Composite diaphragm and lithium ion battery

Abstract

The invention relates to a composite diaphragm and a lithium ion battery. The composite diaphragm comprises a base membrane which is provided with a first surface and a second surface which are opposite; the first ceramic layer is positioned on the first surface of the base film; the first high-temperature-resistant layer is positioned on one side, far away from the second surface, of the first ceramic layer; the second ceramic layer is positioned on one side of the second surface of the base film; and the second high-temperature-resistant layer is positioned between the second surface of the base film and the second ceramic layer.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a composite separator and a lithium-ion battery. Background Technology

[0002] In high-energy-density lithium-ion batteries, the separator, as a key component ensuring safety, not only needs to possess good ion conductivity but also needs to maintain dimensional stability at high temperatures to prevent short circuits between the positive and negative electrodes due to thermal shrinkage. To this end, existing technologies often employ composite high-temperature resistant materials on the surface of polyolefin-based films to improve overall thermal stability. However, as battery systems evolve towards high-nickel cathodes and silicon-carbon anodes, the cathode side faces challenges such as high-voltage oxidation, lattice oxygen release, and free radical attack, while the anode side faces challenges such as strong reducing properties, lithium dendrite growth, and interfacial side reactions. For example, while PTFE (polytetrafluoroethylene) exhibits excellent oxidation resistance, its interfacial stability with the active lithium anode is poor, and direct contact may lead to continuous side reactions and battery performance degradation. Traditional composite separator structures face new interfacial compatibility challenges.

[0003] Therefore, there is an urgent need for a new type of diaphragm structure design that can overcome the limitations of symmetry and adapt to the functional differences between the positive and negative electrodes. Summary of the Invention

[0004] The technical problem to be solved by the embodiments of the present invention is to provide a composite separator and a lithium-ion battery that can overcome the symmetry limitation and adapt to the functional differences between the positive and negative electrodes.

[0005] To address the aforementioned technical problems, the present invention provides a composite separator, comprising: a base membrane having opposing first and second sides; a first ceramic layer located on the first side of the base membrane; a first high-temperature resistant layer located on the side of the first ceramic layer away from the second side; a second ceramic layer located on the side of the second side of the base membrane; and a second high-temperature resistant layer located between the second side of the base membrane and the second ceramic layer.

[0006] In one feasible implementation, the first side of the base film faces the negative electrode, and the first high-temperature resistant layer is a high-temperature resistant polymer film compatible with the negative electrode.

[0007] In one feasible embodiment, the material of the high-temperature resistant polymer film is selected from one or a mixture of multiple of polyphenylene sulfide, polyethersulfone, polyurethane, polyethylene terephthalate, polyimide, polybenzimidazole (PBI), and polyphenylene ether.

[0008] In one feasible implementation, the second high-temperature resistant layer is a PTFE porous membrane.

[0009] In one feasible embodiment, the composite membrane further includes an adhesive layer located between the second high-temperature resistant layer and the second surface, for bonding the second high-temperature resistant layer to the second surface of the base membrane.

[0010] In one feasible embodiment, the adhesive layer includes a second adhesive, which includes one or more of water-based adhesives and oil-based adhesives.

[0011] In one feasible implementation, the thickness of the first high-temperature resistant layer is 10 micrometers to 25 micrometers.

[0012] In one feasible implementation, the thickness of the second high-temperature resistant layer is 10 micrometers to 25 micrometers.

[0013] In one feasible implementation, the thickness of the first ceramic layer is 0.5 micrometers to 6 micrometers.

[0014] In one feasible implementation, the thickness of the second ceramic layer is 0.5 micrometers to 6 micrometers.

[0015] In one feasible implementation, the first ceramic layer comprises a plurality of ceramic particles, and the second ceramic layer comprises a plurality of ceramic particles.

[0016] In one feasible implementation, the ceramic particles comprise one or a mixture of more than one of oxide ceramics, nitride ceramics, and carbide ceramics.

[0017] In one feasible implementation, the first ceramic layer further includes a first adhesive, and the second ceramic layer further includes a first adhesive, wherein the first adhesive comprises one or a mixture of more than one of water-based adhesives and oil-based adhesives.

[0018] Accordingly, this application also provides a lithium-ion battery, including a positive electrode, a negative electrode and the aforementioned composite separator, wherein the composite separator is located between the positive electrode and the negative electrode.

[0019] The composite separator provided by this invention comprises a ceramic layer and a high-temperature resistant layer arranged in a consistent order on both sides of a base membrane, representing a heterogeneous layout on the positive and negative electrode sides of the base membrane. On the positive electrode side, the high-temperature resistant layer can be directly or indirectly exposed to a high-voltage environment, and its chemical inertness helps resist oxygen release and free radical attack from the positive electrode. At the same time, the ceramic layer further enhances thermal stability and oxygen adsorption capacity. On the negative electrode side, the high-temperature resistant layer in contact with the negative electrode is defined as a high-temperature resistant polymer film compatible with the negative electrode, avoiding interfacial side reactions and optimizing the separator layout, thereby improving battery performance. Attached Figure Description

[0020] Figure 1This is a schematic diagram of the composite diaphragm according to the first embodiment of the present invention; Figure 2 This is a schematic diagram of the composite diaphragm according to the second embodiment of the present invention.

[0021] The reference numerals in the figure: 10-Composite separator, 11-Base membrane, 12-First high temperature resistant layer, 13-First ceramic layer, 14-Adhesive layer, 15-Second high temperature resistant layer, 16-Second ceramic layer; 20-Composite separator, 21-Base membrane, 22-First high temperature resistant layer, 23-First ceramic layer, 24-Adhesive layer, 25-Second high temperature resistant layer, 26-Second ceramic layer; A - First side, B - Second side, -E - Negative electrode side, +E - Positive electrode side. Detailed Implementation

[0022] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] Please see Figure 1 The composite separator 10 of the first embodiment of the present invention includes a base membrane 11, a first ceramic layer 13, a first high-temperature resistant layer 12, a second ceramic layer 16, and a second high-temperature resistant layer 15. The base membrane 11 has a first side A and a second side B facing each other; the first ceramic layer 13 is located on the first side A of the base membrane 11; the first high-temperature resistant layer 12 is located on the side of the first ceramic layer 13 away from the second side B; the second ceramic layer 16 is located on the side of the base membrane 11 on the second side B; and the second high-temperature resistant layer 15 is located between the second side B of the base membrane 11 and the second ceramic layer 16. In the composite separator 10 provided by the present invention, the ceramic layers and high-temperature resistant layers on both sides of the base membrane 11 are asymmetrically arranged, that is, the positive and negative electrode sides of the base membrane 11 have a heterogeneous layout. Thus, different arrangements of the ceramic layers and high-temperature resistant layers can be set according to the different characteristics of the positive electrode side (+E) and the negative electrode side (-E).

[0025] This invention addresses the inherent contradiction between the high-pressure oxidation environment on the positive electrode side and the relatively reducing environment on the negative electrode side. It achieves a more optimized functional configuration by using two different layer sequences on the positive and negative electrode sides: one consisting of a "base film / high-temperature resistant layer / ceramic layer," and the other consisting of a "base film / ceramic layer / high-temperature resistant layer." On the positive electrode side, the outer ceramic layer and the inner high-temperature resistant layer provide dual protection against oxidation and for thermal stability. On the negative electrode side, a specific compatible polymer contact layer maintains thermal safety while avoiding interfacial side reactions that might be caused by traditional materials such as PTFE. This design based on interfacial chemistry characteristics achieves overall optimization of the separator performance and extends battery life.

[0026] Based on the aforementioned embodiment, the first surface A of the base film 11 faces the negative electrode, and the first high-temperature resistant layer 12 is a high-temperature resistant polymer film compatible with the negative electrode. Alternatively, the first surface A of the base film 11 is the negative electrode side (-E), and the second surface B is the positive electrode side (+E). That is, on the positive electrode side (+E) of the base film 11, the second ceramic layer 16 is the outermost layer, and the second high-temperature resistant layer 15 is located between the second ceramic layer 16 and the base film 11. On the negative electrode side (-E), the first high-temperature resistant layer 12 is the outermost layer, and the first ceramic layer 13 is located between the first high-temperature resistant layer 12 and the base film 11. Specifically, the first high-temperature resistant layer 12, the outermost layer on the negative electrode side (-E), is a high-temperature resistant polymer film compatible with the negative electrode. In other words, the first high-temperature resistant layer 12 does not react with the negative electrode. On the positive electrode side +E, the second ceramic layer 16 is set as the outermost layer, and the second high-temperature resistant layer 15 is located inside it. This can fully utilize the adsorption and passivation effect of the ceramic layer on the oxygen release products of the high-nickel positive electrode, suppress free radical chain reactions, and at the same time, the inner high-temperature resistant material provides thermal dimensional stability. On the negative electrode side -E, the first high-temperature resistant layer 12 is set as the outermost layer, and the first ceramic layer 13 is located inside it. The outer high-temperature resistant material is a lithium-compatible polymer (such as PES, PET, PPS, etc.). Its molecular structure is stable and there are no easily reduced functional groups. It can avoid side reactions such as defluorination or hydrogen production in a strongly reducing environment, effectively protect the integrity of the SEI film, and improve interface stability. At the same time, the material itself has excellent heat resistance, which can prevent the base film 11 from shrinking at high temperatures and ensure thermal safety. This solves the chemical instability problem of the negative electrode and retains the core supporting role of the high-temperature resistant layer for thermal safety, significantly improving the cycle life, safety and reliability of the battery in a high-energy-density system.

[0027] Based on the aforementioned embodiments, the material of the high-temperature resistant polymer is selected from one or a mixture of multiple of polyphenylene sulfide, polyethersulfone, polyurethane, polyethylene terephthalate, polyimide, polybenzimidazole (PBI), and polyphenylene ether. These materials are not easily softened or degraded under battery operation and high-temperature storage conditions, effectively supporting the separator structure and preventing thermal shrinkage of the base film 11. More importantly, the main chains of these materials do not contain weak bonds or active functional groups (such as CF bonds) that are easily reduced by lithium. In particular, polymers such as PI, PBI, and PPS, which contain rigid aromatic rings and stable heterocyclic structures, exhibit good electrochemical stability in the strong reducing environment of the negative electrode and are not prone to side reactions such as dehydrogenation, bond breaking, or gas generation, thus avoiding damage to the SEI film. At the same time, some materials (such as PES and PU) contain polar groups and have good electrolyte affinity, which is beneficial to improving the wettability of the separator-negative electrode interface, promoting uniform lithium ion transport, and inhibiting lithium dendrite growth. By selecting one or more of the above mixtures as the high-temperature resistant material for the outermost layer of the negative electrode -E, long-term interfacial compatibility with the negative electrode is achieved, while mechanical strength, thermal stability, and ion conductivity are also taken into account.

[0028] It should be noted that the first high-temperature resistant layer 12 and the second high-temperature resistant layer 15 in this invention are prefabricated independent porous membrane layers formed by pretreatment of high-temperature resistant polymer materials compatible with the negative electrode. They have a complete and self-supporting microporous structure and are prefabricated through a separate membrane-making process, rather than being a coating layer directly formed on the base film or ceramic layer through subsequent coating or other methods.

[0029] Preferably, pre-fabricated films of the same material are used as the first high-temperature resistant layer 12 and the second high-temperature resistant layer 15. However, the second high-temperature resistant layer 15 can preferably be a PTFE porous membrane to take advantage of its antioxidant properties on the positive electrode side; while the first high-temperature resistant layer 12 is made of a high-temperature resistant polymer membrane other than PTFE that is compatible with the negative electrode, so as to avoid interfacial side reactions that may be caused by direct contact between PTFE and the negative electrode.

[0030] The base membrane 11 can be selected from polyolefin (such as PE, PP, PE / PP, PE / PP / PE, PP / PE / PP) membranes, non-woven base membranes, or composite membranes of the above materials. Using these commercially viable and technologically mature membranes as the base membrane 11 not only ensures that the separator possesses good mechanical strength, electrochemical stability, and inherent thermal shutdown function, but also makes the composite separator 10 easy to integrate into the existing battery manufacturing industry chain, possessing excellent mass production feasibility and cost-effectiveness.

[0031] It is understood that the present invention does not impose any restrictions on the material of the base film 11. Any film that can be used as a lithium battery separator substrate, including known base films 11 modified by various physical or chemical methods, falls within the protection scope of the present invention.

[0032] Based on the aforementioned embodiments, the first ceramic layer 13 includes a plurality of ceramic particles. The second ceramic layer 16 is configured similarly to the first ceramic layer 13 and also includes a plurality of ceramic particles.

[0033] Based on the aforementioned embodiments, the ceramic particles include one or a mixture of oxide ceramics, nitride ceramics, and carbide ceramics. Introducing these highly heat-resistant ceramic particles can greatly enhance the thermal insulation and thermal dimensional stability of the coating, making the composite separator 10 less prone to melting and shrinkage at high temperatures, thereby effectively preventing battery thermal runaway. Furthermore, adding ceramic-based solid electrolyte particles can also enhance ionic conductivity and suppress lithium dendrite puncture to a certain extent, further improving battery safety and rate performance.

[0034] It is understood that a wide variety of ceramic particles can be used in this invention. For example, oxide ceramics include silicon dioxide, boehmite, alumina, zirconium oxide, titanium oxide, magnesium oxide, zinc oxide, aluminum hydroxide, etc.; nitride ceramics include boron nitride, silicon nitride, etc.; carbides include silicon carbide, titanium carbide, zirconium carbide, tungsten carbide, boron carbide, etc. These materials have excellent electrochemical stability and heat resistance, and are preferred embodiments of this invention. In addition, ceramic-based solid electrolytes (such as lithium lanthanum zirconium oxide LLZO, lithium lanthanum titanium oxide LLTO, etc.) can also be used as a special type of ceramic particle due to their inherent lithium-ion conductivity.

[0035] In summary, all ceramic particle materials that can meet the basic requirements of electrochemical stability and heat resistance and can be applied to lithium-ion battery systems fall within the protection scope of this invention.

[0036] It should be noted that although the core of this invention lies in the asymmetrical design of the overall diaphragm structure, this does not preclude the implementation of schemes where the first and second ceramic layers use the same ceramic particle formulation. From the perspectives of simplifying the production process, controlling raw material costs, and ensuring quality stability, using the same ceramic particle material in both ceramic layers is the preferred implementation. This symmetrical material selection does not contradict the asymmetrical layered structure design of this invention; on the contrary, while ensuring the simplicity of the production process, the layered structure achieves differentiated functional configurations.

[0037] Based on the aforementioned embodiments, the thickness of the first ceramic layer 13 and the second ceramic layer 16 is 0.5 micrometers to 6 micrometers. Controlling the ceramic layer thickness within this optimized range ensures sufficient thermal stability and mechanical reinforcement of the composite diaphragm 10 while avoiding problems such as decreased overall porosity, reduced ionic conductivity, or reduced flexibility due to excessive coating thickness, thus achieving an optimal balance between the diaphragm's thermal safety and electrochemical performance. Furthermore, the thickness of the first ceramic layer 13 and the second ceramic layer 16 can be, but is not limited to, 0.5 micrometers, 0.8 micrometers, 1.0 micrometers, 2 micrometers, 3 micrometers, 4 micrometers, 5 micrometers, or 6 micrometers, as well as specific values ​​between these values.

[0038] Based on the aforementioned embodiments, the thickness of the first high-temperature resistant layer 12 and the second high-temperature resistant layer 15 is 10 micrometers to 25 micrometers. Controlling the thickness of the high-temperature resistant layer within this range ensures it possesses sufficiently high porosity and excellent electrolyte retention, thereby providing unobstructed migration channels for lithium ions and reducing battery internal resistance. Simultaneously, this thickness of the high-temperature resistant layer also maintains good flexibility and mechanical strength, and does not affect the overall processability of the separator after being combined with the ceramic layer. Furthermore, the thickness of the first high-temperature resistant layer 12 and the second high-temperature resistant layer 15 can be, but is not limited to, 10 micrometers, 15 micrometers, 20 micrometers, or 25 micrometers, or specific values ​​between these values.

[0039] Preferably, the first ceramic layer 13 and the second ceramic layer 16 have the same thickness, and the first high-temperature resistant layer 12 and the second high-temperature resistant layer 15 have the same thickness. This symmetrical thickness design is mainly based on manufacturing process considerations, enabling better control of tension uniformity during the composite process, avoiding curling problems caused by thickness differences on both sides, and improving the overall flatness and winding processability of the separator. It should be noted that the symmetry of thickness ensures processing reliability, while the asymmetry of the layer sequence enables adaptation to the positive and negative electrode interface environment; the two are independent yet work together.

[0040] Based on the aforementioned embodiments, the second high-temperature resistant layer 15 is a PTFE porous membrane. The thickness of the second high-temperature resistant layer 15 is 10 micrometers to 35 micrometers. Controlling the thickness of the PTFE porous membrane within this range ensures that it has sufficiently high porosity and excellent electrolyte retention, thereby providing unobstructed migration channels for lithium ions and reducing the internal resistance of the battery. At the same time, the PTFE porous membrane of this thickness can also maintain good flexibility and mechanical strength, and will not affect the overall processability of the separator after being composited with the ceramic layer. Furthermore, the thickness of the PTFE porous membrane can be, but is not limited to, 10 micrometers, 15 micrometers, 20 micrometers, 25 micrometers, 30 micrometers, or 35 micrometers, as well as specific values ​​between the above values.

[0041] It should be noted that this PTFE porous membrane is an independent pre-fabricated membrane, rather than a functional layer formed in situ on the surface of the base membrane 11 through coating or other methods. It is a microporous film formed from PTFE material through processes such as extrusion and stretching, and its microscopic structure exhibits a three-dimensional network of porous pores composed of interconnected fibrous structures. The PTFE porous membrane described in this application refers only to PTFE membranes with a porous structure, and not specifically to a product or structure named "PTFE porous membrane." This application does not have specific requirements regarding the pore structure of PTFE.

[0042] Based on the foregoing embodiments, the first ceramic layer 13 further includes a first adhesive, and the second ceramic layer 16 further includes a first adhesive. The first adhesive includes one or a mixture of more than one of water-based adhesives and oil-based adhesives.

[0043] This application does not impose any special restrictions on the specific type of binder. Any binder component suitable for battery systems can be used in this invention without departing from the inventive concept of this application.

[0044] For example, the waterborne adhesive includes any one or a mixture of several of the following: cellulose acetate (CA), methylcellulose (MC), sodium carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), styrene-butadiene rubber (SBR), nitrile rubber (NBR), styrene-ethylene-butene-styrene copolymer (SEBS), styrene-butadiene-styrene copolymer (SBS), polyvinyl alcohol (PVA), polyacrylamide (PAM), polyacrylic acid (PAA), sodium polyacrylate (NaPAA), lithium polyacrylate (LiPAA), polyacrylic acid copolymers (such as polyacrylic acid-polyacrylonitrile copolymer, polyacrylate-polyacrylonitrile copolymer), waterborne polyurethane (PU), polyethylene oxide (PEO), polyimide, ethylene-vinyl acetate copolymer, epoxy resin, sodium alginate, and lithium alginate.

[0045] For example, the oily adhesive includes any one or a mixture of several of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride copolymers (such as PVDF-HFP copolymer, PVDF-TFE copolymer). The above examples are merely illustrative and are not intended to limit the scope of protection of the present invention.

[0046] Preferably, the adhesive is an oil-based adhesive, which has excellent bonding properties. It can not only ensure a strong bond between ceramic particles and between the ceramic layer and the base film 11, but also form a good bond between the ceramic layer and the high-temperature resistant layer, giving the battery higher overall hardness and interface smoothness.

[0047] Based on the aforementioned embodiments, the composite separator 10 further includes an adhesive layer 14, which is located between the second high-temperature resistant layer 15 and the second surface B, for bonding the second high-temperature resistant layer 15 to the second surface B of the base film 11. Further, the adhesive layer 14 includes a second adhesive, which includes one or a mixture of water-based and oil-based adhesives. Preferably, the adhesive in the adhesive layer 14 is an oil-based adhesive, which includes any one or a mixture of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride copolymers (such as PVDF-HFP copolymer, PVDF-TFE copolymer). This adhesive layer 14 can greatly enhance the adhesion between the second high-temperature resistant layer 15 and the base film 11, ensuring that the separator maintains structural integrity during battery manufacturing and long-term cycling, avoiding interlayer separation, ensuring the stability and reliability of the lithium-ion transport path, and contributing to improving the rate performance and cycle life of the battery.

[0048] The method for preparing the composite diaphragm 10 provided in this embodiment may include the following steps: The ceramic particles, solvent, and first binder are mixed evenly to obtain a ceramic slurry; The ceramic slurry is coated on the first surface A, i.e., the negative electrode side-E, of the base film 11, and dried to form the first ceramic layer 13; and While the solvent in the first ceramic layer 13 has not completely evaporated, the base film 11 with the first ceramic layer 13 is hot-pressed together with the first high-temperature resistant layer 12 to complete the preparation of the negative electrode side -E film layer. An adhesive is applied to the second side B, i.e. the positive electrode side +E, of the base film 11, and the second high-temperature resistant layer 15 is attached to the base film 11 by the adhesive. A ceramic slurry is coated on the outside of the second high-temperature resistant layer 15 and completely dried to form the second ceramic layer 16, thus completing the preparation of the positive electrode side +E membrane layer and obtaining the composite separator 10.

[0049] It should be noted that the order of preparation of the negative electrode-E and positive electrode-+E film layers is not limited. That is, the negative electrode-E film layer of the base film 11 can be prepared first, or the positive electrode film layer of the base film 11 can be prepared first. This application does not impose any restrictions on this.

[0050] The composite separator provided in this application can also have its first surface of the base membrane facing the positive electrode, meaning the second surface is the negative electrode side. Please refer to [link to relevant documentation]. Figure 2The composite membrane 20 of the second embodiment of the present invention includes a base membrane 21, a first ceramic layer 23, a first high-temperature resistant layer 22, a second ceramic layer 26, and a second high-temperature resistant layer 25. The base membrane 21 has a first surface A and a second surface B facing each other; the first ceramic layer 23 is located on the first surface A of the base membrane 21; the first high-temperature resistant layer 22 is located on the side of the first ceramic layer 23 away from the second surface B; the second ceramic layer 26 is located on the side of the base membrane 21 facing the second surface B; and the second high-temperature resistant layer 25 is located between the second surface B of the base membrane 21 and the second ceramic layer 26.

[0051] In this embodiment, on the positive electrode side (+E) of the base membrane 21, the first high-temperature resistant layer 22 is the outermost layer, and the first ceramic layer 23 is located between the first high-temperature resistant layer 22 and the base membrane 21. On the negative electrode side (-E), the second ceramic layer 26 is the outermost layer, and the second high-temperature resistant layer 25 is located between the second ceramic layer 26 and the base membrane 21. The first high-temperature resistant layer 22 and the second high-temperature resistant layer 25 can both be PTFE porous membranes or high-temperature resistant membranes made of different materials. For example, the first high-temperature resistant layer 22 can be a pre-fabricated PTFE porous membrane, and the second high-temperature resistant layer 25 can be a PES microporous membrane.

[0052] Based on the aforementioned embodiments, the composite diaphragm 20 further includes an adhesive layer 24, such as... Figure 2 As shown. The adhesive layer 24 is located between the second high-temperature resistant layer 25 and the base film 21, and is used to bond the second high-temperature resistant layer 25 to the base film 21.

[0053] The composite separator 20 and the base membrane 21 provided in this embodiment have a bi-sided heterogeneous configuration on the positive and negative electrode sides.

[0054] It should be noted that the two embodiments described above are identical in physical structure, differing only in the orientation of the composite separator within the battery. When the composite separator is positioned with its first surface A facing the positive electrode, it corresponds to this embodiment; when its first surface A faces the negative electrode, it corresponds to the aforementioned embodiment. This configuration allows for adaptation to different design requirements by adjusting the placement orientation.

[0055] Regardless of the orientation in which the composite separator is configured in the battery, it achieves adaptation to the positive and negative electrode interface environment through the asymmetric layered structure of "base film / high temperature resistant layer / ceramic layer" and "base film / ceramic layer / high temperature resistant layer", thus synergistically improving the overall performance of the battery.

[0056] One embodiment of the lithium-ion battery includes the composite separator of any of the above-described embodiments. The lithium-ion battery further includes a positive electrode and a negative electrode, with the composite separator located between the positive and negative electrodes.

[0057] For example, the positive electrode includes a positive current collector and a positive active material layer coated thereon, the active material layer including a positive active substance, and may also add conductive agents and / or binders as needed; any known positive active substances may be used in this application without departing from the inventive concept of this application.

[0058] The negative electrode includes a negative electrode current collector and a negative electrode active material layer coated thereon. The active material layer includes a negative electrode active substance and may also include conductive agents and / or binders as needed.

[0059] Meanwhile, the negative electrode can also be metallic lithium or a lithium-based composite.

[0060] It is understood that the description of the electrode structure in this application is a typical example, but the scope of protection is not limited thereto and also covers other structural forms known in the art. The active material includes known single materials, coating materials, doped materials, nanocomposites, and derivatives obtained through other optimization methods. Meanwhile, the conductive agent, binder, current collector, and other components include conventional and functionalized forms. Any known combination of materials and structural design that does not depart from the core concept of this invention is applicable to this application and will not be elaborated upon here.

[0061] The lithium-ion battery of this invention includes the aforementioned composite separator. This composite separator has a ceramic layer and a high-temperature resistant layer arranged in a consistent order on both sides of a base film, representing a heterogeneous layout on the positive and negative electrode sides of the base film. On the positive electrode side, the high-temperature resistant layer can be directly or indirectly exposed to a high-voltage environment. Its chemical inertness helps resist oxygen release from the positive electrode and free radical attack, while the ceramic layer further enhances thermal stability and oxygen adsorption capacity. On the negative electrode side, the high-temperature resistant layer in contact with the negative electrode is defined as a high-temperature resistant polymer film compatible with the negative electrode, avoiding interfacial side reactions and optimizing the separator layout, thereby improving battery performance.

[0062] Referring to the above embodiments, in order to make the technical solution of the present invention more specific, clear and easy to understand, examples of the technical solution of the present invention are given below. However, it should be noted that the content to be protected by the present invention is not limited to the following embodiments.

[0063] The base film is a PE base film with a thickness of 12 micrometers.

[0064] Preparation method of ceramic slurry: Al2O3 ceramic particles and PVDF binder are dispersed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 90:10, and stirred and mixed evenly, with a solid content of 40%.

[0065] Preparation method of adhesive: Add PVDF-HFP copolymer to NMP solvent to prepare an adhesive solution with a solid content of 10%.

[0066] Example 1 The above-mentioned ceramic slurry was coated on the first side A of the PE base film and dried at 60°C until semi-dry to form a first ceramic layer with a thickness of about 3 micrometers. A polyphenylene sulfide (PPS) porous membrane with a first high-temperature resistant layer thickness of 12 micrometers was then hot-pressed onto the first ceramic layer.

[0067] The adhesive described above is applied to the second side (B) of the PE base film, and a PTFE porous membrane with a thickness of 12 micrometers is bonded to the base film through the adhesive layer. Then, the ceramic slurry described above is applied to the outer side of the PTFE porous membrane and completely dried to form a second ceramic layer with a thickness of about 3 micrometers, thus obtaining a composite membrane. In other words, the composite separator in this embodiment consists of the following layers from the positive electrode side to the negative electrode side: second ceramic layer - PTFE porous membrane - adhesive layer - PE base membrane - first ceramic layer - PPS membrane.

[0068] Example 2 Similar to Example 1, except that no adhesive layer is provided on the positive electrode side, and the PTFE porous pre-made membrane and the base membrane are directly hot-pressed together.

[0069] Example 3 Similar to Example 1, except that the 12-micron PTFE porous membrane is replaced with a 12-micron polyphenylene sulfide (PPS) porous membrane, making the high-temperature resistant layers on both sides of the base membrane consistent.

[0070] Example 4 Similar to Example 1, except that the thickness of both the PPS and PTFE films is 20 micrometers, and the thickness of both the first and second ceramic layers is 1 micrometer.

[0071] Example 5 Similar to Example 1, except that the first high-temperature resistant layer on the negative electrode side is replaced by a polyimide (PI) film with a thickness of 12 micrometers instead of a PPS film.

[0072] Example 6 Using the same composite separator as in Example 1, the separator is placed in reverse during battery assembly, so that the first side A (original negative electrode side) faces the positive electrode and the second side B (original positive electrode side) faces the negative electrode. That is to say, in this embodiment, the sequence from the negative electrode side to the positive electrode side is: second ceramic layer - PTFE porous membrane - adhesive layer - PE base film - first ceramic layer - PPS film.

[0073] Comparative Example 1 On both sides of the PE base film, the same process as in Example 1 is used. First, ceramic layers are prepared on both sides of the base film, and then composited with the PTFE porous membrane. That is to say, in this example, from the negative electrode side to the positive electrode side, the sequence is: PTFE porous membrane - ceramic layer - PE base film - ceramic layer - PTFE porous membrane.

[0074] Battery cycle test: Temperature: 25℃±2℃ ① Charge to the termination voltage at 1C or the specified current, cut off current 0.05C, and let stand for 30 minutes; ② Discharge at 1C until the final discharge voltage (2.75V), record the discharge capacity, and let stand for 30 minutes; Repeat steps ① to ②, and record the discharge capacity in the 500th cycle. Capacity retention rate after 500 cycles = discharge capacity of the 500th cycle / initial discharge capacity * 100%.

[0075] The test results are as follows: Table 1 Test results of Examples 1-6 and Comparative Examples The composite separator provided by this invention optimizes the interface environment between the positive and negative electrodes of the battery through an asymmetric structural design. On the positive electrode side, the ceramic layer fully utilizes its adsorption and passivation effects on oxygen release products, while the chemical inertness of PTFE material resists oxidation under high voltage conditions. On the negative electrode side, a lithium-compatible high-temperature resistant polymer is used to directly contact the negative electrode, fundamentally avoiding interfacial side reactions that may be caused by PTFE and effectively protecting the integrity of the SEI film.

[0076] Test data shows that, compared with the comparative embodiment with a symmetrical structure, the cycle life of the embodiment of the present invention is significantly improved. This verifies that the asymmetric heterogeneous layout can simultaneously meet the oxidation resistance requirements of the positive electrode side and the interface stability requirements of the negative electrode side, significantly improving the overall battery performance.

[0077] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0078] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A composite diaphragm, characterized in that, The composite diaphragm comprises: The base film has a first side and a second side that are opposite to each other; The first ceramic layer is located on the first surface of the base film; The first high-temperature resistant layer is located on the side of the first ceramic layer away from the second surface; The second ceramic layer is located on one side of the second surface of the base film; The second high-temperature resistant layer is located between the second surface of the base film and the second ceramic layer.

2. The composite diaphragm according to claim 1, characterized in that, The first side of the base film faces the negative electrode, and the first high-temperature resistant layer is a high-temperature resistant polymer film compatible with the negative electrode.

3. The composite diaphragm according to claim 2, characterized in that, The material of the high-temperature resistant polymer film is selected from one or a mixture of multiple of polyphenylene sulfide, polyethersulfone, polyurethane, polyethylene terephthalate, polyimide, polybenzimidazole, and polyphenylene ether.

4. The composite diaphragm according to claim 2, characterized in that, The second high-temperature resistant layer is a PTFE porous membrane.

5. The composite diaphragm according to claim 4, characterized in that, The composite membrane further includes an adhesive layer located between the second high-temperature resistant layer and the second surface, which is used to bond the second high-temperature resistant layer to the second surface of the base membrane.

6. The composite diaphragm according to claim 5, characterized in that, The adhesive layer includes a second adhesive, which includes one or a mixture of water-based adhesives and oil-based adhesives.

7. The composite diaphragm according to claim 1, characterized in that, The thickness of the first high-temperature resistant layer is 10 micrometers to 25 micrometers; The thickness of the second high-temperature resistant layer is 10 micrometers to 25 micrometers; The thickness of the first ceramic layer is 0.5 micrometers to 6 micrometers; The thickness of the second ceramic layer is 0.5 micrometers to 6 micrometers.

8. The composite diaphragm according to claim 1, characterized in that, The first ceramic layer includes a plurality of ceramic particles, and the second ceramic layer includes a plurality of ceramic particles; The ceramic particles include one or a mixture of oxide ceramics, nitride ceramics and carbide ceramics.

9. The composite diaphragm according to claim 3, characterized in that, The first ceramic layer further includes a first adhesive, and the second ceramic layer further includes a first adhesive, wherein the first adhesive includes one or a mixture of water-based adhesives and oil-based adhesives.

10. A lithium-ion battery, characterized in that, The composite membrane included in any one of claims 1 to 9.

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