Diaphragm and battery

Abstract

The invention provides a diaphragm and a battery, the diaphragm comprises a base material layer and a first coating located on the surface of one side or two sides of the base material layer, the first coating comprises first particles, the first particles are organic matters containing nitrogen heterocyclic rings, and the average sphericity degree of the first particles is 0.2-0.8, the battery comprises the diaphragm, and the first coating can be applied to the battery. When the diaphragm is impacted by external force and / or falls off, the impact energy can be dispersed, the influence of the impact amount on the diaphragm is reduced, and the impact passing rate and the falling passing rate of the battery are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a separator and a battery comprising the same. BACKGROUND

[0002] In modern battery technology, the safety of the battery is a crucial consideration factor, and the separator as a key functional material plays a crucial role in ensuring the safe operation of the battery. With the wide application of batteries in various mobile devices, electric vehicles and other fields, the use environment of the battery is becoming increasingly complex, and the battery is subjected to impact or drop from time to time. The internal short circuit caused by the mechanical damage of the separator under external mechanical stress has become one of the main causes of battery safety failure.

[0003] The core role of the separator in the battery is to prevent the direct contact of the positive and negative electrodes to prevent short circuit, while allowing the smooth passage of lithium ions to ensure the normal charging and discharging of the battery. However, when the battery is subjected to impact or drop, external force will have a serious impact on the battery structure. For example, during transportation, the battery may be impacted due to the jolt and collision of the vehicle; in daily use, the accidental drop of handheld devices can also cause the battery to be impacted. Under the action of these external forces, the internal components of the battery are prone to deformation and displacement, causing the separator to be pierced or torn and fail, resulting in short circuit between the positive and negative electrodes. This situation not only causes the battery capacity to drop sharply and the function to fail, but also may trigger a thermal runaway reaction, and even some batteries may overheat, smoke and other dangerous conditions. SUMMARY

[0004] In order to overcome the problem in the prior art that the separator is easily pierced or torn and fails when the battery is subjected to external impact or drop, thereby reducing the impact passing rate and drop passing rate of the battery, the present application provides a separator and a battery comprising the same. The separator of the present application can disperse impact energy when the battery is subjected to external impact or drop, reduce the impact of impact amount on the separator, and improve the external impact passing rate and drop passing rate of the battery.

[0005] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a separator, wherein the separator comprises a substrate layer and a first coating layer located on one side or both sides of the substrate layer, the first coating layer comprises first particles, the composition of the first particles is a nitrogen-containing heterocyclic organic matter, the nitrogen-containing heterocyclic organic matter has a layered crystal structure, and the average sphericity of the first particles is 0.2-0.8.

[0006] The second aspect of the present application provides a battery comprising the separator of the first aspect of the present application.

[0007] Through the above technical solution, the present application has at least the following advantages compared with the prior art:

[0008] The first coating in the diaphragm of the present application comprises first particles of organic matter containing nitrogen heterocycle, and when the battery is impacted by external force or falls, the lamellar crystal structure of the first particles is prone to slip between layers, and the low surface energy characteristics of the first particles can cause a certain slip between the first particles, so that the force in the same direction is divergent from different directions, thereby dispersing the energy of impact and fall, reducing the risk of the diaphragm being pierced and causing failure, and further improving the impact pass rate and fall pass rate of the battery; and by controlling the average sphericity of the first particles, the first particles in the diaphragm have suitable bulk density and effective slip effect, further improving the impact pass rate and fall pass rate of the battery.

[0009] Other features and advantages of the present application will be described in detail in the following specific embodiments.

[0010] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The ranges and values should be construed to be approximations that allow for significant variation. Various ranges of values that are stated herein are considered to be approximate values that can vary by a small amount. Endpoints of various ranges of values, endpoints of various ranges of values and individual point values, and individual point values can be combined to create one or more new ranges of values that are considered to be specifically disclosed herein. DETAILED DESCRIPTION

[0011] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and explanatory and are not intended to limit the present application. Herein, the data ranges include the endpoints unless otherwise specified.

[0012] It should be noted that the "first", "second" and the like numerical representation in the present application is only used to distinguish different substances or use methods, and does not represent the difference in order.

[0013] The first aspect of the present application provides a diaphragm, wherein the diaphragm comprises a substrate layer and a first coating layer on one side or both sides of the substrate layer, and the first coating layer comprises first particles, and the composition of the first particles is organic matter containing nitrogen heterocycle, the organic matter containing nitrogen heterocycle has a lamellar crystal structure, and the average sphericity of the first particles is 0.2-0.8 (for example, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75 or 0.8).

[0014] In the present application, the average sphericity of the first particles refers to that the sum of the areas of all first particles in a certain area is equal to a circle, and the ratio of the diameter of the equivalent circle to the circumference of the equivalent circle is the average sphericity of the first particles.

[0015] In the present application, the average sphericity of the first particles can be tested by the following method: taking a first coating surface particle image by scanning electron microscope (SEM), in the image, in an arbitrarily selected 100 μm x 100 μm area, combining with a graphics analysis software (for example, ImageJ, NanoMeasurer, Matlab, etc.), identifying the first particles, calculating the radius r1 of the equivalent circle of the single first particle projection perimeter and the radius r2 of the equivalent circle of the first particle projection area, the sphericity of a single first particle = r2 / r1, the sphericity of 100 first particles is taken as an average value, the above operation is repeated 5 times, and the average value is taken as the final test result. Wherein, the scanning image can be obtained by using scanning electron microscope (Hitachi Ltd. S-3400N) to observe the surface of the diaphragm.

[0016] Since the first particles of the present application are composed of nitrogen-containing heterocyclic organic matter, the crystal structure of the nitrogen-containing heterocyclic organic matter contains a strong intramolecular hydrogen bond network that saturates all high-energy active sites, making the exposed surface chemically inert with uniform charge distribution, only providing weak van der Waals forces, while having high stability (intra-layer strong) and low friction, low adhesion (inter-layer / surface weak) characteristics, which can make the surface energy of the first particles lower, thereby reducing the friction and adhesion wear of the first particle surface, that is, the first particle surface is easy to slip. Moreover, the structure of the first particles is a layered crystal structure formed by molecules through hydrogen bonds (which can be understood as a structure similar to the stacking of graphite lamellae). In this layered crystal structure, the interlayer force is mainly hydrogen bond and van der Waals force, which are weak chemical forces. When the battery is impacted or dropped by external force, on the one hand, the layered crystal structure of the first particles in the diaphragm is easy to slide relatively between layers, on the other hand, a certain slip occurs between the first particles, and the combination of the two makes the force in the same direction diverge from different directions, thereby dispersing the impact and drop energy and reducing the risk of diaphragm failure, improving the impact pass rate of the battery; when the battery is impacted or dropped by external force, foreign matter produced externally or internally contacts the diaphragm, which will cause lateral slip on the surface of the first particles. Through lateral slip, the force of the foreign matter can be dispersed, the risk of diaphragm failure can be reduced, and the drop pass rate of the battery can be improved.

[0017] When the average sphericity of the first particles is less than 0.2, the average sphericity of the first particles is too small, the packing density of the first particles in the first coating is too small, the first coating is too loose, the first coating is easy to fall off under the expansion stress of the electrode in the high-temperature cycle process, which leads to a large interface impedance and reduces the high-temperature cycle performance of the battery; when the average sphericity of the first particles is greater than 0.8, the average sphericity of the first particles is too large, the packing density of the first particles in the first coating is too large, which is not conducive to the interlayer slip of the first particles and the relative slip between the first particles, thereby not conducive to the dispersion of impact energy. Controlling the average sphericity of the first particles in the above range can make the first particles in the first coating have appropriate packing density and good slip effect, thereby reducing the risk of failure of the separator and improving the high-temperature cycle performance, impact passing rate and drop passing rate of the battery.

[0018] In the present application, by controlling the composition of the first particles in the first coating and the average sphericity of the first particles, compared with the prior art, the direction of the failure of the separator when the battery is subjected to external force impact or drop can be reduced, and the impact passing rate and drop passing rate of the battery can be improved. In order to further improve the effect, one or more of the technical features can be further optimized.

[0019] In some embodiments, the average sphericity of the first particles is 0.25-0.55.

[0020] In some embodiments, the cohesion F between the first particles in the first coating is 5 N / m≤F≤60 N / m (for example, 5 N / m, 10 N / m, 15 N / m, 20 N / m, 25 N / m, 30 N / m, 35 N / m, 40 N / m, 45 N / m, 50 N / m, 55 N / m or 60 N / m). Controlling the cohesion between the first particles in the first coating to be in the above range, when the battery is impacted or dropped, the first particles are easy to slip, which can effectively disperse the impact energy brought by the impact or drop, thereby improving the impact passing rate and drop passing rate of the battery; when F>60 N / m, the cohesion between the first particles is too large, which is not conducive to the slip between the first particles to disperse the impact energy, thereby not conducive to the further improvement of the impact passing rate and drop passing rate of the battery; when F<5 N / m, the cohesion between the first particles is too small, the first particles in the first coating of the separator are easy to fall off under the expansion stress of the electrode in the high-temperature cycle process, the interface stability is poor, the interface impedance is large, the high-temperature cycle performance of the battery is reduced, and the battery also produces foreign matter protrusions, causing the appearance of the battery to be poor, and in severe cases, even leading to the shrinkage or melting of the separator at high temperature, increasing the risk of internal short circuit of the battery.

[0021] In this invention, the cohesive force of the first particle can be changed by adjusting the sphericity of the first particle and / or the weight ratio of the first binder in the first coating.

[0022] In this invention, the cohesive force F between the first particles in the first coating is measured by the following method: First, three test samples with dimensions of 20mm × 100mm are arbitrarily cut from the diaphragm, and the non-test surfaces of the test samples are attached to a stainless steel plate using double-sided tape; then, green adhesive is applied to the test surfaces of the test samples and compacted with a pressure roller, and the ends of the test samples are bent 180°; finally, a tensile testing machine is used to peel off the green adhesive at a speed of 50mm / min. When the area of ​​the first particle remaining on the substrate layer surface accounts for more than 10% of the area on the substrate layer surface, and the area of ​​the first particle peeled off by the green adhesive accounts for no less than 50% of the area on the substrate layer surface, the peeling force at this time is recorded as the cohesive force between the first particles in the first coating. The peeling forces of these three test samples are tested, and the average value is calculated as the final test result. The method combines SEM measurement of the area of ​​the first particle remaining on the substrate layer surface... The percentage of the area of ​​the first particle remaining on the surface of the substrate layer and the percentage of the area of ​​the first particle peeled off by the green adhesive on the surface of the substrate layer are determined as follows: A SEM image of the substrate layer surface is obtained. A region of 100μm*100μm is randomly divided on the substrate layer surface. This region is then divided into uniform squares of 400*400. If the area of ​​the first particle remaining on the substrate layer surface in a square exceeds half the area of ​​the square, it indicates that the square is occupied by the first particle; otherwise, it indicates that the square is not occupied by the first particle. The total number of squares occupied by the first particle is recorded as X, and the total number of squares not occupied by the first particle is recorded as Y. The percentage of the area of ​​the first particle remaining on the substrate layer surface is calculated as [X / (400*400)]×100%, and the percentage of the area of ​​the first particle peeled off by the green adhesive on the substrate layer surface is calculated as [Y / (400*400)]×100%.

[0023] In some embodiments, the proportion of first particles with a sphericity of 0.2-0.7 (e.g., 0.2, 0.25, 0.30, 0.35, 0.4, 0.45, or 0.5) in the first particles is greater than or equal to 80% (e.g., 80%, 82%, 85%, 88%, 90%, 92%, 95%, or 100%). Controlling the proportion of first particles with a sphericity of 0.2-0.7 within the aforementioned range ensures that these particles are the dominant particles, thereby further enhancing the overall packing density and slippage effect of the first particles.

[0024] In this invention, the proportion of first particles with a sphericity of 0.2-0.7 is measured using the following method: A scanning electron microscope (SEM) image of the first coating surface particles is captured. In the image, within an arbitrarily selected 100μm × 100μm area, the number of all first particles, N1, is counted. Sphericity is defined as the ratio of the area equivalent radius to the perimeter equivalent radius of the first particle, calculated using image analysis software (e.g., ImageJ, NanoMeasurer, Matlab, etc.). The number of first particles with a sphericity of 0.2-0.7, N2, is then counted. N2 / N1 represents the proportion of first particles with a sphericity of 0.2-0.7 in the first particles. This process is repeated five times, and the average value is the final test result. The scanned images can be obtained by observing the surface of the diaphragm using a scanning electron microscope (S-3400N manufactured by Hitachi, Ltd.).

[0025] In some embodiments, the number of edges of a single first particle is less than or equal to 8 (e.g., 0, 1, 2, 3, 4, 5, 6, 7, or 8). Controlling the number of edges of a single first particle within the above range can reduce the number of edges of the first particle, making the surface of the first particle smoother, thereby further improving the slippage between the first particles.

[0026] In some embodiments, the first particle has a layered crystal structure dominated by weak hydrogen bonds and van der Waals forces. This layered crystal structure can be understood as a structure similar to the stacked layers of graphite. In the layered crystal structure of the first particle, the interlayer forces are dominated by weak hydrogen bonds and van der Waals forces. When subjected to external forces, the interlayer frictional resistance is small, and relative sliding easily occurs, thereby further enhancing the interlayer slippage of the first particle crystal and further dispersing the impact energy.

[0027] In some embodiments, the surface of the first particle has recesses, and the number of recesses is less than or equal to 6 (e.g., 0, 1, 2, 3, 4, 5, or 6). Controlling the number of recesses on the surface of the first particle within the above range makes it difficult for the first particles to interlock, weakening the mechanical interlocking effect between the first particles, and making it easier for the first particles to slip. When the number of recesses is greater than 6, the interlocking effect between the first particles is enhanced, which is not conducive to further improving the relative slippage between the first particles.

[0028] In some embodiments, the number of recesses is 0.

[0029] In this invention, the number of recesses refers to the total number of visible recesses on the surface of a single first particle within an arbitrarily selected 100μm × 100μm area in an image of the first coating surface taken by a scanning electron microscope (SEM). The number of recesses can be measured by the following method: An image of the first particle on the first coating surface is taken using a scanning electron microscope (SEM). Within the image, within an arbitrarily selected 100μm × 100μm area, all visible recesses on the surfaces of any 100 first particles are depicted. The number of visible recesses on the surface of each of these 100 first particles is counted. This operation is repeated 5 times. The total number of visible recesses observed on the surface of each first particle is less than or equal to 6, meaning there are no first particles with more than 6 recesses within the field of view.

[0030] In some embodiments, the diameter of the recess is no greater than 1 μm, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1 μm.

[0031] In this invention, the diameter of the recess refers to the maximum distance between any two points on the edge line of a single visible recess on the surface of a single first particle within an arbitrarily selected 100μm × 100μm area in an image of the first coating surface taken by a scanning electron microscope (SEM). The diameter of the recess can be measured by the following method: An image of the first particle on the surface of the first coating is taken using a scanning electron microscope (SEM). In the image, within an arbitrarily selected 100μm × 100μm area, the edge lines of all visible recesses on the surface of any 100 first particles are drawn. If no 100 first particles are observed in a single image, multiple images are taken until a total of 100 are obtained. The maximum distance between any two points on the edge line of each visible recess on the surface of each of these 100 particles is counted. This maximum value is the diameter of the recess. This operation is repeated 5 times. The diameter of all visible recesses on the surface of all observed first particles is no greater than 1μm.

[0032] In some embodiments, the particle size distribution width A of the first particle satisfies: 0.5≤A≤5 (e.g., 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5), where A=(D9-D1) / D5, D9 is the Dv90 of the first particle, D1 is the Dv10 of the first particle, and D5 is the Dv50 of the first particle. Controlling the particle size distribution width of the first particle to satisfy the above relationship means that the particle size distribution of the first particle is relatively wide, that is, the first particle group includes not only the first particles with larger diameters, but also the first particles with medium and small diameters. The first particles with different diameters form obvious differences in size, which moderately reduces the overall regularity of the first particles and reduces the overall sliding resistance between the first particles, thereby further improving the sliding between the first particles. When A < 0.5, the particle size distribution of the first particle is relatively narrow, which is not conducive to further improving the sliding between the first particles. When A > 5, the particle size distribution of the first particle is relatively too wide, the thickness of the first coating increases, resulting in a loss of battery energy density.

[0033] In this invention, Dv90, Dv50, and Dv10 of the first particle refer to the particle sizes corresponding to 90%, 50%, and 10% of the cumulative volumetric particle size distribution percentage of the first particles, arranged in ascending order of particle size. In this invention, the volumetric particle size distribution of the first particle can be obtained by arbitrarily selecting a 100μm × 100μm area in the SEM image of the first coating surface and performing measurement and statistical processing using image analysis software (e.g., ImageJ, NanoMeasurer, Matlab, etc.). The Dv90, Dv50, and Dv10 of the first particle can also be obtained by testing with a laser particle size analyzer.

[0034] In some embodiments, the particle size distribution width A of the first particle satisfies: 1≤A≤3.5.

[0035] In some embodiments, the average specific surface area of ​​the first particle is 6m². 2 / g-30m 2 / g, for example, 6m 2 / g, 10m 2 / g、14m 2 / g、18m 2 / g、22m 2 / g、26m 2 / g or 30m 2 / g.

[0036] In some embodiments, in the Raman spectrum of the first particle, at 1000 cm⁻¹ -1 -3000cm -1At least one characteristic peak exists within the specified range. When the Raman spectrum of the first particle contains at least one characteristic peak within the specified range, it indicates that the first particle has a layered crystal structure formed by hydrogen bonds, and the interlayer forces are mainly weak hydrogen bonds and van der Waals forces. When the first particle with this layered crystal structure is subjected to external force, the interlayers are more likely to slide relative to each other, thereby dispersing the impact energy and further improving the impact pass rate and drop pass rate of the battery.

[0037] In some embodiments, the nitrogen-containing heterocyclic organic compound is selected from one or more of uracil, melamine, melamine cyanurate, melamine thiocyanate, 1,2-aminopyridine, and 2-amino-4,6-diphenylthiopyrimidine.

[0038] 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%, or 99%.

[0039] In some embodiments, the first coating includes a first adhesive, which includes one or more of polyvinyl alcohol, styrene-butadiene rubber, ethylene-vinyl acetate copolymer, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polymethyl methacrylate, polybutyl methacrylate, styrene-acrylic latex, polyacrylonitrile, ethyl polyacrylate, polyvinyl acetate, polyacrylate, polyvinylidene fluoride polyurethane, polyvinylidene fluoride-hexafluoropropylene, or copolymer systems derived from the above polymers.

[0040] In some embodiments, the first adhesive in the first coating comprises 1%-10% by weight, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0041] In some embodiments, the thickness of the first coating is 0.2μm-5μm, for example 0.2μm, 0.8μm, 1.4μm, 2.0μm, 2.6μm, 3.2μm, 3.8μm, 4.4μm or 5μm.

[0042] In some embodiments, the diaphragm includes a second coating located on the surface of the first coating and / or the surface of the substrate layer.

[0043] In some embodiments, the diaphragm includes a substrate layer, a first coating layer, and a second coating layer, wherein the first coating layer is located on one side surface of the substrate layer, and the second coating layer is located on the surface of the first coating layer.

[0044] In some embodiments, the diaphragm includes a substrate layer, a first coating, and a second coating, wherein the first coating is located on one side surface of the substrate layer, and the second coating is located on the surface of the first coating and the other side surface of the substrate layer.

[0045] In some embodiments, the diaphragm includes a substrate layer, a first coating layer, and a second coating layer, wherein the first coating layer is located on both sides of the substrate layer, and the second coating layer is located on the surface of each first coating layer away from the substrate layer.

[0046] In some embodiments, the second coating comprises a second particle, the composition of which includes a polymer, said polymer including one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyhexafluoropropylene, fluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, acrylate-acrylonitrile copolymer, acrylate-styrene copolymer, acrylate-acrylonitrile-ethylene copolymer, styrene-acrylate-acrylonitrile copolymer, ethylhexyl acrylate-methyl methacrylate copolymer, butyl acrylate-methyl methacrylate copolymer, methyl acrylate-N,N-dimethylacrylamide copolymer, ethyl acrylate-2-(diethylamino)ethyl acrylate copolymer, ethyl acrylate-N,N-diethylacrylamide copolymer, and ethyl acrylate-2-(diethylamino)ethyl acrylate. In the aforementioned substances, acrylate-acrylonitrile copolymer, acrylate-styrene copolymer, acrylate-acrylonitrile-ethylene copolymer and styrene-acrylate-acrylonitrile copolymer, acrylate refers to a class of monomers, and the acrylate is selected from one of butyl acrylate, methyl methacrylate, methyl acrylate, ethyl acrylate, isobutyl acrylate and ethylhexyl acrylate.

[0047] In some embodiments, the thickness of the second coating is 0.5μm-5μm, for example, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm.

[0048] In some embodiments, the porosity of the substrate layer is 25%-70%, for example, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%.

[0049] In some embodiments, the thickness of the substrate layer is 2μm-10μm, for example, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm.

[0050] In some embodiments, the puncture strength of the substrate layer is 250gf-600gf, for example, 250gf, 300gf, 350gf, 400gf, 450gf, 500gf, 550gf or 600gf.

[0051] When a battery is impacted or dropped, it will withstand significant impact forces. The substrate layer has a certain puncture strength to resist localized concentrated stress, preventing misalignment or breakage of the substrate layer. It can also delay or prevent internal and external foreign objects from penetrating the separator, thereby preventing short circuits caused by shorting between the positive and negative electrodes. Controlling the puncture strength of the substrate layer within the aforementioned range can significantly improve its resistance to breakage under different external force scenarios, ensuring the integrity of the separator in impact and drop tests, and enhancing the separator's resistance to foreign object puncture. This further improves the battery's impact pass rate and drop pass rate. Furthermore, the improved resistance to foreign object puncture also effectively resists internal short circuits during high-temperature cycling when volume expansion occurs, further enhancing the battery's high-temperature cycling performance. When the puncture strength of the substrate layer exceeds the aforementioned range, the substrate layer's toughness decreases, making it prone to cracking, chipping, or shattering when impacted by foreign objects. This is detrimental to improving the battery's impact pass rate and drop pass rate, and also reduces the battery's interface performance and cycle performance.

[0052] In this invention, the puncture strength of the substrate layer can be measured by the following method: cut a test sample of 60mm*600mm in any size from the diaphragm substrate layer, lay the test sample flat in the fixture of the universal tensile testing machine and clamp it, select the puncture strength test item, puncture at a rate of (100±10)mm / min, read the puncture strength test result from the test report, repeat 3 times and take the average value as the puncture strength of the substrate layer.

[0053] In some embodiments, the substrate layer is a porous layer formed by interwoven polymer fibers, the average diameter of which is 50nm-500nm (e.g., 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm).

[0054] In some embodiments, the polymer fiber comprises one or more of the following polymer derivatives: 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 the polymer derivatives thereof.

[0055] A second aspect of the present invention provides a battery comprising a housing, an electrode assembly, and an electrolyte, wherein the electrode assembly and the electrolyte are located within a containment space formed by the housing, and the electrode assembly comprises a positive electrode, a negative electrode, and a separator as described in the first aspect of the present invention.

[0056] In some embodiments, the casing is a steel casing with a thickness of 40μm-400μm, such as 40μm, 80μm, 120μm, 160μm, 200μm, 240μm, 280μm, 320μm, 360μm, or 400μm. The steel casing has a much higher hardness than the aluminum-plastic film, and its thickness is controlled within the aforementioned range, which can prevent foreign objects from piercing the steel casing, further improving the battery's drop or puncture safety.

[0057] In some embodiments, the housing includes a first wall, the first wall including a first through hole and a pressure relief device.

[0058] In some embodiments, the pressure relief device covers the first through hole, and the pressure relief device includes an adhesive film that forms a pressure relief channel connecting the interior and exterior of the housing when the adhesive film melts or loses its adhesion.

[0059] When a battery is dropped or impacted, it is prone to internal short circuits and generates high temperature and pressure. The casing may rupture, catch fire, or explode. When the internal heat reaches the threshold for melting or losing adhesion of the adhesive film, the adhesive film fails. The pressure relief device forms a pressure relief channel connecting the inside and outside of the casing, which can quickly release high-pressure gas and heat, prevent thermal runaway from escalating, and improve the battery's drop or impact safety, thereby further improving the battery's impact pass rate and drop pass rate.

[0060] In some embodiments, the housing includes a second wall that includes grooves.

[0061] In some embodiments, the ratio of the depth of the groove to the thickness of the second wall is 0.1-0.95 (e.g., 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 0.95). When the internal pressure of the housing reaches a threshold, the groove breaks to form a pressure relief channel connecting the inside and outside of the housing.

[0062] A groove is provided in the second wall, and the ratio of the depth of the groove to the thickness of the second wall is controlled within the above range. When the battery is dropped or impacted, when the internal pressure of the casing reaches the threshold, the groove can break to form a pressure relief channel connecting the inside and outside of the casing. This can quickly release high-pressure gas and heat, prevent thermal runaway from escalating, and improve the battery's drop or puncture safety, thereby further improving the battery's impact pass rate and drop pass rate.

[0063] In some embodiments, the electrolyte comprises cyclic carbonate, the separator comprises a substrate layer, a first coating and a second coating, the first coating is located on one or both surfaces of the substrate layer, the second coating is located on the surface of the first coating, and the battery satisfies the following relationship: 2.5≤(D×E) / d≤2300 (e.g., 2.5, 5, 10, 20, 50, 100, 150, 200, 300, 500, 1000, 1500 or 2300), where d is the average particle size of the second particles in μm, E is the weight percentage of cyclic carbonate in the electrolyte, and D is the average diameter of the fibers in the substrate layer in nm.

[0064] In a battery system, the first particle has certain slip characteristics, which can effectively disperse the impact energy from impacts or drops. However, during battery cycling, the slip characteristics of the first particle will cause it to fall off under the stress generated by the repeated expansion of the battery, eventually leading to pitting on the battery surface. Research has found that cyclic carbonate can penetrate into the fiber of the substrate layer, causing it to swell moderately. At the same time, the cyclic carbonate also causes the second particle to swell moderately, thereby significantly enhancing the adhesion of the substrate layer and the second coating to the first particle in the first coating, effectively preventing the first particle from falling off during battery cycling expansion and preventing pitting on the battery surface.

[0065] Based on this, the relationship between the weight percentage of cyclic carbonate in the electrolyte, the average diameter of the fibers in the substrate layer, and the average particle size of the second particles is controlled to ensure that the battery satisfies the above-mentioned relationship. The cyclic carbonate, substrate layer fibers, and second particles work synergistically to lock the first particles in the first coating between the substrate layer surface and the second coating, preventing the first particles from falling off during high-temperature cycling expansion, preventing pitting on the battery surface, and improving the battery's high-temperature cycling performance. When (D×E) / d < 2.5, the weight percentage of cyclic carbonate in the electrolyte is too low, resulting in insufficient swelling of the substrate layer fibers and second particles. The first particles in the first coating are prone to falling off during high-temperature cycling expansion, leading to pitting on the battery surface or damage to the substrate layer. If the average diameter of the fiber in the separator layer is too small or the average particle size of the second particle is too small, the first particle cannot be locked between the fiber in the separator layer and the second particle after being swollen by the cyclic carbonate. The first particle falls off during the high-temperature cycling expansion process of the battery, resulting in pitting on the battery surface. When (D×E) / d>2300, the weight ratio of cyclic carbonate in the electrolyte is too high, the electrolyte viscosity is too high, and the battery cycle performance is reduced. Alternatively, if the average diameter of the fiber in the separator substrate is too large, the porosity of the substrate layer deteriorates, thereby reducing the consistency of lithium-ion transport rate and reducing the battery cycle stability. Or, if the particle size of the second particle is too large, the distance between the separator and the electrode increases, the interfacial performance between the separator and the electrode decreases, and ultimately the battery cycle performance is reduced.

[0066] In this invention, when the second particle comprises particles of two different sizes, the average particle size of the second particle is the average of the average particle sizes of the two particles. This can be achieved by arbitrarily selecting a 100μm×100μm area in the SEM image of the coating surface, identifying and randomly selecting 100 second particles of the first particle size and 100 second particles of the second particle size, and drawing a rectangle with the smallest area that completely surrounds one second particle of the first particle size. That is, drawing a rectangle whose edge of the second particle of the first particle size is tangent to the four sides of the rectangle. The length of the long side of the rectangle is the diameter of the second particle of the first particle size. If there are not enough particles in a single image, multiple images can be taken until 100 second particles of the first particle size are observed. The 100 particles are then calculated. The arithmetic mean of the diameters of the second particles of the first particle size is the average diameter of the second particles of the first particle size. Draw the rectangle with the smallest area that completely surrounds one second particle of the second particle size, that is, draw the rectangle whose edge of the second particle of the second particle size is tangent to the four sides of the rectangle. The length of the long side of the rectangle is the diameter of the second particle of the second particle size. If there are not enough particles in a single image, multiple images can be taken until 100 second particles of the second particle size are observed. Calculate the arithmetic mean of the diameters of the 100 second particles of the second particle size, which is the average diameter of the second particles of the second particle size. Calculate the average of the average diameters of the second particles of the first particle size and the average diameters of the second particles of the second particle size, which is the average diameter of the second particle.

[0067] In this invention, when the second particle consists only of the same type of particle, the average particle size of the second particle can be determined by randomly selecting 100 second particles of 100μm×100μm from the SEM image of the coating surface, identifying and randomly selecting 100 second particles, and drawing a rectangle with the smallest area that completely surrounds one second particle, i.e., drawing a rectangle whose edge of the second particle is tangent to the four sides of the rectangle. The length of the long side of the rectangle is the diameter of the second particle. If there are not enough particles in a single image, multiple images can be taken until 100 second particles are observed. The arithmetic mean of the particle sizes of the 100 second particles is then calculated, which is the average particle size of the second particle.

[0068] In this invention, the average diameter of the fibers in the substrate layer is obtained by scanning electron microscopy (SEM). Specifically, a high-magnification SEM image of the membrane substrate layer is acquired. In an arbitrary 100μm×100μm area on the surface of the substrate layer, the diameter of any 100 fibers is measured. If no 100 fibers are observed in a single image, multiple images are taken until the total number of fibers reaches 100. The average diameter of the 100 fibers is then counted. The above operation is repeated 5 times, and the average value of the 5 measurements is the average diameter of the fiber.

[0069] In this invention, the weight percentage of cyclic carbonates in the electrolyte is obtained by gas chromatography (GC).

[0070] In some embodiments, the battery satisfies the following relationship: 3≤(D×E) / d≤2000.

[0071] In some embodiments, the first coating is located on one side surface of the substrate layer, and the side of the separator with the first coating corresponds to the positive electrode active layer.

[0072] In some embodiments, the average particle size of the second particle is 0.1 μm-1 μm, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1 μm.

[0073] In some embodiments, the second particle comprises only one type of particle with an average particle size of 0.5 μm-1 μm.

[0074] In some embodiments, the second particle comprises only one type of particle with an average particle size of 0.1 μm-0.2 μm.

[0075] In some embodiments, the second particle includes two types of particles: a second particle with a particle size of 0.1 μm-0.2 μm and a second particle with a particle size of 0.5 μm-1 μm.

[0076] In some embodiments, the average diameter D of the fibers in the substrate layer is 50nm-500nm, for example, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm or 500nm.

[0077] In some embodiments, the weight percentage E of the cyclic carbonate in the electrolyte is 5%-50%, specifically 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%.

[0078] According to one specific implementation, D is 50-500, E is 5%-50%, and d is 0.1-1. The battery satisfies the following relationship: 2.5≤(D×E) / d≤2300.

[0079] According to one specific implementation, D is 50-500, E is 5%-50%, and d is 0.1-1. The battery satisfies the following relationship: 3≤(D×E) / d≤2000.

[0080] In some embodiments, the cyclic carbonate is selected from at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, vinylene carbonate, and propylene sulfite.

[0081] In some embodiments, the cyclic carbonate is selected from at least one of ethylene carbonate and propylene carbonate. Ethylene carbonate and propylene carbonate have high dielectric parameters, which improve the conductivity and thermal stability of the electrolyte and are beneficial to the safety performance of the battery.

[0082] In some embodiments, the electrolyte includes lithium salt, solvent, and additives.

[0083] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0084] In some embodiments, the solvent in the electrolyte may include, in addition to cyclic carbonates, at least one of the following: difluoroethyl acetate (DFEA), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0085] In some embodiments, the additive includes at least one of dinitrile compounds, trinitrile compounds, fluorinated chain carbonates, and sulfur-containing oxygen double bond compounds.

[0086] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer located on one or both sides of the negative electrode current collector surface, wherein the negative electrode active layer includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder.

[0087] In some embodiments, the negative electrode active material includes a silicon-based material selected from one or more of silicon oxide compounds (e.g., SiOx / C), silicon-carbon composites (e.g., Si / C), elemental silicon, silicon alloys, and silicon nitride compounds.

[0088] In some embodiments, the silicon-based material is a silicon-carbon composite, and the average particle size of the silicon-carbon composite is 5 μm-12 μm.

[0089] In some embodiments, the silicon-carbon composite comprises porous carbon and elemental silicon particles, the elemental silicon particles being deposited in the pores of the porous carbon.

[0090] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active layer located on one or both sides of the surface of the positive current collector. The positive active layer includes a positive active material, a positive conductive agent, and a positive binder.

[0091] In some embodiments, the positive electrode active material includes one or more of lithium nickel oxide, lithium titanate, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide.

[0092] In some embodiments, the positive electrode conductive agent includes one or more of conductive carbon black, carbon nanotubes, conductive graphite, and graphene.

[0093] In some embodiments, the positive electrode binder includes one or more of polyvinylidene fluoride (PVDF), acrylic acid-modified PVDF, polyacrylate polymers, acrylic polymers, polytetrafluoroethylene, polyacrylonitrile, polyimide, styrene-butadiene rubber, and styrene-acrylic rubber.

[0094] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0095] Example 1

[0096] (1) Preparation of positive electrode

[0097] Lithium cobalt oxide, polyvinylidene fluoride (PVDF 500) binder, and conductive agent (conductive carbon black: carbon nanotubes = 2:1) were mixed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 95.5:2.5:2 and continuously stirred under the action of a stirrer to form a homogeneous and fluid positive electrode slurry. Subsequently, the positive electrode slurry was coated on both sides of an aluminum foil with a thickness of 10 μm and dried in a vacuum oven at 120 °C for 6 hours. Then, it was rolled and slit to obtain the positive electrode sheet.

[0098] (2) Preparation of negative electrode

[0099] Graphite, silicon-carbon composite, binder (styrene-butadiene rubber (SBR): sodium hydroxymethyl cellulose = 3:1), and conductive agent (conductive carbon black: carbon nanotubes = 2:3) were mixed in an aqueous solvent at a weight ratio of 94:3:2:1 and continuously stirred under the action of a stirrer to form a homogeneous and fluid negative electrode slurry. Subsequently, the slurry was coated on both sides of a 10 μm thick copper foil and dried in a vacuum oven at 120 °C for 6 hours. Then, it was rolled and slit to obtain the desired negative electrode sheet.

[0100] (3) Electrolyte preparation

[0101] In an argon-filled glove box (moisture <1ppm, oxygen <1ppm), propyl propionate and ethyl propionate solvents were mixed at a weight ratio of 70:30. Then, ethylene carbonate and propylene carbonate solvents at a weight ratio of 1:1 were slowly added and mixed to form a homogeneous solvent. Subsequently, 14wt% LiPF6, 3wt% 1,3,6-hexanetrionitrile, and 0.3wt% lithium bis(oxalato)borate (LiBOB) were added and stirred until homogeneous to obtain the desired lithium-ion battery electrolyte. In the electrolyte, the weight percentage of ethylene carbonate was 17.8%, the weight percentage of propylene carbonate was 17.8%, and the weight percentage of cyclic carbonates was 35.6% (E = 35.6%).

[0102] (4) Preparation of the diaphragm

[0103] A slurry with a solid content of 30% was obtained by blending the first particle (melamine cyanurate), the first binder (sodium carboxymethyl cellulose: polyacrylate = 1:9), and deionized water. Based on 100% solids mass, the mass ratio of the first particle to the first binder was 94:6. After thorough mixing, the slurry was coated onto one side of polyethylene (substrate layer) using a gravure roller. After drying in a multi-section oven at 60°C, a first coating was formed. The first particle had an average sphericity of 0.4, a cohesive force F between the first particles in the first coating of 32 N / m, and 90% of the first particles had a sphericity of 0.2-0.7. Each first particle had 6 edges, 0 recesses, a particle size distribution width A of 2.8, and an average specific surface area of ​​18.4 m². 2 / g, in the Raman spectrum of the first particle, at 1000cm -1 -3000cm -1 Characteristic peaks exist within the range, the porosity of the substrate layer is 40%, the thickness of the substrate layer is 7μm, the puncture strength of the substrate layer is 325gf, and the average diameter of the fibers in the substrate layer is 389.3nm (D is 389.3).

[0104] Methyl methacrylate-acrylonitrile copolymer (second particles) was blended with deionized water to obtain a mixed slurry with a solid content of 10%. After thorough stirring and dispersion, the slurry was coated onto the surface of the first coating away from the substrate layer and the surface of the substrate layer on the other side through a gravure roller. After drying in a multi-section oven at 60°C, a second coating was formed on the surface of the first coating and the surface of the substrate layer, respectively. The thickness of both second coatings was 2 μm, and the average particle size of the second particles in both second coatings was 0.65 μm (d = 0.65).

[0105] The desired diaphragm is thus prepared.

[0106] (5) Preparation of lithium-ion batteries

[0107] The above-prepared positive electrode sheet, separator, and negative electrode sheet are wound to form a bare cell. Then, the bare cell is placed in an aluminum-plastic film, and the prepared electrolyte is injected into the dried bare cell. After vacuum sealing, room temperature standing, and high temperature formation, the desired lithium-ion battery is obtained. Among them, (D×E) / d=(389.3×35.6%) / 0.65=213.2, and the battery casing is an aluminum-plastic film.

[0108] Example 2 group

[0109] This set of examples illustrates the effects that occur when the average sphericity of the first particles in the first coating changes.

[0110] Example 2-1

[0111] This embodiment is based on Embodiment 1, except that the average sphericity of the first particles in the first coating is 0.25, the cohesive force F between the first particles in the first coating is 15 N / m, and the proportion of first particles with a sphericity of 0.2-0.7 is 83%.

[0112] Example 2-2

[0113] This embodiment is based on Embodiment 1, except that the average sphericity of the first particles in the first coating is 0.55, the cohesive force F between the first particles in the first coating is 40 N / m, and the proportion of first particles with a sphericity of 0.2-0.7 is 86%.

[0114] Example 2-3

[0115] This embodiment is based on Embodiment 1, except that the average sphericity of the first particles in the first coating is 0.2, the cohesive force F between the first particles in the first coating is 11 N / m, and the proportion of first particles with a sphericity of 0.2-0.7 is 82%.

[0116] Examples 2-4

[0117] This embodiment is based on Embodiment 1, except that the average sphericity of the first particles in the first coating is 0.8, the cohesive force F between the first particles in the first coating is 58 N / m, and the proportion of first particles with a sphericity of 0.2-0.7 is 89%.

[0118] Example 3 Group

[0119] This set of examples illustrates the effects that occur when the composition of the first particle changes.

[0120] Example 3-1

[0121] This embodiment is based on Embodiment 1, except that the first particle contains guanine.

[0122] Example 3-2

[0123] This embodiment is based on Embodiment 1, except that the first particle is composed of uracil.

[0124] Example 4 group

[0125] This set of examples illustrates the effects of changes in the cohesive force between the first particles in the first coating.

[0126] Example 4-1

[0127] This embodiment is based on Embodiment 1, except that the cohesive force between the first particles in the first coating is 5 N / m (F is 5 N / m), and the weight percentage of the first particles in the first coating is 98%, while the weight percentage of the first adhesive is 2%.

[0128] Example 4-2

[0129] This embodiment is based on Embodiment 1, except that the cohesive force between the first particles in the first coating is 60 N / m (F is 60 N / m), and the weight percentage of the first particles in the first coating is 93%, while the weight percentage of the first adhesive is 7%.

[0130] Example 4-3

[0131] This embodiment is based on Embodiment 1, except that the cohesive force between the first particles in the first coating is 3 N / m (F is 3 N / m), and the weight percentage of the first particles in the first coating is 98%, while the weight percentage of the first adhesive is 2%.

[0132] Example 4-4

[0133] This embodiment is based on Embodiment 1, except that the cohesive force between the first particles in the first coating is 68 N / m (F is 68 N / m), and the weight percentage of the first particles in the first coating is 93%, while the weight percentage of the first adhesive is 7%.

[0134] Example 5

[0135] This embodiment is based on Embodiment 1, except that the number of first particles with a sphericity of 0.2-0.7 accounts for 70% of the total number of first particles.

[0136] Example 6 group

[0137] This set of examples illustrates the effects of changing the number of surface recesses on the first particle.

[0138] Example 6-1

[0139] This embodiment is based on Embodiment 1, except that the number of surface recesses of the first particle is 2, and the diameter of the surface recesses of the first particle is 0.3 μm.

[0140] Example 6-2

[0141] This embodiment is based on Embodiment 1, except that the number of surface recesses of the first particle is 4, and the diameter of the surface recesses of the first particle is 0.3 μm.

[0142] Example 6-3

[0143] This embodiment is based on Embodiment 1, except that the number of surface recesses of the first particle is 9, and the diameter of the surface recesses of the first particle is 0.3 μm.

[0144] Example 7 group

[0145] This set of examples illustrates the effects that occur when the particle size distribution width of the first particle changes.

[0146] Example 7-1

[0147] This embodiment is based on Embodiment 1, except that the particle size distribution width of the first particle is 1 (A is 1), and the average specific surface area of ​​the first particle is 18m². 2 / g, the cohesive force between the first particles in the first coating is 35N / m (F is 35N / m).

[0148] Example 7-2

[0149] This embodiment is based on Embodiment 1, except that the particle size distribution width of the first particle is 3.5 (A is 3.5), and the average specific surface area of ​​the first particle is 16.3 m². 2 / g, the cohesive force between the first particles in the first coating is 47 N / m (F is 47 N / m).

[0150] Example 7-3

[0151] This embodiment is based on Embodiment 1, except that the particle size distribution width of the first particle is 0.5 (A is 0.5), and the average specific surface area of ​​the first particle is 19.6 m². 2 / g, the cohesive force between the first particles in the first coating is 30N / m (F is 30N / m).

[0152] Example 7-4

[0153] This embodiment is based on Embodiment 1, except that the particle size distribution width of the first particle is 5 (A is 5), and the average specific surface area of ​​the first particle is 15.5 m². 2 / g, the cohesive force between the first particles in the first coating is 51 N / m (F is 51 N / m).

[0154] Example 7-5

[0155] This embodiment is based on Embodiment 1, except that the particle size distribution width of the first particle is 0.1 (A is 0.1), and the average specific surface area of ​​the first particle is 21.2 m². 2 / g, the cohesive force between the first particles in the first coating is 28 N / m (F is 28 N / m).

[0156] Examples 7-6

[0157] This embodiment is based on Embodiment 1, except that the particle size distribution width of the first particle is 8 (A is 8), and the average specific surface area of ​​the first particle is 14.6 m². 2 / g, the cohesive force between the first particles in the first coating is 56 N / m (F is 56 N / m).

[0158] Example 8 group

[0159] This set of examples illustrates the effects of changes in the puncture strength of the substrate layer.

[0160] Example 8-1

[0161] This embodiment is based on Embodiment 1, except that the puncture strength of the substrate layer is 250 gf.

[0162] Example 8-2

[0163] This embodiment is based on Embodiment 1, except that the puncture strength of the substrate layer is 600gf.

[0164] Example 8-3

[0165] This embodiment is based on Embodiment 1, except that the puncture strength of the substrate layer is 200gf.

[0166] Example 8-4

[0167] This embodiment is based on Embodiment 1, except that the puncture strength of the substrate layer is 700gf.

[0168] Example 9 group

[0169] This set of examples illustrates the effects of changes in (D×E) / d.

[0170] Example 9-1

[0171] This embodiment is based on Example 1, except that the weight percentage of cyclic carbonate in the electrolyte is 40% (E is 40%), the average diameter of the fibers in the substrate layer is 500 nm (D is 500), the average particle size of the second particle is 0.1 μm (d is 0.1), and (D×E) / d=(500×40%) / 0.1=2000.

[0172] Example 9-2

[0173] This embodiment is based on Example 1, except that the weight percentage of cyclic carbonate in the electrolyte is 5% (E is 5%), the average diameter of the fibers in the substrate layer is 50nm (D is 50), the average particle size of the second particle is 1μm (d is 1), and (D×E) / d=(50×5%) / 1=2.5.

[0174] Example 9-3

[0175] This embodiment is based on Example 1, except that the weight percentage of cyclic carbonate in the electrolyte is 45% (E is 45%), the average diameter of the fibers in the substrate layer is 500 nm (D is 500), the average particle size of the second particle is 0.1 μm (d is 0.1), and (D×E) / d=(500×45%) / 0.1=2250.

[0176] Example 9-4

[0177] This embodiment is based on Example 1, except that the weight percentage of cyclic carbonate in the electrolyte is 4.5% (E is 4.5%), the average diameter of the fibers in the substrate layer is 44nm (D is 44), the average particle size of the second particle is 0.07μm (d is 0.07), and (D×E) / d=(44×4.5%) / 0.07=28.

[0178] Example 9-5

[0179] This embodiment is based on Example 1, except that the weight percentage of cyclic carbonate in the electrolyte is 58% (E is 58%), the average diameter of the fibers in the substrate layer is 515 nm (D is 515), the average particle size of the second particle is 1.6 μm (d is 1.6), and (D×E) / d=(515×58%) / 1.6=187.

[0180] Examples 9-6

[0181] This embodiment is based on Example 1, except that the weight percentage of cyclic carbonate in the electrolyte is 4.5% (E is 4.5%), the average diameter of the fibers in the substrate layer is 50nm (D is 50), the average particle size of the second particle is 1μm (d is 1), and (D×E) / d=(50×4.5%) / 1=2.

[0182] Examples 9-7

[0183] This embodiment is based on Example 1, except that the weight percentage of cyclic carbonate in the electrolyte is 50% (E is 50%), the average diameter of the fibers in the substrate layer is 500 nm (D is 500), the average particle size of the second particle is 0.1 μm (d is 0.1), and (D×E) / d=(500×50%) / 0.1=2500.

[0184] Example 10 group

[0185] This set of examples illustrates the effects of changes to the battery casing.

[0186] Example 10-1

[0187] This embodiment is based on embodiments 2-3, except that the battery casing is a steel casing. The battery casing includes a first wall and a second wall. In the second wall, the ratio of the depth of the groove to the thickness of the second wall is 0.1.

[0188] Example 10-2

[0189] This embodiment is carried out with reference to embodiments 2-3, except that the battery casing is a steel casing and the battery casing includes a first wall and a second wall. In the second wall, the ratio of the depth of the groove to the thickness of the second wall is 0.95.

[0190] Example 10-3

[0191] This embodiment is carried out with reference to Embodiments 2-3, except that the battery casing is a steel casing and the battery casing includes a first wall and a second wall. In the second wall, the ratio of the depth of the groove to the thickness of the second wall is 0.07.

[0192] Example 10-4

[0193] This embodiment is based on embodiments 2-3, except that the battery casing is a steel casing. The battery casing includes a first wall and a second wall. In the second wall, the ratio of the depth of the groove to the thickness of the second wall is 0.4.

[0194] Comparative Example 1

[0195] This embodiment is based on Embodiment 1, except that the first particle is composed of aluminum oxide.

[0196] Comparative Example 2

[0197] This embodiment is based on Embodiment 1, except that the first particle is composed of polyacrylonitrile.

[0198] Comparative Example 3

[0199] This embodiment is based on Embodiment 1, except that the average sphericity of the first particles in the first coating is 0.1, the cohesive force F between the first particles in the first coating is 6 N / m, and the proportion of the first particles with a sphericity of 0.2-0.7 is 20%.

[0200] Comparative Example 4

[0201] This embodiment is based on Embodiment 1, except that the average sphericity of the first particles in the first coating is 1, the cohesive force F between the first particles in the first coating is 60 N / m, and the proportion of first particles with a sphericity of 0.2-0.7 is 93%.

[0202] Test case

[0203] The batteries prepared in the examples and comparative examples were subjected to the following performance tests, and the test results are shown in Table 1:

[0204] (1) Impact pass rate:

[0205] At 25℃, the battery is discharged at 0.5C to the lower limit voltage (3V); left to stand for 10 minutes, and then charged at a constant current of 0.7C to the upper limit voltage (4.5V). The voltage is then kept constant until the cutoff current is 0.02C. At this point, the battery is fully charged. After the battery is fully charged, a metal needle with a spherical tip (diameter 6mm±0.2mm) is passed through the center of the lithium-ion battery at a constant speed of 30mm / s and held for 300s. If the lithium-ion battery does not catch fire or explode, it is considered to have passed. 25 samples are tested, and the number of batteries that pass is recorded as X. The result is recorded as "X / 25".

[0206] (2) Fall pass rate:

[0207] At 25℃, the lithium-ion battery was charged at a constant current of 0.5C to 4.5V, then charged at a constant voltage of 0.05C. After standing for 60 minutes, the voltage of the lithium-ion battery before the drop test was measured. The lithium-ion battery was placed in a fixture and dropped freely from a height of 1.5m above the ground using a drop device in the following order: head-tail-right corner of head-right corner of tail-left corner of head-left corner of tail (angle: 45±15°), repeated 4 times. After the drop test, the battery was left to stand at room temperature for 24 hours, and the voltage of the lithium-ion battery was measured and recorded. The appearance of the lithium-ion battery was checked and photographed before and after the test. The criteria for passing the drop test were: voltage drop <30mV, no fire or explosion of the battery. 25 samples were tested, and the number of batteries that passed was recorded as X, and the result was recorded as "X / 25".

[0208] (3) Capacity retention rate during 25℃ cycling:

[0209] At 25℃±2℃, the battery was charged at a constant current of 1C to the upper limit voltage of 4.5V, then charged at a constant voltage to 0.05C, allowed to rest for 5 minutes, and then discharged at a constant current of 0.7C to 3V, allowed to rest for 5 minutes. The initial discharge capacity was recorded as C0. The cycle was: charged at a constant current of 1C to the upper limit voltage of 4.5V, then charged at a constant voltage to 0.05C, allowed to rest for 5 minutes, and then discharged at a constant current of 0.7C to 3V. After 800 cycles, the discharge capacity was recorded as C1, and the capacity retention rate was (C1 / C0)×100%.

[0210] (4) Capacity retention rate during 45℃ cycling:

[0211] At 45±2℃, the battery was charged at a constant current of 1C to the upper limit voltage of 4.5V, the cutoff current was 0.05C, and it was left to stand for 5 minutes. Then it was discharged at a constant current of 0.7C to 3V. The initial discharge capacity was recorded as C0, and it was left to stand for 5 minutes.

[0212] Cyclic charging method: Charge the battery at a constant current of 1C to 4.5V, cut off the current at 0.05C, let it rest for 5 minutes, then discharge it at a constant current of 0.7C to 3V, and let it rest for 5 minutes. After 500 cycles, charge the battery at a constant current of 1C to the upper limit voltage of 4.5V, cut off the current at 0.05C, let it rest for 5 minutes, then discharge it at a constant current of 0.7C to 3V. Record the final discharge capacity as C1, let it rest for 5 minutes, and then calculate the capacity retention rate as (C1 / C0) × 100%.

[0213] Table 1

[0214]

[0215]

[0216] As can be seen from Table 3, by comparing the comparative examples and the embodiments, the impact pass rate and drop pass rate of the embodiments are significantly improved, the high temperature capacity retention rate is improved, and the room temperature cycling capacity retention rate is improved. This indicates that by controlling the composition of the first particles in the first coating and the average sphericity of the first particles, the first particles in the first coating have both suitable packing density and effective slippage effect. When the battery is subjected to external impact or drop, the impact stress can be dispersed, the stability of the separator structure can be maintained, the impact pass rate and drop pass rate of the battery can be improved, and the high temperature cycling performance and room temperature cycling performance can be improved.

[0217] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A diaphragm, characterized in that, The diaphragm includes a substrate layer and a first coating layer located on one or both sides of the substrate layer. The first coating layer includes first particles, the first particles being composed of nitrogen-containing heterocyclic organic compounds having a layered crystal structure, and the average sphericity of the first particles being 0.2-0.

8.

2. The diaphragm according to claim 1, wherein, The cohesive force F between the first particles in the first coating is 5 N / m ≤ F ≤ 60 N / m; And / or, in the first particle, the proportion of the first particles with a sphericity of 0.2-0.7 is greater than or equal to 80%; And / or, the number of edges of a single first particle is less than or equal to 8.

3. The diaphragm according to claim 1, wherein, The surface of the first particle has recesses, and the number of recesses in a single first particle is less than or equal to 6. Preferably, the diameter of a single recess is no greater than 1 μm.

4. The diaphragm according to claim 1, wherein, The particle size distribution width A of the first particle satisfies: 0.5≤A≤5, where A=(D9-D1) / D5, D9 is the Dv90 of the first particle, D1 is the Dv10 of the first particle, and D5 is the Dv50 of the first particle. And / or, the average specific surface area of ​​the first particle is 6m². 2 / g-30m 2 / g; And / or, in the Raman spectrum of the first particle, at 1000 cm⁻¹ -1 -3000cm -1 There is at least one characteristic peak within the range; And / or, the nitrogen-containing heterocyclic organic compound is selected from one or more of uracil, melamine, melamine cyanurate, melamine thiocyanate, guanine, 4-amino-2,6-dihydroxypyrimidine, 1,2-aminopyridine, and 2-amino-4,6-diphenylthiopyrimidine.

5. The diaphragm according to any one of claims 1-4, wherein, In the first coating, the weight percentage of the first particles is 90%-99%; And / or, the first coating includes a first adhesive, wherein the weight percentage of the first adhesive in the first coating is 1%-10%; And / or, the diaphragm includes a second coating located on the surface of the first coating and / or the surface of the substrate layer, the second coating including second particles having an average particle size of 0.1 μm-1 μm; And / or, the porosity of the substrate layer is 25%-70%; And / or, the thickness of the substrate layer is 2μm-10μm; And / or, the puncture strength of the substrate layer is 250gf-600gf; And / or, the substrate layer is a porous layer formed by interwoven polymer fibers, the average diameter of which is 50nm-500nm.

6. The diaphragm according to claim 5, wherein, The thickness of the second coating is 0.5μm-5μm; And / or, the first adhesive comprises one or more of the following: polyvinyl alcohol, styrene-butadiene rubber, ethylene-vinyl acetate copolymer, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polymethyl methacrylate, polybutyl methacrylate, styrene-acrylic latex, polyacrylonitrile, ethyl polyacrylate, polyvinyl acetate, polyacrylate, polyvinylidene fluoride polyurethane, polyvinylidene fluoride-hexafluoropropylene, or copolymer systems derived from the above polymers; And / or, the second particle is composed of a polymer, said polymer including one or more of the following: polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyhexafluoropropylene, fluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, acrylate-acrylonitrile copolymer, acrylate-styrene copolymer, acrylate-acrylonitrile-ethylene copolymer, styrene-acrylate-acrylonitrile copolymer, ethylhexyl acrylate-methyl methacrylate copolymer, butyl acrylate-methyl methacrylate copolymer, methyl acrylate-N,N-dimethylacrylamide copolymer, ethyl acrylate-2-(diethylamino)ethyl acrylate copolymer, ethyl acrylate-N,N-diethylacrylamide copolymer, and ethyl acrylate-2-(diethylamino)ethyl acrylate. And / or, the composition of the substrate layer includes one or more of the following polymer derivatives: 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 poly(m-phenylene isophthalamide).

7. A battery, characterized in that, The battery includes a casing, an electrode assembly, and an electrolyte, wherein the electrode assembly and the electrolyte are located within a containment space formed by the casing, and the electrode assembly includes a positive electrode, a negative electrode, and a separator according to any one of claims 1-6.

8. The battery according to claim 7, wherein, The separator includes a second coating located on the surface of the first coating and / or the surface of the substrate layer. The second coating includes second particles. The electrolyte includes cyclic carbonates. The battery satisfies the following relationship: 2.5 ≤ (D×E) / d ≤ 2300, where d is the average particle size of the second particles in μm, E is the weight percentage of cyclic carbonates in the electrolyte, and D is the average diameter of the fibers in the substrate layer in nm.

9. The battery according to claim 8, wherein, The weight percentage E of cyclic carbonates in the electrolyte is 5%-50%; And / or, the average diameter D of the fibers in the substrate layer is 50nm-500nm; And / or, the average particle size of the second particle is 0.1 μm-1 μm; And / or, the battery satisfies the following relationship: 3≤(D×E) / d≤2000; And / or, the cyclic carbonate is selected from at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, vinylene carbonate, and propylene sulfite.

10. The battery according to claim 7, wherein, The housing includes a first wall, which includes a first through hole and a pressure relief device; Preferably, the pressure relief device covers the first through hole, and the pressure relief device includes an adhesive film. When the adhesive film melts or loses its adhesion, the pressure relief device forms a first pressure relief channel connecting the interior and exterior of the housing. And / or, the housing includes a second wall, the second wall including a groove; Preferably, the ratio of the depth of the groove to the thickness of the second wall is 0.1-0.

95. When the internal pressure of the housing reaches a threshold, the groove breaks to form a first pressure relief channel connecting the inside and outside of the housing.

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