Composite diaphragm and preparation method thereof, secondary battery and electric equipment

Abstract

The invention relates to the technical field of batteries, in particular to a composite diaphragm and a preparation method thereof, a secondary battery and electric equipment. The composite diaphragm comprises a substrate and porous bonding layers, wherein an organic heat-resistant layer is arranged between the substrate and at least one porous bonding layer; the porous bonding layer comprises organic particles and a first bonding polymer; the organic heat-resistant layer comprises organic particles and a second bonding polymer; the organic particles comprise at least one organic compound containing an aromatic ring or an aromatic heterocyclic ring, and the organic compound contains at least one atom of nitrogen, oxygen, fluorine, chlorine, sulfur and phosphorus or a group thereof. Organic particles with high heat resistance are added, so that the thermal safety and the cycle performance of the battery can be improved, transition metal ions and side reaction products generated in the cycle process of the battery can be complexed, and an SEI film is protected; the organic heat-resistant layer can obviously improve the temperature resistance and the safety performance of the composite diaphragm; and the porous bonding layer can enable the composite diaphragm to be fully attached to the pole piece, and can maintain the stability of the organic heat-resistant layer.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a composite separator and its preparation method, a secondary battery, and an electrical device. Background Technology

[0002] Safety is the primary prerequisite for battery development. As one of the four major components of a battery, the separator plays a crucial role in battery safety. To improve battery safety, existing technologies employ inorganic particles and polymers to form a coating on the substrate surface, thereby improving the substrate's heat resistance and enhancing the safety of the separator in battery applications.

[0003] However, as inert particles, inorganic particles cannot suppress dynamic side reactions during battery cycling. Furthermore, the coating formed by the accumulation of inorganic particles increases the separator thickness, prolongs the lithium-ion migration channels, increases the battery's internal resistance, and results in poor cycle performance. With the development of high-energy-density and high-voltage battery systems, the contribution of inorganic particles as inert materials can no longer meet the demands.

[0004] In view of the above, this application is hereby submitted. Summary of the Invention

[0005] The primary objective of this application is to provide a composite separator that, by adding organic particles to a porous adhesive layer and an organic heat-resistant layer, can stabilize the crystal structure of the positive electrode material, improve the stability of both the positive and negative electrodes, and enhance the thermal safety and cycle performance of the battery. Furthermore, the organic particles can effectively complex transition metal ions and by-reaction products generated during battery cycling through coordination bonds, thus protecting the SEI film. By setting an organic heat-resistant layer, the temperature resistance and safety performance of the composite separator can be significantly improved. By setting a porous adhesive layer, not only can it provide adhesive force to ensure full adhesion between the composite separator and the electrode, but it can also maintain the stability of the organic heat-resistant layer as a surface layer.

[0006] The second objective of this application is to provide a method for preparing a composite diaphragm.

[0007] A third objective of this application is to provide a secondary battery.

[0008] The fourth objective of this application is to provide an electrical appliance.

[0009] In order to achieve the above-mentioned objectives of this application, the following technical solution is adopted: The present invention first provides a composite membrane, comprising a substrate and a porous adhesive layer disposed on one or both sides of the substrate, wherein an organic heat-resistant layer is further disposed between the substrate and at least one layer of the porous adhesive layer; wherein the porous adhesive layer comprises organic particles and a first adhesive polymer; the organic heat-resistant layer comprises organic particles and a second adhesive polymer; the organic particles comprise at least one organic compound containing an aromatic ring or aromatic heterocyclic structure, and the organic compound contains at least one atom or group thereof selected from nitrogen, oxygen, fluorine, chlorine, sulfur and phosphorus.

[0010] Furthermore, the wavelength H of the ultraviolet-visible absorption peak of the organic particles satisfies: 180nm≤H≤350nm.

[0011] Further, the organic particles include at least one of aromatic polyimide, fluorinated polyimide, polyetheretherketone, polybenzoxazole, sulfonated polyetheretherketone, polyphenylene sulfide sulfone, polyethersulfone, polyaryletheretherketone, polybenzobisoxazole, polyethylene chloride terephthalate, tetrachlorobisphenol A polyarylether ester, polychlorobenzoxazole ester, polybenzodithiophene sulfone, melamine cyanurate, polybenzimidazole imide, melamine-pyromellitic acid, melamine phosphate, melamine borate, melamine oxalate, melamine phthalate, melamine-naphthalenetetracarboxylic acid, and PEI / PET core-shell microspheres.

[0012] Furthermore, the median volumetric particle size of the organic particles is 0.01~2μm.

[0013] Furthermore, the organic particles include a first organic particle with a median volume diameter of D1 and a second organic particle with a median volume diameter of D2, wherein D1 is not equal to D2.

[0014] Further, the first bonding polymer includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, acrylonitrile-acrylate copolymer, acrylic acid-acrylate copolymer, styrene-acrylate copolymer, polyaramid, polyimide, polyamide-imide, polyetherimide, polyphenylene sulfide, polyethersulfone, and polyarylsulfone.

[0015] Furthermore, the first bonding polymer includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, acrylonitrile-acrylate copolymer, polyaramid, and polyimide.

[0016] Furthermore, the second adhesive polymer contains at least one functional group selected from carboxyl, hydroxyl, amide, primary amine, secondary amine, cyano, isocyanoacrylate, and acrylate, and the glass transition temperature T of the second adhesive polymer is... g Greater than 120℃.

[0017] Further, the second adhesive polymer includes at least one of polyacrylamide, polyacrylic acid, polymethacrylic acid, ethylene-acrylic acid copolymer, polymethyl methacrylate, polybutyl methacrylate, polyacrylonitrile, polyvinyl alcohol, and polypropylene glycol.

[0018] Furthermore, the organic heat-resistant layer also contains additives.

[0019] Furthermore, the additive includes at least one of sodium polyacrylate, polyacrylamide, polyether-modified siloxane, isopropanolamine, alkynyl alcohol, fatty alcohol polyoxyethylene ether, polyester-modified siloxane, alkynyl glycol ether, ethanol, and isopropanol.

[0020] Furthermore, the mass ratio of the organic particles in the organic heat-resistant layer to the second adhesive polymer is 99:1 to 80:20.

[0021] Furthermore, the thickness of the organic heat-resistant layer is 0.5~4μm.

[0022] Furthermore, the ratio of the basis weight m to the thickness h of the organic heat-resistant layer is 0.4~1.2, where m is in g / m. 2 The unit of h is μm.

[0023] Furthermore, the basis weight of the organic heat-resistant layer is 0.5~4 g / m³. 2 .

[0024] Furthermore, the mass ratio of organic particles in the porous adhesive layer to the first adhesive polymer is 10:90 to 70:30.

[0025] Furthermore, the thickness of the porous adhesive layer is 0.2~6μm.

[0026] Furthermore, the basis weight of the porous adhesive layer is 0.3~3 g / m³. 2 .

[0027] Furthermore, the mass ratio of the organic heat-resistant layer to the porous adhesive layer is 0.5~5:1.

[0028] Furthermore, the substrate comprises a polyolefin substrate.

[0029] Furthermore, the needle penetration strength of the polyolefin substrate is greater than 300 gf.

[0030] Furthermore, the needle penetration strength of the polyolefin substrate is greater than 500 gf.

[0031] Furthermore, the longitudinal shrinkage rate (MD) of the composite diaphragm at 130℃ / h is 1%~15%.

[0032] Furthermore, the lateral shrinkage rate (TD) of the composite diaphragm at 130℃ / h is 1%~15%.

[0033] Furthermore, the peel force between the organic heat-resistant layer and the porous adhesive layer is 5~80 N / m.

[0034] The present invention further provides a method for preparing the above-mentioned composite membrane, comprising the following steps: coating a first slurry containing organic particles and a second binder polymer onto at least one surface of a substrate, and drying it to form an organic heat-resistant layer; coating a second slurry containing organic particles and a first binder polymer onto the surface of the organic heat-resistant layer and / or the substrate, and drying it to form a porous binder layer, thereby obtaining a composite membrane.

[0035] The present invention also provides a secondary battery comprising the above-mentioned composite separator.

[0036] Furthermore, the secondary battery also includes a positive electrode, a negative electrode, and an electrolyte.

[0037] Furthermore, the positive electrode and / or the negative electrode contain the organic particles.

[0038] The present invention also provides an electrical device comprising the aforementioned secondary battery.

[0039] Compared with the prior art, the beneficial effects of this application are as follows: (1) The composite separator provided in this application can stabilize the crystal structure of the positive electrode material, improve the stability of the positive and negative electrodes, and improve the thermal safety and cycle performance of the battery by adding organic particles to the porous adhesive layer and the organic heat-resistant layer. The organic particles can effectively complex the transition metal ions and by-reaction products generated during battery cycling through coordination bonds, thus protecting the SEI film. By setting the organic heat-resistant layer, the temperature resistance and safety performance of the composite separator can be significantly improved. By setting the porous adhesive layer, not only can it provide adhesive force to fully bond the composite separator with the electrode, but it can also maintain the stability of the organic heat-resistant layer as a surface layer.

[0040] (2) The composite separator provided in this application can prevent the spread of fire when the battery is punctured by external force, side reaction, short circuit, etc., and the inert gas generated by the decomposition of organic particles can prevent the spread of fire. The carbonyl group can promote dehydration and cyclization reaction, forming a dense carbon layer to isolate oxygen and heat. It can also quench the free radicals of the combustion chain reaction and delay the spread of flame.

[0041] (3) The composite separator provided in this application uses organic particles that are lighter than inorganic particles in the same volume. Compared with inorganic particles, the weight of the coating can be reduced, which reduces the burden on the battery and achieves the lightweighting of the separator. This is beneficial to the application and development of batteries in the high energy density low-altitude economic field. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0043] Figure 1 A schematic diagram of the first structure of the composite diaphragm provided in this application; Figure 2 A schematic diagram of a second structure of the composite diaphragm provided in this application; Figure 3 A schematic diagram of a third structure of the composite diaphragm provided in this application; Figure 4 The UV-Vis absorption spectrum of polyethersulfone provided in this application; Figure 5 The UV-Vis absorption spectrum of melamine cyanurate provided in this application. Detailed Implementation

[0044] The technical solution of this application will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are only some embodiments of this application, not all embodiments, and are only used to illustrate this application, and should not be regarded as limiting the scope of this application. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0045] Unless otherwise specified, in this application, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0046] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0047] Unless otherwise specified, in this application, "one or more" or "at least one" refers to any one, two, or more of the listed items. "Several" refers to any two or more.

[0048] In a first aspect, this application provides a composite membrane, which includes a substrate and a porous adhesive layer disposed on one or both sides of the substrate, and an organic heat-resistant layer is further disposed between the substrate and at least one porous adhesive layer.

[0049] That is, the composite membrane includes at least one organic heat-resistant layer and at least one porous adhesive layer. The porous adhesive layer can be directly disposed on the surface of the substrate or disposed on the surface of the organic heat-resistant layer (in which case the organic heat-resistant layer is disposed between the substrate and the porous adhesive layer).

[0050] Specifically, see Figure 1 The diagram shown is a schematic diagram of the first type of composite membrane structure. It can be seen that the composite membrane includes an organic heat-resistant layer and a porous adhesive layer. The organic heat-resistant layer is disposed between the substrate and the porous adhesive layer. That is, the composite membrane includes a substrate, an organic heat-resistant layer and a porous adhesive layer stacked in sequence.

[0051] See Figure 2 The diagram shown is a schematic diagram of the second structure of the composite membrane. It can be seen that the composite membrane includes two organic heat-resistant layers and two porous adhesive layers. The two organic heat-resistant layers are respectively disposed between the substrate and the two porous adhesive layers. That is, the composite membrane includes a porous adhesive layer, an organic heat-resistant layer, a substrate, an organic heat-resistant layer and a porous adhesive layer stacked in sequence.

[0052] See Figure 3 The diagram shown illustrates a third type of composite membrane structure. It can be seen that the composite membrane includes one organic heat-resistant layer and two porous adhesive layers. The organic heat-resistant layer is disposed between the substrate and the porous adhesive layer, and the porous adhesive layer is directly disposed on the surface of the substrate on the side furthest from the organic heat-resistant layer. In other words, the composite membrane comprises a porous adhesive layer, a substrate, an organic heat-resistant layer, and a porous adhesive layer stacked sequentially.

[0053] The porous adhesive layer contains organic particles and a first adhesive polymer.

[0054] The organic heat-resistant layer contains organic particles and a second bonding polymer.

[0055] The organic particles in the porous adhesive layer and the organic particles in the organic heat-resistant layer can be of the same or different types.

[0056] Organic particles include at least one organic compound containing an aromatic ring or aromatic heterocyclic structure, and the organic compound contains at least one atom or group selected from nitrogen, oxygen, fluorine, chlorine, sulfur and phosphorus.

[0057] The organic particles used in this application possess high heat resistance, ensuring the stability of the composite separator at high temperatures. Specifically, the aromatic ring units, aromatic heterocyclic units, conjugated structures formed by heteroatoms, or π-electron structures abundant in the organic particles can, on the one hand, stabilize the crystal structure of the cathode material, suppress irreversible structural phase transitions in cathode materials (such as lithium cobalt oxide, NCM, lithium manganese iron phosphate, etc., but not limited to these), improve the stability of both the positive and negative electrodes, and thus enhance the thermal safety and cycle performance of the battery. On the other hand, the organic particles are rich in strongly polar groups, providing lone electron pairs, which can effectively complex transition metal ions and by-reaction products generated during battery cycling through coordination bonds, preventing damage to the SEI film of the negative electrode. By introducing at least one atom or group of nitrogen, oxygen, fluorine, chlorine, sulfur, and phosphorus into the organic particles, their heat resistance and oxidation resistance can be further improved, preventing deterioration of safety performance.

[0058] Therefore, by setting an organic heat-resistant layer formed by organic particles and a second bonding polymer, this application can significantly improve the temperature resistance of the composite separator and the safety performance of the battery at high temperatures. Simultaneously, the porous bonding layer, as a transition area between the organic heat-resistant layer and the electrode, provides adhesion to ensure full bonding between the composite separator and the electrode. Furthermore, as a surface layer, it maintains the stability of the organic heat-resistant layer, and the organic particles distributed within it further remove transition metal ions, greatly improving the cycle life of the battery.

[0059] Furthermore, when a battery is subjected to instantaneous high-temperature combustion caused by external force puncture, side reactions, or short circuits, the inert gas produced by the decomposition of organic particles can inhibit the spread of fire, and carbonyl groups can promote dehydration and cyclization reactions, forming a dense carbon layer that isolates oxygen and heat. It can also quench free radicals in the combustion chain reaction and slow down the spread of flames.

[0060] Furthermore, with the rapid development of robotics, aerospace, and low-altitude economy, lightweighting is becoming increasingly important. The organic particles used in this application are lighter than inorganic particles for the same volume, which can reduce the weight of the coating, lighten the load on the battery, and achieve lightweighting of the separator. This is beneficial for the application and development of batteries in the high-energy-density low-altitude economy field.

[0061] In some specific implementations, the wavelength of the ultraviolet-visible absorption peak of the organic particles (i.e., the absorption wavelength of the ultraviolet-visible spectral absorption test) H satisfies: 180nm≤H≤350nm, including but not limited to any two values ​​between 180nm, 200nm, 230nm, 250nm, 280nm, 290nm, 300nm, 320nm, 330nm, and 350nm.

[0062] The wavelength H of the ultraviolet-visible absorption peak refers to the wavelength in which a strong absorption peak occurs, within the range of 180–350 nm. The absorption peak can exhibit a monotonically decreasing absorption value on one side or on both sides. The absorption peak can have a apex or not. An apexless peak includes at least one of the following: a plateau region composed of multiple small peaks or a plateau region of an irregular fluctuation curve. For example, see [link to relevant documentation]. Figure 4 The image shown is the UV-Vis absorption spectrum of polyethersulfone; see also... Figure 5 The image shows the UV-Vis absorption spectrum of melamine cyanurate. The π-π conjugated structure formed by aromatic rings, heterocyclic aromatic rings, and heteroatoms in organic particles requires energy for π electrons to transition to an excited state. The UV-Vis absorption peak appears in a shorter wavelength range (the short-wavelength region excites π electrons to the activated state, i.e., π→π*). The UV-Vis absorption wavelength of aromatic ring units is around 180 nm. After adding substituents or heteroatoms, the wavelength redshifts to above 180 nm. However, as the π-π conjugated structure lengthens, the maximum absorption wavelength in the UV spectrum continues to shift towards longer wavelengths. This phenomenon is mainly because as the conjugated structure lengthens, the overlap range of the π electron clouds increases, the energy difference between molecular orbitals decreases, and the energy required for electron transitions decreases. However, the chain entanglement and π-π stacking in the large conjugated structure make many potentially effective metal ion adsorption sites unreachable, leading to a decrease in metal ion adsorption capacity. Simultaneously, the decreased electron transition capacity also reduces the redox stability of the material. As the conjugated structure lengthens, the rigid conjugated chains promote ordered arrangement, increasing crystallinity and rigidity, which is detrimental to lithium-ion conduction. The inventors discovered that when the ultraviolet absorption peak is in the range of 180~350nm, the transition metal ion capture effect of organic particles is significant, resulting in lower battery internal resistance and significantly improved safety and cycle performance. However, when the absorption peak range expands (maximum wavelength > 350nm), the capture effect of organic particles on transition metal ions decreases, and the lithium-ion conduction efficiency also decreases significantly, while the internal resistance increases, which is detrimental to the long cycle life performance of lithium batteries.

[0063] In some specific embodiments, the organic particles include at least one of aromatic polyimide, fluorinated polyimide, polyetheretherketone, polybenzoxazole, sulfonated polyetheretherketone, polyphenylene sulfide sulfone, polyethersulfone, polyaryletheretherketone, polybenzobisoxazole, polyethylene chloride terephthalate, tetrachlorobisphenol A type polyarylether ester, polychlorobenzoxazole ester, polybenzodithiophene sulfone, melamine cyanurate, polybenzimidazole imide, melamine-pyromellitic acid, melamine phosphate, melamine borate, melamine oxalate, melamine phthalate, melamine-naphthalenetetracarboxylic acid, and PEI / PET core-shell microspheres.

[0064] In some specific embodiments, the volumetric median particle size (Dv50) of the organic particles is 0.01~2 μm, for example, 0.01 μm, 0.1 μm, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.3 μm, 1.5 μm, 1.8 μm, or 2 μm. With the particle size within the above range, micron-scale coatings can be fabricated while maintaining uniformity. Furthermore, the stacking of particles creates numerous porous channels, facilitating lithium-ion transport and heavy metal ion capture.

[0065] In some specific embodiments, the organic particles include a first organic particle with a median volume diameter of D1 and a second organic particle with a median volume diameter of D2, wherein D1 is not equal to D2.

[0066] Using organic particles of different sizes, the distribution map measured by the laser particle size analyzer showed a double peak. The distribution of organic particles with two different sizes effectively increases the porosity between particles, especially at the adjacent positions of large and small particles. This helps reduce the tortuosity of the coating and improves ion migration speed. Simultaneously, increasing the roughness of the organic heat-resistant layer significantly improves the adhesion between the porous adhesive layer and the organic heat-resistant layer, enhancing the protective effect of the porous adhesive layer on the organic heat-resistant layer.

[0067] Organic particles can also have a uniform particle size distribution. The distribution map measured by the laser particle size analyzer shows a normal distribution with a single peak.

[0068] The shape of organic particles can be any of the following: spherical, rod-shaped, sheet-like, layered, polygonal, porous, or irregular; this application does not limit this.

[0069] In some specific embodiments, the first bonding polymer includes at least one selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, acrylonitrile-acrylate copolymer, acrylic acid-acrylate copolymer, styrene-acrylate copolymer, polyaramid, polyimide, polyamide-imide, polyetherimide, polyphenylene sulfide, polyethersulfone, and polyarylsulfone. Preferably, the first bonding polymer includes at least one selected from polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, acrylonitrile-acrylate copolymer, polyaramid, and polyimide.

[0070] In some specific embodiments, the second adhesive polymer contains at least one functional group selected from carboxyl, hydroxyl, amide, primary amine, secondary amine, cyano (i.e., nitrile), isocyanoacrylate, and acrylate, and the glass transition temperature T of the second adhesive polymer is... gThe temperature should be greater than 120°C, preferably greater than 150°C, and more preferably greater than 180°C. Organic particles have a lower density than inorganic particles, resulting in a lower basis weight for the same coating thickness (i.e., volume). This reduces the force required to bind the substrate material (such as polyolefins) to deform at high temperatures. This application utilizes organic particles with high T... g The bonding of the second adhesive polymer can enhance the stress of the organic heat-resistant layer at high temperatures, ensuring the thermal safety and stability of the composite membrane.

[0071] In some specific embodiments, the second adhesive polymer includes at least one of polyacrylamide, polyacrylic acid, polymethacrylic acid, ethylene-acrylic acid copolymer, polymethyl methacrylate, polybutyl methacrylate, polyacrylonitrile, polyvinyl alcohol, and polypropylene glycol.

[0072] In some specific embodiments, the organic heat-resistant layer also contains additives. These additives serve to disperse and wet the layers, enabling the organic heat-resistant layer to spread better on the substrate and improving its uniformity.

[0073] In some specific embodiments, the additives include at least one of sodium polyacrylate, polyacrylamide, polyether-modified siloxane, isopropanolamine, alkynyl alcohol, fatty alcohol polyoxyethylene ether, polyester-modified siloxane, alkynyl glycol ether, ethanol, and isopropanol.

[0074] In some specific embodiments, the mass ratio of organic particles in the organic heat-resistant layer to the second binder polymer is 99:1 to 80:20, for example, 99:1, 95:5, 90:10, 85:15, or 80:20. Controlling the amount of organic particles within this range is beneficial for complexing transition metal ions and reaction byproducts, protecting the SEI film, and ensuring the safety and stability of the composite separator. If the organic particle content is too low, it will reduce the complexing effect of transition metal ions, temperature resistance, and flame retardant properties; if the organic particle content is too high, it will affect the adhesion between the organic heat-resistant layer and the substrate, or between the separator and the electrode, affecting the safety and stability of the battery.

[0075] In some specific embodiments, the thickness of the organic heat-resistant layer is 0.5~4μm, for example, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, or 4μm. Using this thickness range balances low battery internal resistance and high safety performance. If the organic heat-resistant layer is too thick, it will increase the ion migration channels, increasing the battery internal resistance; if the organic heat-resistant layer is too thin, its temperature resistance will be poor, unable to support the deformation of the separator at high temperatures, reducing the separator's safety.

[0076] In some specific embodiments, the ratio of the basis weight m of the organic heat-resistant layer to its thickness h is 0.4 to 1.2 (i.e., 0.4 to 1.2:1), for example, 0.4, 0.5, 0.6, 0.8, 0.9, 1, or 1.2. Here, the unit of m is g / m³. 2 The unit of h is μm. This indicates that the organic heat-resistant layer is lighter, which is beneficial for achieving lightweight composite membranes.

[0077] In some specific embodiments, the basis weight of the organic heat-resistant layer is 0.5~4 g / m². 2 For example, 0.5g / m 2 1g / m 2 1.5g / m 2 2g / m 2 2.5g / m 2 3g / m 2 3.5g / m 2 or 4g / m 2 Controlling the basis weight of the organic heat-resistant layer within this range is beneficial for balancing the heat resistance and cycle performance of the composite separator. If the basis weight of the organic heat-resistant layer is too low, the heat resistance will decrease, and it will be unable to maintain the stability of the cathode material under high voltage and effectively capture free heavy metal ions; if the basis weight of the organic heat-resistant layer is too high, the thickness of the organic heat-resistant layer will be too large, the lithium-ion transport channels will increase, and the internal resistance will deteriorate severely.

[0078] In some specific embodiments, the organic heat-resistant layer has a full-coat structure, which can be a coating of uniform thickness or a coating with regular or irregular height differences in the thickness direction. A full-coat structure means that the coating forms a continuous film that completely covers the substrate surface, leaving no exposed areas. Since the substrate has poor high-temperature heat resistance, the diaphragm may shrink at high temperatures, potentially causing safety issues. This invention, by setting the organic heat-resistant layer to a full-coat structure, ensures the heat resistance of the diaphragm; that is, the coating provides support to the substrate at high temperatures, preventing shrinkage.

[0079] In some specific embodiments, the mass ratio of organic particles to the first bonding polymer in the porous adhesive layer is 10:90 to 70:30, for example, 10:90, 15:85, 20:80, 30:70, 40:60, 50:50, 60:40, or 70:30. Controlling this mass ratio is beneficial to improving the performance of the porous adhesive layer and the composite membrane. However, if there are too many organic particles, they are prone to detachment during the pore-forming process of the porous adhesive layer, making it difficult to form a porous structure; if the content of the first bonding polymer is too high, the pore-forming effect is poor, and closed pores are easily formed.

[0080] In some specific embodiments, the thickness of the porous adhesive layer is 0.2~6μm, for example, 0.2μm, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 5μm, or 6μm. Using this thickness range ensures the safety performance of the composite separator and the battery made from it. If the thickness of the porous adhesive layer is too thin, it cannot effectively perform secondary removal of metal transition ions, and its protective effect on organic particles on the surface of the organic heat-resistant layer is reduced, leading to the detachment of the organic heat-resistant layer during battery cycling and causing battery safety issues.

[0081] In some specific embodiments, the basis weight of the porous adhesive layer is 0.3~3 g / m³. 2 For example, 0.3g / m 2 0.5g / m 2 1g / m 2 1.5g / m 2 2g / m 2 2.5g / m 2 or 3g / m 2 If the basis weight of the porous adhesive layer is too low, its adhesion will be poor; if the basis weight of the porous adhesive layer is too high, closed pores will occur during the preparation of the porous adhesive layer.

[0082] In some specific embodiments, the porous adhesive layer can be a fully coated structure or a partially coated structure. A fully coated structure refers to a coating that partially covers the surface of the substrate, leaving exposed areas. The porous adhesive layer primarily functions as an adhesive layer and serves as a reinforced area for heavy metal ion capture; therefore, the porous adhesive layer can be either a fully coated structure or a partially coated structure.

[0083] In some specific embodiments, the mass ratio (i.e., weight ratio) of the organic heat-resistant layer to the porous adhesive layer is 0.5 to 5:1, for example, 0.5:1, 1:1, 2:1, 3:1, 4:1, or 5:1. This ensures the heat resistance and adhesion of the composite separator. If the mass ratio is too low, the proportion of the first adhesive polymer in the porous adhesive layer penetrating into the organic heat-resistant layer increases after coating, which is detrimental to reducing the internal resistance of the composite separator. If the ratio is too high, the cohesion between the porous adhesive layer and the organic heat-resistant layer decreases, leading to a decrease in the adhesion between the composite separator and the electrode.

[0084] In some specific implementations, the substrate includes a polyolefin substrate.

[0085] In some specific embodiments, the needle penetration strength of the polyolefin substrate is greater than 300 gf, preferably greater than 500 gf. Since the compressive strength of organic particles is lower than that of inorganic particles, using a high-strength polyolefin substrate can improve the overall puncture resistance of the composite membrane and enhance its comprehensive physical and electrochemical properties.

[0086] In some specific implementations, the longitudinal shrinkage rate (MD) of the composite diaphragm at 130°C / h is 1% to 15%, for example, 1%, 3%, 5%, 8%, 10%, 12% or 15%.

[0087] In some specific implementations, the transverse shrinkage rate (TD) of the composite diaphragm at 130°C / h is 1% to 15%, for example, 1%, 3%, 5%, 8%, 10%, 12%, or 15%.

[0088] In some specific embodiments, the peel force between the organic heat-resistant layer and the porous adhesive layer is 5~80 N / m, for example 5 N / m, 10 N / m, 20 N / m, 30 N / m, 40 N / m, 50 N / m, 60 N / m, 70 N / m or 80 N / m.

[0089] In some specific embodiments, the manganese ion capture capacity of the composite membrane is ≥7000 mg / Kg, preferably ≥8000 mg / Kg, and more preferably ≥9000 mg / Kg.

[0090] Secondly, this application provides a method for preparing the above-mentioned composite membrane, comprising the following steps: A first slurry containing organic particles and a second binder polymer is coated onto at least one surface of a substrate, and after drying, an organic heat-resistant layer is formed to obtain a semi-finished product. Then, a second slurry containing organic particles and the first binder polymer is coated onto the surface of the organic heat-resistant layer and / or the substrate in the semi-finished product, and after drying, a porous binder layer is formed to obtain a composite membrane.

[0091] Organic particles stabilize the crystal structure of the cathode material, improving the battery's thermal safety and cycle performance; they also complex transition metal ions and reaction byproducts, protecting the SEI film. The organic heat-resistant layer possesses high temperature resistance, enhancing the temperature resistance and safety performance of the composite separator. The porous adhesive layer maintains the stability of the composite separator and the positive and negative electrodes, improving battery safety and cycle performance.

[0092] Furthermore, this method uses organic particles instead of traditional inorganic particles, which enables the lightweighting of composite membranes.

[0093] Thirdly, this application provides a secondary battery comprising the aforementioned composite separator.

[0094] This secondary battery boasts high safety performance and a long cycle life.

[0095] In some specific implementations, the secondary battery also includes a positive electrode, a negative electrode, and an electrolyte.

[0096] In some specific implementations, the positive and / or negative electrode sheets contain organic particles. By adding organic particles to the positive and / or negative electrode sheets, the mechanical bonding force and van der Waals force between the composite separator and the positive and / or negative electrode sheets can be improved, thus protecting the stability of the positive and negative electrode materials under high temperature and high pressure conditions.

[0097] In some specific embodiments, the positive electrode sheet includes a positive current collector and a positive active layer, the negative electrode sheet includes a negative current collector and a negative active layer, and the positive active layer and / or the negative active layer contains the aforementioned organic particles.

[0098] In some specific embodiments, the positive electrode sheet includes a positive current collector, a positive active layer, and a first non-fully covered coating; the negative electrode sheet includes a negative current collector, a negative active layer, and a second non-fully covered coating. The first non-fully covered coating and / or the second non-fully covered coating contains the aforementioned organic particles. That is, the first non-fully covered coating partially covers the positive active layer, and the second non-fully covered coating partially covers the negative active layer. The shape of the first non-fully covered coating and / or the second non-fully covered coating can be a regular shape or an irregular shape, including but not limited to at least one of striped, dotted, circular, and elliptical shapes.

[0099] Fourthly, this application provides an electrical device that includes the aforementioned secondary battery.

[0100] It is understood that electrical equipment includes any device, apparatus, or system containing the aforementioned secondary batteries, such as laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, and large household batteries, but is not limited to these.

[0101] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this application. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0102] Example 1 The method for preparing the composite diaphragm provided in this embodiment includes the following steps: (1) Take 60g of polyacrylic acid (second binder polymer) with a solid content of 20% (T gA solution at 182°C was added to a 1L stirred tank containing 320g of deionized water (solvent) and stirred at 1000rpm for 20min. Then, 135g of polyethersulfone powder (organic particles containing aromatic ring structures, oxygen atoms (present in ether bonds and sulfone groups) and sulfur atoms (present in sulfone groups) with a volume median particle size Dv50 of 0.66μm and a UV-Vis absorption peak wavelength H satisfying 180nm≤H≤350nm) was added and dispersed by stirring at 2000rpm for 3h. Then, 2g of sodium polyacrylate (additive) was added and stirred at 500rpm for 30min to obtain a polyethersulfone aqueous slurry (second slurry) (i.e., the mass ratio of organic particles in the organic heat-resistant layer to the second binder polymer is 91.8:8.2). The polyethersulfone aqueous slurry was coated onto a surface of a polyethylene substrate with a needle-punching strength of 510 gf and a thickness of 7 μm using a microgravure plate, and then dried in an oven to form an organic heat-resistant layer, thus obtaining a semi-finished product. The thickness and mass of the organic heat-resistant layer, and the ratio of mass to thickness, are shown in Table 1.

[0103] (2) 1 kg of DMAC (N,N-dimethylacetamide, solvent) was placed in a 2 L stirred tank, and 40 g of PVDF (polyvinylidene fluoride, first binder polymer) was added. The mixture was stirred at 25 °C and 1500 rpm for 4 h to dissolve it. Then, 40 g of polyethersulfone powder (organic particles with a particle size Dv50 as in step (1)) was added, and the mixture was stirred for another 1 h to obtain a polyethersulfone oily slurry (first slurry) (i.e., the mass ratio of organic particles to the first binder polymer in the porous binder layer is 50:50). The polyethersulfone oily slurry was coated onto the surface of the organic heat-resistant layer in the above semi-finished product using a micro-gravure roller, and then passed through a coagulation bath with aqueous solutions of 60% DMAC, 10% DMAC, and 5% DMAC in sequence. After that, it was dried in an oven at 70 °C to form a porous binder layer and obtain a composite membrane. The thickness and mass of the porous binder layer, and the mass ratio of the organic heat-resistant layer and the porous binder layer are shown in Table 2.

[0104] The composite membrane prepared in this embodiment includes a substrate, an organic heat-resistant layer, and a porous adhesive layer stacked sequentially, such as... Figure 1 As shown.

[0105] Example 2 The preparation method of the composite membrane provided in this embodiment is basically the same as that in Example 1, except that: in steps (1) and (2), half the mass of polyethersulfone powder is taken and replaced with polyethersulfone powder with a median volume particle size Dv50 of 1.2 μm (that is, a first organic particle with a median volume particle size D1 and a second organic particle with a median volume particle size D2 are added at the same time, where D1 is not equal to D2).

[0106] Examples 3 to 8 The preparation methods of the composite membranes provided in Examples 3 to 8 are basically the same as those in Example 1, except that different types and Dv50 organic particles are used in steps (1) and (2), as shown in Table 1. It is understood that due to the different organic particles, the thickness of the organic heat-resistant layer, the mass of the organic heat-resistant layer, the ratio of the mass to the thickness of the organic heat-resistant layer, the basis weight of the organic heat-resistant layer, the thickness of the porous adhesive layer, the mass of the porous adhesive layer, the basis weight of the porous adhesive layer, and the mass ratio of the organic heat-resistant layer to the porous adhesive layer are also different, as shown in Table 1.

[0107] Among them, aromatic polyimide contains an aromatic ring structure, containing nitrogen and oxygen atoms (present in the amide group), and the ultraviolet-visible absorption peak wavelength H is 180~330nm.

[0108] Polyaryletherketones contain aromatic ring structures and oxygen atoms (present in ether bonds and carbonyl groups). The wavelength H of the ultraviolet-visible absorption peak is 180~300nm.

[0109] Polyether ether ketone contains an aromatic ring structure and oxygen atoms (present in ether bonds and carbonyl groups). Its ultraviolet-visible absorption peak wavelength H is 180~320nm.

[0110] Melamine borate contains an aromatic heterocyclic structure, containing nitrogen and oxygen atoms (found in aromatic heterocycles and borates), and its ultraviolet-visible absorption peak wavelength H is 180~290nm.

[0111] Melamine phosphate contains an aromatic heterocyclic structure, containing nitrogen, oxygen and phosphorus atoms (present in the aromatic heterocyclic structure and phosphate), and its ultraviolet-visible absorption peak wavelength H is 180~290nm.

[0112] Melamine cyanurate contains an aromatic heterocyclic structure, containing nitrogen and oxygen atoms (present in the aromatic heterocyclic structure), and its ultraviolet-visible absorption peak wavelength H is 180~290nm.

[0113] Example 9 The preparation method of the composite membrane provided in this embodiment is basically the same as that in Example 1, except that in step (2), PVDF (first bonding polymer) is replaced with an equal mass of polymethyl methacrylate.

[0114] Example 10 The preparation method of the composite membrane provided in this embodiment is basically the same as that in Example 1, except that in step (2), PVDF (first bonding polymer) is replaced with an equal mass of polyetherimide.

[0115] Example 11 The preparation method of the composite membrane provided in this embodiment is basically the same as that in Example 1, except that in step (1), the polyacrylic acid solution (second bonding polymer) is replaced with polyacrylonitrile (containing cyano) of equal mass based on polypropylene.

[0116] Example 12 The preparation method of the composite membrane provided in this embodiment is basically the same as that in Example 1, except that in step (1), the polyacrylic acid solution (second bonding polymer) is replaced with polyvinyl alcohol (containing hydroxyl groups) of equal mass based on polypropylene.

[0117] Example 13 The preparation method of the composite membrane provided in this embodiment is basically the same as that in Example 1, except that in step (1), sodium polyacrylate (additive) is replaced with an equal mass of isopropanolamine.

[0118] Example 14 The preparation method of the composite membrane provided in this embodiment is basically the same as that in Example 1, except that in step (1), the mass of polyethersulfone powder is replaced with 68g, that is, the mass ratio of organic particles in the organic heat-resistant layer to the second bonding polymer is 85:15.

[0119] Example 15 The preparation method of the composite membrane provided in this embodiment is basically the same as that in Example 1, except that in step (2), the mass of polyethersulfone powder is replaced with 10g, that is, the mass ratio of organic particles in the porous adhesive layer to the first adhesive polymer is 20:80.

[0120] Example 16 The preparation method of the composite diaphragm provided in this embodiment is basically the same as that in Example 1, except that in step (1), the needle punch strength of the polyethylene substrate is replaced with 240 gf.

[0121] Comparative Example 1 The preparation method of the composite membrane provided in this comparative example is basically the same as that in Example 1, except that in steps (1) and (2), the polyethersulfone powder is replaced with an equal mass of poly(m-phenylene isophthalamide) (poly(m-phenylene isophthalamide) contains an aromatic ring structure and contains nitrogen atoms (present in amides), and its ultraviolet-visible absorption peak wavelength range is 200nm~400nm).

[0122] Comparative Example 2 The preparation method of the composite membrane provided in this comparative example is basically the same as that in Example 1, except that in steps (1) and (2), the polyethersulfone powder is replaced with an equal mass of polyetherimide (polyetherimide contains an aromatic ring structure, contains oxygen atoms and nitrogen atoms (existing in ether bonds and imides), and its ultraviolet-visible absorption peak wavelength range is 200nm~450nm).

[0123] Comparative Example 3 The method for preparing the composite diaphragm provided in this comparative example includes the following steps: (1) 80g of inorganic alumina powder (inorganic particles) with a median particle size D50 of 0.85μm was added to a 1L stirred tank, along with 0.5g of ammonium polyacrylate, 0.8g of sodium carboxymethyl cellulose, and 25g of polyacrylic acid solution with a solid content of 25%. The mixture was stirred at 1000rpm for 4h at 25℃ to obtain an inorganic alumina aqueous slurry. This inorganic alumina aqueous slurry was coated onto a surface of a polyethylene substrate with a needle punch strength of 510gf and a thickness of 7μm using a microgravure plate, and then dried in an oven to form a first inorganic particle layer, thus obtaining a semi-finished product. The thickness and mass of the first inorganic particle layer, and the ratio of mass to thickness, are shown in Table 1.

[0124] (2) 1 kg of DMAC was placed in a 2 L stirred tank, and 40 g of PVDF was added. The mixture was stirred at 1500 rpm at 25 °C for 4 h to dissolve it. Then, 40 g of inorganic alumina powder (inorganic particles) with a volume median particle size D50 of 0.85 μm was added, and the mixture was stirred for another 1 h to obtain an alumina oily slurry. The alumina oily slurry was coated onto the surface of the first inorganic particle layer in the above semi-finished product using a micro-gravure roller, and then passed through a coagulation bath with aqueous solutions of 60% DMAC, 10% DMAC, and 5% DMAC in sequence. After that, it was dried in an oven at 70 °C to form a second inorganic particle layer, thus obtaining a composite membrane. The thickness and mass of the second inorganic particle layer, and the mass ratios of the first and second inorganic particle layers are shown in Table 2.

[0125] Comparative Example 4 The preparation method of the composite membrane provided in this comparative example is basically the same as that in Example 1, except that in step (1), the mass of polyethersulfone powder is replaced with 12g, that is, the mass ratio of organic particles in the organic heat-resistant layer to the second bonding polymer is 50:50.

[0126] In the embodiments and comparative examples above, the following method was used to test the wavelength H of the ultraviolet-visible absorption peak of organic particles: Ultraviolet-visible absorption spectroscopy (UV-Vis): A Shimadzu UV-3600iPlus instrument (Japan) was used, with barium sulfate scanning the baseline from 185-800 nm. Slit width: 20 nm, realistic mode: absorption mode. After the baseline scan was completed, the sample fixing device was removed, the barium sulfate powder was cleaned, and dried under an infrared lamp. Organic particle powder was added to a 2 mm sample cell, tightened, and placed in the sample holder. The absorption wavelength H range of the organic particles was then measured.

[0127] In the embodiments and comparative examples above, the thicknesses of the organic heat-resistant layer and the porous adhesive layer were measured using the following method: The thicknesses of the substrate, the semi-finished product (substrate + organic heat-resistant layer), and the composite diaphragm (substrate + organic heat-resistant layer + porous adhesive layer) were measured using a Marl thickness gauge, and were d0, d1, and d2, respectively. Therefore, the thickness of the organic heat-resistant layer = d1 - d0, and the thickness of the porous adhesive layer = d2 - d1. Five sets of tests were repeated, and the average value was taken.

[0128] In the embodiments and comparative examples above, the mass of the organic heat-resistant layer and the porous adhesive layer was measured using the following method: Five sets each of the substrate, semi-finished product, and composite membrane samples were taken, each sample measuring 100mm × 100mm, and weighed in a five-position electronic balance. The average value was then calculated. The mass of the organic heat-resistant layer = the mass of the semi-finished product - the mass of the substrate; the mass of the porous adhesive layer = the mass of the composite membrane - the mass of the semi-finished product. The mass ratio of the organic heat-resistant layer to the porous adhesive layer was then calculated.

[0129] In the embodiments and comparative examples above, the needle penetration strength of the polyolefin substrate was tested using the following method: The polyolefin substrate was cut to a size of 120mm × 120mm, laid flat and fixed in a needle-punching fixture, and then the needle-punching fixture was fixed on a tensile testing machine. The polyolefin substrate was punctured at a test speed of 50mm / min. After the test, the maximum force was recorded in gf. Five groups of samples were tested, and the average value was taken.

[0130] In the embodiments and comparative examples above of this application, the glass transition temperature T of the second adhesive polymer was tested using the following method. g Differential scanning calorimetry was used. 5-10 mg of sample was weighed in a 40 mL aluminum crucible. A nitrogen atmosphere was selected for the test. The temperature range was -80℃ to 300℃. The sample was heated at a rate of 10℃ / min. The glass transition temperature was obtained by analyzing the test curve.

[0131] The types and particle sizes (Dv50) of organic particles used in each embodiment and comparative example; the thickness and basis weight of the organic heat-resistant layers obtained in each embodiment and comparative example; the basis weight to thickness ratio of the organic heat-resistant layers obtained in each embodiment and comparative example; the basis weight of the organic heat-resistant layers obtained in each embodiment and comparative example; and the types and glass transition temperatures (T) of the second bonding polymers used in each embodiment and comparative example. g The strength of the substrates used in each embodiment and comparative example is shown in Table 1.

[0132] Table 1

[0133] The thickness and basis weight of the porous adhesive layer obtained in each embodiment and comparative example, as well as the weight ratio (i.e., mass ratio) of the organic heat-resistant layer to the porous adhesive layer obtained in each embodiment and comparative example, are shown in Table 2.

[0134] Table 2

[0135] Experimental Example The peel force between the organic heat-resistant layer and the porous adhesive layer prepared in each embodiment and comparative example was tested, and the test results are shown in Table 3. Specifically, a composite diaphragm sample with a size of 50mm × 150mm was taken and fixed to a steel plate with double-sided tape, with the coated side of the composite diaphragm facing upwards. Then, 3M transparent tape was pasted onto the coated surface of the composite diaphragm, and a hand-held pressure roller was used to roll it back and forth three times. An electric tensile testing machine (Shenzhen Hengsili Measurement Instrument Co., Ltd. HL990-AL) was used to peel the 3M tape at a speed of 50mm / min, with a peel length of 20mm. After the test, the average peel force value was recorded. Peel force (N / m) = average peel force value (N) / width of transparent tape (m).

[0136] The longitudinal shrinkage rate (MD) and transverse shrinkage rate (TD) of the composite diaphragms prepared in each embodiment and comparative example were tested at 130℃ / h, and the test results are shown in Table 3. Specifically, the oven was started and the baking temperature was set to 130℃. After the temperature inside the oven reached the set value, a composite diaphragm sample with a length × width = 200mm × 100mm was taken, marked with the MD and TD directions, placed between A4 sheets of paper, and laid flat in the oven. After baking for 1 hour, the sample was removed and allowed to stand for 10 minutes. The dimensions of the diaphragm after baking in the MD and TD directions were measured, and the diaphragm shrinkage rate was calculated.

[0137] The manganese ion capture capacity of the composite membranes prepared in each embodiment and comparative example was tested, and the test results are shown in Table 3. Specifically, the manganese ion capture capacity (unit: mg / Kg) of the composite membrane was measured by inductively coupled plasma optical emission spectrometry (ICP). The method was as follows: MnCl2 was dissolved in an electrolyte (1 mol / L LiPF6, mass ratio of ethylene carbonate: methyl ethyl carbonate: diethyl carbonate = 3:5:2) to obtain the manganese ion stock solution. The composite membrane was cut into 100mm × 100mm pieces and placed in a container containing a certain amount of manganese ion stock solution, and left to stand at room temperature for 24 hours. The composite membrane was then removed, washed twice with ethanol, and air-dried before testing.

[0138] The composite separators prepared in each embodiment and comparative example were used to prepare lithium-ion batteries according to the following method: The positive electrode active materials lithium manganese oxide, conductive carbon black, and polyvinylidene fluoride were dissolved in NMP at a weight ratio of 94.5:3.0:2.5, stirred evenly to form a positive electrode slurry, which was then coated onto both sides of the positive electrode current collector aluminum foil, dried, rolled, and cut to obtain the positive electrode sheet. The negative electrode active materials artificial graphite, sodium carboxymethyl cellulose, and styrene-butadiene rubber were dispersed in deionized water at a weight ratio of 97:1.5:1.5, stirred evenly to form a negative electrode slurry, which was then coated onto both sides of the negative electrode current collector copper foil, dried, rolled, and cut to obtain the negative electrode sheet. The positive electrode sheet, composite separator, and negative electrode sheet were sequentially wound and shaped by winding, and then hot-pressed to obtain the electrochemical electrode assembly. Each electrode assembly is packaged, and the packaged cells are placed in an oven and baked at 90°C for 12 hours. Then, electrolyte is injected, and the injected batteries are left to stand at high temperature for 24 hours, and then left to stand at room temperature for 24 hours. After standing, the cells are pre-charged, formed, and tested for capacity.

[0139] The manganese ion deposition rate of the transition metal negative electrode was tested according to the following method: (1) Manganese ion deposition rate R = manganese ion deposition amount of negative electrode / manganese ion loss amount of positive electrode; (2) The manganese ion adsorption amount of the negative electrode and the manganese ion loss amount of the positive electrode of the lithium-ion battery were obtained by inductively coupled plasma optical emission spectrometry (ICP). The specific method is as follows: The lithium battery that has not been cycled was discharged to 3.0V, and then the positive and negative electrodes were disassembled and soaked in ethyl methyl carbonate for 3h, and then soaked in ethanol for 0.5h before being taken out and dried at room temperature. A 50mm×50mm sample was cut, and the manganese ion loss amount of the positive electrode and the manganese ion deposition amount of the negative electrode of the lithium battery that has not been cycled were tested by ICP. Similarly, the manganese ion loss amount of the positive electrode and the manganese ion deposition amount of the negative electrode were tested after 500 cycles. Five groups of batteries that have not been cycled and those that have been cycled were taken, and the average manganese ion loss amount of the positive electrode and the average manganese ion deposition amount of the negative electrode were calculated. The manganese ion loss of the positive electrode is calculated by subtracting the manganese ion loss of the positive electrode after 500 cycles from the manganese ion loss after no cycle test; the manganese ion deposition of the negative electrode is calculated by subtracting the manganese ion deposition of the negative electrode after 500 cycles from the manganese ion deposition of the negative electrode after no cycles. The test results are shown in Table 3.

[0140] The high-temperature cycle capacity retention rate was tested as follows: After winding, the lithium-ion battery was baked at 80℃ for 48 hours, injected with electrolyte, and then left to stand at room temperature for 18 hours. It was then placed in a hot-pressing formation machine for pretreatment at 45℃ / 1MPa for 1 hour. The battery was charged at 0.5C to 4.4V at 45℃, then charged at a constant voltage to 0.02C, and then discharged at a constant current of 0.5C to 3V. This was recorded as the first charge-discharge cycle of the lithium battery, and the corresponding discharge capacity was recorded as Q0. The above charge-discharge cycle was repeated, and the discharge capacity corresponding to the 400th cycle was recorded as Q1. Therefore, the high-temperature capacity retention rate of the lithium battery is P = (Q1 / Q0) × 100%. The test results are shown in Table 3. It can be understood that a higher capacity cycle retention rate indicates less lithium-ion loss during the battery cycle and better battery cycle performance. There are many reasons for lithium-ion degradation. In addition to factors related to the performance of the positive and negative electrode active materials, the increased internal resistance of the battery at high temperatures, the HF generated by the reaction of trace water with LiPF6 eroding the positive electrode material, the damage of the SEI film of the negative electrode by transition metal ions, and the irreversible changes in the crystal lattice caused by oxygen release from the positive electrode under high temperature and high pressure may all be among the reasons for capacity decay.

[0141] The battery puncture safety test was conducted as follows: a 4mm steel needle was used, and the puncture experiment was performed at a puncture speed of 30mm / s. Ten lithium-ion batteries were taken from each group, and the fire occurrence of the lithium-ion batteries was observed. The pass rate was calculated as follows: puncture pass rate = 1 - (number of lithium-ion batteries that caught fire / total number of lithium-ion batteries tested). The test results are shown in Table 3.

[0142] Table 3

[0143] As shown in Tables 1, 2, and 3, compared to the comparative examples, the composite membranes in each embodiment significantly improved manganese ion capture and significantly reduced manganese ion deposition at the negative electrode. Specifically, the substrate needle penetration strength in Example 16 did not affect the adsorption effect of the composite membrane coating on manganese ions. Comparing Examples 1 and 2, it was found that the difference in manganese ion adsorption capacity between the two composite membranes was not significant; however, after lithium-ion battery cycling, the latter, with its two different particle size distributions of organic particles, was more conducive to reducing manganese ion deposition at the negative electrode. Comparing Examples 1 and Examples 9-15, it was found that by using appropriate types of first and second binder polymers and additives, or by controlling the appropriate ratio of the organic heat-resistant layer and the porous binder layer, the various properties of the composite membrane remained basically stable.

[0144] Comparative Examples 1-16 and Comparative Examples 1-2 revealed that when the wavelength range of the ultraviolet-visible absorption peak of organic particles was expanded (maximum wavelength > 350 nm), the capture effect of organic particles on transition metal ions decreased, but was still slightly higher than that of inorganic particle alumina composite film.

[0145] Comparing Examples 1-16 and Comparative Example 3, it was found that although the ratio of the mass to thickness of the organic heat-resistant layer was less than that of the inorganic heat-resistant layer, under the same thickness conditions, the 130°C shrinkage rate of the composite membrane formed by the organic particles, the second bonding polymer, and the first bonding polymer was basically the same as that of the alumina inorganic coating membrane.

[0146] In the battery nail penetration test, the pass rate in Examples 1-15 was 0.9-1.0. The composite separator containing organic particles, due to its large number of carbonyl groups and heteroatoms and complex structure, absorbs heat and gases generated by side reactions under extreme temperature conditions, thus improving battery safety. Example 16 used a low-strength polyethylene substrate, leading to a decrease in the cell nail penetration test pass rate; the base film's nail penetration strength affects battery safety to some extent. Comparative Examples 1 and 2 showed reduced manganese ion capture effectiveness, with a nail penetration test pass rate of only 0.3.

[0147] The capacity retention rates of Examples 1-15 and Example 16 after 400 cycles were basically consistent, indicating that organic particles significantly contributed to the capacity retention rate during high-pressure cycling. This is attributed to the complex structure of the carbonyl groups and heteroatoms in the organic particles. High-pressure oxygen release at the positive electrode, the deposition of transition metal ions damaging the SEI film at the negative electrode, abnormal gas generation such as HF / CO, and temperature rise during cycling are all important factors affecting capacity. Clearly, organic particles have a significant advantage over the inorganic alumina of Comparative Example 3 in mitigating these side reactions. Comparative Examples 1 and 2, however, exhibited faster capacity decay.

[0148] Comparative studies of Examples 1-16 and Comparative Example 4 revealed that when an excessive amount of the second binder polymer was added to the organic heat-resistant layer, the shrinkage resistance, ion trapping effect, and electrical properties all decreased. This is because an excessive amount of the second binder polymer leads to a significant increase in the air permeability of the organic heat-resistant layer, and the polymer's heat resistance is worse than that of the organic particles, thus reducing the heat resistance of the organic heat-resistant layer. Simultaneously, the low content of organic particles per unit coating thickness results in an increased manganese ion deposition rate on the negative electrode, affecting the electrical properties.

[0149] In summary, this application stabilizes the crystal structure of the cathode material, improves the stability of both the positive and negative electrodes, and enhances the thermal safety and cycle performance of the battery by adding organic particles to the porous adhesive layer and the organic heat-resistant layer. Furthermore, the organic particles effectively complex transition metal ions and by-reaction products generated during battery cycling through coordination bonds, protecting the SEI film. The organic heat-resistant layer significantly improves the temperature resistance and safety performance of the composite separator. The porous adhesive layer not only provides adhesion to ensure a strong bond between the composite separator and the electrode, but also maintains the stability of the organic heat-resistant layer as a surface layer. When the battery experiences instantaneous high-temperature combustion due to external force puncture, side reactions, or short circuits, the inert gas generated by the decomposition of the organic particles can inhibit the spread of fire, and the carbonyl groups can promote dehydration and cyclization reactions, forming a dense carbon layer that isolates oxygen and heat. This also quenches free radicals in the combustion chain reaction, slowing flame propagation. In addition, this application achieves a lightweight separator.

[0150] Although this application has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of this application and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of this application; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application; therefore, this means that all such substitutions and modifications that fall within the scope of this application are included in the appended claims.

Claims

1. A composite diaphragm, characterized in that, It includes a substrate and a porous adhesive layer disposed on one or both sides of the substrate, and an organic heat-resistant layer is further disposed between the substrate and at least one layer of the porous adhesive layer; The porous adhesive layer comprises organic particles and a first adhesive polymer; The organic heat-resistant layer comprises organic particles and a second bonding polymer; The organic particles include at least one organic compound containing an aromatic ring or aromatic heterocyclic structure, and the organic compound contains at least one atom or group selected from nitrogen, oxygen, fluorine, chlorine, sulfur and phosphorus.

2. The composite diaphragm according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The wavelength H of the ultraviolet-visible absorption peak of the organic particles satisfies: 180nm≤H≤350nm; (2) The organic particles include at least one of aromatic polyimide, fluorinated polyimide, polyether ether ketone, polybenzoxazole, sulfonated polyether ether ketone, polyphenylene sulfide sulfone, polyether sulfone, polyarylether ether ketone, polybenzobisoxazole, polyethylene chloride terephthalate, tetrachlorobisphenol A polyarylether ester, polychlorobenzoxazole ester, polybenzodithiophene sulfone, melamine cyanurate, polybenzimidazole imide, melamine-pyromellitic acid, melamine phosphate, melamine borate, melamine oxalate, melamine phthalate, melamine-naphthalenetetracarboxylic acid, and PEI / PET core-shell microspheres; (3) The median volume diameter of the organic particles is 0.01~2μm; (4) The organic particles include a first organic particle with a median volume diameter of D1 and a second organic particle with a median volume diameter of D2, wherein D1 is not equal to D2.

3. The composite diaphragm according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The first bonding polymer includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, acrylonitrile-acrylate copolymer, acrylic acid-acrylate copolymer, styrene-acrylate copolymer, polyaramid, polyimide, polyamide-imide, polyetherimide, polyphenylene sulfide, polyethersulfone, and polyarylsulfone; preferably, the first bonding polymer includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, acrylonitrile-acrylate copolymer, polyaramid, and polyimide; (2) The second adhesive polymer contains at least one functional group selected from carboxyl, hydroxyl, amide, primary amine, secondary amine, cyano, isocyanoacrylate, and acrylate, and the glass transition temperature T of the second adhesive polymer is [missing information]. g The temperature is greater than 120°C; preferably, the second adhesive polymer includes at least one of polyacrylamide, polyacrylic acid, polymethacrylic acid, ethylene-acrylic acid copolymer, polymethyl methacrylate, polybutyl methacrylate, polyacrylonitrile, polyvinyl alcohol, and polypropylene glycol.

4. The composite diaphragm according to claim 1, characterized in that, The organic heat-resistant layer also contains additives; Preferably, the additive includes at least one of sodium polyacrylate, polyacrylamide, polyether-modified siloxane, isopropanolamine, alkynyl alcohol, fatty alcohol polyoxyethylene ether, polyester-modified siloxane, alkynyl glycol ether, ethanol, and isopropanol.

5. The composite diaphragm according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The mass ratio of the organic particles in the organic heat-resistant layer to the second adhesive polymer is 99:1 to 80:20; (2) The thickness of the organic heat-resistant layer is 0.5~4μm; (3) The ratio of the basis weight m to the thickness h of the organic heat-resistant layer is 0.4~1.2, where the unit of m is g / m. 2 The unit of h is μm; (4) The basis weight of the organic heat-resistant layer is 0.5~4 g / m 2 .

6. The composite diaphragm according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The mass ratio of the organic particles in the porous adhesive layer to the first adhesive polymer is 10:90~70:30; (2) The thickness of the porous adhesive layer is 0.2~6μm; (3) The basis weight of the porous adhesive layer is 0.3~3 g / m 2 ; (4) The mass ratio of the organic heat-resistant layer to the porous adhesive layer is 0.5~5:1; (5) The substrate includes a polyolefin substrate; preferably, the needle penetration strength of the polyolefin substrate is greater than 300 gf, more preferably greater than 500 gf.

7. The composite separator according to any one of claims 1 to 6, characterized in that, At least one of the following conditions must be met: (1) The longitudinal shrinkage rate (MD) of the composite diaphragm at 130℃ / h is 1%~15%; (2) The transverse shrinkage rate (TD) of the composite diaphragm at 130℃ / h is 1%~15%; (3) The peel force between the organic heat-resistant layer and the porous adhesive layer is 5~80 N / m.

8. The method for preparing the composite separator according to any one of claims 1 to 7, characterized in that, Includes the following steps: A first slurry containing organic particles and a second binder polymer is coated onto at least one surface of a substrate and dried to form an organic heat-resistant layer. A second slurry containing organic particles and a first binder polymer is coated onto the surface of the organic heat-resistant layer and / or the substrate, and after drying, a porous binder layer is formed to obtain a composite membrane.

9. A secondary battery, characterized in that, Includes the composite diaphragm as described in any one of claims 1 to 7; Preferably, the secondary battery further includes a positive electrode, a negative electrode, and an electrolyte; more preferably, the positive electrode and / or the negative electrode contain the organic particles.

10. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 9.

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