Diaphragm, electrochemical device, and electronic device

Abstract

The application discloses a diaphragm, an electrochemical device and an electronic device, and belongs to the field of electrochemical energy storage. The diaphragm is used in the electrochemical device, and the diaphragm comprises a base film and a coating arranged on one side or both sides of the base film. The coating comprises a first coating and a plurality of second coatings arranged on the side of the first coating away from the base film. The plurality of second coatings are alternately arranged along the length direction of the first coating. The first coating comprises first inorganic particles and a heat-sensitive polymer. The melting point of the heat-sensitive polymer is 85 DEG C to 130 DEG C. The particle size Dv50 of the first inorganic particles is alpha. The particle size Dv50 of the heat-sensitive polymer is beta. Alpha and beta satisfy the following conditions: beta = alpha + n, 0.3 mu m <= alpha <= 7.1 mu m, and 0 <= n <= 0.2. The diaphragm can improve the cycle performance and thermal abuse performance of the electrochemical device.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, and particularly to membranes, electrochemical devices, and electronic devices. Background Technology

[0002] Inside a battery, the separator acts as a physical barrier between the positive and negative electrodes, its core function being to prevent short circuits while allowing lithium ions to pass freely. Currently, the high-temperature thermal shrinkage performance of the separator has been improved due to the common addition of a ceramic layer to the base film, but the risk of thermal abuse still exists in the battery. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this application provides a separator, an electrochemical device, and an electronic device, aiming to solve the problem of thermal abuse risk in batteries.

[0004] To achieve the above objectives, this application proposes a diaphragm for an electrochemical device. The diaphragm includes a base membrane and coatings disposed on one or both sides of the base membrane. The coatings include a first coating and a plurality of second coatings disposed on the side of the first coating away from the base membrane. The plurality of second coatings are alternately arranged along the length of the first coating. The first coating includes first inorganic particles and a thermosensitive polymer. The melting point of the thermosensitive polymer is 85°C to 130°C. The particle size Dv50 of the first inorganic particles is α, and the particle size Dv50 of the thermosensitive polymer is β. α and β satisfy: β = α + n, 0.3 μm ≤ α ≤ 7.1 μm, 0 ≤ n ≤ 0.2.

[0005] In some embodiments, based on the mass of the first coating, the mass fraction of the thermosensitive polymer is M1, and the mass fraction of the first inorganic particles is M2, wherein M1 and M2 satisfy: 5%≤M1≤50%, 10%≤M2≤90%.

[0006] In some embodiments, the spacing between the plurality of second coatings is a, the width of the second coating is b, and a, b, and M1 satisfy the following relationships: 0.2mm≤0.1M1+a≤0.8mm, 2a≤b≤3a.

[0007] In some embodiments, the orthographic projection of the second coating in the thickness direction of the diaphragm is a parallelogram, and the long side of the parallelogram forms an angle c with the length direction of the diaphragm, where c satisfies 0° < c < 90°.

[0008] In some embodiments, the area occupied by the orthographic projection of the plurality of second coatings in the thickness direction of the diaphragm is 60% to 90% of the area of ​​the base film.

[0009] In some embodiments, the air permeability of the second coating is 8 sec / 100cc to 20 sec / 100cc.

[0010] In some embodiments, the second coating comprises second inorganic particles and a polymer, wherein the polymer has a mass of M3 and the second inorganic particles have a mass of M4, and M3:M4 = (6~7):(3~4).

[0011] In some embodiments, the thermosensitive polymer includes at least one of polyethylene, polypropylene, modified polyamide, and polymethyl methacrylate; and / or, the polymer includes at least one of polyvinylidene fluoride homopolymer, polyvinylidene fluoride copolymer, (polyvinylidene fluoride-hexafluoropropylene) copolymer, polyetherimide, polyacrylic acid, polyacrylate, and polymethyl methacrylate; and / or, the first inorganic particle and the second inorganic particle are each independently selected from at least one of alumina, boehmite, magnesium hydroxide, aluminum hydroxide, silicon dioxide, silicon hydroxide, barium sulfate, zirconium oxide, calcium oxide, titanium dioxide, and cerium dioxide.

[0012] To achieve the above objectives, this application also proposes an electrochemical device comprising an electrode, an electrolyte, and the aforementioned diaphragm.

[0013] To achieve the above objectives, this application also proposes an electronic device including the aforementioned electrochemical device.

[0014] The beneficial effects of this application are as follows: This application provides a separator for electrochemical devices. The first coating, bonded to the base film, comprises inorganic particles and a thermosensitive polymer. When the internal temperature of the battery abnormally rises due to thermal abuse and reaches the melting point of the thermosensitive polymer, the polymer rapidly melts, flows, and blocks the micropores between the first coating, the base film, and the second coating, hindering further lithium-ion migration and actively cutting off the ion current. Furthermore, the inorganic particles and the thermosensitive polymer have similar particle sizes, allowing for uniform dispersion and improving the efficiency of micropore sealing. Simultaneously, multiple gaps exist between the alternating second coatings, which facilitate electrolyte wetting and storage. These gaps provide expansion buffer space for deformation during charge-discharge cycles and allow for more uniform heat distribution from the electrodes, preventing excessive local heat concentration at high temperatures and thus avoiding exacerbating battery thermal abuse. Therefore, the separator of this application can efficiently block ion transport under thermal abuse conditions, improve the separator's electrolyte storage capacity and heat dispersion effect, and simultaneously improve the cycle life and thermal safety performance of the electrochemical device. Attached Figure Description

[0015] The embodiments described in this application are not limited to the accompanying drawings, which are only some of the embodiments described herein. Those skilled in the art can obtain drawings of other embodiments based on the content of this application.

[0016] Figure 1 This is a schematic diagram of the diaphragm cross-section in one embodiment of this application; Figure 2 This is a top view of the diaphragm in one embodiment of this application; Figure 3 This is a top view of the diaphragm in another embodiment of this application.

[0017] Labeling explanation: 1-base film, 201-first coating, 202-second coating. Detailed Implementation

[0018] General terminology: The term "Dv50" is defined as the particle size at 50% of the cumulative volume percentage distribution obtained under instrumental testing.

[0019] The term "heat-sensitive polymer" refers to a polymeric material whose structure or physicochemical properties change significantly when the external temperature changes.

[0020] The term "homogeneous polymer" refers to a polymer compound formed by the polymerization reaction of a single monomer. Its structure is relatively simple and uniform, and all repeating units come from the same monomer.

[0021] The term "copolymer" refers to a polymerization reaction in which two or more monomers participate. The resulting polymer contains two or more monomer units, and is therefore a copolymer.

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. The embodiments of this application may omit unnecessary detailed descriptions.

[0023] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0024] As used herein, the terms “approximately,” “generally,” “substantially,” and “about” are used to describe and indicate minor variations. When used in conjunction with an event or situation, these terms may refer to examples in which the event or situation occurred precisely or in examples in which the event or situation occurred very approximately.

[0025] Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0026] In the detailed description and claims, a list of items connected by the terms "one of," "among," "a kind of," or other similar terms may mean any of the listed items. For example, if items A and B are listed, then the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, then the phrase "one of A, B, and C" means only A; only B; or only C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0027] In the detailed description and claims, the list of items connected by the term "at least one of" can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C.

[0028] Throughout this specification, references to “implementation,” “partial implementation,” “one implementation,” “another approach,” “specific approach,” or “partial approach” mean that at least one implementation or embodiment in this application includes the specific features, structures, materials, or characteristics described in that implementation or embodiment.

[0029] In this application, numerical ranges are involved. Unless otherwise specified, the numerical ranges mentioned above are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form a range not explicitly stated.

[0030] Inside a battery, the separator acts as a physical barrier between the positive and negative electrodes, its core function being to prevent short circuits while allowing lithium ions to pass freely. Currently, the high-temperature performance of separators has been improved due to the common addition of ceramic layers to the base film, but the risk of thermal abuse still exists in batteries.

[0031] In view of this, this application proposes a diaphragm for use in an electrochemical device, with reference to... Figures 1 to 2 The diaphragm includes a base membrane and a coating disposed on one or both sides of the base membrane. The coating includes a first coating 201 and a plurality of second coatings 202 disposed on the side of the first coating 201 away from the base membrane 1. The plurality of second coatings 202 are alternately arranged along the length direction of the first coating. The first coating 201 includes first inorganic particles and a thermosensitive polymer. The melting point of the thermosensitive polymer is 85℃~130℃. The particle size Dv50 of the first inorganic particles 201 is α, and the particle size Dv50 of the thermosensitive polymer is β. α and β satisfy: β=α+n, 0.3μm≤α≤7.1μm, 0≤n≤0.2.

[0032] The first coating 201, bonded to the base film, comprises inorganic particles and a thermosensitive polymer. When the internal temperature of the battery rises abnormally due to abuse and reaches the melting point of the thermosensitive polymer (85°C to 130°C), the polymer rapidly melts, flows, and blocks the micropores between the first coating 201, the base film 1, and the second coating 202, significantly hindering the continued migration of lithium ions and actively cutting off the ion current. Multiple gaps exist between the alternating second coatings 202, allowing for rapid wetting and storage of the electrolyte. These gaps facilitate electrolyte wetting and storage, and provide expansion buffer space for deformation during charge-discharge cycles, while also ensuring a more uniform heat distribution from the electrodes, preventing excessive local heat concentration at high temperatures and thus avoiding further thermal abuse of the battery.

[0033] In some embodiments, the inorganic particles and the thermosensitive polymer particles with similar particle sizes α and β can be uniformly dispersed in the first coating 201. When thermal shutdown occurs, the slightly smaller inorganic particles can more effectively fill the gaps between the thermosensitive polymer skeleton particles, achieving rapid micropore plugging and improving the sensitivity of shutdown and the efficiency of micropore plugging.

[0034] For example, the particle size Dv50α of the inorganic particles can be 0.3μm, 0.5μm, 0.7μm, 0.9μm, 1.1μm, 1.3μm, 1.5μm, 1.7μm, 1.9μm, 2.1μm, 2.3μm, 2.5μm, 2.7μm, 2.9μm, 3.1μm, 3.3μm, 3.5μm, 3.7μm, 3.9μm, 4.1μm, 4.3μm, 4.5μm, 4.7μm, 4.9μm, 5.1μm, 5.3μm, 5.5μm, 5.7μm, 5.9μm, 6.1μm, 6.3μm, 6.5μm, 6.7μm, 6.9μm, 7.1μm, or fall within the range of any two of the above values.

[0035] For example, the particle size Dv50β of the thermosensitive polymer can be 0.3μm, 0.5μm, 0.7μm, 0.9μm, 1.1μm, 1.3μm, 1.5μm, 1.7μm, 1.9μm, 2.1μm, 2.3μm, 2.5μm, 2.7μm, 2.9μm, 3.1μm, 3.3μm, 3.5μm, 3.7μm, 3.9μm, 4.1μm, 4.3μm, 4.5μm, 4.7μm, 4.9μm, 5.1μm, 5.3μm, 5.5μm, 5.7μm, 5.9μm, 6.1μm, 6.3μm, 6.5μm, 6.7μm, 6.9μm, 7.1μm, 7.3μm, or within the range of any two of the above values.

[0036] Preferably, the particle size Dv50 β of the thermosensitive polymer is 0.3 μm to 2 μm. More preferably, the particle size Dv50 β of the thermosensitive polymer is 0.3 μm to 0.9 μm.

[0037] According to some embodiments of this application, the first coating 201 further includes a binder. When the inorganic particles in the first coating have a large particle size or a high content, a small amount can be added as per industry practice to enhance the adhesion between the base film and multiple second coatings. The binder includes at least one of polyvinylidene fluoride, polyvinyl alcohol, polyacrylonitrile, polyvinyl acetate, styrene-butadiene latex, styrene-acrylic latex, polyacrylic acid, polyvinylidene fluoride homopolymer, polyvinylidene fluoride copolymer, polyetherimide, polyacrylic acid, polyacrylate, and polymethacrylic acid.

[0038] According to some embodiments of this application, in the cell structure, the second coating 202 is bonded to the positive electrode of the electrochemical device. The layered transition metal oxide in the positive electrode will decompose under high temperature conditions, releasing oxygen and generating a large amount of heat with the electrolyte, further pushing up the temperature. Therefore, the low melting point polymer in the first coating of the separator will melt and close rapidly under this high temperature condition, blocking ion flow and preventing the internal temperature of the battery from rising further. At the same time, the coating spacing in the second coating makes the heat distribution between the positive electrode and the separator interface more uniform.

[0039] According to some embodiments of this application, the orthographic projection of the second coating in the thickness direction of the separator is an alternating arrangement of rectangles, parallelograms, corrugations, broken lines, dot lattices, etc., as long as multiple second coatings can achieve stable bonding between the separator and the electrode. In some embodiments, stable bonding means that the adhesion force between the second coating and the positive electrode is ≥4N / m under the conditions of 85°C and 1.2MPa.

[0040] According to some embodiments of this application, the selection of the base membrane is not particularly limited, as long as it is a commonly used separator base membrane in secondary batteries. In particular, a base membrane with low resistance to electrolyte ion movement and excellent electrolyte permeability is preferred, including at least one of polyolefins, polyesters, polyacetals, polyamides, polyethylene terephthalate, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyacrylonitrile, polyvinylidene fluoride, polyoxymethylene, polyoxymethylene, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polysulfone, and polymethyl methacrylate. Some non-limiting examples of polyolefins include at least one of polyethylene (PE), ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), polypropylene (PP), polyethylene-polypropylene copolymer (PE-PP), and polyethylene-polypropylene-polyethylene copolymer.

[0041] According to some embodiments of this application, the thickness of the base film 1 is 3 μm to 20 μm.

[0042] For example, the thickness of the base film is 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, or within any two of the above values.

[0043] According to some embodiments of this application, the thickness of the first coating 201 is 0.5 μm to 1 μm.

[0044] For example, the thickness of the first inorganic coating can be 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, or 1.0 μm, or fall within the range of any two of the above values. Preferably, the thickness of the first coating is 0.5 μm to 0.75 μm.

[0045] According to some embodiments of this application, the thickness of the second coating 202 is 0.5 μm to 1 μm.

[0046] For example, the thickness of the first inorganic coating can be 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, or 1.0 μm, or fall within the range of any two of the above values. Preferably, the thickness of the second coating is 0.75 μm to 1 μm.

[0047] According to some embodiments of this application, a first coating layer 201 and a plurality of alternately arranged second coating layers 202 are sequentially stacked on both sides of the base film 1. According to other embodiments, a first coating layer 201 and a plurality of alternately arranged second coating layers 202 are sequentially disposed on one side of the base film 1, while the other side is a conventional ceramic coating and / or a conventional adhesive layer.

[0048] According to some embodiments of this application, based on the mass of the first coating, the mass fraction of the thermosensitive polymer is M1, and the mass fraction of the first inorganic particles is M2, wherein M1 and M2 satisfy: 5%≤M1≤50%, 10%≤M2≤90%.

[0049] According to some embodiments of this application, under the premise that M1 satisfies 5%≤M1≤50%, if the mass ratio of the thermosensitive polymer material is less than 5%, the melting and plugging effect is not obvious, the heat spreads rapidly, and the structure of the positive electrode active material collapses under high temperature conditions, resulting in cell thermal failure. If the mass ratio of the thermosensitive polymer is greater than 50%, black spots and lithium plating are likely to appear at the interface of the battery during long-term cycling, reducing the cycle life of the battery.

[0050] For example, based on the mass of the first coating, the mass M1 of the thermosensitive polymer can be 5%, 8%, 11%, 14%, 17%, 20%, 23%, 26%, 29%, 32%, 35%, 38%, 41%, 44%, 47%, 50%, or within any two of the above values. Preferably, the mass M1 of the thermosensitive polymer is 10% to 30%.

[0051] For example, based on the mass of the first coating, the mass M2 of the first inorganic particles can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or within the range of any two of the above values. Preferably, the mass M2 of the first inorganic particles is 50% to 95%.

[0052] According to some embodiments of this application, see Figure 3 The second coating 202 is projected as a parallelogram in the thickness direction of the diaphragm. The long side of the parallelogram forms an angle c with the length direction of the diaphragm, where c satisfies 0° < c < 90°.

[0053] Compared to the scheme where the orthographic projection is a rectangle, the orthographic projection is an inclined parallelogram, which prevents the first coating edge from being aligned and superimposed multiple times during winding, effectively disperses the mechanical stress generated during separator winding and operation, avoids stress concentration, provides more balanced interfacial adhesion, and optimizes electrolyte distribution, ultimately significantly improving battery manufacturing yield, safety performance and cycle durability.

[0054] For example, c can be 3°, 5°, 10°, 15°, 20°, 25°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85°, 89°, or within the range of any two of the above values.

[0055] According to some embodiments of this application, the area occupied by the orthographic projection of the plurality of second coatings 202 in the thickness direction of the diaphragm is 60% to 90% of the area of ​​the base film.

[0056] The lower limit of 60% of the second coating area ensures sufficient mechanical adhesion between the separator and the electrode, guaranteeing the interface stability and structural safety of the battery; the upper limit of 90% of the second coating area leaves gaps for electrolyte wetting and ion transport, preventing the increase in battery internal resistance caused by excessive coverage of the second coating when the first coating is already in place.

[0057] For example, the area occupied by the second coating is 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, or 90% of the base film area, or falls within the range of any two of the above values. Preferably, the area occupied by the second coating is 70% to 85% of the base film area.

[0058] According to some embodiments of this application, the spacing between the plurality of second coatings 202 is a, the width of the second coating 202 is b, and a, b, and M1 satisfy the following relationship: 0.2mm≤0.1M1+a≤0.8mm, 2a≤b≤3a.

[0059] If M1 is large (high content of thermosensitive polymer), the thermal shutdown effect is stronger, but it may affect the ionic conductivity at normal temperature. By limiting 0.1M1+a to between 0.2 mm and 0.8 mm, it is ensured that the spacing a of the second coating is adjusted accordingly when M1 changes: when M1 increases, a can be appropriately reduced to keep the total not exceeding the upper limit and avoid excessive gap leading to thermal shutdown delay; when M1 decreases, a can be increased to ensure sufficient ion channels.

[0060] The coating width b is moderately larger than the spacing a by 2 to 3 times to provide continuous mechanical support and suppress the shrinkage or deformation of the diaphragm at high temperatures. At the same time, b should not be too large to hinder ion diffusion, while b should not be too small to provide sufficient support for the mechanical properties of the diaphragm.

[0061] For example, the spacing 'a' between the plurality of second coatings 202 can be 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, or 0.8 mm, or fall within the range of any two of the above values. Preferably, the spacing 'a' between the plurality of second coatings 202 can be 0.2 to 0.4 mm.

[0062] According to some embodiments of this application, the width b of the second coating 202 can be 0.4mm, 0.6mm, 0.8mm, 1.0mm, 1.2mm, 1.4mm, 1.6mm, 1.8mm, 2.0mm, 2.2mm, or 2.4mm, or fall within the range of any two of the above values. Preferably, the width b of the plurality of second coatings 202 is 0.6mm to 0.8mm.

[0063] In some embodiments, the preparation of the second coating 202 includes roll coating using a gravure roller with a specially designed gap.

[0064] According to some embodiments of this application, the air permeability of the second coating 202 is 8 sec / 100cc to 20 sec / 100cc.

[0065] Thanks to the thermal shutdown effect of the first coating, the second coating is able to reduce the permeability to this range without posing a safety hazard. The low permeability of the second coating within this range enables lower ion migration resistance, resulting in excellent high-rate performance and low internal resistance of the battery under normal operating conditions, providing an efficient ion transport channel. On the other hand, the low permeability characteristic is usually related to its dense microstructure, which manifests as strong mechanical strength of the coating.

[0066] For example, the air permeability of the second coating 202 is 10 sec / 100cc, 11 sec / 100cc, 12 sec / 100cc, 13 sec / 100cc, 14 sec / 100cc, 15 sec / 100cc, 16 sec / 100cc, 17 sec / 100cc, 18 sec / 100cc, 19 sec / 100cc, 20 sec / 100cc, or within the range of any two of the above values.

[0067] According to some embodiments of this application, the second coating comprises second inorganic particles and a polymer, wherein the mass of the polymer is M3 and the mass of the second inorganic particles is M4, and M3:M4 = (6~7):(3~4).

[0068] The second inorganic particles dispersed in the polymer matrix enhance the rigidity, puncture resistance, and heat resistance of the second coating. Together with the first inorganic particles in the first coating, they inhibit the thermal shrinkage of the base film at high temperatures, providing the diaphragm with consistent thermal dimensional stability.

[0069] For example, M3:M4 can be 6.0:4.0, 6.2:3.8, 6.4:3.6, 6.6:3.4, 6.8:3.2, 7.0:3.0, or fall within the range of any two of the above values.

[0070] In some embodiments, the polymer of the second coating can be selected from any polymers that can achieve an adhesion force of ≥4 N / m between the second coating and the positive electrode sheet under the conditions of 85°C and 1.2 MPa, provided that the above-mentioned spacing and width are met.

[0071] According to some embodiments of this application, the thermosensitive polymer includes at least one of polyethylene, polypropylene, modified polyamide, and polymethyl methacrylate.

[0072] According to some embodiments of this application, the heat-sensitive polymer is polyethylene (PE). Polyethylene has high crystallinity and a narrow melting range. When polyethylene reaches its melting point, it can quickly melt and plug the pores, providing rapid and sensitive thermal shutdown in the early stages of battery thermal abuse and preventing further deterioration of thermal abuse.

[0073] According to some embodiments of this application, the heat-sensitive polymer is polypropylene (PP). Polypropylene has a slightly higher melting point than polyethylene, and compared to polyethylene, it can provide better skeletal support for the coating, thereby improving the puncture resistance and overall rigidity of the first coating of the diaphragm.

[0074] According to some embodiments of this application, the thermosensitive polymer is polymethyl methacrylate (PMMA). PMMA has excellent affinity and wettability for carbonate electrolytes and good compatibility with commonly used binders such as PVDF. When thermal abuse does not occur, PMMA, when used as the first coating, can reduce the contact angle between the first coating and the electrolyte in the gap between the second coating and the second coating, thereby effectively reducing the battery's internal resistance and improving rate performance and cycle life. When thermal abuse occurs, PMMA softens and flows, participating in the pore blockage.

[0075] According to some embodiments of this application, the thermosensitive polymer-modified polyamide involves adjusting its thermal response temperature to the range of 85°C to 130°C through copolymerization, blending, or other methods. Compared to the three materials mentioned above, the modified polyamide can impart higher mechanical strength to the first coating, effectively resisting lithium dendrite penetration and physical damage during the manufacturing process, and providing better protection against lithium plating.

[0076] According to some embodiments of this application, the polymer of the second coating includes at least one selected from polyvinylidene fluoride homopolymer, polyvinylidene fluoride copolymer, (polyvinylidene fluoride-hexafluoropropylene) copolymer, polyetherimide, polyacrylic acid, polyacrylate, and polymethacrylic acid. Preferably, the polymer of the second coating includes at least one selected from polyvinylidene fluoride homopolymer, polyvinylidene fluoride copolymer, and (polyvinylidene fluoride-hexafluoropropylene) copolymer.

[0077] According to some embodiments of this application, the first inorganic particle and the second inorganic particle are each independently selected from at least one of alumina, boehmite, magnesium hydroxide, aluminum hydroxide, silicon dioxide, silicon hydroxide, barium sulfate, zirconium oxide, calcium oxide, titanium dioxide, and cerium dioxide. The microscopic shape of the inorganic particles can be square, plate-like, spherical, etc., and can be regular or irregular.

[0078] To address the aforementioned problems, this application also proposes an electrochemical device, wherein the electrochemical device battery cell includes an electrode, an electrolyte, and the aforementioned separator. The electrochemical device is one of a battery cell, a battery module, or a battery pack.

[0079] An electrochemical device includes any device in which an electrochemical reaction occurs to convert chemical energy into electrical energy and vice versa. Specific, non-limiting examples include all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0080] According to some embodiments of this application, regardless of how the positive electrode, negative electrode and electrolyte are conventionally selected, as long as the battery cell includes the above-mentioned separator, the battery cell can obtain the aforementioned beneficial effects.

[0081] According to some embodiments of this application, the positive electrode sheet includes a positive current collector and a positive active material layer, wherein the positive active material layer includes a positive conductive agent, a positive active material, and a positive binder.

[0082] According to some embodiments of this application, the positive electrode conductive agent includes carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, mesoporous carbon, etc.

[0083] According to some embodiments of this application, the positive electrode active material is selected from LiCoO2, LiNiO2, and LiNi. x Mn y O2, Li 1+ z Ni x Mn y Co 1-x-y O2, LiNi x Co y Al z The group consisting of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, Li2MnO3, LiFeO2, LiFePO4, LiMnPO4, and combinations thereof, wherein each x is independently 0.2 to 0.9; each y is independently 0.1 to 0.45; and each z is independently 0 to 0.2. The positive electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as positive electrode active materials.

[0084] According to some embodiments of this application, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer. The positive electrode binder of this application is not limited to the above materials, but also includes other materials that can be used as battery positive electrode binders.

[0085] According to some embodiments of this application, the negative electrode sheet includes a negative current collector and a negative electrode active material layer, wherein the negative electrode active material layer includes a negative electrode conductive agent, a negative electrode active material, and a negative electrode binder.

[0086] According to some embodiments of this application, the negative electrode conductive agent may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon tubes, carbon nanotubes, activated carbon, and mesoporous carbon.

[0087] According to some embodiments of this application, the negative electrode active material may include natural graphite particles, synthetic graphite particles, hard carbon, soft carbon, mesophase carbon microspheres (MCMB), Sn, SnO2, SnO, Li4Ti5O 12 The negative electrode active material is selected from at least one of LTO, Si material, silicon-carbon (Si-C) composite material, silicon-nitrogen (Si-N) composite material, and silicon-oxygen (Si-O) composite material. The negative electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as negative electrode active materials for batteries.

[0088] According to some embodiments of this application, the negative electrode binder may include at least one of polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, polyacrylamide, styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylic acid-acrylonitrile-acrylamide copolymer, acrylic acid-acrylonitrile-acrylate copolymer, acrylonitrile-butadiene rubber, nitrile rubber, acrylonitrile-styrene-butadiene copolymer, acryloyl rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, carboxymethyl chitosan, polyester, polyamide, polyether, polyimide, polycarboxylic acid ester, polycarboxylic acid, polyurethane, alginate, fluorinated polymer, chlorinated polymer, polyvinylidene fluoride, and poly(vinylidene fluoride)-hexafluoropropylene. The negative electrode binder of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as battery negative electrode binders.

[0089] According to some embodiments of this application, the electrolyte of the electrochemical device may include an organic solvent and a lithium salt. The use of organic solvents is not limited, as long as they can serve as a medium for the movement of ions participating in the battery's electrochemical reaction. Specifically, the organic solvent may be an ester-based solvent, such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone, etc.; an ether-based solvent, such as dibutyl ether, tetrahydrofuran, etc.; a ketone-based solvent, such as cyclohexanone; an aromatic hydrocarbon-based solvent, such as benzene, fluorobenzene, etc.; a carbonate-based solvent, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), etc.; an alcohol-based solvent, such as ethanol, isopropanol, etc.; or a nitrile, such as R-CN (where R is a straight-chain, branched, or cyclic C3 to C4 chain). 20The solvents include hydrocarbon groups (which may include double bonds, aromatic rings, or ether bonds); amide solvents, such as dimethylformamide; dioxolane solvents, such as 1,3-dioxolane; or sulfolane solvents, etc. Preferably, carbonate solvents are preferred, and more preferably cyclic carbonates with high ionic conductivity and high dielectric constant, such as ethylene carbonate or propylene carbonate, which can improve the charge-discharge performance of the battery, in mixtures with low-viscosity linear carbonate compounds (such as ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.).

[0090] The lithium salt can be any compound that can provide lithium ions for lithium secondary batteries, without any particular limitation. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. The concentration of the lithium salt is preferably in the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, thereby exhibiting excellent electrolyte performance, and lithium ions can move effectively.

[0091] To address the aforementioned problems, this application also provides an electronic device, including the electrochemical device described in this application.

[0092] The application of the electrochemical device in this application is not particularly limited, and it can be used in any electronic device known in the prior art. According to some embodiments of this application, the electronic device includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, android robots, etc.

[0093] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the reagents used, unless otherwise specified, are commercially available reagents and materials. The source information of the raw materials used in the following examples and comparative examples is for illustrative purposes only and does not constitute any restriction on the procurement of raw materials. Those skilled in the art will know that the relevant raw materials can be obtained through other commercial channels or prepared by conventional methods in the art.

[0094] The CAS numbers and supplier information for the main raw materials used in this application are as follows: .

[0095] Example 1 1. Preparation of the diaphragm Slurry preparation: Alumina particles with a Dv50 of 0.5 μm and polyethylene with a particle size of 0.3 μm are mixed at a mass ratio of 80:20. A small amount of binder polyacrylic acid is added to the solvent (N-methylpyrrolidone (NMP)). After stirring and dispersing completely, the first coating slurry is obtained. A polymer (polyvinylidene fluoride-hexafluoropropylene) copolymer is mixed with alumina particles at a mass ratio of 7:3. The mixture is added to the NMP solvent and stirred and dispersed completely to obtain the second coating slurry. Diaphragm Coating: A polyethylene membrane with a porosity of 36% and an air permeability of 145 sec / 100cc is used as the base membrane. A conventional boehmite ceramic layer is coated on one side of the base membrane with a coating thickness of 0.5 μm. A first coating slurry is applied to the side of the base membrane opposite to the conventional boehmite ceramic layer, with a coating thickness of 0.5 μm. After drying, a second coating slurry is applied to the first coating using a specially designed gap roller. The coating width of the coated area is 0.70 mm, and the spacing between multiple second coatings is... The first layer has a thickness of 0.35 mm, the second layer has a thickness of 0.75 μm, and the second layer has an air permeability of 9 sec / 100cc. The area occupied by the orthogonal projection of multiple second layers in the thickness direction of the diaphragm is 85% of the area of ​​the base film. Then, a conventional adhesive layer is coated on the conventional boehmite ceramic layer using a micro-gravure roller coating method. The coating thickness is 0.75 μm, and the adhesive layer has an air permeability of 13 sec / 100cc. After the coated diaphragm is cleaned and dried by a coagulation bath mixed solution (NMP) and an aqueous solution, the diaphragm is obtained.

[0096] 2. Preparation of the positive electrode sheet Lithium cobalt oxide (CCO), acetylene black (CCO), and polyvinylidene fluoride (PVDF) (CCO) binder were mixed in a mass ratio of 82:8:10 and stirred evenly under vacuum to obtain a CCO slurry with a solid content of 75.2%–78.2%. Aluminum foil was used as the CCO current collector, and the CCO slurry was uniformly coated on both sides of an 8μm aluminum foil. After drying, cold pressing, and cutting, the CCO electrode sheet was obtained.

[0097] 3. Preparation of negative electrode sheet Artificial graphite (anode active material), acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) are thoroughly mixed in a deionized water solvent system at a mass ratio of 96:1:1.5:1.5 to obtain a cathode slurry with a solid content of 34.5% to 37.5%. This slurry is coated onto Cu foil (anode current collector), dried, cold-pressed, and slit to obtain the cathode sheet.

[0098] 4. Preparation of electrolyte In a dry argon-atmospheric glove box, propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) were mixed in a mass ratio of 30:30:40 to obtain an organic solvent. Lithium salt LiPF6 was then added to the organic solvent, dissolved, and mixed thoroughly to obtain the electrolyte. The mass concentration of LiPF6 in the electrolyte was 8%.

[0099] 5. Preparation of lithium-ion secondary batteries The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes for safety isolation. The electrode assembly is then wound to form the final electrode assembly. This assembly is placed in a packaging shell, infused with electrolyte, and sealed to obtain a lithium-ion secondary battery.

[0100] Examples 2 to 14 Examples 2-14 use the same preparation method as Example 1, but differ from Example 1 in that: the type, particle size and proportion of the thermosensitive polymer in the first coating, the particle size and proportion of alumina in the first coating, and the composition and structural parameters of the second coating are different.

[0101] Comparative Example 1 Comparative Example 1 uses the same preparation method as Example 1, but differs from Example 1 in that: the first coating does not contain a heat-sensitive polymer, the first coating consists of alumina particles with a Dv50 of 0.5 μm and a proportion of 80 wt% and a binder of polyacrylic acid of 20 wt%, and the second coating is not arranged alternately.

[0102] Comparative Example 2 Comparative Example 2 uses the same preparation method as Example 1, except that the first coating does not contain a heat-sensitive polymer. The first coating consists of alumina particles with a Dv50 of 0.4 μm, accounting for 80 wt%, and a binder of polyacrylic acid of 20 wt%.

[0103] Comparative Example 3 Comparative Example 3 uses the same preparation method as Example 1, but differs from Example 1 in that the second coating is completely coated on the first coating and is not arranged alternately.

[0104] Comparative Example 4 Comparative Example 4 was prepared using the same method as Example 1, except that the Dv50 of the thermosensitive polymer was 0.05 μm and the Dv50 of the alumina particles was 0.5 μm.

[0105] Comparative Example 5 Comparative Example 5 was prepared using the same method as Example 1, except that the Dv50 of the thermosensitive polymer was 0.3 μm and the Dv50 of the alumina particles was 0.2 μm.

[0106] The parameters of the examples and comparative examples are recorded in Table 2.

[0107] Furthermore, performance tests were conducted on the above embodiments and comparative examples, and the test methods are as follows: (1) Dv50 test Particle size distribution D50 was measured using a Mastersizer3000+ laser diffractometer to obtain the particle size at 50% of the cumulative volume % distribution.

[0108] (2) Air permeability test The permeability was assessed using a Gurley 4110N permeability meter at a constant pressure difference of 1.23 kPa by measuring the time required for 100 mL of gas to pass through a dry second-coated sample.

[0109] (3) Capacity retention test The lithium-ion batteries prepared in the examples and comparative examples were placed in an environment of 25°C, first left to stand for 1 hour, then charged at a constant current of 3.5C to 4.53V, then charged at a constant voltage of 4.53V to the cutoff rate of 0.25C, left to stand for 5 minutes, and then discharged at a constant current of 0.7C to 3.0V, and cycled 800 times.

[0110] (4) Cell thickness expansion rate test Using the YPZ-110 cell in-situ expansion test system, the equipment constant pressure was set to 600g. The battery was placed in an environment of 25℃ and left to stand for 4 hours. The same number of cycles of cell charging and discharging were used in the (3) capacity retention rate test to obtain the cell thickness expansion rate.

[0111] (5) Liquid retention coefficient test The test was conducted in accordance with the national standard GB / T39748.6-2021.

[0112] (6) Lithium plating test At a temperature of 25°C, the separators prepared in the examples and comparative examples were assembled into lithium-ion batteries. The batteries were charged at a constant current of 3C to 4.35V, then charged at a constant current and voltage of 1.8C to 4.48V, with a cutoff current of 0.05C, and then discharged at 0.7C to 3.0V. Following the above charge-discharge cycle, the lithium-ion batteries were subjected to 50 cycles to obtain fully charged batteries. The battery interface was then disassembled, the state of the negative electrode was photographed, the area of ​​lithium plating on the interface was counted, and the lithium plating level was evaluated according to the standards in Table 1.

[0113] Table 1. Evaluation Criteria for Lithium Plaque Grade on Negative Electrode Sheets After Charge and Discharge of Lithium-ion Batteries .

[0114] (7) Thermal abuse test Five lithium-ion samples were prepared for both the examples and the comparative examples. The batteries were charged to 3.0V at a constant current and constant voltage of 1C. The cells were then placed in a high-temperature environment for 30 minutes (temperature ≥ 130°C).

[0115] The results of the examples and comparative examples are recorded in Table 3.

[0116] Table 2. Parameters of Examples and Comparative Examples

[0117] Table 3. Performance Results of Examples and Comparative Examples .

[0118] The performance results show that, according to Examples 1-7 and Comparative Examples 1, 2, and 3, when the composite separator in Example 1 is used, the overall cell performance remains optimal, and the battery thermal abuse performance can be improved by ≥2°C without deteriorating the cycle capacity retention rate and thickness expansion rate.

[0119] The results of Examples 1, 5, and 6 and Comparative Examples 4-5 show that the larger the Dv50β of the thermosensitive polymer, the more significant its impact on cycle performance and thickness expansion rate. Under the same area, the larger the Dv50 of the thermosensitive polymer, the lower its ionic conductivity, and the easier it is for lithium plating to occur at the negative electrode interface. However, the smaller the Dv50 of the thermosensitive polymer, the less significant its melting and plugging effect under high temperature conditions, thus failing to improve thermal abuse performance. Furthermore, the larger the Dv50 of both inorganic particles and the thermosensitive polymer, the more difficult it is to process.

[0120] The results from Examples 1, 8-10, and Comparative Example 3 show that the spacing 'a' of the second coating is preferably around 0.35 mm. In Example 8, the spacing is small, and the improvement in capacity retention and thickness rebound rate is not significant. In Examples 9 and 10, the spacing is large, and the adhesion between the separator and the electrode is weakened, affecting the battery cycle performance. In Comparative Example 3, the second coating has no spacing, which leads to the failure of the thermal abuse test before 133°C, and also has a significant adverse effect on cycle performance and liquid retention.

[0121] The results of Examples 10-12 and Example 1 show that, with the same coating spacing, the smaller the coating width, the weaker the adhesion between the separator and the electrode; the larger the coating width, the more it affects the liquid retention effect and deteriorates the battery cycle performance.

[0122] The results of Examples 13-14 and Comparative Example 5 show that when the mass ratio of inorganic particles in the second coating decreases or is absent, the liquid retention coefficient decreases, which exacerbates lithium plating on the negative electrode, thereby reducing the capacity retention rate and increasing the thickness expansion.

[0123] In summary, this invention improves the electrolyte storage space of the battery cell by optimizing the mass ratio and average particle size of low-melting-point polymers in the inorganic coating, as well as the distribution pattern and spacing of the polymer coating, resulting in a composite coating structure that maintains a relatively thin separator. This leads to a significant improvement in the long-cycle performance and thermal abuse resistance of the prepared secondary battery. Furthermore, the separator fabrication method is simple, easy to implement, and has promising application prospects.

[0124] When the term "embodiment" is used in the specification, it means that the invention has at least one embodiment that includes the specific feature, structure, material, or property. Therefore, expressions such as "in some embodiments," "in certain embodiments," and "exemplary" used throughout the document do not necessarily refer to the same embodiment. Furthermore, the specific feature, structure, material, or property can be combined in any suitable manner in one or more embodiments.

[0125] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the invention, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the invention.

Claims

1. A diaphragm for use in an electrochemical device, characterized in that, The diaphragm includes a base membrane and a coating disposed on one or both sides of the base membrane. The coating includes a first coating and a plurality of second coatings disposed on the side of the first coating away from the base membrane. The plurality of second coatings are arranged alternately along the length of the first coating. The first coating comprises first inorganic particles and a thermosensitive polymer, wherein the melting point of the thermosensitive polymer is 85℃~130℃, the particle size Dv50 of the first inorganic particles is α, and the particle size Dv50 of the thermosensitive polymer is β, wherein α and β satisfy: β=α+n, 0.3μm≤α≤7.1μm, 0≤n≤0.

2.

2. The diaphragm according to claim 1, characterized in that, Based on the mass of the first coating, the mass fraction of the thermosensitive polymer is M1, and the mass fraction of the first inorganic particles is M2, where M1 and M2 satisfy: 5%≤M1≤50%， 10%≤M2≤90%。 3. The diaphragm according to claim 2, characterized in that, The spacing between the plurality of second coatings is a, and the width of the second coating is b. a, b, and M1 satisfy the following relationships: 0.2mm≤0.1M1+a≤0.8mm, 2a≤b≤3a.

4. The diaphragm according to claim 1, characterized in that, The second coating is projected onto the membrane thickness direction as a parallelogram, and the long side of the parallelogram forms an angle c with the length direction of the membrane, where c satisfies 0° < c < 90°.

5. The diaphragm according to claim 4, characterized in that, The area occupied by the orthographic projection of the plurality of second coatings in the thickness direction of the diaphragm is 60% to 90% of the area of ​​the base film.

6. The diaphragm according to claim 5, characterized in that, The air permeability of the second coating is 8 sec / 100cc to 20 sec / 100cc.

7. The diaphragm according to claim 1, characterized in that, The second coating comprises second inorganic particles and a polymer, wherein the polymer has a mass of M3 and the second inorganic particles have a mass of M4, and M3:M4 = (6~7):(3~4).

8. The diaphragm according to any one of claims 1 to 7, characterized in that, The thermosensitive polymer includes at least one of polyethylene, polypropylene, modified polyamide, and polymethyl methacrylate; And / or, the polymer includes at least one of polyvinylidene fluoride homopolymer, polyvinylidene fluoride copolymer, (polyvinylidene fluoride-hexafluoropropylene) copolymer, polyetherimide, polyacrylic acid, polyacrylate, and polymethacrylic acid; And / or, the first inorganic particle and the second inorganic particle are each independently selected from at least one of alumina, boehmite, magnesium hydroxide, aluminum hydroxide, silicon dioxide, silicon hydroxide, barium sulfate, zirconium oxide, calcium oxide, titanium dioxide, and cerium dioxide.

9. An electrochemical device, characterized in that, It includes electrodes, electrolyte, and a diaphragm according to any one of claims 1 to 8.

10. An electronic device, characterized in that, Includes the electrochemical device as described in claim 9.

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