Diaphragm and battery

Abstract

The invention relates to the technical field of batteries, in particular to a diaphragm and a battery comprising the diaphragm, the diaphragm comprises a base material layer and a functional coating located on the surface of one side or two sides of the base material layer, the functional coating comprises first polymer particles and first heat-resistant particles, and the first polymer particles and the first heat-resistant particles are arranged in any 10 [mu] m * 10 [mu] m range of the surface of the functional coating. The number of the first heat-resistant particles ranges from 100 to 2000. The diaphragm disclosed by the invention can still keep an excellent barrier effect at a high temperature, effectively reduces the short-circuit risk of the battery, can delay the thermal runaway dynamic process of a positive electrode material, and improves the high-temperature stability of the positive electrode material. The battery provided by the invention has excellent high-temperature thermal stability and safety.

Description

Technical Field

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

[0002] Current lithium-ion battery technology is rapidly evolving towards high energy density, but thermal stability issues under high-temperature conditions are becoming increasingly prominent. Commercial polyolefin-based diaphragms have significant thermal shrinkage defects in high-temperature environments, which can easily lead to electrode contact and increase the risk of battery short circuits. At the same time, positive electrode materials such as ternary materials (such as NCM) and lithium cobalt oxide are prone to active substance oxygen release during high-temperature charge and discharge cycles, and are accompanied by irreversible destruction of the crystal structure, inducing lattice instability. The released active oxygen reacts violently with the electrolyte in an exothermic reaction, causing heat accumulation, ultimately leading to thermal runaway and safety failure of the battery, while accelerating battery capacity decay. Although existing ceramic composite diaphragms can partially improve the heat resistance of diaphragms, their practical application still faces technical bottlenecks.

[0003] Based on this, there is an urgent need to develop a new type of diaphragm that can maintain excellent barrier effect at high temperatures, effectively reduce the risk of battery short circuit, and delay the thermal runaway kinetics of the positive electrode material, improve its high-temperature stability, thereby enhancing the overall thermal stability and safety of the battery. Summary of the Invention

[0004] Based on the above problems, the present invention provides a diaphragm and a battery comprising the diaphragm. The functional coating of the diaphragm of the present invention includes first polymer particles, which can delay the thermal runaway kinetic process of the positive electrode material and improve its high-temperature stability; moreover, the functional coating comprising the first polymer particles also includes first heat-resistant particles, and at the same time regulates the number of the first heat-resistant particles per unit area of the functional coating surface, thereby forming uniform heat transfer sites and a complete heat transfer network structure at the interface between the diaphragm and the electrode, preventing the localized accumulation of heat at the interface from causing damage to the diaphragm, thereby improving the thermal stability and thermal safety performance of the battery as a whole.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] The first aspect of the present invention provides a diaphragm, which includes a substrate layer and a functional coating located on one side or both sides of the substrate layer, the functional coating including first polymer particles and first heat-resistant particles, and the number of the first heat-resistant particles is 100-2000 within any 10μm×10μm range on the surface of the functional coating.

[0007] A second aspect of the present invention provides a battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and the separator according to the first aspect of the present invention, wherein the separator is located between the positive electrode sheet and the negative electrode sheet.

[0008] Through the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0009] The diaphragm provided by the present invention has a functional coating comprising first polymer particles disposed on the surface of a substrate layer, forming an intelligent composite diaphragm system with temperature-responsive properties. When the battery is subjected to high-temperature shock, the functional coating can achieve multiple barrier protection effects of the diaphragm through a solid-liquid phase transition process: on the one hand, by actively absorbing the latent heat of the phase change, the thermal runaway dynamics are significantly delayed, the temperature gradient distribution within the battery is improved, and the structural collapse of the positive electrode active material at high temperatures is effectively delayed; on the other hand, the molten polymer can enhance the interface integrity between the electrode and the diaphragm through dynamic filling, ensuring that the diaphragm can still maintain excellent barrier properties under high-temperature conditions. Furthermore, since the first polymer particles themselves have a low thermal conductivity, which may cause localized heat accumulation at the interface between the diaphragm and the electrode, leading to the risk of membrane rupture, the functional coating comprising the first polymer particles also includes first heat-resistant particles. By precisely controlling the distribution of the first heat-resistant particles per unit area of the functional coating, a uniform heat transfer site and a complete heat transfer network structure can be formed at the interface between the diaphragm and the electrode, preventing localized heat accumulation at the interface that could cause diaphragm damage, thereby improving the overall thermal stability and thermal safety performance of the battery.

[0010] Other features and advantages of the present invention will be described in detail in the following detailed description.

[0011] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Shown is a SEM image of the surface of the functional coating provided by one embodiment of the present invention.

[0013] Figure 2 Shown are the SEM image and EDS elemental analysis diagram of the surface of the functional coating provided by one embodiment of the present invention.

[0014] Figure 3 Shown is a schematic structural diagram of the diaphragm provided by the present invention.

[0015] Description of reference numerals:

[0016] The substrate layer 100 , the functional coating layer 200 , the first polymer particles 210 , the first heat-resistant particles 220 , and the polymer adhesive layer 300 . DETAILED DESCRIPTION

[0017] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention. In this article, unless otherwise specified, data ranges include endpoints.

[0018] It should be noted that the numerical expressions such as "first" and "second" in the present disclosure are only used to distinguish different substances or usage methods, and do not represent a difference in order.

[0019] The first aspect of the present invention provides a diaphragm, comprising a substrate layer 100 and a functional coating 200 located on one or both sides of the substrate layer 100, wherein the functional coating 200 comprises first polymer particles 210 and first heat-resistant particles 220, and within any 10 μm×10 μm area on the surface of the functional coating 200, the number of the first heat-resistant particles 220 is 100-2000. In one embodiment, as Figure 3 As shown, the separator includes a substrate layer 100 and a functional coating layer 200 located on one surface of the substrate layer 100 . The functional coating layer 200 includes first polymer particles 210 and first heat-resistant particles 220 .

[0020] The separator of the present invention includes a substrate layer 100 and a functional coating 200 located on one or both surfaces of the substrate layer 100. The functional coating 200 contains both first polymer particles 210 and first heat-resistant particles 220. The surface particle distribution characteristics of the functional coating 200 are as follows: within a 10 μm×10 μm microscopic observation area selected at random on the surface of the functional coating 200, the number of the first heat-resistant particles 220 is 100 to 2000, as determined by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). It should be noted that when the functional coating 200 is located on both sides of the substrate layer 100, the number of first heat-resistant particles on both sides of the functional coating can be the same or different. For example, the number of first heat-resistant particles within a 10 μm×10 μm area selected at random on the surface of the functional coating facing the positive electrode can be greater than, less than, or equal to the number of first heat-resistant particles within a 10 μm×10 μm area selected at random on the surface of the functional coating facing the negative electrode. In addition, specifically, the method for statistically determining the number of first heat-resistant particles within any 10 μm×10 μm range on the surface of the functional coating using a scanning electron microscope (SEM) is as follows: a scanning image of the surface of the diaphragm functional coating is obtained using a scanning electron microscope (SEM) at a magnification of 10,000 times, such as Figure 1As shown, the first polymer particles 210 and the first heat-resistant particles 220 have large morphological differences, and then a region to be tested is selected in the scanned image, such as Figure 2 As shown, the main element composition and distribution of each particle in the test area are scanned by EDS, and the particle category is defined according to the difference in element type (the first polymer particles are enriched in C element, and the first polymer particles are enriched in C element and can be characterized by C element; the first heat-resistant particles can be identified by other characteristic elements other than C element, such as O element, Al element, Mg element, etc.), and then the number of first heat-resistant particles in the functional coating with an area of 10μm×10μm in the test area is counted, the position of the test area is changed, and the above process is repeated 5 times, and the average value of the number is recorded as the final value.

[0021] The diaphragm provided by the present invention has a functional coating layer comprising first polymer particles provided on the surface of the substrate layer. The first polymer particles are temperature-responsive modified polymers, which are conducive to forming an intelligent composite diaphragm system with temperature-responsive characteristics. When the battery encounters high-temperature shock, the functional coating with the first polymer particles triggers a solid-liquid phase change in a high-temperature environment to achieve the synergistic effect of multiple barrier protection technologies: on the one hand, it can significantly delay the thermal runaway kinetic process by actively absorbing latent heat, improve the temperature gradient distribution inside the battery, reduce the heating rate inside the battery, and inhibit the positive electrode active material from releasing oxygen and causing structural collapse at high temperature, thereby effectively delaying the occurrence of thermal runaway and improving the high-temperature stability and safety performance of the battery; on the other hand, the first polymer particles in the functional coating undergo a phase change from solid to liquid by absorbing heat inside the battery. The liquid phase first polymer has a certain fluidity and can dynamically fill between the electrode and the diaphragm, thereby repairing the interface defects between the electrode and the diaphragm, enhancing the interface integrity between the electrode and the diaphragm, and ensuring that the diaphragm can still maintain excellent barrier properties in a high-temperature environment, thereby effectively reducing the risk of battery short circuit. In addition, the liquid phase first polymer can also hinder the transmission of lithium ions, achieving a breakthrough optimization of thermo-electrochemical performance and further improving the thermal stability and thermal safety of the battery.

[0022] Furthermore, although the first polymer particles in the functional coating have an excellent ability to absorb heat from the positive electrode, the low thermal conductivity of the first polymer material itself may cause local accumulation of heat and cause the risk of film rupture. The functional coating of the present invention also contains first heat-resistant particles. The first heat-resistant particles with excellent thermal conductivity effectively alleviate the problem of low thermal conductivity of the first polymer particles, and by regulating the number distribution of the first heat-resistant particles per unit area (10 μm × 10 μm) of the functional coating, the number of the first heat-resistant particles is 100-2000 within any 10 μm × 10 μm range on the surface of the functional coating, for example, 100, 110, 120, 130, 140, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900 or 2000 particles can form uniform heat transfer sites and a complete heat transfer network structure at the interface between the diaphragm and the electrode, so that the heat absorbed by the first polymer particles can be quickly transferred out, preventing local accumulation of heat at the interface from causing film rupture, thereby improving the thermal stability and thermal safety performance of the battery as a whole.

[0023] Specifically, the selection of the number range of the above-mentioned first heat-resistant particles is based on the following technical considerations: when the number density of the first heat-resistant particles is less than 100 particles / (10 μm) 2 When the number density of the first heat-resistant particles exceeds 2000 / (10μm), it is difficult to form a continuous heat transfer network path, resulting in uneven distribution of heat transfer sites and reduced uniformity of heat conduction. 2 When the number of first polymer particles is increased, the distribution space will be compressed, resulting in a decrease in the number of first polymer particles. This will not only affect the barrier performance of the separator, but also lead to a decrease in the performance of the functional coating in absorbing latent heat, which is not conducive to reducing the temperature rise rate and delaying the structural collapse of the positive electrode active material at high temperatures. On the other hand, the number of first heat-resistant particles is larger, and the particles are more likely to agglomerate, which is not conducive to forming a uniform heat transfer site. By strictly limiting the number of particles to this range, a complete and uniform heat transfer network structure can be constructed, thereby effectively improving the local accumulation of heat in the separator, reducing the risk of membrane rupture, and further improving the thermal safety of the battery.

[0024] In summary, the separator provided in the present invention can maintain excellent barrier properties even at high temperatures, effectively reducing the risk of battery short circuits. It can also delay the thermal runaway kinetics of the positive electrode material, inhibiting the collapse of the positive electrode structure, and improving the high-temperature thermal stability and safety of the battery. Based on this, in order to further improve the effect, one or more of the technical features can be further optimized.

[0025] In a specific embodiment, within any 10 μm×10 μm range on the surface of the functional coating, the number of the first heat-resistant particles is 200-1000.

[0026] In a specific embodiment, within any 10μm×10μm range on the surface of the functional coating, the coverage of the first heat-resistant particles is 10%-80%, for example, 10%, 20%, 30%, 40%, 50%, 60%, 70% or 80%. The coverage of the first heat-resistant particles refers to the ratio of the orthographic projection area of the first heat-resistant particles on the surface of the substrate layer to the total surface area of the substrate layer. The orthographic projection area and coverage of the first heat-resistant particles on the surface of the substrate layer can be obtained by the following method: referring to the aforementioned scanning electron microscope (SEM) method for statistically determining the number of first heat-resistant particles within any 10μm×10μm range on the surface of the functional coating of the diaphragm, after distinguishing the types of particles by analyzing the EDS element distribution map, the total projection area of the first heat-resistant particles within any 10μm×10μm range is counted using software, and finally Then calculate the coverage; specifically, divide any 10μm×10μm area on the surface of the diaphragm functional coating into 50×50 uniform squares, and calculate the total number X of squares occupied by the first heat-resistant particles (when the first heat-resistant particles occupy more than or equal to half of the square area, they are regarded as occupied; when the first heat-resistant particles occupy less than half of the square area, they are regarded as unoccupied), then the coverage of the first heat-resistant particles = X / (50×50)×100%, change the selected position of the area to be measured, repeat the above operation 5 times, and take the average value as the coverage of the first heat-resistant particles on the surface of the substrate layer.

[0027] The present invention regulates the number of first heat-resistant particles per unit area of the functional coating, taking into account that the first heat-resistant particles have better thermal conductivity and can alleviate the problem of low thermal conductivity of the first polymer particles; based on this, the present invention further regulates the coverage rate of the first heat-resistant particles per unit area of the functional coating, which can optimize the distribution of the first heat-resistant particles on the surface of the diaphragm functional layer per unit area, and realize dual regulation of quantity and distribution, further improving the integrity and uniformity of the heat transfer network structure, thereby effectively improving the local accumulation of heat in the diaphragm, and helping to further reduce the risk of membrane rupture caused by local heat accumulation.

[0028] In a preferred embodiment, within any 10 μm×10 μm range on the surface of the functional coating, the coverage of the first heat-resistant particles is 15%-55%.

[0029] In one embodiment, the ratio of the average particle size of the first polymer particles to the average particle size of the first heat-resistant particles is 0.1-10, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.

[0030] In another specific embodiment, the ratio of the average particle size of the first polymer particles to the average particle size of the first heat-resistant particles is 0.5-5.

[0031] The selection of the particle size of the first polymer particles and the first heat-resistant particles has a certain adaptability. When the ratio of the average particle size of the first polymer particles to the average particle size of the first heat-resistant particles is within an appropriate range, the dispersion of the first polymer particles and the first heat-resistant particles can be guaranteed to be the best, thereby further improving the uniformity of the heat-conducting network; and when the ratio of the average particle size of the first polymer particles to the average particle size of the first heat-resistant particles is too small, it will cause the first polymer particles to be unevenly distributed and locally relatively aggregated, which is not conducive to constructing a good and uniform heat absorption site, and thus lose the uniformity of the heat absorption network; when the ratio of the average particle size of the first polymer particles to the average particle size of the first heat-resistant particles is too large, it will cause the first heat-resistant particles to be unevenly distributed and the heat-resistant particles to accumulate locally, which will cause the heat transfer network to be incomplete, the risk of local heat accumulation to increase, and the risk of membrane rupture to increase.

[0032] In one specific embodiment, the average particle size n1 of the first polymer is 0.1 μm-3.5 μm.

[0033] In another specific embodiment, the average particle size n1 of the first polymer is 0.2 μm-2 μm.

[0034] In a specific embodiment, the average particle size n1 of the first heat-resistant particles is 0.1 μm-2.5 μm.

[0035] In another specific embodiment, the average particle size n1 of the first heat-resistant particles is 0.2 μm-2 μm.

[0036] The average particle size of the first polymer particles and the average particle size of the first heat-resistant particles can be measured by the following method: Taking the average particle size of the first polymer particles as an example, on a scanned image of the functional coating surface of the separator obtained using a SEM, depict the smallest square or rectangle that completely encloses the area of one first polymer particle. That is, depict a square or rectangle where the edge of the first polymer particle is in contact with the four sides of the square or rectangle. The length of one side of the square or the length of the long side of the rectangle is the particle size of the first polymer particle. In an arbitrarily selected 10μm*10μm area on the functional coating surface, measure the particle sizes of 50 first polymer particles and average the number of these measurements as the average particle size. Repeat this operation three times, and the average value is the average particle size of the first polymer particles. It should be noted that if the number of particles in the captured image is less than 50, multiple images are captured, and the number average of the particle sizes of the total 50 first polymer particles is set as the average particle size. The scanned image can be obtained by observing the surface of the functional coating at a magnification of 10,000 using an electrolytic emission scanning electron microscope (S-3400N, manufactured by Hitachi, Ltd.).

[0037] In one embodiment, the diaphragm satisfies the following relationship: 30%≤(V1 / (V1+V2)) 0.5 *100% < 100%, for example, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 100%, wherein V1 is the average volume of the first polymer particles, and V2 is the average volume of the first heat-resistant particles. By controlling the volume relationship between the two, the stacking of the first polymer particles and the first heat-resistant particles can be effectively improved. The aforementioned regulation of the coverage of the first heat-resistant particles is to improve the distribution of heat transfer sites at the interface between the diaphragm and the positive electrode, and by regulating the volume relationship between the first polymer particles and the first heat-resistant particles, the heat transfer sites in the thickness direction dimension of the functional coating are increased, which is equivalent to improving the uniformity of the heat transfer network from a three-dimensional spatial perspective. Therefore, it is beneficial to further improve the uniformity of the heat transfer network, reduce local heat accumulation, and enhance the thermal safety of the battery.

[0038] In a preferred embodiment, 45%≤(V1 / (V1+V2)) 0.5 *100%≤95%.

[0039] In one embodiment, the volume content of the first polymer particles in the functional coating is 15%-80%, for example, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%. It will be appreciated that if functional coatings are provided on both sides of the substrate layer, the volume content of the first polymer particles in the functional coatings on both sides will fall within this range, but the actual values may be the same or different. In a preferred embodiment, the volume content of the first polymer particles in the functional coating is 50%-75%.

[0040] In one specific embodiment, the volume content of the first heat-resistant particles in the functional coating is 20%-85%, for example, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or 85%. It will be understood that if functional coatings are provided on both sides of the substrate layer, the volume content of the first heat-resistant particles in the functional coatings on both sides will meet this range, but the actual values may be the same or different. In a preferred embodiment, the volume content of the first heat-resistant particles in the functional coating is 25%-50%.

[0041] In the present invention, the average volume V1 of the first polymer particles, the average volume V2 of the first heat-resistant particles, the volume content of the first polymer particles in the functional coating and the volume content of the first heat-resistant particles in the functional coating can be obtained by focused ion beam scanning electron microscopy (FIB-SEM) technology.

[0042] In a specific embodiment, the first polymer particles contain carbon and oxygen, and the first heat-resistant particles contain one or more of the elements O, Al, Mg, Ba, Zn, Ca, Si, P, and Ti.

[0043] In one embodiment, the first polymer particles include a first polymer, the main chain of the first polymer is a saturated alkane, at least some of the carbon atoms on the main chain are connected to a group R, and the group R is *-(CC-R1) x1 -(CC-R2) x2 -(CC-R3) x3 -(CC-R4) x4 -(CC-R5) x5 , x1, x2, x3, x4, x5 are the same or different and are positive integers of 0-10 and x1, x2, x3, x4, x5 are not 0 at the same time, R1, R2, R3, R4, R5 are each independently selected from *-halogen, *-COOH, *-T2COOT1, T1 and T2 are each independently selected from methyl, ethyl, n-propyl, and isopropyl, and * represents a connecting end.

[0044] The main chain of the first polymer can be a saturated alkane, which is a carbon-carbon single bond (-CC-). It is understood that the main chain of the first polymer is a carbon-carbon single bond. At least some (≥1) carbon atoms on the main chain are connected to a group R, and among the carbon atoms on the main chain, at least some (≥1) carbon atoms are connected to a group R. It is understood that the first polymer includes ≥1 (for example, 1, 5, 10, 15, 20, 25, 30, 35 or 40) groups R. When the first polymer includes >1 group R, R1, R2, R3, R4, and R5 in any two groups R may be the same or different, and x1, x2, x3, x4, and x5 in any two groups R may be the same or different.

[0045] The number of hydrogen atoms in the group R is not expressed. The number of hydrogen atoms can be determined based on the specific structure of the group R. However, it should be noted that the carbon atoms in the group R satisfy four single bonds. For example, when x1 is 1, and x2, x3, x4, and x5 are all 0, the group R is *-CH2-CH2-R1; when x1 is 3, x2 is 1, x3 is 5, and x4 and x5 are all 0, the group R is *-(CH2-CH-R1)3-(CH2-CH-R2)-(CH2-CH-R3)4-CH2-CH2-R3.

[0046] R1, R2, R3, .....R5 may be the same or different and are independently selected from *-halogen, *-COOH, *-T2COOT1. * indicates the connection end. There are two connecting ends in the formula, and the two connecting ends are connected to two different adjacent carbon atoms. For example, R1 is Then the group R is

[0047]

[0048] In one embodiment, T1 and T2 are each independently selected from methyl, ethyl, n-propyl, and isopropyl.

[0049] In one embodiment, the halogen is selected from one or more of F, Cl and Br.

[0050] In one embodiment, the number average molecular weight of the first polymer is 1200-7000, for example, 1200, 1500, 2000, 3000, 4000, 5000, 5500, 5900, 6000, 6500 or 7000. The number average molecular weight of the first polymer can be measured by gel permeation chromatography.

[0051] In one embodiment, x1+x2+x3+x4+x5≤40 (e.g., 1, 5, 10, 15, 20, 25, 30, 35, or 40).

[0052] In one embodiment, the first polymer particles do not contain any metal elements.

[0053] In one embodiment, no emulsifier or pH regulator is added during the preparation of the first polymer.

[0054] In a specific embodiment, the pH regulator is one or more of Na2CO3, NaHCO3, MgO, Mg(OH)2, aluminum sulfate, potassium hydrogen phosphate, potassium phosphate dihydrate and calcium phosphate.

[0055] In a specific embodiment, the first polymer particles are composed of polyethylene containing modified groups, wherein the modified groups are carbonyl (*-CO), carboxyl (*-COOH), and ester (*-COO-*).

[0056] The components of the first polymer particles of the present invention include a first polymer, the main chain of the first polymer is a saturated alkane, and at least some of the carbon atoms on the main chain are connected to a group R. Based on the structure of the first polymer, when the battery is in a high temperature state, the first polymer particles including the first polymer melt from a solid state to a liquid state. This process requires the absorption of sufficient heat. At this time, the first polymer particles can slow down the temperature rise rate of the battery by absorbing latent heat, thereby preventing the positive electrode material from releasing oxygen at high temperature and causing structural collapse, delaying the time for thermal runaway to occur, and providing a buffer for the thermal runaway reaction of the battery, thereby improving the thermal stability of the battery under high temperature conditions and enhancing the safety performance of the battery. At the same time, the molten first polymer particles have a certain fluidity. When there is a spacer near the first polymer particles, the first polymer particles can absorb the latent heat and slow down the temperature rise rate of the battery. The membrane is punctured (for example, the diaphragm is punctured by small particles on the surface of the positive electrode), and the interface defects between the diaphragm and the electrode can be dynamically repaired. This dynamic repair effect can reduce the gaps and defects at the interface, reduce the generation of heat, and achieve a breakthrough optimization of the thermo-electrochemical performance; and the groups R in the first polymer are all polar groups, which have strong electronegativity and usually contain lone pairs of electrons in the atomic orbitals, while the metal ions in the positive electrode material contain empty orbitals. The two combine with each other to form a stable coordination bond (taking *-COOH as an example, *-COOH can be at least partially deprotonated in the electrolyte to form a negatively charged carboxylate (-COO-), and the oxygen atom of the carboxylate carries a lone pair of electrons, which can be coordinated with the transition metal ions (such as Ni) on the surface of the positive electrode material through monodentate or bidentate coordination. 3+, Co3+, Mn3+) combine to form a stable metal-carboxylic acid coordination bond). This coordination effect can block the escape path of lattice oxygen in the positive electrode material, inhibit the oxygen release reaction of the positive electrode material at high temperature or high voltage (such as Ni-O bond breakage), cut off the chain reaction that causes thermal runaway of the battery, and further improve the thermal stability of the battery. At the same time, it can also reduce the structural distortion of the positive electrode material during the cycle (such as layered → spinel phase transition), effectively inhibit the structural degradation of the positive electrode material, improve the structural stability of the positive electrode material, and enable the battery to maintain a high energy density. The polar group R in the first polymer can also reduce the surface energy of the polymer particles, thereby enhancing the interfacial interaction between the diaphragm and the electrode. The polar groups R have an electrostatic repulsion effect, which can improve the dispersion stability of the first polymer particles, inhibit agglomeration, achieve monodisperse morphology control, make the thickness of the diaphragm more uniform, improve the consistency of the diaphragm performance, facilitate the transmission of lithium ions, and enhance the cycle stability of the battery.

[0057] In one specific embodiment, the weight content of impurity elements in the first polymer particles is no more than 20 ppm, and the impurity elements include one or more of Al, Cr, Cu, K, Mg, Mn, Ni, Pb, Ca, and Na. The weight content of impurity elements in the first polymer particles is no more than 20 ppm. It is understood that when the impurity elements include one type (e.g., Na), the weight content of the impurity element (Na) in the first polymer particles is no more than 20 ppm; when the impurity elements include multiple types (e.g., Al, Ni, and Pb), the weight content of each element in the first polymer particles is no more than 20 ppm (i.e., the weight content of Al in the first polymer particles is no more than 20 ppm, the weight content of Ni in the first polymer particles is no more than 20 ppm, and the weight content of Pb in the first polymer particles is no more than 20 ppm).

[0058] During the preparation process of the first polymer particles, impurity elements are inevitably introduced. These impurity elements may increase the weight of the battery and affect the heat dissipation performance of the battery. Moreover, these impurity elements are metallic elements and have magnetism under the action of electric current. Magnetic impurities may generate eddy currents inside the battery, causing the battery temperature to rise and affecting the stability of the battery. In addition, certain impurity elements (for example, chromium Cr may form chromium oxide or release chromium vapor at high temperatures; lead Pb may evaporate at high temperatures to form lead vapor; manganese Mn may form manganese oxide or release manganese vapor at high temperatures) may release harmful gases at high temperatures, affecting the safe use of the battery. Therefore, the present invention controls the weight content of impurity elements in the first polymer particles to be no more than 20 ppm (for example, 20 ppm, 18 ppm, 15 ppm, 13 ppm, 10 ppm, 8 ppm, 5 ppm, 3 ppm, 1 ppm, 0.5 ppm, 0.1 ppm or 0), and avoids the introduction of impurity elements as much as possible during the preparation process of the first polymer particles. On the one hand, it can avoid that when the first polymer particles are melted, the impurity elements diffuse along with the liquid first polymer particles to affect the stability of the crystal structure of the positive electrode material, causing the positive electrode material to evolve oxygen and generate heat. On the other hand, it can also avoid the side reaction of impurity elements with the electrolyte at high temperature, producing gas and releasing heat, aggravating the thermal runaway of the battery, and affecting the safety performance of the battery.

[0059] In a specific embodiment, the components of the first heat-resistant particles include one or more of aluminum oxide, boehmite, magnesium oxide, magnesium hydroxide, barium sulfate, barium titanate, zinc oxide, calcium oxide, silicon dioxide, silicon carbide, nickel oxide and lithium aluminum titanium phosphate.

[0060] In a specific embodiment, the functional coating further includes a polymer binder, and the polymer binder includes polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyimide, polyacrylonitrile, polymethyl (meth)acrylate, aramid resin, poly (meth)acrylic acid, styrene-butadiene rubber, polyvinyl alcohol, polyvinyl acetate, carboxymethyl cellulose, sodium carboxymethyl cellulose, carboxyethyl cellulose, polyacrylamide, phenolic resin, epoxy resin, water-based polyurethane, ethylene-vinyl acetate copolymer, polyacrylic copolymer, lithium polystyrene sulfonate, water-based silicone resin, nitrile-polyvinyl chloride blend, styrene acrylic latex, pure styrene latex, etc. and one or more blends and copolymers derived from the aforementioned polymer modifications.

[0061] In one embodiment, the thickness of the functional coating is 0.5 μm-5 μm, for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm.

[0062] In a specific embodiment, the diaphragm further comprises a polymer adhesive layer 300, and the polymer adhesive layer 300 is located on the surface of the substrate layer 100 and / or the surface of the functional coating 200. It is understood that when the functional coating is provided on both sides of the substrate layer, the polymer adhesive layer 300 is located on the surface of the functional coating 200; when the functional coating is provided on one side of the substrate layer, the polymer adhesive layer 300 on one side is located on the surface of the substrate layer 100 and on the surface of the functional coating 200 on the other side, as shown in FIG. Figure 3 shown.

[0063] In one embodiment, the polymer adhesive layer is located on the surface of the substrate layer and the surface of the functional coating layer, such as Figure 3 shown.

[0064] In one embodiment, the polymer adhesive layer is located on the surface of the functional coating.

[0065] According to a specific embodiment, Figure 3 As shown, the diaphragm includes a substrate layer, a functional coating layer and a polymer adhesive layer, wherein the functional coating layer is located on the surface of one side of the substrate layer, and the polymer adhesive layer is located on the surface of the other side of the substrate layer and the surface of the functional coating layer.

[0066] According to a specific embodiment, the diaphragm includes a substrate layer, a functional coating layer and a polymer adhesive layer, wherein the functional coating layer is located on surfaces on both sides of the substrate layer, and the polymer adhesive layer is located on a surface of one of the functional coating layers.

[0067] According to a specific embodiment, the diaphragm includes a substrate layer, a functional coating layer and a polymer adhesive layer. The functional coating layer is located on the surfaces of both sides of the substrate layer, and the polymer adhesive layer is located on the surfaces of the two functional coating layers.

[0068] In a specific embodiment, the polymer adhesive layer includes a second polymer, and the second polymer includes one or more of polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene modified and its copolymers, polyacrylonitrile, polymethyl methacrylate (PMMA), polyacrylic acid, polyvinyl alcohol and its copolymer-modified polyvinyl alcohol, polyvinyl acetate, polyacrylamide, phenolic resin, epoxy resin, ethylene-vinyl acetate copolymer, polyacrylic copolymer, lithium polystyrene sulfonate, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-chlorotrifluoroethylene, polyethylene oxide and cyanoethyl polyvinyl alcohol.

[0069] In one embodiment, the coverage of the polymer adhesive layer is 15%-100%, for example, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%.

[0070] In the present invention, the substrate layer and the functional coating layer can be collectively referred to as a carrier layer, and the polymer adhesive layer can be located on one side or both sides of the carrier layer. The coverage of the polymer adhesive layer refers to the proportion of the positive projection area of the polymer adhesive layer on the surface of the carrier layer to the surface area of the carrier layer. It can be understood that if polymer adhesive layers are provided on both sides of the carrier layer, the coverage of the polymer adhesive layers on both sides meets this range, but the actual values can be the same or different. The positive projection area and coverage of the polymer adhesive layer on the surface of the carrier layer can refer to the test method for the coverage of heat-resistant particles. The coverage range of the polymer adhesive layer must be greater than or equal to 15%. This is because when the coverage of the polymer adhesive layer is less than 15%, effective bonding and good interface contact between the diaphragm and the electrode cannot be guaranteed.

[0071] In a specific embodiment, the coverage P1 of the polymer adhesive layer is 60%<P1≤100%, for example, 61%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%; the polymer adhesive layer also includes second heat-resistant particles, and the weight content of the second heat-resistant particles in the polymer adhesive layer is 10%-80%, for example, 10%, 11%, 12%, 13%, 14%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%. When the coverage of the polymer adhesive layer is high (for example, 60%<P1≤100%), since the thermal conductivity of the second polymer in the polymer adhesive layer is poor, the thermal conductivity of the polymer adhesive layer can be improved by adding the second heat-resistant particles, thereby ensuring that the heat transfer network in the thickness direction of the diaphragm is more uniform; therefore, the coverage of the polymer adhesive layer and the weight content of the second heat-resistant particles in the polymer adhesive layer are controlled within the above range at the same time, which can ensure good contact between the diaphragm and the electrode (including the positive electrode and / or the negative electrode) while also having a good heat transfer effect, thereby avoiding local heat accumulation, improving the thermal stability of the battery, and enhancing the safety performance of the battery.

[0072] In a specific embodiment, the coverage P1 of the polymer adhesive layer is 15%≤P1≤60%, for example, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 59% or 60%, and the polymer adhesive layer does not include second heat-resistant particles. When the coverage of the polymer adhesive layer is low (for example, 15%≤P1≤60%), the thermal conductivity of the polymer adhesive layer will not be affected without adding the second heat-resistant particles, and the adhesion between the polymer adhesive layer and the electrode can also be guaranteed.

[0073] In a specific embodiment, the components of the second heat-resistant particles include one or more of aluminum oxide, boehmite, magnesium oxide, magnesium hydroxide, barium sulfate, barium titanate, zinc oxide, calcium oxide, silicon dioxide, silicon carbide, nickel oxide and lithium aluminum titanium phosphate.

[0074] In one embodiment, the peel force between the polymer adhesive layer and the substrate layer is 10 N / m to 200 N / m, for example, 10 N / m, 20 N / m, 30 N / m, 40 N / m, 50 N / m, 60 N / m, 70 N / m, 80 N / m, 90 N / m, 100 N / m, 110 N / m, 120 N / m, 130 N / m, 140 N / m, 150 N / m, 160 N / m, 170 N / m, 180 N / m, 190 N / m, or 200 N / m. When a functional coating is provided on one side of the substrate layer, the polymer adhesive layer on one side is directly located on the surface of the substrate layer, and the polymer adhesive layer on the other side is located on the surface of the functional coating. In this case, the peel force between the polymer adhesive layer and the substrate layer can represent both the peel force when the polymer adhesive layer is in direct contact with the substrate layer and the peel force between the polymer adhesive layer and the functional coating connected to the substrate layer.

[0075] In one embodiment, the substrate layer comprises a third polymer, and the third polymer comprises one or more of polyethylene, polypropylene, polyimide, polystyrene, polyacrylonitrile, polyethersulfone, polyphenylene sulfide, and polytetrafluoroethylene. The substrate layer may be made of the third polymer.

[0076] In a specific embodiment, the peeling force between the functional coating and the substrate layer is 10N / m-200N / m, for example, 10N / m, 20N / m, 30N / m, 40N / m, 50N / m, 60N / m, 70N / m, 80N / m, 90N / m, 100N / m, 110N / m, 120N / m, 130N / m, 140N / m, 150N / m, 160N / m, 170N / m, 180N / m, 190N / m or 200N / m. The peeling force between the functional coating and the substrate layer can represent the peeling force between a single functional coating and the substrate layer, or can represent the peeling force between the entire "polymer adhesive layer + functional coating" and the substrate layer. When the functional coating is provided on one side of the substrate layer, the polymer adhesive layer on the other side is directly located on the surface of the substrate layer. At this time, the peeling force between the functional coating and the substrate layer represents the peeling force when the single functional coating is in direct contact with the substrate layer. When functional coatings are provided on both sides of the substrate layer, the polymer adhesive layer is located on the surface of the functional coating. At this time, the peeling force between the functional coating and the substrate layer can refer to the peeling force between a single functional coating and the substrate layer, or the peeling force between the entire "polymer adhesive layer + functional coating" and the substrate layer.

[0077] The peel force between the polymer adhesive layer and the substrate layer is measured as follows: Cut a 200mm long and 20mm wide membrane strip and secure it to a steel plate with double-sided tape. Apply 15mm wide 3M tape to the membrane surface and apply it once with a 2kg roller. Using a universal tensile testing machine, with the upper clamp holding the tape and the lower clamp holding the steel plate, perform a 180°C peel test at a test speed of 100mm / min and a test displacement of 100mm. Repeat the test 3-5 times and take the average value to determine the peel force between the polymer adhesive layer and the substrate layer. The peel force between the functional coating and the substrate layer can be measured using the same method described above, performing a 180°C peel test on the side of the substrate layer with the functional coating.

[0078] In one embodiment, the thickness of the substrate layer is 3 μm-16 μm, for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or 16 μm.

[0079] A second aspect of the present invention provides a battery, comprising a positive electrode sheet, a negative electrode sheet, and the separator according to the first aspect of the present invention, wherein the separator is located between the positive electrode sheet and the negative electrode sheet.

[0080] In a specific embodiment, the bonding force between the diaphragm and the positive electrode sheet is 2N / m-50N / m, for example, 2N / m, 4N / m, 6N / m, 8N / m, 10N / m, 12N / m, 14N / m, 16N / m, 18N / m, 20N / m, 22N / m, 24N / m, 26N / m, 28N / m, 30N / m, 32N / m, 34N / m, 36N / m, 38N / m, 40N / m, 42N / m, 44N / m, 46N / m, 48N / m or 50N / m.

[0081] In the present invention, the bonding strength between the diaphragm and the positive electrode sheet can be tested by the following method: disassembling the battery cell to obtain a sample in which the positive electrode sheet and the diaphragm are bonded together, and cutting the above sample with a size of 100 mm in length and 15 mm in width; fixing the diaphragm and the positive electrode sheet in the above sample on the upper clamp and the lower clamp of the universal tensile testing machine respectively; then peeling the above sample 180°, the test speed is 100 mm / min, the test displacement distance is 100 mm, the experiment is repeated 5 times and the average value is taken as the bonding strength between the diaphragm and the positive electrode sheet.

[0082] In one example, the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer located on one or both sides of the positive electrode current collector, the positive electrode active layer includes a positive electrode material, and the positive electrode material includes a lithium cobalt oxide material and / or a nickel-cobalt-manganese ternary material.

[0083] In one example, based on the total weight of the positive electrode active layer, the weight content of the positive electrode material is 94.6%-98.5% (e.g., 94.6%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98% or 98.5%).

[0084] In one example, based on the total weight of the positive electrode active layer, the weight content of the positive electrode material is 95.6%-98.1%.

[0085] In one example, the positive electrode active layer further includes a positive electrode conductor and a positive electrode binder.

[0086] In one example, the positive electrode conductive agent includes one or more of conductive carbon black (Super P), carbon nanotubes, conductive graphite, and graphene.

[0087] In one example, the positive electrode binder includes one or more of polyvinylidene fluoride (PVDF), acrylic acid-modified PVDF, polyacrylate polymers, polyimide, styrene-butadiene rubber, and styrene-acrylic rubber.

[0088] In one example, based on the total weight of the positive electrode active layer, the weight content of the positive electrode conductor is 1.1%-2.5% (for example, 1.1%, 1.3%, 1.5%, 1.8%, 2%, 2.3% or 2.5%), and the weight content of the positive electrode binder is in the range of 0.4%-2.9% (for example, 0.4%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5% or 2.9%).

[0089] In one example, based on the total weight of the positive electrode active layer, the weight content of the positive electrode conductor is 1.3%-2.3%, and the weight content of the positive electrode binder is 0.6%-2.1%.

[0090] In the present invention, the negative electrode sheet may be a conventional negative electrode sheet in the art, for example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer located on one side or both sides of the negative electrode current collector.

[0091] In one example, the battery further includes an electrolyte.

[0092] In one embodiment, the separator includes a substrate layer and a functional coating located on one surface of the substrate layer, the functional coating is located on the side of the separator close to the positive electrode sheet, the functional coating includes first polymer particles and first heat-resistant particles, and the number of the first heat-resistant particles is 200-1000 within any 10 μm×10 μm range on the surface of the functional coating. The electrolyte includes a cyclic carbonate and a linear carbonate, and the weight ratio of the linear carbonate to the cyclic carbonate satisfies 0.2-1 (for example, 0.2, 0.25, 0.3, 0.31, 0.32, 0.33, 0.34, 0.35 , 0.36, 0.37, 0.38, 0.39, 0.4, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9 or 1); based on the total weight of the electrolyte, the weight content of the cyclic carbonate is 5%-25% (for example, 5%, 10%, 15%, 20% or 25%), and the weight content of the linear carbonate is 5%-20% (for example, 5%, 10%, 15% or 20%).

[0093] In one example, the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, and butylene carbonate, and the linear carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and methylpropyl carbonate.

[0094] In one example, the weight ratio of the linear carbonate to the cyclic carbonate satisfies 0.3-0.7.

[0095] Cyclic carbonate solvents have a swelling effect on the first polymer particles with polar groups. This is because cyclic carbonate solvents have high polarity and strong solubility, are compatible with the first polymer with polar groups, and can penetrate into the interior of the first polymer particles, causing the first polymer particles to swell. When the first polymer particles swell, their particle size increases, which helps to reduce the distance between the polar groups on the surface of the first polymer particles and the surface of the positive electrode active particles, thereby preventing oxygen evolution of the positive electrode active particles and improving the uniformity of the interfacial heat transfer between the separator and the positive electrode. However, when the first polymer particles swell too much, the free space of the electrolyte will be too small, resulting in uneven electrolyte distribution, resulting in localized liquid depletion in the pores of the active particles and reduced uniformity of the interfacial heat transfer between the separator and the positive electrode. When the first polymer particles swell too little, the distance between the polar groups on the surface of the first polymer particles and the positive electrode particles will increase, which is not conducive to the coordination of the polar groups on the surface of the first polymer particles with the positive electrode active particles. Therefore, it is necessary to properly control the swelling degree of the first polymer particles. Linear carbonates will not swell the first polymer particles with polar groups, and their viscosity is low and their fluidity is good, which can increase the fluidity between the diaphragm and the positive electrode. Therefore, when the weight content ratio of cyclic carbonates and linear carbonates in the electrolyte is adjusted to meet the aforementioned range, the first polymer particles can maintain appropriate swelling, which can improve the electrolyte content and fluidity between the diaphragm and the positive electrode, and is beneficial to the coordination effect between the polar groups and the positive electrode active particles at high temperatures, preventing oxygen evolution of the positive electrode active particles, and further improving the uniformity of interfacial heat transfer between the diaphragm and the positive electrode, preventing heat accumulation from causing membrane rupture, so that the battery has both higher safety performance and higher cycle performance.

[0096] In one embodiment, the battery is a lithium-ion secondary battery.

[0097] The present invention will be described in detail below through examples. The examples described in the present invention are only some examples of the present invention, not all examples. All other examples obtained by persons of ordinary skill in the art based on the examples of the present invention without creative work are within the scope of protection of the present invention.

[0098] Example 1

[0099] (1) Preparation of positive electrode sheet

[0100] Lithium cobalt oxide, binder polyvinylidene fluoride (PVDF 500), and conductive carbon material (Super P: carbon nanotubes = 2:1) were mixed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 97.5:2:2.5. A blender was used to continuously stir the mixture into a uniform, fluid cathode slurry. The slurry was then coated onto aluminum foil and dried in a 120°C vacuum oven for 6 hours. The resulting cathode sheets were then rolled and slit.

[0101] (2) Preparation of negative electrode sheet

[0102] Graphite, silicon carbon, conductive carbon black (Super P), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber are mixed in a water solvent at a weight ratio of 91:7:1:0.5:0.5. A blender is used to continuously stir the mixture into a uniform, fluid negative electrode slurry. The slurry is then coated on copper foil and dried in a 120°C vacuum oven for 6 hours. The resulting negative electrode sheets are then rolled and slit.

[0103] (3) Preparation of electrolyte

[0104] In an argon-filled glove box (moisture <1ppm, oxygen <1ppm), ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate were mixed in a mass ratio of 10:10:10:70 to form a uniform solvent (the weight ratio of linear carbonate to cyclic carbonate was 0.5). 15.5wt% LiPF6, 2wt% 1,3-propane sultone, 3wt% 1,3,6-hexanetrinitrile, and 10wt% fluoroethylene carbonate were slowly added. After stirring, the desired lithium-ion battery electrolyte was obtained.

[0105] (4) Preparation of diaphragm

[0106] 30 parts of first polymer particles (R1 in the group R on the first polymer main chain of the first polymer particles is *-COOH, R3 is *-CH2CH2COOCH3, R5 is *-COOH, and the number average molecular weight of the first polymer is 3555), 68 parts of first heat-resistant particles of aluminum oxide, 1 part of polymethyl methacrylate and 1 part of polyethylene glycol are added to 860 parts of distilled water, and mixed evenly to obtain a mixed slurry 1. The mixed slurry 1 is coated on one side surface of the diaphragm base layer (polyethylene base film, thickness of 5 μm) by micro-gravure, and dried in a multi-section oven at 60°C to obtain a diaphragm with a mixed coating of first heat-resistant particles and first polymer particles with a thickness of 2 μm.

[0107] 10 parts by weight of polymethyl methacrylate (PMMA) and 90 parts by weight of deionized water were mixed, stirred and dissolved thoroughly, and then stirred and dispersed uniformly to obtain a mixed slurry 2 with a solid content of 10%. The mixed slurry 2 was coated on both sides of the above-mentioned diaphragm by a gravure roller, and dried in a multi-section oven at 60°C to form a polymer adhesive layer. The thickness of the single-sided polymer adhesive layer was 2 μm, and the coverage of the polymer adhesive layer was 40%. The structural diagram of the formed diaphragm is shown as follows: Figure 3 shown.

[0108] (5) Preparation of lithium-ion batteries

[0109] The positive electrode sheet, separator, and negative electrode sheet prepared above are wound to prepare a bare battery cell, wherein the first heat-resistant particles and the first polymer particles mixed coating of the separator are arranged on the positive electrode sheet side; then the bare battery cell is placed in an aluminum-plastic film (as shown in Table 1), and the prepared electrolyte is injected into the dried bare battery cell. After vacuum packaging, room temperature standing, high-temperature formation and other processes, the desired lithium-ion battery is obtained.

[0110] Example 2 group

[0111] The preparation method of the lithium-ion battery in this embodiment refers to Example 1, with the only difference being that the number of first heat-resistant particles and the coverage of the first heat-resistant particles within any 10 μm×10 μm range on the surface of the functional coating are changed, as shown in Table 1.

[0112] Example 3 group

[0113] The preparation method of the lithium-ion battery in this embodiment refers to Example 1, with the only difference being that the average volume V1 of the first polymer particles and the average volume V2 of the first heat-resistant particles are changed, as shown in Table 1.

[0114] Example 4 Group

[0115] The preparation method of the lithium-ion battery in this embodiment refers to that in Example 1, the only difference is that the coverage of the polymer glue layer and the specific composition of the polymer glue layer are changed, as shown in Table 1.

[0116] Example 5 group

[0117] The preparation method of the lithium ion battery in this embodiment refers to Example 1, with the only difference being that the specific selection of the first polymer in the first polymer particles is changed, specifically:

[0118] In Example 5-1, in the first polymer particles, R1 of the groups R on the first polymer main chain is *-COOH, R3 is *-COOH, and R5 is *-CH2CH2COOCH3, and the number average molecular weight is 3602;

[0119] In Example 5-2, in the first polymer particles, R1 of the groups R on the first polymer main chain is *-CH2CH2COOCH3, R4 is *-COOH, and the number average molecular weight is 3588;

[0120] The details are shown in Table 1.

[0121] Example 6

[0122] The preparation method of the lithium-ion battery in this embodiment refers to that in Example 1, with the only difference being the composition of the electrolyte during the preparation of the electrolyte, specifically:

[0123] Example 6-1, electrolyte composition: Ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate solvents were mixed at a ratio of 15:10:5:70 to form a uniform solvent (the weight ratio of linear carbonate to cyclic carbonate was 0.2);

[0124] Example 6-2, electrolyte composition: Ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate solvents were mixed at a ratio of 10:10:20:60 to form a uniform solvent (the weight ratio of the linear carbonate to the cyclic carbonate was 1);

[0125] Example 6-3, electrolyte composition: ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate solvents were mixed at a ratio of 20:20:5:55 to form a uniform solvent (the weight ratio of linear carbonate to cyclic carbonate was 0.125);

[0126] Example 6-4, electrolyte composition: ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate solvents were mixed at a ratio of 5:5:15:75 to form a uniform solvent (the weight ratio of linear carbonate to cyclic carbonate was 1.5);

[0127] Example 6-5, composition of the electrolyte: ethylene carbonate, propylene carbonate, propyl propionate, and ethyl propionate solvents are mixed in a mass ratio of 15:15:50:20 to form a uniform solvent (excluding linear carbonate).

[0128] Comparative Example 1

[0129] The preparation method of the lithium-ion battery in this comparative example refers to Example 1, with the only difference being that the number of the first heat-resistant particles and the coverage of the first heat-resistant particles within any 10 μm×10 μm range on the surface of the functional coating are changed, as specifically shown in Table 1.

[0130] Table 1

[0131]

[0132] Table 2

[0133]

[0134]

[0135] Test Method

[0136] (1) Furnace temperature test

[0137] The fully charged cells obtained after charging and discharging the lithium-ion batteries prepared in the above embodiments and comparative examples were placed in an oven and heated at 5°C / min. The batteries to be tested in each embodiment and comparative example were divided into three groups. The three groups were heated to different temperatures (130°C / 132°C / 135°C) and kept warm for 1 hour. The pass rate of the batteries in each group that passed the oven temperature test was obtained. The judgment standard for a single battery to pass the oven temperature test was: the battery cell was considered to have passed if it did not catch fire or explode. The oven temperature test pass rate of each group of batteries was calculated as follows: the number of passed batteries / the total number of test batteries. The total number of test batteries in each group of embodiments and comparative examples was 10 pcs. The test results are recorded in Table 3.

[0138] (2) 25℃ discharge temperature rise test

[0139] The test temperature was 25°C ± 2°C. The lithium ion batteries prepared in the above examples and comparative examples were charged at a constant current of 1C to the upper limit voltage (4.5V), then charged at a constant voltage of 4.5V to 0.05C, and allowed to stand for 30 minutes. Then, they were discharged at a constant current of 9C to 3V, and allowed to stand for 5 minutes. The surface temperature of the battery cell was monitored, and the highest surface temperature of the battery cell during the discharge process was taken as the temperature rise temperature (°C) at the discharge rate. The test results of the lithium ion batteries prepared in each group of examples and comparative examples are recorded in Table 3.

[0140] Table 3

[0141]

[0142] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A diaphragm, characterized in that: The diaphragm includes a substrate layer and a functional coating located on one or both sides of the substrate layer. The functional coating includes first polymer particles and first heat-resistant particles. Within any 10μm×10μm range on the surface of the functional coating, the number of the first heat-resistant particles is 100-2000.

2. The diaphragm according to claim 1, wherein In any 10 μm×10 μm range on the surface of the functional coating, the number of the first heat-resistant particles is 200-1000; and / or, within any 10 μm×10 μm range on the surface of the functional coating, the coverage of the first heat-resistant particles is 10%-80%; and / or, the ratio of the average particle size of the first polymer particles to the average particle size of the first heat-resistant particles is 0.1-10, preferably 0.5-5; And / or, the diaphragm satisfies the following relationship: 30%≤(V1 / (V1+V2)) 0.5 *100%<100%, wherein V1 is the average volume of the first polymer particles, and V2 is the average volume of the first heat-resistant particles; and / or, the volume content of the first polymer particles in the functional coating is 15%-80%, preferably 50%-75%; And / or, the volume content of the first heat-resistant particles in the functional coating is 20%-85%, preferably 25%-50%.

3. The diaphragm according to claim 1, wherein The components of the first polymer particles include a first polymer, the main chain of the first polymer is a saturated alkane, at least some of the carbon atoms on the main chain are connected to a group R, and the group R is *-(CC-R1) x1 -(CC-R2) x2 -(CC-R3) x3 -(CC-R4) x4 -(CC-R5) x5 , x1, x2, x3, x4, x5 are the same or different and are positive integers of 0-10 and x1, x2, x3, x4, x5 are not 0 at the same time, R1, R2, R3, R4, R5 are each independently selected from *-halogen, *-COOH, *-T2COOT1, T1 and T2 are each independently selected from methyl, ethyl, n-propyl, and isopropyl, and * represents a connecting end. The diaphragm according to claim 3 , wherein: Halogen is selected from one or more of F, Cl and Br; and / or, the number average molecular weight of the first polymer is 1200-7000; And / or, x1+x2+x3+x4+x5≤40.

5. The diaphragm according to any one of claims 1 to 4, wherein The diaphragm further comprises a polymer adhesive layer, which is located on the surface of the substrate layer and / or the surface of the functional coating layer, and the coverage of the polymer adhesive layer is 15%-100%; Preferably, the peeling force between the polymer adhesive layer and the substrate layer is 10 N / m-200 N / m; Preferably, the polymer adhesive layer includes a second polymer, and the second polymer includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene modified and its copolymers, polyacrylonitrile, polymethyl methacrylate, polyacrylic acid, polyvinyl alcohol and its copolymer-modified polyvinyl alcohol, polyvinyl acetate, polyacrylamide, phenolic resin, epoxy resin, ethylene-vinyl acetate copolymer, polyacrylic copolymer, lithium polystyrene sulfonate, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-chlorotrifluoroethylene, polyethylene oxide and cyanoethyl polyvinyl alcohol. The diaphragm according to claim 5 , wherein: The coverage rate P1 of the polymer adhesive layer is 60%<P1≤100%, and the polymer adhesive layer further includes second heat-resistant particles, and the weight content of the second heat-resistant particles in the polymer adhesive layer is 10%-80%; And / or, the coverage rate P1 of the polymer adhesive layer is 15%≤P1≤60%.

7. The diaphragm according to any one of claims 1 to 4, wherein: The composition of the first heat-resistant particles includes one or more of aluminum oxide, boehmite, magnesium oxide, magnesium hydroxide, barium sulfate, barium titanate, zinc oxide, calcium oxide, silicon dioxide, silicon carbide, nickel oxide and lithium aluminum titanium phosphate; And / or, the functional coating further comprises a polymer binder, wherein the polymer binder comprises polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyimide, polyacrylonitrile, polymethyl (meth)acrylate, aramid resin, poly (meth)acrylic acid, styrene-butadiene rubber, polyvinyl alcohol, polyvinyl acetate, carboxymethyl cellulose, sodium carboxymethyl cellulose, carboxyethyl cellulose, polyacrylamide, phenolic resin, epoxy resin, water-based polyurethane, ethylene-vinyl acetate copolymer, polyacrylic copolymer, lithium polystyrene sulfonate, water-based silicone resin, nitrile-polyvinyl chloride blend, styrene-acrylic latex, pure styrene latex, and one or more blends and copolymers derived from the aforementioned polymer modifications; And / or, the component of the substrate layer includes a third polymer, and the third polymer includes one or more of polyethylene, polypropylene, polyimide, polystyrene, polyacrylonitrile, polyethersulfone, polyphenylene sulfide and polytetrafluoroethylene; and / or, the peeling force between the functional coating and the substrate layer is 10 N / m-200 N / m; And / or, the thickness of the functional coating is 0.5 μm-5 μm; And / or, the thickness of the substrate layer is 3 μm-16 μm.

8. A battery, characterized in that: The battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and the separator according to any one of claims 1 to 7, wherein the separator is located between the positive electrode sheet and the negative electrode sheet.

9. The battery according to claim 8, wherein The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer located on one side or both sides of the positive electrode current collector, wherein the positive electrode active layer includes a positive electrode material, and the positive electrode material includes a lithium cobalt oxide material and / or a nickel-cobalt-manganese ternary material; And / or, the bonding force between the separator and the positive electrode sheet is 2N / m-50N / m.

10. The battery according to claim 8, wherein The separator includes a substrate layer and a functional coating located on one surface of the substrate layer, the functional coating being located on the side of the separator close to the positive electrode sheet, the functional coating including the first polymer particles and the first heat-resistant particles, the number of the first heat-resistant particles being 200-1000 within any 10 μm×10 μm range on the surface of the functional coating, and the electrolyte including cyclic carbonate and linear carbonate; Based on the total weight of the electrolyte, the weight ratio of the linear carbonate to the cyclic carbonate satisfies 0.2-1, the weight content of the cyclic carbonate is 5%-25%, and the weight content of the linear carbonate is 5%-20%.

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