Composite separator, method for manufacturing the same, and battery

Abstract

The application relates to the technical field of batteries, in particular to a composite diaphragm, a preparation method thereof and a battery. The composite diaphragm comprises a base material layer and a modified polymer, the base material layer has a porous structure, and the modified polymer is located in the porous structure; the composite diaphragm has a first endothermic peak and a second endothermic peak under DSC testing, the first endothermic peak is located at 110 DEG C-160 DEG C, and the second endothermic peak is located at 168 DEG C-295 DEG C. The composite diaphragm of the application has the following advantages: the modified polymer is located in the porous structure, the difference between the thickness t2 of the composite diaphragm and the thickness t1 of the base material layer is 0, the composite diaphragm has the first endothermic peak and the second endothermic peak under DSC testing, the composite diaphragm is favorable for improving the film breaking temperature of the composite diaphragm, reducing the closed pore temperature, improving the heat resistance, avoiding powder falling, having good structural stability, and improving the energy density of the battery cell.

Description

Technical Field

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

[0002] As a crucial component of lithium-ion batteries, the separator is located between the positive and negative electrodes, acting as a barrier to prevent internal short circuits while allowing lithium ions to pass freely, ensuring the battery's charging and discharging capabilities. Polyolefin materials have become a key raw material for commercially available separators due to their low cost, high chemical stability, and good electrochemical stability. However, polyolefin-based separators generally have melting points below 180°C and deform significantly at high temperatures. When the temperature of a lithium-ion battery rises due to external and internal factors, leading to abnormal overheating, the separator is prone to melting and rupture, causing internal short circuits and posing a serious danger to the user's life. Therefore, separators with zero coating thickness improve the cell's energy density, reduce thermal shrinkage, and increase the rupture temperature and pore-closing temperature.

[0003] To improve the safety performance of lithium batteries, existing technologies employ methods such as adding a ceramic coating to the surface of the separator. For example, patent application CN117559082A discloses a ceramic slurry for lithium battery separators and its preparation method. The prepared ceramic slurry, when applied to a lithium battery separator, maintains excellent high-temperature resistance even in ultra-thin separators, significantly improving lithium battery safety. Furthermore, by using two polyacrylate binders in a specific mass ratio, the separator not only exhibits good air permeability but also excellent peel strength. However, the increased thickness of the lithium-ion battery separator due to ceramic slurry and the resulting powder shedding due to poor ceramic adhesion are drawbacks of this process. For example, patent CN105336901A provides a method for preparing a high-performance interpore-coated separator by coating a thin layer of high-temperature resistant resin on the separator surface and between the pores. This high-temperature resistant coating covers the base film surface and the interpore framework, resulting in a composite separator with microporous structures on both the surface and interior. The permeability is not significantly different from the base film, and the increase in weight and thickness after coating is minimal, which is beneficial for improving the volumetric energy density ratio of the battery, enhancing the separator's heat resistance, and improving its wettability with the electrolyte. However, the presence of microporous structures on both the surface and interior of the composite separator easily leads to pore blockage by the high-temperature polymer. Furthermore, the composite separator underwent a heat shrinkage test at 105℃ / 1h, indicating that pore blockage and heat resistance are generally drawbacks of this process.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] One object of this invention is to provide a composite diaphragm to solve the technical problem of poor heat resistance in existing diaphragms. The composite diaphragm of this invention has a high rupture temperature, good heat resistance, and good structural stability.

[0006] Another objective of this invention is to provide a method for preparing a composite diaphragm that is simple and easy to implement, and through the coordination of each step, the heat resistance of the diaphragm can be improved.

[0007] Another object of the present invention is to provide a battery.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0009] A composite membrane includes a substrate layer and a modified polymer, wherein the substrate layer has a porous structure and the modified polymer is located in the porous structure; the composite membrane has a first endothermic peak and a second endothermic peak under DSC testing, wherein the first endothermic peak is located at 110℃~160℃ and the second endothermic peak is located at 168℃~295℃.

[0010] In some embodiments, the peak width W1 of the first endothermic peak is 7–12°C.

[0011] In some embodiments, the energy integral F1 of the first endothermic peak is 800–950 mJ.

[0012] In some embodiments, the peak width W2 of the second endothermic peak is 50–80°C.

[0013] In some embodiments, the energy integral F2 of the second endothermic peak is 100–600 mJ.

[0014] In some embodiments, the energy integral F2 of the second endothermic peak and the energy integral F1 of the first endothermic peak satisfy the following relationship: 10% ≤ F2 / F1 × 100% ≤ 75%.

[0015] In some embodiments, the difference between the thickness t2 of the composite membrane and the thickness t1 of the substrate layer satisfies: t2-t1=0.

[0016] In some embodiments, the modified polymer is obtained by polymerization of at least two photosensitive polymerizing monomers, and at least one of the photosensitive polymerizing monomers is a binary or multi-component polymerizing monomer.

[0017] In some embodiments, the modified polymer in the composite membrane has a mass content of 40% to 60%.

[0018] In some embodiments, the photopolymerizable monomer includes at least two of pentaerythritol triacrylate, hyperbranched acrylic resin, polyurethane acrylate, 1,6-hexanediol diacrylate, dipentaerythritol hexaacrylate, and acrylic epoxy resin.

[0019] In some embodiments, the thickness t1 of the substrate layer is 3–15 μm; the pore size of the substrate layer The surface density M1 of the substrate layer is 50–70 nm; the surface density M1 of the substrate layer is 1.8–5 g / m³. 2 The air permeability Q1 of the substrate layer is 30-75 s / 100cc; the film breaking temperature MD1 of the substrate layer is 150-170℃; the heat shrinkage rate R1 of the substrate layer at 130℃ is 30%-35% in the longitudinal direction and 29%-34% in the transverse direction.

[0020] In some embodiments, the areal density M2 of the composite membrane is 2.5–7 g / m³. 2 .

[0021] In some embodiments, the air permeability Q2 of the composite diaphragm is 110–330 s / 100cc.

[0022] In some embodiments, the pore size of the composite membrane The wavelength is 40–65 nm.

[0023] In some embodiments, the membrane rupture temperature MD2 of the composite diaphragm is 170–220°C.

[0024] In some embodiments, the heat shrinkage rate R2 of the composite diaphragm at 130°C is: 0.5% to 7.5% in the longitudinal direction and 0.8% to 9% in the transverse direction.

[0025] The method for preparing the composite membrane as described above includes the following steps:

[0026] A mixture of at least two photosensitive polymerizable monomers, a photoinitiator, and an additive is heat-treated to obtain a modifier solution; the modifier solution is then used to coat the substrate layer, which is dried and then cured under ultraviolet light.

[0027] In some embodiments, the photoinitiator includes at least one selected from 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 2-isopropylthioxanthraphenone.

[0028] In some embodiments, the photoinitiator has a mass content of 0.5% to 10% in the mixed system.

[0029] In some embodiments, the photosensitive polymeric monomer has a mass content of 82% to 92% in the mixed system.

[0030] In some embodiments, the photosensitive polymerizing monomer is selected from a first monomer and a second monomer, wherein the first monomer is pentaerythritol triacrylate, 1,6-hexanediol diacrylate, or dipentaerythritol hexaacrylate, and the second monomer is a hyperbranched acrylic resin, a polyurethane acrylate, or an acrylic epoxy resin; the mass ratio of the first monomer to the second monomer is (1-4):(1-2).

[0031] In some embodiments, the additive includes at least one of a silane coupling agent, a light stabilizer, and a wetting agent.

[0032] In some embodiments, the silane coupling agent in the mixture contains 0.5% to 3% by mass; the light stabilizer in the mixture contains 0.1% to 4% by mass; and the wetting agent in the mixture contains 0.1% to 2% by mass.

[0033] In some embodiments, the heat treatment temperature is 50–60°C, and the heat treatment time is 30–120 seconds.

[0034] In some embodiments, the coating process is performed 1 to 3 times.

[0035] In some embodiments, the drying process includes nitrogen blowing.

[0036] In some embodiments, the number of UV curing cycles is 1 to 6, and the duration of each UV curing cycle is 15 to 35 seconds.

[0037] A battery comprising the aforementioned composite separator.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] (1) In the composite separator of the present invention, the modified polymer is located in the porous structure to achieve a zero-thickness coating, that is, the difference between the thickness t2 of the composite separator and the thickness t1 of the substrate layer is 0; the composite separator has a first endothermic peak and a second endothermic peak under DSC test, which is beneficial to improve the membrane breaking temperature of the composite separator, reduce the closed-cell temperature, improve the heat resistance, and there is no powder shedding phenomenon. It has good structural stability and can improve the energy density of the battery cell.

[0040] (2) The preparation method of the composite membrane of the present invention is simple and easy to implement. The substrate layer is treated with a modifier solution, and a modified polymer is formed under ultraviolet curing and placed in the porous structure of the substrate layer. The resulting composite membrane has excellent membrane breaking temperature, good heat resistance, no powder shedding, and good structural stability.

[0041] (3) The battery of the present invention has good cycle performance and rate performance, and high safety performance. Attached Figure Description

[0042] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in 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 the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0043] Figure 1 This is a pore size distribution diagram of the composite membrane in Embodiment 1 of the present invention;

[0044] Figure 2 The image shows a differential scanning calorimetry (DSC) chart of the composite membrane in Embodiment 1 of the present invention.

[0045] Figure 3 This is a pore size distribution diagram of the composite membrane in Embodiment 2 of the present invention;

[0046] Figure 4 This is a differential scanning calorimetry (DSC) graph of the composite membrane in Embodiment 2 of the present invention;

[0047] Figure 5 This is a pore size distribution diagram of the composite membrane in Embodiment 3 of the present invention;

[0048] Figure 6 This is a differential scanning calorimetry (DSC) graph of the composite membrane in Embodiment 3 of the present invention;

[0049] Figure 7 This is a pore size distribution diagram of the composite membrane in Embodiment 4 of the present invention;

[0050] Figure 8 This is a differential scanning calorimetry (DSC) graph of the composite membrane in Embodiment 4 of the present invention;

[0051] Figure 9 This is a pore size distribution diagram of the composite membrane in Embodiment 5 of the present invention;

[0052] Figure 10 This is a differential scanning calorimetry (DSC) graph of the composite membrane in Embodiment 5 of the present invention;

[0053] Figure 11 This is a pore size distribution diagram of the composite membrane in Comparative Example 1 of the present invention;

[0054] Figure 12 This is a differential scanning calorimetry (DSC) graph of the composite membrane in Comparative Example 1 of the present invention.

[0055] Figure 13 This is a pore size distribution diagram of the composite membrane in Comparative Example 2 of the present invention;

[0056] Figure 14This is a differential scanning calorimetry (DSC) graph of the composite membrane in Comparative Example 2 of the present invention. Detailed Implementation

[0057] The embodiments of the present invention 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 the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0058] According to one aspect of the present invention, the present invention relates to a composite membrane comprising a substrate layer and a modified polymer, the substrate layer having a porous structure, the modified polymer being located within the porous structure; the composite membrane exhibits a first endothermic peak and a second endothermic peak under DSC (differential scanning calorimetry) testing, the first endothermic peak being located between 110°C and 160°C, and the second endothermic peak being located between 168°C and 295°C; the DSC testing conditions are: nitrogen atmosphere, continuously increasing the temperature from 30°C to 300°C at a temperature change rate of 5°C / min.

[0059] The composite separator of the present invention has a modified polymer located in a porous structure to achieve a zero-thickness coating, that is, the difference between the thickness t2 of the composite separator and the thickness t1 of the substrate layer satisfies: t2-t1=0; the composite separator has a first endothermic peak and a second endothermic peak under DSC testing, which is beneficial to improve the membrane breaking temperature, reduce the pore closing temperature, improve heat resistance, and there is no powder shedding phenomenon. It has good structural stability and can improve the energy density of the battery cell.

[0060] In some embodiments, the peak length of the first endothermic peak is 100–170°C, for example, 105.82°C–167.43°C, 116.41°C–153.77°C, etc. In some embodiments, the first endothermic peak is located at 110°C, 115°C, 120°C, 130°C, 135°C, 140°C, 150°C, 160°C, etc., or any value between two of these ranges. In some embodiments, the peak width W1 of the first endothermic peak is 7–12°C, including but not limited to 7°C, 7.5°C, 8°C, 9°C, 10°C, 10.5°C, 11°C, 11.5°C, 12°C, etc., or any value between two of these ranges. The energy integral F1 of the first endothermic peak is 800 to 950 mJ, including but not limited to 800 mJ, 820 mJ, 850 mJ, 880 mJ, 900 mJ, 920 mJ, 950 mJ, etc., or any value between the two.

[0061] In some embodiments, the peak length of the second endothermic peak is 160–300°C, for example, 166.89°C–289.92°C, 171.73°C–293.16°C, etc. In some embodiments, the second endothermic peak is located at 168°C, 170°C, 180°C, 185°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 295°C, etc., or any range between two of these. In some embodiments, the peak width W2 of the second endothermic peak is 50–80°C, including but not limited to 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, or 80°C, or any range between two of these. In some embodiments, the energy integral F2 of the second endothermic peak is 100 to 600 mJ, including but not limited to 100 mJ, 200 mJ, 250 mJ, 300 mJ, 350 mJ, 400 mJ, 500 mJ or 600 mJ.

[0062] In some implementations, the energy integral F2 of the second endothermic peak and the energy integral F1 of the first endothermic peak satisfy the following relationship: 10% ≤ F2 / F1×100% ≤ 75%, where F2 / F1×100% can be, for example, 15%, 20%, 35%, 40%, 50%, 60%, 70%, 75%, etc., or any value between the two.

[0063] In some embodiments, the modified polymer in the composite diaphragm has a mass content of 40% to 60%, including but not limited to 40%, 45%, 50%, 55%, 60%, or any value between the two. The modified polymer of the present invention has a suitable mass content, which is beneficial for ensuring that the composite diaphragm has suitable air permeability and areal density, and for improving the membrane rupture temperature and heat resistance of the composite diaphragm.

[0064] In some embodiments, the modified polymer is obtained by polymerization of at least two photopolymerizable monomers, and at least one photopolymerizable monomer is a binary or multi-component polymerizable monomer. In some embodiments, the photopolymerizable monomer includes at least two of pentaerythritol triacrylate, hyperbranched acrylic resin, polyurethane acrylate, 1,6-hexanediol diacrylate, dipentaerythritol hexaacrylate, and acrylic epoxy resin.

[0065] In some embodiments, the substrate layer is made of polyolefin, such as ethylene and / or polypropylene. Polyolefin polymers possess good mechanical strength, excellent chemical stability, and electrical insulation properties, preventing the separator from rupturing and causing a short circuit between the positive and negative electrodes due to internal or external factors. In some embodiments, the thickness t1 of the substrate layer is 3–15 μm (e.g., 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 15 μm, etc.); the pore size of the substrate layer… The nanometer diameter is 50–70 nm (e.g., 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, etc.); the areal density M1 of the substrate layer is 1.8–5 g / m². 2 (e.g., 1.8g / m 2 2g / m 2 2.5g / m 2 3g / m 2 4g / m 2 or 5g / m 2 (etc.); the air permeability value Q1 of the substrate layer is 30-75s / 100cc (e.g., 30s / 100cc, 40s / 100cc, 50s / 100cc, 60s / 100cc, 70s / 100cc, 75s / 100cc, etc.); the film breaking temperature MD1 of the substrate layer is 150-170℃ (e.g., 150℃, 155℃, 160℃, 165℃, 170℃, etc.); the heat shrinkage rate R1 of the substrate layer at 130℃ is: longitudinal (MD) 30%-35% (e.g., 30%, 31%, 32%, 33% or 35%, etc.), transverse (TD) 29%-34% (e.g., 29%, 30%, 31%, 32% or 34%, etc.). The present invention uses a substrate layer with suitable conditions, which is more conducive to the composite with modified polymers, thereby obtaining a composite membrane with high membrane breaking temperature, good heat resistance and good structural stability.

[0066] In some embodiments, the areal density M2 of the composite membrane is 2.5–7 g / m³. 2 Including but not limited to 2.5g / m 2 3g / m 2 4g / m 2 5g / m 2 6g / m 2 7g / m 2 The permeability Q2 of the composite membrane is 110–330 s / 100 cc, including but not limited to 110 s / 100 cc, 115 s / 100 cc, 120 s / 100 cc, 125 s / 100 cc, 130 s / 100 cc, etc., or any value between two ranges. In some embodiments, the pore size of the composite membrane... The nm diameter is 40–65 nm, including but not limited to 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, etc., or any value between two of these. The membrane rupture temperature MD2 of the composite membrane is 170–220 °C, for example, 170 °C, 180 °C, 190 °C, 200 °C, 210 °C, 220 °C, etc., or any value between two of these. In some embodiments, the heat shrinkage rate R2 of the composite membrane at 130 °C is: 0.5%–7.5% in the longitudinal direction, for example, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, or 7.5%, etc., and 0.8%–9% in the transverse direction, for example, 0.8%, 1%, 2%, 4%, 5%, 6%, 8%, or 9%, etc. The composite membrane of the present invention has suitable air permeability, suitable areal density, high membrane rupture temperature, and good heat resistance.

[0067] According to another aspect of the present invention, the present invention also relates to a method for preparing the above-mentioned composite separator, comprising the following steps:

[0068] A mixture of at least two photosensitive polymerizable monomers, a photoinitiator, and an additive is heat-treated to obtain a modifier solution; the modifier solution is then used to coat the substrate layer, which is dried and then cured under ultraviolet light.

[0069] The preparation method of the composite diaphragm of the present invention is simple and easy to implement. The substrate layer is treated with a modifier solution, and a modified polymer is formed under ultraviolet curing. The modified polymer is contained in the porous structure of the substrate layer, avoiding severe pore blockage. The resulting composite diaphragm has excellent membrane breakage temperature, good heat resistance, no powder shedding, and good structural stability.

[0070] In some embodiments, the photoinitiator includes at least one selected from 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 2-isopropylthioxanthone. The photoinitiator is present in the mixture at a mass content of 0.5% to 10%, for example, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value between these ranges. The use of a suitable photoinitiator in this invention is more conducive to the polymerization reaction of photosensitive monomers to form modified polymers.

[0071] In some embodiments, the photopolymer monomer has a mass content of 82% to 92% in the mixed system, such as 82%, 85%, 90%, 92%, or any value between the two.

[0072] In some embodiments, the photopolymerizable monomer is selected from a first monomer and a second monomer. The first monomer is pentaerythritol triacrylate, 1,6-hexanediol diacrylate, or dipentaerythritol hexaacrylate, and the second monomer is a hyperbranched acrylic resin, a polyurethane acrylate, or an acrylic epoxy resin. The mass ratio of the first monomer to the second monomer is (1-4):(1-2), for example, 1:1, 2:1, 3:1, 4:1, etc.

[0073] In some embodiments, the additive includes at least one selected from silane coupling agents, light stabilizers, and wetting agents. In some embodiments, the silane coupling agent is present in the mixture at a mass content of 0.5% to 3%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, or 3%. The silane coupling agent is selected from at least one selected from methacryloxymethyltrimethoxysilane, methacryloxypropyltrimethoxysilane, and methacryloxymethyltriethoxysilane. The light stabilizer is present in the mixture at a mass content of 0.1% to 4%, for example, 0.1%, 0.5%, 1%, 1.5%, 2%, 3.5%, or 4%. The wetting agent is present in the mixture at a mass content of 0.1% to 2%, for example, 0.1%, 0.5%, 1%, 1.5%, or 2%. The wetting agent includes at least one selected from polyoxyethylene ether, polyoxypropylene ether, and silicone oil.

[0074] In some embodiments, the heat treatment temperature is 50–60°C, including but not limited to 50°C, 52°C, 55°C, 58°C, and 60°C. The heat treatment time is 30–120 seconds, for example, 30 seconds, 40 seconds, 50 seconds, 60 seconds, 80 seconds, 100 seconds, or 120 seconds. Suitable heat treatment conditions are more conducive to the mixing of materials and the formation of a homogeneous modifier solution.

[0075] In some implementations, the coating process is performed 1 to 3 times, for example, once, twice, or three times.

[0076] In some embodiments, the number of UV curing cycles is 1 to 6, such as 1, 2, 3, 4, 5, or 6 times; the duration of each UV curing cycle is 15 to 35 seconds, such as 15 seconds, 20 seconds, 25 seconds, 30 seconds, or 35 seconds. Suitable UV curing conditions are more conducive to the composite of the modified polymer and the substrate layer, improving the structural stability of the composite membrane and preventing powder shedding. UV lamps are used for UV curing.

[0077] According to another aspect of the invention, the invention also relates to a battery comprising the aforementioned composite separator.

[0078] The battery of this invention has excellent cycle performance, rate performance and safety performance.

[0079] In some embodiments, the battery of the present invention includes the above-described separator, positive electrode, negative electrode, and electrolyte.

[0080] The following explanation, combined with specific embodiments and comparative examples, further illustrates the point.

[0081] Example 1

[0082] A composite separator includes a substrate layer and a modified polymer. The substrate layer has a porous structure, and the modified polymer is located within the porous structure. The composite separator has a thickness t2 of 5 μm and an areal density M2 of 4.2 g / m³. 2 The air permeability value Q2 is 155s / 100cc, and the pore size is... The thickness is 48.0 nm, the film breakage temperature MD2 is 192.7℃, and the thermal shrinkage rate at 130℃ is MD 3.8% and TD 4.7%.

[0083] In DSC measurements of the composite diaphragm, the peak path of the first melting peak during the heating process is T1, the energy integral is F1, and the peak value within T1 is T. 01 The peak width is W1; the peak path of the second melting peak is T2, the energy integral is F2, and the peak value in T2 is T. 02 Peak width is W2; T1 = 112.42℃ - 161.08℃; F1 = 902.41mJ; T 01 =145.88℃; W1=7.7℃; T2=178.31℃-291.96℃; F2=256.1mJ; T 02 =219.05℃; W2=61.84℃.

[0084] This embodiment provides a method for preparing a composite separator, including the following steps:

[0085] (1) Add the photosensitive polymerization monomer, photoinitiator, and additives to a mixer. The photosensitive polymerization monomer is pentaerythritol triacrylate and acrylic hyperbranched resin. The photoinitiator is TPO (2,4,6-trimethylbenzoyl-diphenylphosphine oxide). The additives are light stabilizer 1076, silane coupling agent (methacryloyloxypropyltrimethoxysilane), and wetting agent (polyoxyethylene ether). By mass percentage, pentaerythritol triacrylate is 45%, acrylic hyperbranched resin is 45%, photoinitiator is 4%, light stabilizer is 2%, silane coupling agent is 2%, and wetting agent is 2%. Maintain the temperature at 55℃, stir evenly for 80s, filter, and the obtained solution is the modifier solution.

[0086] (2) Cut out an existing polyethylene substrate as the substrate layer. The thickness t1 of the substrate layer is 5μm, and the pore size is... The wavelength is 56.0 nm, and the areal density M1 is 2.5 g / m². 2The air permeability value Q1 is 57s / 100cc, the film breaking temperature MD1 is 152.8℃, the heat shrinkage rate at 130℃ is MD 34.5%, and TD 33.7%.

[0087] (3) Apply the modifier solution to the substrate layer obtained in step (2) three times, dry it with nitrogen, and cure it under nitrogen with UV light for 6 times / 32s to obtain a composite membrane.

[0088] Example 2

[0089] A high-composite membrane without ceramic coating on its surface includes a substrate layer and a modified polymer. The substrate layer has a porous structure, and the modified polymer is located within the porous structure. The composite membrane has a thickness t2 of 9 μm and an areal density M2 of 6.5 g / m³. 2 The air permeability value Q2 is 75s / 100cc, and the pore size is... The thickness is 65.0 nm, the film breakage temperature MD2 is 217.6℃, and the thermal shrinkage rate at 130℃ is: MD 0.7%, TD 1.0%.

[0090] In DSC measurements of the composite diaphragm, the peak path of the first melting peak during the heating process is T1, the energy integral is F1, and the peak value within T1 is T. 01 The peak width is W1; the peak path of the second melting peak is T2, the energy integral is F2, and the peak value in T2 is T. 02 Peak width is W2; T1 = 105.82℃ - 167.43℃; F1 = 808.69mJ; T 01 =144.88℃; W1=8.46℃; T2=166.89℃-289.92℃; F2=582.45mJ; T 02 =226.12℃; W2=75.21℃.

[0091] This embodiment provides a method for preparing a composite separator, including the following steps:

[0092] (1) Add the photosensitive polymerization monomer, photoinitiator, and additives to the mixer. The photosensitive polymerization monomer is pentaerythritol triacrylate and polyurethane acrylate. The photoinitiator is TPO (2,4,6-trimethylbenzoyl-diphenylphosphine oxide). The additives are light stabilizer 1076, silane coupling agent (methacryloyloxypropyltrimethoxysilane), and wetting agent (polyoxyethylene ether). By mass percentage, pentaerythritol triacrylate is 54%, polyurethane acrylate is 36%, photoinitiator is 4%, light stabilizer is 2%, silane coupling agent is 2%, and wetting agent is 2%. Maintain the temperature at 33°C, stir evenly for 80 seconds, filter, and the obtained solution is the modifier solution.

[0093] (2) Cut out an existing polypropylene substrate as the substrate layer. The thickness t1 of the substrate layer is 9 μm, and the pore size is [missing information]. The wavelength is 66.0 nm, and the areal density M1 is 4.8 g / m². 2 The air permeability value Q1 is 30s / 100cc, the film breaking temperature MD1 is 166.7℃, the heat shrinkage rate at 130℃ is MD 34.5%, and TD 33.7%.

[0094] (3) Apply the modifier solution to the substrate layer obtained in step (2) once, dry it with nitrogen, and cure it under nitrogen with UV light twice for 32 seconds to obtain a composite membrane.

[0095] Example 3

[0096] A composite separator includes a substrate layer and a modified polymer. The substrate layer has a porous structure, and the modified polymer is located within the porous structure. The composite separator has a thickness t2 of 7 μm and an areal density M2 of 4.8 g / m³. 2 The air permeability value Q2 is 116s / 100cc, and the pore size is... The thickness is 47.0 nm, the film breakage temperature MD2 is 203.9℃, and the thermal shrinkage rate at 130℃ is: MD 1.6% and TD 1.8%.

[0097] In DSC measurements of the composite diaphragm, the peak path of the first melting peak during the heating process is T1, the energy integral is F1, and the peak value within T1 is T. 01 The peak width is W1; the peak path of the second melting peak is T2, the energy integral is F2, and the peak value in T2 is T. 02 Peak width is W2; T1 = 116.41℃ - 153.77℃; F1 = 870.77mJ; T 01 =142.97℃; W1=7.87℃; T2=171.73℃-293.16℃; F2=454.88mJ; T 02 =212.65℃; W2=69.58℃.

[0098] This embodiment provides a method for preparing a composite separator, including the following steps:

[0099] (1) Add the photosensitive polymerizing monomer, photoinitiator, and additives to a mixer. The photosensitive polymerizing monomer is 1,6-hexanediol diacrylate and polyurethane acrylate. The photoinitiator is 184 (1-hydroxycyclohexylphenyl ketone). The additives are light stabilizer 1076, silane coupling agent (methacryloyloxypropyltrimethoxysilane), and wetting agent (polyoxyethylene ether). By mass percentage, 1,6-hexanediol diacrylate is 45%, polyurethane acrylate is 45%, photoinitiator is 3%, light stabilizer is 3%, silane coupling agent is 2%, and wetting agent is 2%. Maintain the temperature at 55°C, stir evenly for 80 seconds, filter, and the obtained solution is the modifier solution.

[0100] (2) Take out the existing polyethylene substrate as the substrate layer; the thickness t1 of the substrate layer is 7μm, and the pore size is... The wavelength is 58.0 nm, and the areal density M1 is 2.8 g / m². 2 The air permeability value Q1 is 54s / 100cc, the film breaking temperature MD1 is 153.4℃, the heat shrinkage rate at 130℃ is MD34.5%, and the TD is 33.7%.

[0101] (3) Apply the modifier solution to the substrate layer obtained in step (2) once, dry it with nitrogen, and cure it with UV light once for 16 seconds under nitrogen to obtain a composite membrane.

[0102] Example 4

[0103] A composite separator includes a substrate layer and a modified polymer. The substrate layer has a porous structure, and the modified polymer is located within the porous structure. The composite separator has a thickness t2 of 3.5 μm and an areal density M2 of 2.7 g / m³. 2 The air permeability value Q2 is 185s / 100cc, and the pore size is... The thickness is 44.0 nm, the film breakage temperature MD2 is 184.7℃, and the thermal shrinkage rate at 130℃ is MD 3.5% and TD 4.2%.

[0104] In DSC measurements of the composite diaphragm, the peak path of the first melting peak during the heating process is T1, the energy integral is F1, and the peak value within T1 is T. 01 The peak width is W1; the peak path of the second melting peak is T2, the energy integral is F2, and the peak value in T2 is T. 02 Peak width is W2; T1 = 119.07℃ - 163.78℃; F1 = 839.30mJ; T 01 =145.04℃; W1=10.10℃; T2=203.46℃-293.23℃; F2=187.77mJ; T 02 =218.15℃; W2=52.76℃.

[0105] This embodiment provides a method for preparing a composite separator, including the following steps:

[0106] (1) Add the photosensitive polymerization monomer, photoinitiator, and additives to the mixer. The photosensitive polymerization monomer is dipentaerythritol hexaacrylate and acrylic epoxy resin. The photoinitiator is ITX (2-isopropylthioxanthraquinone). The additives are light stabilizer 1076, silane coupling agent (methacryloyloxypropyltrimethoxysilane), and wetting agent (polyoxyethylene ether). By mass percentage, dipentaerythritol hexaacrylate is 54%, polyurethane acrylate is 36%, photoinitiator is 3%, light stabilizer is 3%, silane coupling agent is 2%, and wetting agent is 2%. Maintain the temperature at 55℃, stir evenly for 80s, filter, and the obtained solution is the modifier solution.

[0107] (2) Cut out the existing polyethylene substrate as the substrate layer. The substrate thickness t1 is 3.5 μm, and the substrate pore size is... The wavelength is 53.0 nm, and the areal density M1 is 1.8 g / m². 2 Air permeability 75s / 100cc, film breakage temperature MD1 is 151.6℃, heat shrinkage rate at 130℃: MD3 4.5%, TD 33.7%.

[0108] (3) Apply the modifier solution to the substrate layer obtained in step (2) twice, dry it with nitrogen, and cure it under nitrogen with UV light twice for 32 seconds to obtain a composite membrane.

[0109] Example 5

[0110] A composite separator includes a substrate layer and a modified polymer. The substrate layer has a porous structure, and the modified polymer is located within the porous structure. The composite separator has a thickness t2 of 5 μm and an areal density M2 of 3.5 g / m³. 2 The air permeability value Q2 is 325s / 100cc, and the pore size is... The thickness is 42.0 nm, the film breakage temperature MD2 is 173.6℃, ​​the thermal shrinkage rate at 130℃ is MD 7.2%, and TD 8.6%.

[0111] In DSC measurements of the composite diaphragm, the peak path of the first melting peak during the heating process is T1, the energy integral is F1, and the peak value within T1 is T. 01 The peak width is W1; the peak path of the second melting peak is T2, the energy integral is F2, and the peak value in T2 is T. 02 Peak width is W2; T1 = 114.95℃ - 158.94℃; F1 = 884.70mJ; T 01 =145.91℃; W1=7.84℃; T2=162.53℃-292.53℃; F2=109.73mJ; T 02=223.83℃; W2=52.44℃.

[0112] This embodiment provides a method for preparing a composite separator, including the following steps:

[0113] (1) Add the photosensitive polymerizing monomer, photoinitiator, and additives to a mixer. The photosensitive polymerizing monomer is 1,6-hexanediol diacrylate and acrylic hyperbranched resin. The photoinitiator is 184 (1-hydroxycyclohexylphenyl ketone). The additives are light stabilizer 1076, silane coupling agent (methacryloyloxypropyltrimethoxysilane), and wetting agent (polyoxyethylene ether). By mass percentage, 1,6-hexanediol diacrylate is 72%, acrylic hyperbranched resin is 18%, photoinitiator is 4%, light stabilizer is 2%, silane coupling agent is 2%, and wetting agent is 2%. Maintain the temperature at 50°C, stir evenly, filter, and the obtained solution is the modifier solution.

[0114] (2) Take out the existing polyethylene substrate as the substrate layer; the thickness t1 of the substrate layer is 5μm, and the pore size is... The wavelength is 56.0 nm, and the areal density M1 is 2.5 g / m². 2 The air permeability value Q1 is 57s / 100cc, the film breaking temperature MD1 is 152.8℃, and the heat shrinkage rate at 130℃ is MD34.5% and TD33.7%.

[0115] (3) Apply the modifier solution to the substrate layer obtained in step (2) once, and dry it with nitrogen to obtain a composite membrane.

[0116] Comparative Example 1

[0117] A composite diaphragm, obtained by reacting a substrate and a ceramic slurry, has a thickness t2 of 7 μm and an areal density M2 of 5.8 g / m³. 2 The air permeability value Q2 is 133s / 100cc, and the pore size is... Undetermined; film breakage temperature MD2 was 154.4℃; heat shrinkage rate at 130℃ MD 1.3%; TD 1.9%.

[0118] In the DSC measurement of the composite diaphragm, the peak path of the first melting peak during the heating process is T1, the energy integral is F1, and the peak value in T1 is T. 01 Peak width is W1; T1 = 93.29℃ - 178.08℃; F1 = 768.13mJ; T 01 =136.47℃; W1=18.82℃.

[0119] This embodiment also provides a method for preparing a composite membrane, including the following steps:

[0120] (1) Cut out an existing polyethylene substrate as the substrate layer, with a thickness t1 of 5μm and a pore size of The wavelength is 56.0 nm, and the areal density M1 is 2.5 g / m². 2 The air permeability value Q1 is 57s / 100cc, the film breaking temperature MD1 is 152.8℃, the heat shrinkage rate at 130℃ is MD 34.5%, and TD 33.7%.

[0121] (2) A 2μm thick ceramic coating is applied to the substrate layer obtained in step (1) to obtain a composite diaphragm. The ceramic slurry includes ceramic powder, binder and additives.

[0122] Comparative Example 2

[0123] A composite diaphragm, obtained by reacting a substrate with a high-temperature resistant resin, has a thickness t2 of 6 μm and an areal density M2 of 2.7 g / m³. 2 The air permeability value Q2 is 3739s / 100cc, and the pore size is... Undetermined; film breakage temperature MD2 was 203.2℃; heat shrinkage rate at 130℃ MD 0.4%; TD 0.6%.

[0124] In DSC measurements of the composite diaphragm, the peak path of the first melting peak during the heating process is T1, the energy integral is F1, and the peak value within T1 is T. 01 Peak width is W1; T1 = 85.45℃ - 172.44℃; F1 = 1037.63mJ; T 01 =142.28℃; W1=16.00℃.

[0125] This embodiment also provides a method for preparing a composite membrane, including the following steps:

[0126] (1) Cut out an existing polyethylene substrate as the substrate layer, with a thickness t1 of 5μm and a pore size of The wavelength is 56 nm, and the areal density M1 is 2.5 g / m². 2 The air permeability value Q1 is 57s / 100cc, the film breaking temperature MD1 is 152.8℃, the heat shrinkage rate at 130℃ is MD 34.5%, and TD 33.7%.

[0127] (2) The high-temperature resistant resin is dip-coated onto the substrate layer obtained in step (1) and then dried by hot air to obtain a composite diaphragm; the high-temperature resistant resin includes polyetherimide and cellulose.

[0128] Experimental Example

[0129] The substrate layer and composite membrane of each embodiment and comparative example were subjected to performance tests, including:

[0130] 1. Substrate layer thickness t1, pore size Tests were conducted on areal density M1, air permeability Q1, film rupture temperature MD1, and heat shrinkage rate R1 (MD, TD) at 130℃.

[0131] The thickness t1 of the substrate layer: Take a substrate layer sample with a size of 100×50 (length×width), and when the probe of the thickness gauge gently touches the sample surface, calculate the thickness t1 of the diaphragm based on the small displacement or signal change caused by the thickness change between the probe and the sample surface.

[0132] Areal density M1: Calculated by weight / sample area.

[0133] Air permeability value Q1: It is calculated by placing the sample on an air permeability tester under certain temperature and humidity conditions, maintaining a certain gas pressure on both sides of the sample, and measuring the change in gas pressure on the low-pressure side of the sample.

[0134] aperture A circular substrate layer with a radius of 1.3 cm was taken, and after wetting the sample with liquid, the pore size was calculated by measuring the pressure at which the first bubble flow was generated.

[0135] Broken film temperature MD1: Take a substrate layer sample with a specification of 50×10 (length×width), use the TMA clamp to clamp and fix the sample on the thermomechanical analyzer, and continuously increase the temperature from 40℃ to 250℃ at a temperature change rate of 5℃ / min. During the temperature increase, a curve will appear that rises and then flattens out. The inflection point is the broken film temperature MD1.

[0136] Heat shrinkage rate R1 (MD, TD) at 130℃: Take a substrate sample with dimensions of 100×50 (length×width), and measure the length A1 and width B1 of the sample using an optical projector. Set the oven temperature to 130℃, and after reaching the temperature, place the sample in the oven and keep it at that temperature for 1 hour. After removing it and cooling for 10 minutes, measure the length A2 and width B2 of the sample using a projector. Transverse heat shrinkage of the diaphragm R1 (MD) = (A1-B1) / A1×100%. Longitudinal heat shrinkage of the diaphragm R1 (TD) = (A2-B2) / A2×100%.

[0137] 2. Thickness t2 and pore size of the composite diaphragm The test methods for areal density M2, air permeability Q2, film breakage temperature MD2, and heat shrinkage rate at 130℃ R2 (MD, TD) are the same as those for the substrate layer.

[0138] 3. Follower loss situation.

[0139] The composite diaphragm was stretched in one direction, and the powder shedding phenomenon was observed.

[0140] 4. Differential scanning calorimetry

[0141] Under a nitrogen atmosphere, the temperature is continuously increased from 30°C to 300°C at a rate of 5°C / min. The peak path of the first melting peak during the heating process is T1, the energy integral is F1, and the peak value within T1 is T. 01 The peak width is W1; the peak path of the second melting peak is T2, the energy integral is F2, and the peak value in T2 is T. 02 The peak width is W2; calculate F2 / F1×100%.

[0142] The pore size distribution diagram of the composite membrane in Embodiment 1 of the present invention is shown below. Figure 1 As shown; the differential scanning calorimetry (DSC) chart of the composite membrane in Example 1 is shown below. Figure 2 As shown. The pore size distribution diagram of the composite membrane in Embodiment 2 of the present invention is as follows. Figure 3 As shown; the differential scanning calorimetry (DSC) curve of the composite membrane in Example 2 is shown below. Figure 4 As shown. The pore size distribution diagram of the composite membrane in Embodiment 3 of the present invention is as follows. Figure 5 As shown; the differential scanning calorimetry (DSC) graph of the composite membrane in Example 3 is shown below. Figure 6 As shown. The pore size distribution diagram of the composite membrane in Embodiment 4 of the present invention is as follows. Figure 7 As shown; the differential scanning calorimetry (DSC) curve of the composite membrane in Example 4 is shown below. Figure 8 As shown. The pore size distribution diagram of the composite membrane in Embodiment 5 of the present invention is as follows. Figure 9 As shown. The differential scanning calorimetry (DSC) curve of the composite membrane in Example 5 is shown below. Figure 10 As shown. The pore size distribution diagram of the composite membrane in Comparative Example 1 of the present invention is as follows. Figure 11 As shown; the differential scanning calorimetry (DSC) curve of the composite membrane in Comparative Example 1 is shown below. Figure 12 As shown. The pore size distribution diagram of the composite membrane in Comparative Example 2 of the present invention is as follows. Figure 13 As shown; the differential scanning calorimetry (DSC) curve of the composite membrane in Comparative Example 2 is shown below. Figure 14 As shown.

[0143] The test results are shown in Table 1.

[0144] Table 1 Test Results

[0145]

[0146]

[0147] Note: *1 As shown in the figure, there is no single pore size peak; the test process is mostly linear, with some minor curve changes. *2 As shown in the figure, there is no single pore size peak; the test process is characterized by minor curve changes.

[0148] As shown in Table 1, the composite separator obtained by the method of the present invention has a thickness t2 of t2 and a thickness t1 of t1 of the substrate layer that satisfy t2-t1=0. The composite separator has a first endothermic peak and a second endothermic peak under DSC testing, and has suitable peak value, peak width and energy integral. It is beneficial to improve the membrane breaking temperature of the composite separator, reduce the pore closing temperature, improve the heat resistance, and there is no powder shedding phenomenon. It has good structural stability and can improve the energy density of the battery cell.

[0149] The composite membrane obtained by the method in Comparative Example 1 has only one endothermic peak, exhibits powder shedding, and has a relatively low membrane rupture temperature.

[0150] The composite membrane obtained by the method in Comparative Example 2 has only one endothermic peak and extremely poor air permeability.

[0151] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still 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. Such 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 the present invention.

Claims

1. A composite separator, characterized by, It includes a substrate layer and a modified polymer, wherein the substrate layer has a porous structure and the modified polymer is located in the porous structure; The composite diaphragm exhibits a first endothermic peak and a second endothermic peak under DSC testing. The first endothermic peak is located between 110°C and 160°C, and the second endothermic peak is located between 168°C and 295°C.

2. The composite separator of claim 1, wherein It includes at least one of the following features (1) to (5): (1) The peak width W1 of the first endothermic peak is 7-12℃; (2) The energy integral F1 of the first endothermic peak is 800-950 mJ; (3) The peak width W2 of the second endothermic peak is 50-80℃; (4) The energy integral F2 of the second endothermic peak is 100-600 mJ; (5) The energy integral F2 of the second endothermic peak and the energy integral F1 of the first endothermic peak satisfy the following relationship: 10% ≤ F2 / F1 × 100% ≤ 75%.

3. The composite separator of claim 1, wherein The difference between the thickness t2 of the composite diaphragm and the thickness t1 of the substrate layer satisfies: t2-t1=0.

4. The composite separator of claim 1, wherein It includes at least one of the following features (1) to (2): (1) The modified polymer is obtained by polymerization of at least two photosensitive polymer monomers, and at least one of the photosensitive polymer monomers is a binary or multi-component polymer monomer; (2) In the composite membrane, the mass content of the modified polymer is 40% to 60%.

5. The composite separator of claim 4, wherein The photosensitive polymerizing monomers include at least two of pentaerythritol triacrylate, hyperbranched acrylic resin, polyurethane acrylate, 1,6-hexanediol diacrylate, dipentaerythritol hexaacrylate, and acrylic epoxy resin.

6. The composite separator of claim 1, wherein The thickness t1 of the substrate layer is 3-15 μm; the aperture diameter φ1 of the substrate layer is 50-70 nm; the surface density M1 of the substrate layer is 1.8-5 g / m 2 ; the air permeability Q1 of the substrate layer is 30-75 s / 100 cc; the film breaking temperature MD1 of the substrate layer is 150-170℃; the heat shrinkage R1 of the substrate layer at 130℃ is: 30-35% in the longitudinal direction and 29-34% in the transverse direction.

7. The composite diaphragm according to claim 1, characterized in that, It includes at least one of the following features (1) to (5): (1) the areal density M2 of the composite separator is 2.5 to 7 g / m2 2 ; (2) The air permeability value Q2 of the composite diaphragm is 110~330s / 100cc; (3) The pore size φ2 of the composite membrane is 40-65 nm; (4) The membrane rupture temperature MD2 of the composite diaphragm is 170-220℃; (5) The heat shrinkage rate R2 of the composite diaphragm at 130°C is: 0.5% to 7.5% in the longitudinal direction and 0.8% to 9% in the transverse direction.

8. The method of claim 1 to 7, wherein Includes the following steps: A mixture of at least two photosensitive monomers, a photoinitiator, and an additive is heat-treated to obtain a modifier solution. The substrate layer is coated with the modified agent solution, dried, and then cured under ultraviolet light.

9. The method of claim 8, wherein the composite separator is prepared by a method comprising: It includes at least one of the following features (1) to (10): (1) The photoinitiator includes at least one of 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and 2-isopropylthioxanthrone; (2) The photoinitiator in the mixed system has a mass content of 0.5% to 10%; (3) The photosensitive polymerizable monomer has a mass content of 82% to 92% in the mixed system; (4) The photosensitive polymerizing monomer is selected from the first monomer and the second monomer. The first monomer is pentaerythritol triacrylate, 1,6-hexanediol diacrylate, and dipentaerythritol hexaacrylate. The second monomer is acrylic hyperbranched resin, polyurethane acrylate, and acrylic epoxy resin. The mass ratio of the first monomer to the second monomer is (1-4):(1-2). (5) The additives include at least one of silane coupling agents, light stabilizers and wetting agents; (6) In the additives, the silane coupling agent has a mass content of 0.5% to 3% in the mixed system; the light stabilizer has a mass content of 0.1% to 4% in the mixed system; and the wetting agent has a mass content of 0.1% to 2% in the mixed system. (7) The heat treatment temperature is 50-60℃, and the heat treatment time is 30-120s; (8) The coating process is performed 1 to 3 times; (9) The drying process includes nitrogen blowing treatment; (10) The number of UV curing cycles is 1 to 6, and the UV curing time for each cycle is 15 to 35 seconds.

10. A battery, characterized by The composite membrane comprising any one of claims 1 to 7.

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