fluorinated monomers; these materials combine the excellent properties of PVDF (such as chemical resistance, high temperature resistance, and high mechanical strength) with the functional advantages of other monomers. Acrylate copolymers are polymers formed by copolymerizing acrylate monomers (such as methyl acrylate (MA), ethyl acrylate (EA), butyl acrylate (BA), etc.) with other monomers, such as polyacrylate-polyurethane copolymer (PAA-PU), fluorinated acrylate copolymers (such as P(MMA-FA), polyacrylate-polyethylene oxide (PAA-PEO) block copolymers, etc.).

[0015] As a preferred embodiment of this application, the inorganic particles include at least one of needle-shaped particles and rod-shaped particles.

[0016] As a preferred embodiment of this application, the inorganic particles include at least one of silicon dioxide, barium distitanate, aluminum oxide, potassium titanate, barium metatitanate, silicon suboxide, calcium oxide, magnesium oxide, zinc oxide, titanium dioxide, and barium oxide.

[0017] In a second aspect, this application provides a secondary battery including the separator described in this application.

[0018] The beneficial effects of this application are as follows:

[0019] This application provides a separator with an organic coating containing inorganic particles on an organic substrate. By controlling the size distribution of the inorganic particles and adjusting the relationship between the size of the inorganic particles and the thickness of the coating, the overall adhesion of the coating can be effectively improved. At the same time, the separator has good dimensional stability at different temperatures, good wettability to electrolyte, and high ion transport efficiency. When applied to secondary batteries, it can achieve long cycle life and high safety. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0022] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0023] The present application is further illustrated below with specific embodiments:

[0024] A membrane comprising an organic base layer and an organic coating;

[0025] The organic coating contains inorganic particles, and the organic coating satisfies: D v90 / H≥5;

[0026] Where D v90 μm is the particle size corresponding to the cumulative volume distribution percentage of the inorganic particles reaching 90%, and D v90 =3~120μm; Hμm is the thickness of the organic coating.

[0027] Traditional ceramic-coated modified separators suffer from technical drawbacks such as difficulty in ion transport and inconsistent coating adhesion. While existing technologies incorporate organic materials with high ion transport efficiency and good adhesion into the separator coating, aiming to synergistically leverage the advantages of both organic and ceramic materials to simultaneously improve ion transport efficiency and operational stability, thereby achieving higher rate and cycle performance in secondary batteries, significant compatibility and dispersibility issues exist between organic materials and inorganic particles (such as ceramic particles). Inappropriate compatibility can lead to inorganic particles in the coating not only failing to improve dimensional stability but also causing performance degradation due to particle agglomeration or directional migration. Furthermore, it can easily result in phenomena such as lithium plating in secondary batteries, posing safety risks. Therefore, the technical solution of this application uses inorganic particles in the construction of the separator coating, specifically targeting the D... v90 The particle size corresponding to a cumulative volume distribution percentage of 90% for the inorganic particles is defined, and the D of the inorganic particles is also specified. v90 By combining and controlling the thickness of the coating to establish parameter relationships, it was found that when the coating meets the above-mentioned limitations, under the premise of ensuring high wettability of the electrolyte and thus achieving sufficient ion transport efficiency, inorganic particles can form a non-completely uniform three-dimensional interlocking network structure with organic matter in the organic coating. The inorganic particles are both the skeleton of the organic matter and mutually anchored with the organic matter, effectively reducing the size shrinkage / expansion range of the organic coating. Furthermore, when the organic coating is built on the organic substrate, it can achieve high-strength bonding through a "anchoring" method. Even if the organic matter in the organic coating undergoes certain size changes under the influence of external temperature, the organic coating can still achieve strong connection through the anchoring of inorganic particles without falling off. Ultimately, it can achieve excellent adhesion at different temperatures. When the separator is applied to secondary batteries, it can exhibit long-term cycle stability and safety, and strong adaptability to the working environment temperature.

[0028] In some implementations, the D v90 / H = 5~55.

[0029] Specifically, the D v90 / H = a range of values ​​between one or any two of the following: 5, 8, 10, 12.5, 15, 18, 20, 22, 25, 28, 30, 32, 35, 40, 45, 50, 55.

[0030] In some implementations, the D v90 / H = 20~45.

[0031] In a preferred embodiment of this application, the thickness of the organic coating of the diaphragm not only affects the ion transport efficiency, but also directly affects the distribution of inorganic particles and the bonding strength with the organic matter in the organic coating. The D of the inorganic particles... v90 This will directly affect the volume change of the organic coating due to changes in ambient temperature and the anchoring strength of the organic coating to the organic substrate. When the thickness of the organic coating and the size relationship of the inorganic particles in the separator are selected within the above-mentioned preferred range, the stability and electrochemical performance of the separator when applied to a secondary battery are better.

[0032] In some implementations, the D v90 =10~120μm.

[0033] Specifically, the D v90 = A range of values ​​between one or any two of the following: 10μm, 11μm, 12μm, 15μm, 18μm, 20μm, 22μm, 25μm, 28μm, 30μm, 35μm, 40μm, 45μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, and 120μm.

[0034] In the preferred embodiment of this application, the D of the inorganic particles v90 The test was conducted as follows: The diaphragm was pyrolyzed in air at a temperature of 500℃, while the diaphragm's quality was monitored in real time. After the weight stabilized, the ash was collected, washed with water, and separated to obtain inorganic particles. These inorganic particles were then analyzed using a laser particle size analyzer. v90 The test.

[0035] In some implementations, the D v90 =18~85μm.

[0036] Inorganic particles in organic coatings, their D v90As the organic coating undergoes continuous changes, the porosity of its three-dimensional interlocking network structure varies, resulting in different ion conduction efficiencies. On the other hand, the size of the inorganic particles directly affects the bonding strength between the organic coating and the organic substrate of the separator. If the particle size is large, it may even damage the electrode surface particles during the assembly of the secondary battery with the electrode, affecting the electrochemical performance and even the safety of the secondary battery. If the particle size is small, it may cause local detachment of the organic matter in the organic coating during the operation of the secondary battery, which also affects the electrochemical performance of the secondary battery. When the size of the inorganic particles is within the above-mentioned preferred range, the corresponding separator has a better application effect.

[0037] In some implementations, H = 0.5–5 μm.

[0038] Specifically, H is a range of one or any two of the following: 0.5μm, 0.8μm, 1μm, 1.2μm, 1.5μm, 1.8μm, 2μm, 2.2μm, 2.5μm, 2.8μm, 3μm, 3.2μm, 3.5μm, 3.8μm, 4μm, 4.2μm, 4.5μm, 4.8μm, and 5μm.

[0039] In some implementations, H = 1.8–2.5 μm.

[0040] In some implementations, H = 1.9–2.3 μm.

[0041] In some embodiments, the organic coating is provided on both sides of the organic substrate layer, and the sum of the areal densities of the organic coatings on both sides is 1.3 to 1.65 g / m³. 2 .

[0042] Based on the control design of inorganic particle size and organic coating thickness described in this application, the areal density of the organic coating is moderate, which can balance ion transport, coating adhesion and electrolyte wettability.

[0043] In some embodiments, the inorganic particles in the organic coating have a mass content of 10-50%.

[0044] Specifically, the inorganic particle content in the organic coating is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50% by mass.

[0045] In some embodiments, the organic coating comprises an organic polymer, which includes at least one of polyvinyl alcohol formaldehyde, aromatic amide, polyvinylidene fluoride, polyvinylidene fluoride copolymer, polyamide, polyimide, polyacrylonitrile, polyethylene oxide, polyurethane, polyphenylene ether, acrylate copolymer, and polymethyl methacrylate.

[0046] In some embodiments, the mass ratio of the organic polymer to the inorganic particles is (50:50) to (90:10).

[0047] Furthermore, the mass ratio of the organic polymer to the inorganic particles is (60:40) to (80:20).

[0048] By adjusting the content of organic polymers in the organic coating, the size and number of micropores in the coating can be further adjusted when constructing the three-dimensional interlocking network structure. At the same time, it will also affect the overall viscosity of the organic coating, thereby affecting the electrochemical performance of the separator when applied to secondary batteries. When the mass ratio of organic polymers to inorganic particles is within the above-mentioned preferred range, the overall application effect of the separator is better.

[0049] It should be noted that, in this application, the mass of the organic polymer and inorganic particles is confirmed as follows: the membrane is cut into several parts, dried at 60°C for 24 hours, and weighed and recorded as m0. Then, it is soaked in dimethylacetamide (DMAC) or acetone as a solvent for 2 hours, and ultrasonic treatment is performed simultaneously during the soaking process. The organic substrate is then removed, dried at 60°C for 24 hours, and weighed and recorded as m1. The difference between m0 and m1 is the coating weight. The soaking solution is collected, filtered, and the resulting solid filter material is dried at 60°C and weighed, which is the mass of the inorganic particles. The mass of the organic polymer can be calculated by the difference between the coating weight and the mass of the inorganic particles. If the membrane is in a secondary battery, the secondary battery is discharged beforehand, and then the membrane is disassembled.

[0050] In some embodiments, the inorganic particles include at least one of needle-shaped particles and rod-shaped particles.

[0051] In the technical solution of this application, when the inorganic particles are selected as needle-shaped or rod-shaped particles, their skeleton effect in the organic coating is better. After being combined with organic polymers, they form a three-dimensional structure similar to dendrites, which can not only effectively improve the overall ion transport efficiency of the organic coating, but also improve its wettability to electrolytes. Compared with traditional spherical or ellipsoidal inorganic particles, it can achieve better comprehensive performance.

[0052] More preferably, the inorganic particles include at least one of needle-shaped particles and rod-shaped particles; the inorganic particles also include spherical particles.

[0053] The diaphragm satisfies: X / Y = 0.05 to 2.3, where X = x1 / x2, x1 is the mass of needle-shaped particles and / or rod-shaped particles in the inorganic particles, and x2 is the mass of spherical particles in the inorganic particles;

[0054] Y represents the mass ratio of organic polymer to inorganic particles in the organic coating.

[0055] Those skilled in the art will understand that when calculating the ratio X of x1 and x2, the units of x1 and x2 are consistent. Similarly, when calculating Y, the mass units of organic polymers and inorganic particles are also consistent.

[0056] More preferably, the diaphragm satisfies: X / Y = 0.2~1.

[0057] As mentioned above, when needle-shaped and / or rod-shaped particles are introduced into inorganic particles, the inorganic particles can play an excellent skeletal role in the organic coating. At this time, the compound filling of spherical particles can further improve the compactness of the inorganic three-dimensional skeleton structure while maintaining good electrolyte wettability of the coating, resulting in higher structural strength of the coating. The membrane has better stress resistance during ion conduction. At the same time, when the ratio of needle-shaped and / or rod-shaped particles to spherical particles is within the above-mentioned preferred range, the connection between the organic polymer and inorganic particles is better, and the size and number of micropores in the coating are taken into account. There are sufficient capillary channels required for electrolyte wetting, resulting in good wetting effect. When the membrane is applied to secondary batteries, it has high ion transport efficiency and better electrochemical performance.

[0058] More preferably, the X / Y value is a range of one or any two of the following: 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.

[0059] More preferably, the ratio of x1:x2 is (0.05:0.95) to (0.99:0.01);

[0060] More preferably, x1 / x2 = 0.1 to 5; more preferably, x1 / x2 = 0.6 to 1.5.

[0061] As mentioned above, needle-like and / or rod-like particles and spherical particles of different morphologies can form a three-dimensional strong support structure similar to "reinforced concrete" after being compounded, thereby effectively improving the structural stability and ion conduction efficiency of the separator. However, if too many single particles are compounded during the compounding process, it may lead to problems such as blocked wetting pathways and reduced pore connectivity in the framework structure. It is necessary to simultaneously optimize and control the ratio of inorganic particles to organic polymers. When the X / Y ratio is in a better range and the ratio of the two particles is further within the above-mentioned preferred range, the performance of the separator will be further improved. When the separator is applied to secondary batteries, the electrochemical performance is even better.

[0062] More preferably, Y = 1.5 to 4.

[0063] More preferably, the chemical composition of the spherical particles may be the same as or different from that of the needle-shaped particles and / or rod-shaped particles. When testing the mass ratio of the two types of particles in the diaphragm, the diaphragm is soaked in DMAC or acetone as a solvent for 2 hours, with simultaneous ultrasonic treatment during the soaking process. After soaking, the organic substrate is removed, the soaking liquid is collected, filtered, and the resulting solid filter material is dried at 60°C. The mass m0 of the inorganic particles is then weighed to confirm the chemical composition of the two types of particles. The separated inorganic particles are then subjected to scanning electron microscopy (SEM) EDS (20kX) to confirm their chemical composition. Subsequently, RIGAKU SE XRD is used. If the tests reveal that the two types of particles have the same chemical composition and crystal form, the mixed particles are uniformly dispersed on a glass slide, and an electron microscope image is taken. The spherical particles and needle-shaped and / or rod-shaped particles are identified using image analysis software (ImageJ).

[0064] Calculate the volume of the two types of particles using the following formula:

[0065] Volume of spherical particle: V1 = 4 / 3π(D) 球 / 2) 3

[0066] Volume of needle-shaped and / or rod-shaped particles: V2=π(D 棒 / 2) 2 ×L 棒

[0067] Where D 球 D is the diameter of the spherical particle. 棒 L represents the diameter of needle-like and / or rod-like particles. 棒 The length of needle-shaped and / or rod-shaped particles;

[0068] If 20 particles of each type are tested and the average value is calculated, then the mass ratio X of the two types of particles is the average volume ratio V2 / V1 of the particles.

[0069] If the two types of particles have different crystal forms, the two types of particles and their corresponding content percentages a% and b% are directly confirmed by comparing them with standard cards and using TOPAS software for Rietveld full-spectrum refinement and quantification. The mass of the two types of particles is calculated by m0×a% and m0×b%, and finally the mass ratio of the two is calculated to obtain X.

[0070] In some embodiments, the D of the inorganic particles v50 =10~55μm, D v10 = 0.5~1.5μm. Where, D v50 This refers to the particle size corresponding to a cumulative volume distribution percentage of inorganic particles reaching 50%; D v10It refers to the particle size corresponding to when the cumulative volume distribution percentage of inorganic particles reaches 10%.

[0071] In some embodiments, the inorganic particles satisfy: D1 / D2 = 10 to 65, where D1μm is the average particle size of needle-shaped and / or rod-shaped particles, and D2μm is the average particle size of spherical particles.

[0072] More preferably, the inorganic particles satisfy the following condition: D1 / D2 = 15 to 40.

[0073] When needle-shaped and / or rod-shaped particles and spherical particles are selected as the inorganic framework material of the separator described in this application, the size of each particle will affect the overall material density, compatibility and connectivity with organic polymers, and porosity during the compounding process. When the average particle size ratio of the two particles is within the above-mentioned preferred range, they can achieve a more superior three-dimensional filled stacking system, which not only achieves higher ion conductivity, moderate porosity, and fast electrolyte wetting rate, but also has better overall structural stability, higher compatibility and connectivity with organic polymers, and better electrochemical performance when the separator is applied to a secondary battery.

[0074] More preferably, the range of D1 / D2 is one or any two of the following: 15, 18, 20, 22, 25, 28, 30, 32, 35, 38, 40.

[0075] It should be noted that the average particle size of the needle-shaped and / or rod-shaped particles and spherical particles in the inorganic particles was confirmed by the following test: The diaphragm was soaked in DMAC or acetone as a solvent for 2 hours, and ultrasonic treatment was performed simultaneously during the soaking process. After soaking, the organic substrate was removed, the soaking solution was collected and filtered, and the resulting solid filter material was dried at 60°C. The separated inorganic particles were distinguished by scanning electron microscopy (20kX), and then the particle size was tested by mapping software (the major diameter of rod-shaped and needle-shaped particles was used as the particle size of individual particles). Twenty particles of each type were tested and the average value was calculated to obtain the average particle size.

[0076] In some embodiments, D1 = 3 to 52 μm; more preferably, D1 = 10 to 40 μm.

[0077] In some embodiments, D2 = 0.5–1.5 μm; more preferably, D2 = 0.7–1.2 μm.

[0078] More preferably, the inorganic particles include spherical particles, and the organic coating is provided on both sides of the organic substrate layer, wherein the sum of the areal densities of the organic coatings on both sides is 1.6–1.75 g / m³. 2 .

[0079] Specifically, the inorganic particles include at least one of silicon dioxide, barium distitanate, aluminum oxide, potassium titanate, barium metatitanate, silicon suboxide, calcium oxide, magnesium oxide, zinc oxide, titanium dioxide, and barium oxide.

[0080] Specifically, the inorganic particles can also be boehmite, a type of granular material with composite components.

[0081] In some embodiments, the organic substrate layer comprises at least one of polypropylene and polyethylene.

[0082] In some embodiments, the organic substrate layer has a thickness of 3–20 μm, a porosity of 20–50%, an air permeability of 30–400 sec / 100 cc, and a melting point of 130–160 °C.

[0083] It should be noted that the organic base layer in the diaphragm described in this application can be a self-made product or any one of commercially available polypropylene base membranes, polyethylene base membranes, or composite base membranes.

[0084] In some embodiments, the organic coating in the diaphragm is disposed on one side of the organic substrate layer.

[0085] Specifically, an organic coating is provided on both sides of the organic substrate layer, and the thickness of the diaphragm is 3.5 to 25 μm.

[0086] In this application, when organic coatings are provided on both sides of the organic substrate layer, the thickness H of the organic coating can be tested using the following method: The diaphragm is cut into sections, and the sections are observed under a scanning electron microscope. Image analysis software is used to distinguish and test the thickness of the organic coatings on both sides of the organic substrate layer. Ten test sites are taken on each side at the same magnification for measurement, and the average value is taken to obtain the average thickness h1 and h2 of the organic coatings on both sides. The thickness H of the organic coating is then h1 + h2. When an organic coating is provided on one side of the organic substrate layer, the thickness H of the organic coating can be tested using the following method: The diaphragm is cut into sections, and the sections are observed under a scanning electron microscope. Image analysis software is used to distinguish and test the thickness of the organic coating on the organic substrate layer. Ten test sites are taken at the same magnification for measurement, and the average value is taken to obtain the average value, which is the thickness H of the organic coating.

[0087] In some embodiments, the organic coating is applied onto an organic substrate layer.

[0088] Specifically, the coating includes at least one of gravure coating, extrusion coating, immersion coating, spray coating, dot coating, wire rod coating, and roll coating.

[0089] The organic coating in this application can be constructed on the organic substrate layer using coating methods including but not limited to those described above, as long as it does not affect the limitations of the membrane regarding inorganic particles and thickness.

[0090] In some embodiments, the thickness and density of the organic coating on both sides of the diaphragm may be the same or different.

[0091] In general, the organic coating of the diaphragm described in this application is uniformly coated on both sides. However, those skilled in the art may also use an uneven coating method on both sides according to actual requirements. As long as it does not exceed the limitations of this application and does not affect the technical effect of the diaphragm, it is not restricted.

[0092] In some embodiments, the organic coating is made from a preparation material comprising inorganic particles, an organic polymer, and a solvent. The inorganic particles include at least one of rod-shaped materials, needle-shaped materials, and granular materials, wherein the granular materials contain spherical materials.

[0093] Specifically, the organic coating is prepared by mixing the raw materials, coating them onto an organic substrate, and drying them to obtain the organic coating.

[0094] Specifically, the solvent includes at least one of dimethylacetamide, dichloroethane, dimethylformamide, trichloroethane, chloroform, ethyl acetate, sulfolane, dimethyl sulfoxide, N-methylpyrrolidone, chloroform, dichloromethane, and acetone.

[0095] Specifically, the solvent content in the raw materials is 70-96% by mass.

[0096] This application also provides a secondary battery, which includes the separator.

[0097] In some embodiments, the secondary battery further includes a positive electrode sheet, which comprises a current collector and a positive electrode material layer. The positive electrode material layer comprises a positive electrode active material, including but not limited to LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, and LiNi 0.5 Mn 1.5 The cathode material is selected from at least one of O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, and lithium nickel cobalt manganese oxide, and the mass content of the cathode material in the cathode material layer is 90-99%.

[0098] Specifically, the lithium nickel cobalt manganese oxide includes, but is not limited to, LiNi9Co. 0.5Mn 0.5 At least one of O2, LiNi8Co1Mn1O2, LiNi7Co2Mn1O2, LiNi7Co1Mn2O2, and LiNi6Co2Mn2O2.

[0099] In some embodiments, the positive electrode material layer further includes at least one of a conductive agent and a binder.

[0100] Furthermore, the adhesive comprises at least one of polyvinylidene fluoride, polyvinyl butyral, polytetrafluoroethylene, ethylene-vinyl acetate copolymer, and polyvinyl alcohol.

[0101] Furthermore, the conductive agent includes at least one of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0102] In some embodiments, the thickness of the positive electrode material layer is 70–150 μm.

[0103] In some embodiments, the secondary battery includes a negative electrode.

[0104] In some embodiments, the negative electrode sheet includes a current collector and a negative electrode material layer disposed on the current collector. The negative electrode material layer includes a negative electrode material, and the mass content of the negative electrode material in the negative electrode material layer is 94-98%.

[0105] In some embodiments, the negative electrode material includes at least one of artificial graphite, silicon-doped graphite, silicon-carbon materials, and silicon-oxygen materials.

[0106] In some embodiments, the negative electrode material layer further includes at least one of a conductive agent and a binder.

[0107] More preferably, the adhesive comprises at least one of styrene-butadiene rubber, sodium carboxymethyl cellulose, polyvinylidene fluoride, polyvinyl butyral, polytetrafluoroethylene, ethylene-vinyl acetate copolymer, and polyvinyl alcohol.

[0108] More preferably, the conductive agent includes at least one of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0109] In some embodiments, the thickness of the negative electrode material layer is 50–150 μm.

[0110] In some embodiments, the secondary battery further includes an electrolyte comprising a lithium salt and a solvent. The lithium salt comprises at least one of LiPF6, LiBOB, LiBF4, LiPF6, LiBF4, LiPF6, LiTFSI, LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The solvent comprises at least one of EC, PC, EMC, DMC, DEC, THF, 2-MeTHF, TMS, EA, and MP.

[0111] The present invention is further illustrated below with specific embodiments, which should not be construed as limiting the scope of protection claimed by the present invention:

[0112] Examples 1-3

[0113] A separator and a secondary battery, the preparation method comprising the following steps:

[0114] Preparation of the diaphragm: Commercially available rod-shaped boehmite was used as inorganic particles, and polyvinyl alcohol formal (Maclean CAS63450-15-7) was used as an organic polymer. DMAC was used as a solvent to prepare a slurry with a solvent mass content of 80%. The slurry was then uniformly coated on both sides of a conventional commercially available PE organic base membrane with a thickness of 5 μm, a porosity of 36%, and an air permeability of 143 sec / 100cc by roller coating. After drying, the diaphragm was obtained. The parameters of the diaphragms obtained in each embodiment are shown in Table 1.

[0115] Preparation of the positive electrode sheet:

[0116] Lithium cobalt oxide was used as the positive electrode active material. The material was then mixed with acetylene black (conductive agent) and polyvinylidene fluoride (PVC) (binder) in an N-methylpyrrolidone (NMP) solvent at a mass ratio of 95:3:2 to prepare a slurry. The slurry was coated onto an aluminum foil current collector, dried, cold-pressed, and slit to obtain a positive electrode sheet. The thickness of the positive electrode material layer on the positive electrode sheet was 100 μm.

[0117] Preparation of negative electrode sheet:

[0118] Artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed in water at a mass ratio of 96:1:1.5:1.5 to prepare a slurry. The slurry was coated on a current collector copper foil, dried, cold-pressed, and slit to obtain a negative electrode sheet. The thickness of the negative electrode material layer on the negative electrode sheet was 100 μm.

[0119] Electrolyte preparation:

[0120] The lithium salt LiPF6 was prepared by mixing it with a non-aqueous organic solvent (in a mass ratio of ethylene carbonate: diethyl carbonate: propylene carbonate: propyl propionate: ethylene carbonate = 20:30:20:28:2) at a mass ratio of 8:92.

[0121] Preparation of secondary batteries:

[0122] The positive electrode, separator, and negative electrode are stacked in sequence, then wound up. The resulting electrode assembly is placed in a packaging shell and injected with electrolyte, then sealed to obtain the secondary battery.

[0123] Examples 4-6

[0124] A separator and secondary battery, differing from Examples 1-3 only in that:

[0125] Preparation of the diaphragm: Commercially available needle-shaped potassium titanate was used as inorganic particles, aramid fiber (aromatic amide fiber, Anhui Lico BF1300) was used as an organic polymer, and acetone was used as a solvent to prepare a slurry with a solvent mass content of 80%. Then, the slurry was uniformly coated on both sides of the PE organic base film by roller coating and dried to obtain the diaphragm. The parameters of the diaphragms obtained in each embodiment are shown in Table 1. The PE organic base film is the same as in Example 1.

[0126] Examples 7-8

[0127] A separator and a secondary battery differ from Examples 1-3 only in the parameters for separator preparation, as shown in Table 1.

[0128] Example 9

[0129] A separator and a secondary battery differ from those in Examples 4-6 only in the parameters for separator preparation, as shown in Table 1.

[0130] Examples 10-11

[0131] A separator and a secondary battery differ from Examples 1-3 only in the parameters for separator preparation, as shown in Table 1.

[0132] Example 12

[0133] A separator and a secondary battery differ from those in Examples 4-6 only in the parameters for separator preparation, as shown in Table 1.

[0134] Examples 13-14

[0135] A separator and a secondary battery differ from Examples 1-3 only in the parameters for separator preparation, as shown in Table 1.

[0136] Example 15

[0137] A separator and a secondary battery differ from those in Examples 4-6 only in the parameters for separator preparation, as shown in Table 1.

[0138] Examples 16-17

[0139] A separator and secondary battery, differing from Examples 1-3 only in that:

[0140] Preparation of the diaphragm: Commercially available needle-shaped calcium carbonate was used as inorganic particles, polyacrylonitrile (Shanghai Yuanye Y69247) was used as an organic polymer, and DMAC was used as a solvent to prepare a slurry with a solvent mass content of 80%. Then, the slurry was uniformly coated on both sides of a PE organic base film by roller coating and dried to obtain the diaphragm. The parameters of the diaphragms obtained in each embodiment are shown in Table 1. The PE organic base film is the same as in Example 1.

[0141] Examples 18-20

[0142] A separator and a secondary battery differ from Examples 1-3 only in the parameters for separator preparation, as shown in Table 1.

[0143] Examples 21-30

[0144] A separator and secondary battery, differing from Examples 1-3 only in that:

[0145] Preparation of the separator: Commercially available rod-shaped boehmite and granular silica were used as inorganic particles, and polyvinyl alcohol formaldehyde (Maclean CAS63450-15-7) was used as an organic polymer. DMAC was used as a solvent to prepare a slurry with a solvent mass content of 80%. The slurry was then uniformly coated on both sides of a conventional commercially available PE organic base membrane with a thickness of 5 μm, a porosity of 36%, and an air permeability of 143 sec / 100cc by roller coating. After drying, the separator was obtained. The parameters for preparing the separator were also different.

[0146] Examples 31-34

[0147] A separator and secondary battery, differing from Examples 1-3 only in that:

[0148] Preparation of the diaphragm: Commercially available rod-shaped boehmite and granular alumina were used as inorganic particles, and polyvinyl alcohol formaldehyde (Maclean CAS63450-15-7) was used as an organic polymer. DMAC was used as a solvent to prepare a slurry with a solvent mass content of 80%. The slurry was then uniformly coated on both sides of a conventional commercially available PE organic base membrane with a thickness of 5 μm, a porosity of 36%, and an air permeability of 143 sec / 100cc by roller coating. After drying, the diaphragm was obtained. The parameters for preparing the diaphragm were also different.

[0149] Comparative Examples 1-2

[0150] A separator and a secondary battery differ from Examples 1-3 only in the parameters for separator preparation, as shown in Table 1.

[0151] Comparative Examples 3-4

[0152] A separator and a secondary battery differ from those in Examples 4-6 only in the parameters for separator preparation, as shown in Table 1.

[0153] Comparative Examples 5-6

[0154] A separator and a secondary battery differ from Examples 1-3 only in the parameters for separator preparation, as shown in Table 1.

[0155] Comparative Example 7

[0156] A separator and secondary battery, differing from Example 1 only in that:

[0157] Preparation of the diaphragm: Particulate alumina was used as the inorganic particles, polyvinyl alcohol formaldehyde (Maclean CAS63450-15-7) was used as the organic polymer, and DMAC was used as the solvent to prepare a slurry with a solvent mass content of 80%. Then, it was uniformly coated on both sides of a conventional commercially available PE organic base membrane with a thickness of 5μm, a porosity of 36%, and an air permeability of 143sec / 100cc by roller coating. After drying, the diaphragm was obtained. The parameters for preparing the diaphragm were also different.

[0158] In Table 1, the D v10 D v50 and D v90 That is, the particle size D of the inorganic particles in the organic coating of the diaphragm in the various embodiments and comparative examples. v10 D v50 and D v90 Y is the mass ratio of organic polymer to inorganic particles, X = x1 / x2, x1 is the mass of needle-shaped and / or rod-shaped particles in the inorganic particles, x2 is the mass of spherical particles in the inorganic particles. When the inorganic particles do not contain spherical particles or needle / rod-shaped particles, X is recorded as " / ", and X / Y is also recorded as " / ". D1μm is the average particle size of needle-shaped and / or rod-shaped particles, D2μm is the average particle size of spherical particles. When the inorganic particles do not contain spherical particles or needle / rod-shaped particles, D2 is recorded as " / ", and D1 / D2 is recorded as " / ".

[0159] Organic coating areal density refers to the sum of the areal densities of the organic coatings on both sides of the PE organic base film. H refers to the total thickness of the organic coatings on both sides of the PE organic base film.

[0160] In various embodiments, D1 and D2 are adjusted by controlling the grinding rate of the particles; under the same grinding time, the higher the grinding rate, the smaller D1 and / or D2; v10 D v50 D v90The control is achieved by adjusting the D1 and / or D2 of the two types of particles, as well as the ratio of spherical particles to needle / rod-shaped particles when mixed.

[0161] Table 1

[0162] Example of effect 1

[0163] To verify the effectiveness of the diaphragm obtained by the technical solution of this application, the diaphragms obtained in each embodiment were subjected to lateral and longitudinal shrinkage rate tests at high temperature. The specific method is as follows:

[0164] Instruments: Blower-air drying oven & electronic image testing instrument;

[0165] Step ①: Cut the diaphragm into strips of 20*10cm according to MD*TD;

[0166] Step 2: Measure the length of the initial spline MD*TD using an electronic image measuring instrument, and denote it as L. M0 and L T0 ;

[0167] Step 3: Place the diaphragm between two folded A4 sheets of paper, then place it in a 130℃ forced-air drying oven for 30 minutes;

[0168] Step 4: Remove the diaphragm and measure its MD and TD lengths as L. M and L T ;

[0169] Step 5: Calculate S M =(L M0 -L M ) / L M0 *100%;

[0170] S T =(L T0 -L T ) / L T0 *100%;

[0171] S M S represents the longitudinal shrinkage rate of the diaphragm. T This represents the lateral shrinkage rate of the diaphragm.

[0172] The secondary batteries obtained from each embodiment and comparative example were then subjected to the following performance tests:

[0173] (1) Room temperature cycle performance test: In an environment of 25℃, the first charge and discharge were performed. Constant current and constant voltage charging were performed at a charging current of 0.1C (i.e. the current value that completely discharges the theoretical capacity within 10h) until the upper limit voltage is 4.3V. Then constant current discharge was performed at a discharge current of 1C until the final voltage is 2.5V. The discharge capacity of the first cycle was recorded. Then 300 charge and discharge cycles were performed, and the discharge capacity of the 300th cycle was recorded.

[0174] Cycle capacity retention = (Discharge capacity of the 300th cycle / Discharge capacity of the first cycle) × 100%;

[0175] The test samples were set up as 5 parallel samples, and the final test result was the average of the test results of the 5 parallel samples.

[0176] (2) High temperature cycling performance test: The difference from the normal temperature cycling performance test is that the test environment temperature is 45℃ and the number of cycles is 100.

[0177] (3) Safety test: First, charge each secondary battery to 4.3V at a 1C rate, cut off current of 0.05C, let it stand for 10s, then discharge at an I1C rate for 10s, record the voltage V1 at the end of the discharge, then discharge at an I2C rate for 1s, record the voltage V2 at the end of the discharge, then DCR=|V1-V2| / (I2-I1), where I1 is 0.2C and I2 is 1C.

[0178] The test results are shown in Table 2.

[0179] Table 2

[0180] As shown in Table 2, the separator in the secondary battery described in this application exhibits superior dimensional stability under heat treatment. Overall, the lateral shrinkage rate of the separator in each embodiment does not exceed 20%, and the longitudinal shrinkage rate does not exceed 18.5%. Furthermore, based on the coating control on the separator, high electrolyte wettability and high ion transport efficiency can be achieved after the separator is applied to the secondary battery. After 300 cycles at room temperature, the cycle capacity retention rate can reach over 90%. Even at high temperatures, the secondary batteries in each embodiment also possess ideal electrochemical and safety performance. After 100 cycles at 45°C, the secondary batteries in each embodiment show good performance. The capacity retention rate of the battery can still reach over 90%, and the DCR growth is low. In contrast, the separators obtained in Comparative Examples 1-4, due to improper settings of the relationship between inorganic particles and coating thickness in the separator coating, cannot maintain good dimensional stability under heating conditions. Under the same test, both the lateral shrinkage rate and the longitudinal shrinkage rate exceed 20%. Although the separators can still maintain good cycle stability at room temperature after being applied to secondary batteries, after 100 cycles at 45°C, the capacity retention rate of the secondary battery is less than 90%, and the DCR growth can reach about twice that of the secondary battery in the examples. In addition, the inorganic particles in the separator coatings of Comparative Examples 5 and 6 are either too large or too small, which also makes it difficult to achieve good thermal stability, and the performance of the separators after being applied to secondary batteries is also low.

[0181] Based on the test results of the secondary batteries in Examples 1-17, it can be seen that when constructing the separator coating, the thickness of the coating, the size of the inorganic particles placed on the coating, and the ratio between the two directly affect the dimensional stability of the separator and the ion / electron conduction efficiency. v90 / H is in the range of 20 to 45, or a more suitable coating thickness and inorganic particle size can be selected: preferably the D v90 Within the range of 18–85 μm, and / or when H is between 1.9 and 2.3 μm, based on the “anchoring” effect of inorganic particles and the full compatibility between inorganic particles and organic polymers, the membrane can achieve better wettability, thereby resulting in higher ion / electron conduction efficiency, better bonding strength between the membrane coating and the organic substrate, better overall dimensional stability of the membrane, and better electrochemical performance at high temperatures.

[0182] A comparison of Examples 3 and 18-20 shows that the change in the ratio of organic polymer to inorganic particles on the separator can further adjust the size and number of micropores in the coating when constructing the three-dimensional interlocking network structure. It also affects the overall viscosity of the organic coating, thereby affecting the electrochemical performance of the separator when applied to a secondary battery. When the ratio of the two is further optimized to be in the range of (60:40) to (80:20), the electrochemical performance of the secondary battery is better.

[0183] Furthermore, when the inorganic particles are a combination of spherical and needle / rod-shaped particles, as shown in Examples 21-34, when the mass ratio of the two types of particles and the mass ratio of inorganic particles to organic polymers in the coating are jointly controlled to ensure that the membrane satisfies X / Y = 0.2-1, the membrane exhibits superior mechanical and ion conductivity compared to membranes prepared using needle-shaped or rod-shaped structures as the framework component alone. In particular, when the particle size ratio of the two types of particles preferably satisfies D1 / D2 = 15-40, the membrane's performance can be further improved. However, if there are too many spherical particles, causing the above-mentioned control to fail to meet the preferred range, the three-dimensional framework structure of the membrane may experience particle agglomeration, thus affecting the overall pore adsorption effect of the membrane. If pure spherical particles are used as the framework component, as shown in Comparative Example 7, due to the small size of the spherical particles, they cannot meet the D1 / D2 ratio. v90 Within the defined range of / H, the performance of the diaphragm is similar to that of Comparative Example 1.

[0184] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this article and are not intended to limit the scope of protection of this article. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this article without departing from the essence and scope of the technical solutions of this article.

Claims

A diaphragm, wherein, Includes an organic base layer and an organic coating; The organic coating contains inorganic particles, and the organic coating satisfies: D v90 / H≥5; Where D v90 μm is the particle size corresponding to the cumulative volume distribution percentage of the inorganic particles reaching 90%, and D v90 =3~120μm; Hμm is the thickness of the organic coating. The diaphragm as claimed in claim 1, wherein, The D v90 / H = 5~55. The diaphragm as claimed in claim 1, wherein, The D v90 =10~120μm. The diaphragm as claimed in claim 1, wherein, The H value is 0.5–5 μm. The diaphragm as claimed in claim 1, wherein, The organic substrate layer has organic coatings on both sides, and the sum of the areal densities of the organic coatings on both sides is 1.3 to 1.65 g / m³. 2 . The diaphragm as claimed in claim 1, wherein, The inorganic particles in the organic coating contain 10-50% by mass. The diaphragm as claimed in claim 1, wherein, The organic coating comprises an organic polymer, which includes at least one of polyvinyl alcohol formaldehyde, aramid, polyvinylidene fluoride, polyvinylidene fluoride copolymer, polyamide, polyimide, polyacrylonitrile, polyethylene oxide, polyurethane, polyphenylene ether, acrylate copolymer, and polymethyl methacrylate. The diaphragm as claimed in claim 1, wherein, The inorganic particles include at least one of needle-shaped particles and rod-shaped particles. The diaphragm as described in claim 8, wherein, The inorganic particles include at least one of needle-shaped particles and rod-shaped particles; the inorganic particles also include spherical particles. The diaphragm satisfies: X / Y = 0.05 to 2.3, where X = x1 / x2, x1 is the mass of needle-shaped particles and / or rod-shaped particles in the inorganic particles, and x2 is the mass of spherical particles in the inorganic particles; Y represents the mass ratio of organic polymer to inorganic particles in the organic coating. The diaphragm as described in claim 9, wherein, The x1 / x2 = 0.1 to 5, and / or the Y = 1.5 to 4. The diaphragm as described in claim 9, wherein, The inorganic particles satisfy the following conditions: D1 / D2 = 10 to 65, where D1μm is the average particle size of needle-shaped and / or rod-shaped particles, and D2μm is the average particle size of spherical particles. The diaphragm as claimed in claim 11, wherein, The D1 is 3 to 52 μm; and / or the D2 is 0.5 to 1.5 μm. The diaphragm as described in any one of claims 8 to 12, wherein, The inorganic particles include at least one of silicon dioxide, barium titanate, aluminum oxide, potassium titanate, barium metatitanate, silicon suboxide, calcium oxide, magnesium oxide, zinc oxide, titanium dioxide, and barium oxide. A secondary battery comprising the separator as described in any one of claims 1 to 13.

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