Composite separator, electrochemical device, electronic device, and mobile terminal

Abstract

The application relates to the technical field of battery diaphragm, and provides a composite diaphragm, an electrochemical device, an electronic equipment and a mobile terminal. The composite diaphragm comprises a polyolefin layer, a composite layer combined on one side or two sides of the polyolefin layer, a mixture layer in the composite layer, and an aramid layer combined on one side of the mixture layer, and the mixture layer and the aramid layer are stacked with the polyolefin layer; the mixture layer comprises aramid and first ceramic particles, the first ceramic particles are combined with a coupling agent on the surface; wherein the coupling agent contains an inorganic group and an organic group, the coupling agent is connected with the surface of the first ceramic particles through the inorganic group, and is connected with the aramid through the organic group. The composite diaphragm provided by the application has a breakage temperature > 240 DEG C and a thermal shrinkage rate < 4% at 150 DEG C / 1h, and can effectively solve the problem that a battery is short-circuited and heat runaway occurs due to the thermal shrinkage and melting of the diaphragm, thereby causing a safety hazard.

Description

Technical Field

[0001] This application belongs to the field of battery separator technology, and particularly relates to a composite separator, an electrochemical device, an electronic device, and a mobile terminal. Background Technology

[0002] With the development of electric vehicles, smart terminals, and electronic mobile devices, lithium-ion batteries have become one of the most important components in the electronics and new energy vehicle industries. The separator, as a separating component, is used to isolate the positive and negative electrodes of the battery. As one of the five main materials of lithium-ion batteries, the separator plays a crucial role in battery safety. Currently, the most commonly used separator is polyethylene separator, which typically has a thermal shrinkage rate of MD > 10% (150℃ / 1h) and TD > 10% (150℃ / 1h); and its rupture temperature is typically < 155℃. Therefore, when the battery operates under high-temperature conditions, the separator melts and shrinks severely. Separator damage leads to direct contact between the positive and negative electrodes, triggering a severe short circuit inside the battery and causing thermal runaway.

[0003] To improve the thermal stability of the separator, its surface is typically coated with a layer, usually an inorganic ceramic layer (such as silicon oxide, aluminum oxide, and magnesium oxide), an organic polymer adhesive coating (such as PVDF and PMMA), or an organic high-temperature resistant polymer coating (such as PI and aramid layers). Inorganic ceramic layers and organic high-temperature resistant polymer coatings enhance the thermal stability of the separator, ensuring reliability and safety in high-temperature applications and preventing battery fires or even explosions. Organic polymer adhesive coatings improve interfacial adhesion to the electrode sheets, increasing the overall hardness and strength of the battery, preventing cell deformation, and guaranteeing cell reliability and safety. However, at high temperatures, polymer materials such as aramid undergo a change in molecular chain movement from bond lengths and bond angles to chain segments. This accelerated chain movement causes aramid molecules to curl, resulting in high thermal shrinkage. The thermal shrinkage rate of this coating reaches 6% (150℃ / 1h), reducing battery safety. Summary of the Invention

[0004] The purpose of this application is to provide a composite separator and its preparation method, as well as an electrochemical device, electronic device and mobile terminal containing the above-mentioned composite separator, in order to solve the problem that the high thermal shrinkage rate of the aramid layer on the surface of the separator increases the risk of internal short circuit in the battery and affects the battery safety performance.

[0005] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0006] The first aspect of this application provides a composite membrane, including a polyolefin layer, a composite layer bonded to one or both surfaces of the polyolefin layer, the composite layer including a mixture layer, and an aramid layer bonded to one surface of the mixture layer, wherein the mixture layer and the aramid layer are both stacked with the polyolefin layer.

[0007] The mixture layer comprises aramid and first ceramic particles, the surface of which is bonded with a coupling agent; wherein the coupling agent contains inorganic-philic and organic-philic groups, and the coupling agent is connected to the surface of the first ceramic particles through the inorganic-philic groups and to the aramid through the organic-philic groups.

[0008] The composite separator provided in this application includes a composite layer disposed on one or both surfaces of a polyolefin layer, and the composite layer includes a mixture layer and an aramid layer. The aramid layer can withstand a high temperature of 200°C, thereby increasing the membrane rupture temperature of the composite separator to >200°C. In batteries with a separator containing the aramid layer, the composite separator can withstand high temperatures of 200°C without melting under thermal and mechanical abuse, effectively isolating the positive and negative electrodes of the battery, preventing direct contact between the positive and negative electrodes and thus avoiding severe internal short circuits, thereby improving battery safety. However, the aramid layer has a high thermal shrinkage rate, increasing the risk of internal short circuits in the battery. Based on this, this application introduces a mixture layer containing aramid and first ceramic particles on the surface of the aramid layer, and the surface of the first ceramic particles is bonded with a coupling agent. Because the coupling agent contains both inorganic and organic affinity groups, it acts as a "molecular bridge," connecting one end to the surface of the first ceramic particles and the other end to the aramid fibers in the mixture layer. This enhances the bonding force between the first ceramic particles and the aramid fibers, allowing the aramid fibers to act as a crosslinking agent, fixing the ceramic particles and forming a continuous and stable film layer. Under the action of the coupling agent, the mixture layer exhibits good structural stability, which not only improves the structural stability of the composite separator under high-temperature conditions but also provides rigid support for the aramid molecular chains in the aramid layer. This alleviates the molecular bond curling that occurs at high temperatures, thereby improving the thermal shrinkage performance of the aramid layer and resulting in a thermal shrinkage rate of <4%@150℃ / 1h for the composite separator (i.e., after heat treatment at 150℃ for 1 hour, the thermal shrinkage rate is less than 4%). Batteries containing this mixture layer can mitigate the risk of internal short circuits at the cell ends due to thermal shrinkage of the separator when the composite separator is heated, thus improving battery safety.

[0009] In summary, the composite separator provided in this application has a rupture temperature >240℃ and a thermal shrinkage rate <4%@150℃ / 1h, which can effectively solve the problem of battery short circuits and thermal runaway caused by the separator's easy thermal shrinkage and melting, thus creating safety hazards.

[0010] In one possible implementation of the composite separator of this application, the coupling agent is a silane coupling agent. In this case, the silane coupling agent is bonded to the surface of the first ceramic particles via siloxane groups. Since the surface of the first ceramic particles bonded with the coupling agent has a large number of organophilic groups, these groups can form hydrogen bonds with the aramid molecules dispersed in the first ceramic particles. These hydrogen bonds cause the aramid to be tightly bonded to the first ceramic particles, thereby forming a structurally stable mixture layer. Furthermore, the first ceramic particles in the mixture layer stabilize the aramid layer.

[0011] As one possible embodiment of the composite diaphragm of this application, the silane coupling agent is selected from at least one of vinylsilane, aminosilane, epoxysilane, mercaptosilane, and methacryloxysilane. The siloxane groups in the aforementioned silane coupling agent are bonded to the surface of the first ceramic particles, resulting in the formation of numerous tentacles with vinyl, amino, epoxy, mercapto, or acryloyloxy ends on the surface of the modified first ceramic particles. These tentacles can form hydrogen bonds with the aramid fibers, achieving the connection between the aramid fibers and the first ceramic particles, thereby improving the bonding force between the aramid fibers and the first ceramic particles.

[0012] As one possible embodiment of the composite separator of this application, the weight of the coupling agent in the mixture layer is 0.3-2% of the total weight of the first ceramic particles. Within this range, the coupling agent content can effectively act as a "molecular bridge," improving the bonding force between the first ceramic particles and the aramid fiber. Furthermore, when the coupling agent content is within this range, the amount of coupling agent adhering to the surface of the first ceramic particles is appropriate, resulting in a mixture layer with good air permeability. This allows the composite separator to maintain good air permeability, improves the affinity between the separator and the electrolyte, and increases ionic conductivity. If the coupling agent content is too high, it will reduce the air permeability of the composite separator.

[0013] As one possible implementation of the composite separator of this application, the mixture layer includes a first surface in contact with the aramid layer and a second surface away from the first surface, with the aramid content in the mixture layer gradually increasing along the direction from the second surface to the first surface. In this case, the side closer to the aramid layer has better structural stability, thereby enabling the mixture layer to effectively stabilize the aramid layer through the first ceramic particles therein, reducing the thermal shrinkage rate of the aramid.

[0014] As one possible embodiment of the composite separator of this application, based on the total weight of the mixture layer as 100%, the weight percentage of aramid is 0.1% to 20%, and the weight percentage of the first ceramic particles is 80% to 99.9%. In this case, a small amount of aramid acts as a crosslinking agent to fix the granular first ceramic particles and form a continuous film layer. Simultaneously, because the aramid plays a crosslinking role in the separator particles, it can withstand temperatures above 200°C, allowing the mixture layer to remain intact at temperatures above 200°C, thus increasing the film breakage temperature of the mixture layer. Furthermore, the first ceramic particles in the mixture layer act as rigid supports within the aramid molecular chains, mitigating the molecular bond curling that occurs at high temperatures in the aramid layer, thereby improving the thermal shrinkage performance of the composite separator, resulting in a thermal shrinkage rate of <4%@150°C / 1h. When the composite separator is heated, it can mitigate the risk of internal short circuits at the beginning and end of the battery cell due to the thermal shrinkage of the separator, improving battery safety.

[0015] In one possible embodiment of the composite separator of this application, the thickness of the mixture layer is 0.1-6 μm. In this case, the thickness of the mixture layer can reduce the thermal shrinkage rate of the composite separator; moreover, since the thickness of the mixture layer is within a controllable range, the impact of the mixture layer on the battery energy density can be reduced.

[0016] As one possible embodiment of the composite separator of this application, the thickness of the mixture layer ranges from 1 to 4 μm. When the thickness of the mixture layer is within the above range, it is possible to better balance the effect of reducing the thermal shrinkage rate of the composite separator and reducing the impact of the mixture layer on the battery energy density.

[0017] In one possible embodiment of the composite membrane of this application, the aramid in the mixture layer is at least one of para-aramid and meta-aramid. The aforementioned aramid can achieve crosslinking of the first ceramic particles and increase the membrane breaking temperature of the mixture layer.

[0018] As one possible embodiment of the composite membrane of this application, the median particle size D50 of the first ceramic particles is 0.01–2.0 μm. In this case, the first ceramic particles have a suitable particle size, which can form a dense and complete membrane layer under the crosslinking effect of aramid.

[0019] As one possible implementation of the composite separator of this application, the aramid content by weight is 50% to 100%, with the total weight of the aramid layer being 100%. When the aramid content by weight is 50% or more, the aramid layer can retain the characteristics of the aramid material, effectively increasing the membrane breaking temperature of the composite separator.

[0020] In one possible implementation, the aramid layer is 100% by weight, with the total weight of the aramid layer being 100%. In this case, the aramid layer is composed of aramid and plays a role in increasing the membrane breaking temperature of the composite membrane.

[0021] In another possible implementation, the weight percentage of aramid is between 50% and 100%, but not 100%, based on the total weight of the aramid layer being 100%. In this case, the aramid layer contains aramid and other materials. The other materials include pore-forming agents to impart a certain porosity to the aramid layer.

[0022] As one possible implementation of the composite separator of this application, when the weight percentage of aramid is not 100%, the aramid layer further includes second ceramic particles with a weight percentage of 0-50%. By adding second ceramic particles with a weight percentage of 0-50% to the aramid layer, the porosity of the aramid layer can be increased to above 20%. Furthermore, the second ceramic particles introduced into the aramid layer can improve the thermal stability and thermal shrinkage performance of the aramid layer, ultimately resulting in improved thermal shrinkage performance of the composite separator.

[0023] In one possible embodiment of the composite diaphragm of this application, the median particle size D50 of the second ceramic particles is 0.1 to 1 μm. In this case, the second ceramic particles function as pore-forming particles to increase the porosity of the aramid layer, and the median particle size D50 within the aforementioned range can impart suitable porosity and pore size to the aramid layer.

[0024] In one possible implementation of the composite separator of this application, the thickness of the aramid layer is 0.1-6 μm. In this case, the thickness of the aramid layer can both increase the membrane breaking temperature of the composite separator and reduce the impact of the aramid layer on the battery energy density because the thickness of the aramid layer is within a controllable range.

[0025] As one possible embodiment of the composite separator of this application, the thickness of the aramid layer is 0.5-3 μm. When the thickness of the aramid layer is within the above range, it is possible to better balance the effect of increasing the membrane breaking temperature of the composite separator and reducing the impact of the aramid layer on the battery energy density.

[0026] As one possible embodiment of the composite separator of this application, the aramid layer contains at least one of para-aramid and meta-aramid. The aramid layer obtained in this case has excellent high-temperature resistance, which can impart excellent membrane rupture performance to the composite separator, increasing its rupture temperature and ultimately improving the safety performance of the battery using this composite separator.

[0027] As one possible embodiment of the composite separator of this application, the thickness of the polyolefin layer is 0.2 to 20 μm. Since this application forms a composite layer containing the aforementioned aramid layer and mixture layer on the surface of one layer of the polyolefin layer, the membrane rupture temperature and thermal shrinkage performance of the polyolefin layer are improved. Therefore, the thickness of the polyolefin layer provided by this application can be as low as 0.2 μm. Polyolefin layers with a thickness of 0.2 to 20 μm as the separator matrix can effectively isolate the positive and negative electrodes of the battery.

[0028] As one possible embodiment of the composite separator of this application, the mixture layer is bonded to one side surface of the polyolefin layer, and the aramid layer is bonded to the side surface of the mixture layer opposite to the polyolefin layer. In this case, on the one hand, the aramid layer has better heat resistance, and as a surface protective layer, it can block the influence of high temperature on the polyolefin film layer, making the membrane breakage temperature of the composite separator >240°C; on the other hand, the mixture layer is placed between the aramid layer and the polyolefin layer, providing rigid support for both the polyolefin layer and the aramid layer, mitigating the thermal shrinkage of the composite separator, thereby reducing the thermal shrinkage rate of the composite separator. In addition, from a process processing perspective, this composite separator can be prepared by first forming first ceramic particles on the surface of the polyolefin, and then casting aramid onto the surface of the first ceramic particles. The cast aramid penetrates downward along the pores between the first ceramic particles and spreads outwards on the surface of the first ceramic particles, realizing the preparation of the mixture layer and the aramid layer, improving the process feasibility.

[0029] As one possible embodiment of the composite separator of this application, the composite layer comprises n layers formed by a mixture layer and an aramid layer, where n is an integer from 2 to 5. In this case, the composite layer obtained has the mixture layer and the aramid layer alternately arranged, thereby improving the performance stability of the composite layer.

[0030] A second aspect of this application provides a method for preparing a composite separator, comprising the following steps:

[0031] A pre-formed film is formed on one or both surfaces of the polyolefin layer using a first material;

[0032] A second material is added to the surface of the pre-made film, and then dried to form a first film on the surface of the polyolefin layer, and a second film is formed on the surface of the first film.

[0033] The first film is one of a mixture layer and an aramid layer, and the second film is the other of a mixture layer and an aramid layer. The mixture layer includes aramid and first ceramic particles, and the surface of the first ceramic particles is bonded with a coupling agent.

[0034] The method for preparing the composite separator provided in this application enables the sequential preparation of a mixture layer (or aramid layer) and an aramid layer (or mixture layer) on one or both sides of a polyolefin layer. The first ceramic particles in the mixture layer are bonded to a coupling agent. Since the coupling agent contains both inorganic and organic affinity groups, after adding a second material to the surface of the pre-formed film, the coupling agent bonded to the surface of the first ceramic particles in the pre-formed film or the second material acts as a "molecular bridge" connecting with the aramid forming the mixture layer. This enhances the bonding force between the first ceramic particles and the aramid, allowing the aramid to act as a crosslinking agent, crosslinking and fixing the ceramic particles, and forming a continuous and stable mixture layer. Under the action of the coupling agent, the mixture layer exhibits good structural stability, which not only improves the structural stability of the composite separator under high-temperature conditions but also provides rigid support for the aramid molecular chains in the aramid layer, alleviating the molecular bond curling that occurs at high temperatures. This further improves the thermal shrinkage performance of the adjacent layer, i.e., the aramid layer, resulting in a thermal shrinkage rate of the composite separator of <4%@150℃ / 1h. In this process, the resulting composite separator can increase the separator rupture temperature and simultaneously reduce the separator's thermal shrinkage rate, achieving a thermal shrinkage rate of <4%@150℃ / 1h. The resulting composite film effectively improves the separator's thermal stability, ensuring battery safety.

[0035] In one possible implementation of the composite membrane preparation method of this application, the first film is a mixture layer and the second film is an aramid layer. Correspondingly, the first material is a material containing first ceramic particles, the pre-formed film is a ceramic layer, and the second material is an aramid slurry. In this case, by first forming the first ceramic particles on the surface of the polyolefin and then casting the aramid slurry onto the surface of the first ceramic particles, the preparation of the mixture layer and the aramid layer is achieved, improving the feasibility of the process. Specifically, the first ceramic particles are first laid on the surface of the polyolefin layer to form a ceramic layer, i.e., the pre-formed film. At this time, the ceramic layer formed by the ceramic particle laying has poor stability. When the aramid slurry is cast onto the surface of the ceramic layer, i.e., the surface of the pre-formed film, the aramid in the slurry will penetrate downwards along the pores between the first ceramic particles and spread outwards on the surface of the first ceramic particles. The downward-permeating aramid fills the pores between the first ceramic particles, and the aramid acts as a crosslinking agent to fix the granular first ceramic particles; at the same time, the coupling agent combines with the aramid through hydrogen bonds, thereby crosslinking the first ceramic particles with the aramid through the coupling agent, fixing the first ceramic particles into a film, and after crystallization and solidification, finally forming a structurally stable mixture layer.

[0036] In one possible implementation, the first material is a ceramic slurry. A pre-formed film is formed on one or both surfaces of the polyolefin layer by forming the ceramic slurry on one or both surfaces of the polyolefin layer.

[0037] In some embodiments, the ceramic slurry is a slurry formed by dispersing first ceramic particles with a coupling agent on their surface in a dispersion. In this case, the ceramic slurry is coated on one or both surfaces of the polyolefin layer, and after drying, a pre-formed film of the first ceramic particles is formed on one or both surfaces of the polyolefin layer, with the coupling agent on the surface of the first ceramic particles.

[0038] In some embodiments, the ceramic slurry is a slurry containing a coupling agent, first ceramic particles, and additives. In this case, the ceramic slurry is coated onto one or both surfaces of the polyolefin layer, and after drying, a pre-formed film of first ceramic particles is formed on one or both surfaces of the polyolefin layer, with the coupling agent bonded to the surface of the first ceramic particles. The additives can be at least one of a dispersant, thickener, binder, and wetting agent. The dispersant improves the dispersibility of the first ceramic particles in the slurry; the wetting agent improves the wettability and spreadability of the slurry on the polyolefin surface when the ceramic slurry is coated; the thickener increases the viscosity of the slurry; and the binder binds the first ceramic particles after coating them onto the polyolefin surface, initially fixing them to the polyolefin surface to form a ceramic layer, i.e., the pre-formed film.

[0039] In some embodiments, the ceramic slurry is prepared by dispersing first ceramic particles, a coupling agent, and an additive in deionized water, mixing them, and obtaining the ceramic slurry. Under the action of the additive, the first ceramic particles disperse and form a slurry, which facilitates its coating onto the surface of the polyolefin layer. After coating the polyolefin layer with the ceramic slurry and drying to remove the solvent, a ceramic layer, i.e., a pre-formed film, is formed.

[0040] In some embodiments, the ceramic slurry includes the following components added in the following parts by weight:

[0041]

[0042] In this case, the ceramic slurry formed has good dispersion uniformity between the first ceramic particles and the coupling agent, which is conducive to the uniform binding of the coupling agent to the surface of the first ceramic particles, and thus facilitates the binding of the aramid that enters the pores of the first ceramic particles with the first ceramic particles; at the same time, the slurry has suitable viscosity and spreadability, which is conducive to the initial fixation of the first ceramic particles on the surface of the polyolefin layer.

[0043] In some embodiments, the coupling agent is a silane coupling agent. The silane coupling agent is bonded to the surface of the first ceramic particles via siloxane groups, and has a large number of organophilic groups at its other end. When a second material containing aramid is added to the surface of the pre-formed film, the organophilic groups at the other end of the coupling agent form hydrogen bonds with the aramid molecules entering the gaps between the first ceramic particles. These hydrogen bonds tightly bind the aramid to the first ceramic particles, enhancing the bonding force between the ceramic particles and the aramid, ultimately forming a structurally stable mixture layer. In this case, the rigid support of the first ceramic particles in the mixture layer effectively stabilizes the upper aramid layer and reduces the thermal shrinkage rate of the diaphragm. Exemplarily, the coupling agent is at least one of vinylsilane, aminosilane, epoxysilane, mercaptosilane, and methacryloxysilane, but is not limited thereto. The aforementioned silane coupling agents contain functional groups capable of forming hydrogen bonds with aramid, which facilitates the connection between the aramid and the first ceramic particles and improves the bonding force between them.

[0044] As one possible implementation, the method for preparing the ceramic slurry is as follows:

[0045] The first ceramic particles were dispersed in deionized water, and the silane coupling agent was added to obtain the first ceramic particles modified by the silane coupling agent.

[0046] The dispersant is added to the first ceramic particles modified with the silane coupling agent, and after stirring and mixing, the mixture is milled to obtain a ceramic dispersion.

[0047] The thickener, the binder, and the wetting agent are added to the ceramic dispersion and stirred to obtain the ceramic slurry.

[0048] After mixing the silane coupling agent and the first ceramic particles, a dispersant is added for further mixing to ensure uniform dispersion of the silane coupling agent and the first ceramic particles. Other additives are then added to improve the dispersion uniformity of the silane coupling agent and the first ceramic particles, thereby improving the uniform distribution of the silane coupling agent on the surface of the first ceramic particles. In this case, when a second material containing aramid is added to the surface of the pre-formed film, the aramid enters the pores between the first ceramic particles and connects with them using the silane coupling agent uniformly distributed on the surface of the first ceramic particles, thus fixing the first ceramic particles and ultimately forming a mixture layer, i.e., the first film.

[0049] As a second possible implementation of the method for preparing the composite membrane of this application, the first film is an aramid layer, the second film is a mixture layer, the first material is an aramid slurry, and the second material is a ceramic material. In this case, the aramid slurry is first coated on the surface of the polyolefin layer to form a pre-film; then, ceramic material is added to the surface of the pre-film, and the film is dried to finally form a composite layer consisting of an aramid layer and a mixture layer on the surface of the polyolefin layer.

[0050] In this embodiment, the aramid slurry is a slurry with aramid as the matrix material. In one possible implementation, the aramid slurry is a slurry formed from aramid. In another possible implementation, the aramid slurry contains aramid and additives. In both possible implementations, the aramid slurry is formed on one or both surfaces of the polyolefin layer after the first material is applied to one or both surfaces of the polyolefin layer. In some embodiments, the additives include pore-forming agents.

[0051] In one possible implementation, the aramid slurry has a solid content of 1.5-10%. In this case, the aramid slurry has suitable viscosity and spreading properties, and spreads evenly on the surface of the substrate (ceramic layer or polyolefin layer) to form an aramid layer.

[0052] As one possible implementation, the method for preparing the aramid slurry is as follows:

[0053] An organic solution of phenylenediamine is prepared, cooled to below 10°C, phthaloyl chloride is added, the pH is adjusted to neutral by adding alkali, and a pore-forming agent is added to obtain the aramid slurry.

[0054] This method can directly prepare aramid slurry from raw materials. The method is simple and has strong controllability.

[0055] As one possible implementation, the coating includes one of dip coating, spray coating, doctor blade coating, coating bar coating, and micro-gutter roller coating.

[0056] As one possible implementation, the preparation method further includes immersing the sample obtained after coating with the second slurry into a plasticizing bath before the drying process. Immersing the sample obtained after coating with the second slurry into the plasticizing bath before drying allows the aramid fibers to be in a highly plastic state, facilitating aramid stretching.

[0057] A third aspect of this application provides an electrochemical device, including a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode, wherein the separator is the composite separator described in the first aspect of this application.

[0058] The electrochemical device provided in this application, due to the presence of the aforementioned composite separator, has a low thermal shrinkage rate and a high membrane rupture temperature, which can solve the problems of separator shrinkage and melting, reduce the risk of thermal runaway caused by battery short circuit, and further improve the safety performance of the battery.

[0059] As one possible implementation of the electrochemical device of this application, at least one surface of the composite separator is provided with at least one polymer layer. The polymer layer can improve the interfacial adhesion between the composite separator and the electrode sheet, enhance the overall hardness and strength of the battery, and prevent cell deformation.

[0060] As one possible implementation of the electrochemical device of this application, the polymer layer is a material layer formed from at least one of PVDF, PMMA, dopamine, CMC, SBR, PTFE, and PVA; as another possible implementation of the electrochemical device of this application, the polymer layer is a polymer stack formed from at least two of PVDF, PMMA, dopamine, CMC, SBR, PTFE, and PVA, and the polymers constituting the polymer stack can be one or more of the aforementioned polymers. The aforementioned polymer materials can improve the bonding strength between the composite film containing the first aspect and the electrode sheet, maintaining the stability of the battery structure.

[0061] As one possible implementation of the electrochemical device of this application, the electrochemical device is a lithium secondary battery, a potassium secondary battery, a sodium secondary battery, a zinc secondary battery, a magnesium secondary battery, or an aluminum secondary battery.

[0062] As one possible implementation of the electrochemical device of this application, the structure of the electrochemical device is one or more of the following: a wound structure and a stacked structure.

[0063] As one possible implementation of the electrochemical device of this application, the electrochemical device further includes a packaging shell, and one or more electrochemical device units are packaged within the packaging shell.

[0064] A fourth aspect of this application provides an electronic device, including a housing and electronic components and an electrochemical device housed within the housing, wherein the electrochemical device is the electrochemical device described in the third aspect of this application, and the electrochemical device is used to supply power to the electronic components.

[0065] As one possible implementation of the terminal in this application, the terminal is a computer, mobile phone, tablet, or wearable product.

[0066] The fifth aspect of this application provides a mobile device comprising the electrochemical device described in the third aspect. Attached Figure Description

[0067] Figure 1This is a schematic diagram of the first structure of the composite diaphragm provided in the embodiments of this application;

[0068] Figure 2 This is a schematic diagram of the second structure of the composite diaphragm provided in the embodiments of this application;

[0069] Figure 3 This is a process flow diagram of a composite membrane preparation process provided in the embodiments of this application;

[0070] Figure 4 This is another process flow diagram for preparing the composite diaphragm provided in the embodiments of this application. Detailed Implementation

[0071] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0072] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0073] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0074] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0075] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0076] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0077] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0078] The term "MD" is an abbreviation for "Machine direction," indicating the direction of the machine.

[0079] The term "TD" is an abbreviation for "Transverse direction," meaning perpendicular to the machine direction;

[0080] The term "PE" is an abbreviation for "Polyethylene," which stands for polyethylene.

[0081] The term "DSC" is an abbreviation for "Differential scanning calorimetry".

[0082] The term "SOC" is an abbreviation for "State of charge," which refers to the state of charge.

[0083] The term "PVDF" is an abbreviation for "polyvinylidene fluoride," which stands for polyvinylidene fluoride.

[0084] The term "PMMA" is an abbreviation for "polymethyl methacrylate," which stands for polymethyl methacrylate.

[0085] The term "SBR" is an abbreviation for "Styrene-butadiene," which stands for styrene-butadiene rubber.

[0086] The term "NMP" is an abbreviation for "N-Methyl-2-pyrrolidone," which stands for N-methylpyrrolidone, also known as 1-methyl-2-pyrrolidone.

[0087] The term "CNTs" is an abbreviation for "Carbon nanotubes," which stands for carbon nanotubes.

[0088] The term "CMC" is an abbreviation for "Carboxymethyl Cellulose," which stands for carboxymethyl cellulose.

[0089] The term "SP" is an abbreviation for "Super P," which stands for conductive carbon black.

[0090] The term "PP" is an abbreviation for "Polypropylene," which stands for polypropylene.

[0091] The term "PTFE" is an abbreviation for "Polytetrafluoroethylene," which stands for polytetrafluoroethylene.

[0092] The term "PVA" is an abbreviation for "Polyvinyl alcohol," which stands for polyvinyl alcohol.

[0093] The term "battery" is a device that uses the difference in potential between two electrodes to create a potential difference, thereby allowing electrons to flow and generating an electric current. This device can convert chemical energy into electrical energy.

[0094] The term "positive electrode" is abbreviated as "Cathode" in English. In a galvanic cell, the positive electrode is the electrode from which current flows or which has a higher potential; the positive electrode gains electrons and undergoes a reducing effect. In an electrolytic cell, the positive electrode is the electrode connected to the positive terminal of the power source; it loses electrons and undergoes an oxidizing effect.

[0095] The term "negative electrode" is abbreviated as "Anode" in English. In a galvanic cell, the negative electrode is the electrode into which current flows or the electrode with the lower potential. The negative electrode loses electrons and undergoes oxidation. In an electrolytic cell, the negative electrode is the electrode connected to the negative terminal of the power source and gains electrons and undergoes reduction.

[0096] The term "electrolyte" refers to the medium that provides ion exchange between the positive and negative electrodes of a battery.

[0097] The term "diaphragm" is an abbreviation for "Separator," which refers to the medium used to separate the positive and negative electrodes in a battery cell, preventing them from directly contacting each other and causing a short circuit. The basic characteristics of a diaphragm are porosity (providing channels for ion transport) and electronic insulation (preventing leakage).

[0098] The term "heat abuse" refers to the abuse of battery cells in terms of heat (or high temperature), such as hot box testing (baking battery cells at a high temperature of ≥130 degrees Celsius).

[0099] The term "mechanical abuse" refers to the mechanical misuse of battery cells. Tests such as nail penetration and impact tests can be used to assess mechanical abuse in battery cells.

[0100] The term "elongation" is also known as elongation at break, and it represents the percentage increase in length of a diaphragm when it breaks relative to its initial length. Specifically, a tensile test is performed on the diaphragm under specific conditions. The increase in diaphragm length when it just breaks, divided by the initial length, characterizes the elongation. A higher elongation value means the diaphragm is less likely to break and has better extensibility. Elongation can be divided into longitudinal (MD, along the long side of the diaphragm) elongation and transverse (TD, perpendicular to MD, along the short side of the diaphragm) elongation.

[0101] The term "tensile strength" refers to the critical strength value of a diaphragm under plastic deformation, characterizing its maximum load-bearing capacity under uniform tension. Tensile strength can be defined as the stress obtained by dividing the maximum load force the diaphragm withstands when it just breaks by its initial cross-sectional area. Tensile strength is divided into longitudinal (MD, along the long side of the diaphragm) tensile strength and transverse (TD, perpendicular to MD, along the short side of the diaphragm) tensile strength.

[0102] The term "puncture strength" is expressed as "Puncture strength" in English. It can refer to the force required for a 1.0 mm diameter spherical steel needle to penetrate the diaphragm at a speed of 300 ± 10 mm / min.

[0103] The term "heat shrinkage" refers to the rate of dimensional change of a diaphragm in the longitudinal / transverse (longitudinal MD, along the long side of the diaphragm; transverse TD, perpendicular to MD, along the short side of the diaphragm) directions before and after heating. Test methods for heat shrinkage may include: measuring the dimensions of the diaphragm in the longitudinal / transverse (MD / TD) directions; placing a diaphragm with specific dimensions in the longitudinal / transverse (MD / TD) directions in a constant temperature chamber; heating the constant temperature chamber to a specific temperature; and measuring the dimensions of the diaphragm in the longitudinal / transverse (MD / TD) directions after heating.

[0104] The term "gurley" refers to the degree to which a diaphragm allows gas to pass through. Gurley permeability is measured by the time it takes for a unit volume of gas (100 cc) to pass through the diaphragm at a specific pressure (0.05 MPa).

[0105] The term "occlusion temperature" is expressed as "Obturator temperature" in English. It refers to the temperature at which the diaphragm begins to melt and seal off a portion of the previously formed pores during the heating process.

[0106] The term "rupture temperature" refers to the temperature at which the diaphragm melts to a certain extent and ruptures, causing a partial or complete short circuit.

[0107] In batteries, the separator is primarily used to prevent short circuits between the positive and negative electrodes, playing a crucial role in battery safety. When batteries are subjected to mechanical and thermal abuse, the separator is prone to melting and thermal shrinkage at high temperatures, leading to short circuits between the positive and negative electrodes and thus posing a safety hazard. Therefore, this application provides a composite separator that can improve battery safety performance.

[0108] Specifically, this application provides a composite membrane, including a polyolefin layer, a composite layer bonded to one side surface of the polyolefin layer, the composite layer including a mixture layer, and an aramid layer bonded to one side surface of the mixture layer, wherein the mixture layer or the aramid layer and the polyolefin layer are disposed on the surface of the polyolefin layer.

[0109] In this embodiment, the polyolefin layer serves as the main functional layer of the composite separator, separating the positive and negative electrodes in the battery cell and preventing direct contact and short circuits. Polyolefins are porous, hence also known as porous polyolefins, providing channels for ion transport; simultaneously, they possess electronic insulation properties, preventing leakage. The polyolefin layer in this embodiment is also referred to as a porous polyolefin layer.

[0110] In some embodiments, the polyolefin material in the polyolefin layer may be at least one of polyethylene (PE) and polypropylene (PP). In some embodiments, the polyolefin layer is prepared using one polyolefin material; in some embodiments, the polyolefin layer is made of a composition formed from two or more polyolefins. In this embodiment, the two or more polyolefins may be two or more different types of polyolefin materials. For example, the polyolefin material of the polyolefin layer is a composition of polyethylene (PE) and polypropylene (PP); or it may be two or more polyolefins of the same type but with different viscosity-average molecular weights. For example, the polyolefin material of the polyolefin layer is a composition of multiple polyethylenes with different viscosity-average molecular weights.

[0111] In some embodiments, the thickness of the polyolefin layer is 0.2–20 μm. Because the embodiments of this application form a composite layer containing an aramid layer and a mixture layer on the surface of one layer of the polyolefin layer, the film-breaking temperature and thermal shrinkage performance of the polyolefin layer are improved. Therefore, the thickness of the polyolefin layer provided in this application can be as low as 0.2 μm. Polyolefin layers with a thickness of 0.2–20 μm as the separator substrate can effectively isolate the positive and negative electrodes of the battery. For example, the thickness of the polyolefin layer can be 0.2 μm, 0.5 μm, 0.8 μm, 1.0 μm, 2.0 μm, 3.0 μm, 4.0 μm, 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm, 9.0 μm, 10.0 μm, 11.0 μm, 12.0 μm, 13.0 μm, 14.0 μm, 15.0 μm, 16.0 μm, 17.0 μm, 18.0 μm, 19.0 μm, or 20.0 μm. In some embodiments, the thickness of the polyolefin layer is 0.5-17 μm.

[0112] In this embodiment, a composite layer is provided on one or both surfaces of the polyolefin layer. The composite layer includes a mixture layer and an aramid layer bonded to one surface of the mixture layer. Both the mixture layer and the aramid layer are stacked with the polyolefin layer, i.e., the mixture layer and the aramid layer are arranged parallel to the polyolefin layer.

[0113] In one embodiment, a composite layer is formed on one surface of the polyolefin layer, while the other surface remains untreated (i.e., a blank design is retained). In this case, since the pore-closure temperature of polyolefin is around 140°C, this characteristic allows the battery containing the polyolefin separator to automatically cut off the ion transport channels (the micropores of the polyolefin close) around the pore-closure temperature. By retaining a blank design on one surface of the polyolefin layer, the original pore-closure temperature characteristics of polyolefin can be preserved, giving the battery better safety performance. In another embodiment, a composite layer is formed on both surfaces of the polyolefin layer simultaneously to increase the membrane rupture temperature of the composite separator and reduce its thermal shrinkage rate.

[0114] The aramid material in the aramid layer has a limiting oxygen index greater than 28%, classifying it as a flame-retardant fiber. Due to its flame-retardant properties, using an aramid layer as the protective layer of the polyolefin separator increases the separator's rupture temperature, raising the composite film's rupture temperature to >200℃. This allows the composite separator to withstand temperatures above 200℃ without melting when the battery is subjected to thermal or mechanical abuse, effectively isolating the positive and negative electrodes and preventing direct contact that could lead to severe internal short circuits, thus improving battery safety.

[0115] In some embodiments, the aramid weight percentage is 50% to 100%, with the total weight of the aramid layer being 100%. When the aramid weight percentage is 50% or more, the characteristics of the aramid material can be retained, and the formed aramid layer can effectively increase the membrane breaking temperature of the composite membrane. This embodiment includes two cases: the case where the aramid weight percentage is 100%, and the case where the aramid weight percentage is not 100%.

[0116] In the first embodiment, the weight percentage of aramid is between 50% and 100%, but not 100%, based on the total weight of the aramid layer being 100%. In this case, the aramid layer contains aramid and other materials. For example, based on the total weight of the aramid layer being 100%, the weight percentage of aramid can be a specific weight percentage such as 50%, 55%, 50%, 55%, 50%, 55%, 50%, 55%, 50%, 55%, 50%, 55%, 100%, etc.

[0117] In some embodiments, other materials include pore-forming agents to impart a certain porosity to the aramid layer. The pore-forming agent is one or more inorganic pore-forming agents; exemplary, inorganic pore-forming agents include one or more of lithium chloride, sodium chloride, magnesium chloride, calcium carbonate, calcium chloride, and second ceramic particles.

[0118] In some embodiments, when the weight percentage of aramid is not 100%, the aramid layer includes 0-50% by weight of second ceramic particles, which act as pore-forming agents. By adding 0-50% by weight of second ceramic particles to the aramid layer, the porosity of the aramid layer can be increased to above 20%. Furthermore, the second ceramic particles introduced into the aramid layer can improve its thermal stability and thermal shrinkage properties, ultimately resulting in improved thermal shrinkage properties of the composite membrane. In addition, while a small amount of second ceramic particles plays a pore-forming role, their impact on the properties of the aramid layer is reduced. For example, with the total weight of the aramid layer as 100%, the weight percentage of the second ceramic particles can be 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc.

[0119] The median particle size D50 of the second ceramic particles acting as a pore-forming agent can be 0.01–2 μm. In some embodiments, the median particle size D50 of the second ceramic particles is 0.1–1 μm. In this case, the second ceramic particles function as pore-forming agents to increase the porosity of the aramid layer, and the median particle size D50 being within the aforementioned range can impart suitable porosity and pore size to the aramid layer, which is beneficial for obtaining an aramid layer with better air permeability and heat resistance. For example, the average median particle size D50 of the second ceramic particles can be 0.01μm, 0.02μm, 0.05μm, 0.08μm, 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, or 2.0μm.

[0120] In some embodiments, the second ceramic particle is at least one selected from alumina, silicon dioxide, aluminum oxide, zirconium dioxide, magnesium oxide, zinc oxide, barium oxide, magnesium hydroxide, calcium oxide, boehmite, titanium dioxide, and barium sulfate.

[0121] In the second implementation, with the total weight of the aramid layer being 100%, the weight percentage of aramid is 100%. In this case, the aramid layer is composed of aramid and plays a role in increasing the membrane breaking temperature of the composite membrane. It should be understood that when the weight percentage of aramid in the aramid layer is 100%, the aramid layer also has a certain porosity, but the pore-forming agent has been eliminated during or after the formation of the aramid layer. For example, when using any one or more organic pore-forming agents such as methanol, ethanol, propanol, glycerol, polyethylene glycol, acetone, acetic acid, tetrahydrofuran, polyvinylpyrrolidone, ethyl acetate, petroleum ether, white oil, and paraffin, the pore-forming agent and aramid are used together as raw materials to form a pre-formed film. During the heating and molding process, the organic pore-forming agent volatilizes, forming a porous structure in the aramid layer.

[0122] In some embodiments, the thickness of the aramid layer is 0.1-6 μm. In this case, the thickness of the aramid layer can achieve the effect of increasing the membrane breaking temperature of the composite separator. Since aramid material, as a separator material, does not contribute to the battery capacity, when the aramid content is too high, its volume percentage in the battery also increases, which will reduce the battery energy density. When the thickness of the aramid layer is 0.1-6 μm, the thickness of the aramid layer is within a controllable range, which can reduce the impact of the aramid layer on the battery energy density. For example, the thickness of the aramid layer can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, etc.

[0123] In some embodiments, the thickness of the aramid layer is 0.5-3 μm. When the thickness of the aramid layer is within the above range, it is possible to better balance the effect of increasing the membrane breaking temperature of the composite separator and reducing the impact of the aramid layer on the battery energy density.

[0124] In some embodiments, the aramid layer contains at least one of para-aramid and meta-aramid. The resulting aramid layer exhibits excellent high-temperature resistance, which can impart superior membrane rupture properties to the composite separator, increasing its rupture temperature and ultimately improving the safety performance of batteries using this composite separator.

[0125] In this embodiment, the composite layer further includes a mixture layer comprising aramid fibers and first ceramic particles. The surface of the first ceramic particles is coated with a coupling agent. That is, the ceramic particles in the mixture layer are first ceramic particles modified with a coupling agent. The coupling agent on the surface of the first ceramic particles contains both inorganic and organic affinity groups. Therefore, it acts as a "molecular bridge," connecting one end to the surface of the first ceramic particles and the other end to the aramid fibers in the mixture layer. This enhances the bonding force between the first ceramic particles and the aramid fibers, allowing the aramid fibers to act as a crosslinking agent, crosslinking and fixing the first ceramic particles to form a continuous and stable membrane layer. Under the action of the coupling agent, the mixture layer exhibits good structural stability, which not only improves the structural stability of the composite membrane under high-temperature conditions, but also provides rigid support for the aramid molecular chains in the aramid layer. This alleviates the molecular bond curling that occurs at high temperatures in the aramid polymer bonds, reduces the thermal shrinkage effect of the aramid material, especially the aramid molecules in the aramid layer, and thus improves the thermal shrinkage performance of the aramid layer, resulting in a thermal shrinkage rate of the composite membrane of <4%@150℃ / 1h. Furthermore, the aramid fibers in this layer play a cross-linking role within the ceramic particles. These aramid fibers can withstand temperatures above 200°C, allowing the composite layer to remain intact at these temperatures and increasing its rupture temperature. Batteries containing this composite layer can mitigate the risk of internal short circuits at the cell's beginning and end due to thermal shrinkage of the separator when the composite separator is heated, thus improving battery safety.

[0126] In some embodiments, the coupling agent is a silane coupling agent. In this case, the silane coupling agent is bonded to the surface of the first ceramic particles via siloxane groups. The surface of the first ceramic particles modified with the silane coupling agent has a large number of organophilic groups, which can form hydrogen bonds with the aramid molecular chains dispersed in the ceramic particles. These hydrogen bonds tightly bind the aramid to the first ceramic particles, forming a structurally stable mixture layer. The rigid support of the ceramic particles in the mixture layer further stabilizes the aramid layer. In other words, the silane coupling agent acts as a "molecular bridge" between the ceramic particles and the aramid interface, improving the bonding force between the ceramic particles and the aramid.

[0127] For example, the silane coupling agent is selected from at least one of vinylsilane, aminosilane, epoxysilane, mercaptosilane, and methacryloxysilane. Epoxysilane is also known as an epoxysilane crosslinking agent; mercaptosilane refers to a silane coupling agent containing a mercapto group in its molecule, such as 3-mercaptopropyltriethoxysilane; methacryloxysilane refers to a silane coupling agent containing a methacryloyloxy group in its molecular structure, such as methacryloxymethyltrimethoxysilane. The siloxane groups in the above-mentioned silane coupling agent are bonded to the surface of the first ceramic particles, resulting in the formation of numerous terminal tentacles with vinyl, amino, epoxy, mercapto, and acryloyloxy groups on the surface of the modified first ceramic particles. These terminal tentacles can form hydrogen bonds with aramid fibers, achieving the connection between the aramid fibers and the first ceramic particles, thereby improving the bonding force between the aramid fibers and the first ceramic particles.

[0128] In some embodiments, the weight of the coupling agent in the mixture layer is 0.3-2% of the total weight of the first ceramic particles. Within this range, the coupling agent content can effectively act as a "molecular bridge," improving the bonding force between the first ceramic particles and the aramid fiber. Furthermore, when the coupling agent content is within this range, the appropriate amount of coupling agent adhering to the surface of the first ceramic particles results in a mixture layer with good air permeability. This allows the composite membrane to maintain good air permeability, improving the affinity between the membrane and the electrolyte and increasing ionic conductivity. If the coupling agent content is too high, it will reduce the air permeability of the composite membrane. For example, the coupling agent content in the total weight of ceramic particles is 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2.0wt%, etc.

[0129] In some embodiments, based on the total weight of the mixture layer (100%), the aramid fiber content is 0.1%–20% by weight, and the first ceramic particle content is 80%–99.9% by weight. In this case, a small amount of aramid fiber acts as a crosslinking agent to fix the particulate first ceramic particles and form a continuous film layer. Simultaneously, because the aramid fiber plays a crosslinking role in the separator particles, it can withstand temperatures above 200°C, allowing the mixture layer to remain intact at temperatures above 200°C, thus increasing the film breakage temperature of the mixture layer. Furthermore, the first ceramic particles in the mixture layer act as rigid supports within the aramid fiber molecular chains, mitigating the bond curling of the aramid polymer bonds at high temperatures, maintaining the structure of the aramid layer, and thereby improving the thermal shrinkage performance of the composite separator, resulting in a thermal shrinkage rate of <4%@150°C / 1h. When the composite separator is heated, it can mitigate the risk of internal short circuits at the beginning and end of the battery cell due to the thermal shrinkage of the separator, improving battery safety. For example, based on the total weight of the blended layers as 100%, the weight percentage of aramid can be 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc.

[0130] In some embodiments, the aramid in the mixture layer is at least one of para-aramid and meta-aramid. The aforementioned aramid can achieve crosslinking of the first ceramic particles with the aid of a coupling agent, fixing the first ceramic particles into a film and increasing the film breaking temperature of the mixture layer.

[0131] In some embodiments, the mixture layer comprises a mixture of first ceramic particles and aramid fibers. In some embodiments, the mixture layer contains trace amounts of additives in addition to the first ceramic particles and aramid fibers. In some embodiments, the additives may be selected from at least one of dispersants, thickeners, binders, and wetting agents. When a material containing first ceramic particles is formed on the surface of a film layer, the dispersant helps to improve the dispersibility of the first ceramic particles in the material, such as a slurry; the wetting agent helps to improve the wettability and spreadability of the first ceramic particles on the surface of the polyolefin layer or the aramid layer; the thickener can form a ceramic slurry with a suitable viscosity, allowing the first ceramic particles to be formed on the surface of the polyolefin layer or the aramid layer; the binder can bind the first ceramic particles after they have been formed on the polyolefin surface, and initially fix them to the polyolefin surface.

[0132] For example, the dispersant is one or more of nonionic dispersants such as polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, and polyethylene oxide; for example, the thickener is at least one of sodium carboxymethyl cellulose, hydroxyethyl cellulose, sodium alginate, hydroxypropyl methyl cellulose, and lithium hydroxymethyl cellulose; for example, the binder is at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyamide, sodium carboxymethyl cellulose, styrene-butadiene rubber, acrylate, methacrylic acid-methyl / methyl acrylate-maleic anhydride terpolymer, methacrylic acid-methyl methacrylate-vinyl carbazole terpolymer, and polyimide derivatives; for example, the wetting agent is one or more of polyether siloxane copolymer, Tween-90, fluoroalkyl ethoxylate, fatty alcohol polyoxyethylene ether, sodium butylnaphthalene sulfonate, sodium hydroxyethyl sulfonate, and sodium dodecyl sulfonate.

[0133] In some embodiments, the thickness of the mixture layer is 0.1-6 μm. In this case, the thickness of the mixture layer can reduce the thermal shrinkage rate of the composite separator. Since the first ceramic particles and aramid fibers in the mixture layer do not contribute to the battery capacity as separator materials, when the content of the first ceramic particles and aramid fibers is too high, their volume percentage in the battery also increases, which will lower the battery energy density. When the thickness of the mixture layer is 0.1-6 μm, the thickness of the aramid layer is within a controllable range, which can reduce the impact of the mixture layer on the battery energy density. For example, the thickness of the mixture layer can be specific thicknesses such as 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, and 6.0 μm.

[0134] In some embodiments, the thickness of the hybrid layer ranges from 1 to 4 μm. When the thickness of the hybrid layer is within the above range, it is possible to better balance the effect of reducing the thermal shrinkage rate of the composite separator and reducing the impact of the hybrid layer on the battery energy density.

[0135] In some embodiments, the median particle size D50 of the first ceramic particles is 0.01–2.0 μm. In this case, the first ceramic particles have a suitable particle size, which can form a dense and complete film layer under the crosslinking effect of the aramid. For example, the average median particle size D50 of the ceramic particles can be 0.01 μm, 0.02 μm, 0.05 μm, 0.08 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, or 2.0 μm.

[0136] Based on the above embodiments, the arrangement of the aramid layer and the mixture layer in the composite layer of this application embodiment includes two cases.

[0137] In the first embodiment, in the composite layer, the mixture layer is bonded to at least one surface of the polyolefin layer, and the aramid layer is bonded to the surface of the mixture layer opposite to the polyolefin layer. That is, the mixture layer and the aramid layer are sequentially stacked and bonded on at least one surface of the polyolefin layer.

[0138] In one possible implementation, a composite layer is formed on one side surface of the polyolefin layer, with a mixture layer bonded to one side surface of the polyolefin layer and an aramid layer bonded to the side surface of the mixture layer opposite to the polyolefin layer. In this case, as... Figure 1 As shown, the composite membrane 10 includes a polyolefin 11, a mixture layer 12 bonded to one side of the polyolefin 11, and an aramid layer 13 bonded to the side of the mixture layer 12 facing away from the polyolefin 11. In this case, on the one hand, the aramid layer has better heat resistance and, as a surface protective layer, can block the influence of high temperature on the polyolefin membrane layer, making the membrane breakage temperature of the composite membrane >240°C; on the other hand, the mixture layer is located between the aramid layer and the polyolefin layer, providing rigid support for both the polyolefin layer and the aramid layer, mitigating the thermal shrinkage of the composite membrane, thereby reducing the thermal shrinkage rate of the composite membrane. In addition, from a process processing perspective, this composite membrane can be prepared by first forming first ceramic particles on the surface of the polyolefin, and then casting aramid onto the surface of the first ceramic particles. The cast aramid penetrates downward along the pores between the first ceramic particles and spreads outwards on the surface of the first ceramic particles, thus realizing the preparation of the mixture layer and the aramid layer, improving the process feasibility.

[0139] In one possible implementation, a composite layer is formed on both sides of the polyolefin layer, with a mixture layer bonded to both sides of the polyolefin layer and an aramid layer bonded to the side of the mixture layer facing away from the polyolefin layer.

[0140] In the second embodiment, the aramid layer is bonded to at least one surface of the polyolefin layer, and the mixture layer is bonded to the surface of the aramid layer opposite to the polyolefin layer. That is, the aramid layer and the mixture layer are sequentially stacked on at least one surface of the polyolefin layer. This method of forming a composite layer can also increase the membrane breakage temperature and reduce thermal shrinkage. However, since the first ceramic particles are rigid, the film-forming performance of the mixture layer, whose main component is the first ceramic particles, is not as good as that of the mixture layer obtained by directly casting aramid onto the surface of the first ceramic particles when forming a film on the aramid layer surface.

[0141] In one possible implementation, a composite layer is formed on one surface of the polyolefin layer, an aramid layer is bonded to one surface of the polyolefin layer, and a mixture layer is disposed on the surface of the aramid layer opposite to the polyolefin layer. In this case, as... Figure 2 As shown, the composite membrane 10 includes a polyolefin 11, an aramid layer 13 bonded to one side of the polyolefin 11, and a mixture layer 12 bonded to the aramid layer 13 on the side facing away from the polyolefin 11. In other embodiments of this implementation, a composite layer is formed on one side of the polyolefin layer, the aramid layer in the composite layer is bonded to one side of the polyolefin layer, and the mixture layer is disposed on the side of the aramid layer facing away from the polyolefin layer.

[0142] In one possible implementation, a composite layer is formed on both sides of the polyolefin layer, with an aramid layer bonded to both sides of the polyolefin layer and a mixture layer bonded to the side of the aramid layer facing away from the polyolefin layer.

[0143] In some embodiments, the composite layer comprises n stacks formed of a blended layer and an aramid layer, where n is an integer from 2 to 5. In this case, the blended layer and the aramid layer are alternately arranged, improving the performance stability of the composite layer. Exemplarily, n is 2, 3, 4, or 5. In some embodiments, n is 2 or 3.

[0144] The composite diaphragm provided in this application embodiment can be prepared by the following method.

[0145] Correspondingly, in a second aspect, embodiments of this application provide a method for preparing a composite diaphragm, comprising the following steps:

[0146] S01. A pre-formed film is formed on one or both surfaces of the polyolefin layer using a first material;

[0147] S02. Add a second material to the surface of the pre-made film, heat and dry it to form a first film on the surface of the polyolefin layer, and form a second film on the surface of the first film.

[0148] In this embodiment, the first film is one of a mixture layer and an aramid layer, and the second film is the other of a mixture layer and an aramid layer. The material of the mixture layer includes aramid and first ceramic particles, and the surface of the first ceramic particles is bonded with a coupling agent.

[0149] The embodiments of this application are divided into two implementation scenarios based on the types of the first film and the second film.

[0150] In the first embodiment, the first film is a mixture layer, and the second film is an aramid layer. Correspondingly, the first material is a ceramic material containing first ceramic particles, and the pre-formed film is a ceramic layer formed from the first ceramic particles; the second material is an aramid slurry. In this case, by first forming the first ceramic particles on the surface of the polyolefin, and then casting the aramid slurry onto the surface of the first ceramic particles, the preparation of the mixture layer and the aramid layer is achieved, improving the feasibility of the process. Specifically, the first ceramic particles are first laid on the surface of the polyolefin layer to form a ceramic layer, i.e., the pre-formed film. At this time, the ceramic layer formed by the ceramic particle laying has poor stability. When the aramid slurry is cast onto the surface of the ceramic layer, i.e., the surface of the pre-formed film, the aramid in the slurry will penetrate downwards along the pores between the first ceramic particles and spread outwards on the surface of the first ceramic particles. The downward-permeating aramid fills the pores between the first ceramic particles, and the aramid acts as a crosslinking agent to fix the granular first ceramic particles; at the same time, the coupling agent combines with the aramid through hydrogen bonds, thereby crosslinking the first ceramic particles with the aramid through the coupling agent, fixing the first ceramic particles into a film, and after crystallization and solidification, finally forming a structurally stable mixture layer.

[0151] In this implementation scenario, the method for preparing the composite membrane is as follows: Figure 3 As shown, it includes the following steps:

[0152] S11. A ceramic layer is formed on one or both surfaces of the polyolefin layer using ceramic materials.

[0153] In this step, a ceramic layer is formed on one or both surfaces of the polyolefin layer by forming ceramic material on one or both surfaces of the polyolefin layer.

[0154] In some embodiments, the ceramic material is a ceramic slurry formed by dispersing first ceramic particles with a coupling agent bonded to their surfaces in a dispersion. In this case, the ceramic slurry is coated on one or both surfaces of the polyolefin layer, and after drying to remove the solvent, a ceramic layer formed of the first ceramic particles is formed on one or both surfaces of the polyolefin layer, with the coupling agent bonded to the surface of the first ceramic particles. It should be understood that, since the first ceramic particles are particulate inorganic materials, the ceramic layer formed by this method, with the first ceramic particles forming in a particulate form on the surface of the polyolefin layer, results in a ceramic layer with poor structural stability.

[0155] In some embodiments, the ceramic material is a ceramic slurry containing a coupling agent, first ceramic particles, and additives. In this case, the ceramic slurry is coated onto one or both surfaces of the polyolefin layer, and after drying, a ceramic layer formed by the first ceramic particles is formed on one or both surfaces of the polyolefin layer, and the surface of the first ceramic particles is bonded with a coupling agent. The additives can be at least one of a dispersant, a thickener, a binder, and a wetting agent. The dispersant helps improve the dispersibility of the first ceramic particles in the slurry; the wetting agent, when added to the slurry, improves the wettability and spreadability of the slurry on the polyolefin surface when the ceramic slurry is coated onto the polyolefin surface; the thickener increases the viscosity of the slurry; and the binder can bond the first ceramic particles after they are coated onto the polyolefin surface, initially fixing them to the polyolefin surface to form a first ceramic particle film, i.e., a pre-made film.

[0156] For example, the thickener is at least one of sodium carboxymethyl cellulose, hydroxyethyl cellulose, sodium alginate, hydroxypropyl methyl cellulose, and lithium carboxymethyl cellulose; for example, the binder is at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyamide, sodium carboxymethyl cellulose, styrene-butadiene rubber, acrylate, methacrylic acid-methyl / methyl acrylate-maleic anhydride terpolymer, methacrylic acid-methyl methacrylate-vinyl carbazole terpolymer, and polyimide derivatives; for example, the wetting agent is one or more of polyether siloxane copolymer, Tween-90, fluoroalkyl ethoxylate, fatty alcohol polyoxyethylene ether, sodium butylnaphthalene sulfonate, sodium hydroxyethyl sulfonate, and sodium dodecyl sulfonate; for example, the dispersant is one or more of nonionic dispersants such as polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, and polyethylene oxide.

[0157] In some embodiments, the ceramic slurry is prepared by dispersing first ceramic particles, a coupling agent, and an additive in deionized water, mixing them, and obtaining the ceramic slurry. Under the action of the additive, the first ceramic particles disperse and form a slurry, which facilitates its coating onto the surface of the polyolefin layer. The ceramic slurry is then coated onto the surface of the polyolefin layer, and after drying to remove the solvent, a ceramic layer is formed. At this point, the ceramic layer is the pre-formed film.

[0158] In some embodiments, the ceramic slurry includes the following components added in the following parts by weight:

[0159]

[0160] In this case, the ceramic slurry formed has good dispersion uniformity between the first ceramic particles and the coupling agent, which is conducive to the uniform binding of the coupling agent to the surface of the first ceramic particles, and thus facilitates the binding of the aramid that enters the pores of the first ceramic particles with the first ceramic particles; at the same time, the slurry has suitable viscosity and spreadability, which is conducive to the initial fixation of the first ceramic particles on the surface of the polyolefin layer.

[0161] In some embodiments, the coupling agent is a silane coupling agent. The silane coupling agent is bonded to the surface of the first ceramic particles via siloxane groups. When aramid slurry is added to the surface of the ceramic layer, the aramid slurry enters the pores of the ceramic layer. The organophilic group at the other end of the coupling agent forms hydrogen bonds with the aramid molecules that have entered the gaps between the first ceramic particles. The hydrogen bonding effect causes the aramid to be tightly bonded to the first ceramic particles, thereby fixing the first ceramic particles to the surface of the polyolefin layer and forming a structurally stable mixture layer. Exemplarily, the coupling agent is at least one selected from vinylsilane, aminosilane, epoxysilane, mercaptosilane, and methacryloxysilane.

[0162] As one possible implementation, the method for preparing the ceramic slurry is as follows:

[0163] The first ceramic particles were dispersed in deionized water, and a silane coupling agent was added to obtain the first ceramic particles modified by the silane coupling agent.

[0164] A dispersant was added to the first ceramic particles modified with silane coupling agent, and after stirring and mixing, the mixture was milled to obtain a ceramic dispersion.

[0165] Thickener, binder and wetting agent are added to ceramic dispersion and stirred to obtain ceramic slurry.

[0166] In this method, a dispersant is added after mixing the silane coupling agent and the first ceramic particles to ensure uniform dispersion of the silane coupling agent and the first ceramic particles. Other additives are then added to improve the dispersion uniformity of the silane coupling agent and the first ceramic particles, thereby enhancing the uniform distribution of the silane coupling agent on the surface of the first ceramic particles. In this case, when aramid slurry is added to the surface of the ceramic layer, the aramid enters the pores between the first ceramic particles and connects with them through the uniformly distributed silane coupling agent on the surface of the first ceramic particles, thus fixing the first ceramic particles. Ultimately, a structurally stable mixture layer, i.e., the first film, is formed.

[0167] In some embodiments, the first ceramic particle is at least one selected from silicon dioxide, aluminum oxide, magnesium hydroxide, calcium oxide, boehmite, titanium dioxide, and barium sulfate. In some embodiments, the median particle size D50 of the first ceramic particle is 0.01–2.0 μm.

[0168] In one possible implementation, the method of forming a ceramic layer on one or both surfaces of the polyolefin layer using ceramic materials is as follows: the aforementioned ceramic slurry is coated onto one or both surfaces of the polyolefin layer to form a ceramic layer. The coating method is one of dip coating, spray coating, doctor blade coating, coating bar coating, and micro-gravure roller coating.

[0169] In one possible implementation, the ceramic slurry is coated onto one or both sides of a polyolefin layer, followed by drying to remove the solvent and form a ceramic layer. It should be understood that when the ceramic slurry does not contain additives, after drying, the solvent evaporates, and the first ceramic particles disperse on the surface of the polyolefin layer, resulting in a ceramic layer that is not firmly structured on the polyolefin surface. When the ceramic slurry contains a binder, the binder can bond the first ceramic particles, initially fixing them to the surface of the polyolefin layer to form a ceramic layer. The drying method described above is not strictly limited; a ceramic layer is obtained after drying.

[0170] S12. Add aramid slurry to the surface of the ceramic layer, heat and dry it to form a mixture layer on the surface of the polyolefin layer, and form an aramid layer on the surface of the mixture layer.

[0171] In this step, the aramid slurry is a slurry with aramid as the matrix material. In one possible implementation, the aramid slurry is a slurry formed from aramid. In another possible implementation, the aramid slurry contains aramid and additives.

[0172] In one possible implementation, the additive includes a pore-forming agent. By adding a pore-forming agent, a porous structure can be formed in the aramid layer during its preparation, thereby increasing the porosity of the aramid layer. In some embodiments, the pore-forming agent is one or more inorganic pore-forming agents; exemplary, inorganic pore-forming agents include one or more of lithium chloride, sodium chloride, magnesium chloride, calcium carbonate, calcium chloride, and second ceramic particles.

[0173] In some embodiments, the pore-forming agent is a second ceramic particle. By adding the second ceramic particle to the aramid slurry, the porosity of the aramid layer can be increased to above 20%. Furthermore, the second ceramic particle introduced into the aramid layer can improve its thermal stability and thermal shrinkage properties, ultimately resulting in improved thermal shrinkage properties of the composite membrane. In some embodiments, the second ceramic particle accounts for 0–50 wt% of the total weight of the second ceramic particle and aramid, thereby imparting a suitable porosity to the aramid layer. In this case, a small amount of the second ceramic particle plays a pore-forming role while reducing its impact on the properties of the aramid layer.

[0174] The median particle size D50 of the second ceramic particles acting as a pore-forming agent can be 0.01–2 μm. In some embodiments, the median particle size D50 of the second ceramic particles is 0.1–1 μm. In this case, the second ceramic particles function as pore-forming agents to increase the porosity of the aramid layer, and the median particle size D50 being within the aforementioned range can impart suitable porosity and pore size to the aramid layer, which is beneficial for obtaining an aramid layer with better air permeability and heat resistance.

[0175] In some embodiments, the second ceramic particle is at least one selected from alumina, silicon dioxide, aluminum oxide, zirconium dioxide, magnesium oxide, zinc oxide, barium oxide, magnesium hydroxide, calcium oxide, boehmite, titanium dioxide, and barium sulfate.

[0176] In some embodiments, the pore-forming agent is an organic pore-forming agent, which volatilizes during the heat molding process of the aramid layer, thereby forming micropores in the aramid layer. Exemplarily, the organic pore-forming agent is selected from any one or more of methanol, ethanol, propanol, glycerol, polyethylene glycol, acetone, acetic acid, tetrahydrofuran, polyvinylpyrrolidone, ethyl acetate, petroleum ether, white oil, and paraffin.

[0177] As one possible implementation, the method for preparing aramid sizing is as follows:

[0178] An organic solution of phenylenediamine is prepared, cooled to below 10°C, phthaloyl chloride is added, the pH is adjusted to neutral by adding alkali, and a pore-forming agent is added to obtain aramid slurry.

[0179] This method can directly prepare aramid slurry from raw materials. The method is simple and has strong controllability.

[0180] In some embodiments, the aramid sizing agent is at least one of para-aramid sizing agent and meta-aramid sizing agent. Exemplarily, the preparation method of the aramid sizing agent is as follows: prepare an organic solution of phenylenediamine, cool it to below 10°C, add phthaloyl chloride, adjust the pH to neutral with alkali, and then add second ceramic particles to obtain the aramid sizing agent. This method can directly prepare the aramid sizing agent from the raw materials; the method is simple and has strong operational controllability. The phenylenediamine is either p-phenylenediamine or m-phenylenediamine, and the organic solvent in the organic solution is any one or more of N,N-dimethylacetamide, N-methylpyrrolidone, N,N-dimethylformamide, or dimethyl phthalate. The selection of the pore-forming agent is as described above and will not be repeated here.

[0181] In some embodiments, when preparing aramid slurry, an additive that increases the solubility of aramid may be added. Examples of such additives include lithium chloride and calcium chloride. During heating and stirring, lithium ions and chloride ions in lithium chloride replace the hydrogen bonds between aramid molecules, causing the aramid molecules to separate and accelerating the dissolution of aramid.

[0182] In some embodiments, in the preparation method of aramid slurry, after adding phthaloyl chloride, the mixture is continuously stirred to adjust the pH of the reaction solution to neutral. In some embodiments, an alkali, such as a strong alkali, is added to adjust the pH of the reaction solution. Exemplarily, the alkali can be sodium hydroxide, calcium hydroxide, potassium hydroxide, etc. Next, a pore-forming agent is added, and finally a pale yellow liquid, i.e., aramid slurry, is obtained.

[0183] In the step of adding the pore-forming agent, the amount of pore-forming agent added accounts for 0 to 10% of the total weight of the reaction system.

[0184] In some embodiments, the solid content of the aramid slurry is 1.5-10%. In this case, the aramid slurry has suitable viscosity and spreading properties, and spreads evenly on the surface of the polyolefin layer to form an aramid layer.

[0185] After adding aramid slurry to the surface of the ceramic layer, the aramid in the slurry penetrates downwards along the pores between the first ceramic particles in the ceramic layer and spreads outwards on the surface of the first ceramic particles. The downward-penetrating aramid is distributed in the pores between the first ceramic particles, and the aramid acts as a crosslinking agent to fix the particulate first ceramic particles; at the same time, the coupling agent combines with the aramid through hydrogen bonds, thereby crosslinking the first ceramic particles with the aramid through the coupling agent, fixing the first ceramic particles, and finally forming a structurally stable mixture layer after crystallization and solidification.

[0186] As one possible implementation, the method of adding aramid slurry to the surface of the ceramic layer is to coat the surface of the ceramic layer with aramid slurry. The coating process includes one of dip coating, spray coating, doctor blade coating, coating bar coating, and micro-gravure roller coating.

[0187] After adding aramid slurry to the surface of the ceramic layer and then drying it, during the drying process, on one hand, the aramid flowing into the ceramic layer connects with the first ceramic particles under the action of a coupling agent. This solidification during heating and drying fixes the first ceramic particles to the surface of the polyolefin layer, forming a mixed layer containing the first ceramic particles and aramid. On the other hand, the aramid above the ceramic layer, i.e., the aramid that did not flow into the ceramic layer, solidifies into a film during the heating and drying process, forming an aramid layer. Specifically, when the aramid slurry contains an organic pore-forming agent, the organic pore-forming agent volatilizes and overflows during the heating and drying process, forming a porous structure in the aramid layer. Thus, a mixed layer is formed on the surface of the polyolefin, and an aramid layer is formed on the side of the mixed layer facing away from the polyolefin.

[0188] As one possible implementation, the method for preparing the composite diaphragm further includes immersing a sample coated with aramid slurry into a plasticizing bath before heat drying. Before drying, immersing the sample coated with aramid slurry into the plasticizing bath causes the formed aramid fibers to be in a highly plastic state, facilitating aramid stretching. Exemplarily, the plasticizing bath is N,N-dimethylacetamide, but not limited thereto. After a second drying process, the sample immersed in the plasticizing bath is wound up to finally obtain the composite diaphragm.

[0189] In the second embodiment, the first film is an aramid layer, and the second film is a mixture layer. In this case, the corresponding first material is an aramid slurry, the pre-formed film is an aramid pre-formed layer, and the second material is a ceramic material containing the first ceramic particles.

[0190] In this implementation scenario, the method for preparing the composite membrane is as follows: Figure 4 As shown, it includes the following steps:

[0191] S21. An aramid preform layer is formed on one or both sides of the polyolefin layer using aramid slurry.

[0192] In this step, an aramid preform layer is formed on one or both surfaces of the polyolefin layer by forming an aramid slurry on one or both surfaces of the polyolefin layer.

[0193] Aramid slurry is a slurry with aramid as the matrix material. The composition of aramid slurry (including the components of aramid slurry, the type of additives such as pore-forming agents), solid content, and preparation or formation method are described in step S12 of the first embodiment above, and will not be repeated here for the sake of brevity.

[0194] As one possible implementation, the method of applying aramid slurry to one or both surfaces of the polyolefin layer involves coating one or both surfaces of the polyolefin layer with aramid slurry. The coating process includes one of dip coating, spray coating, doctor blade coating, coating bar coating, and micro-gravure roller coating.

[0195] In one possible implementation, after coating one or both surfaces of the polyolefin layer with an aramid slurry, the slurry's fluidity is reduced by heating or natural drying, allowing it to adhere to the surface of the polyolefin layer, thus obtaining an aramid preform layer. At this stage, the aramid preform layer is not fully cured. Heating can cause the aramid raw material to react and form aramid.

[0196] In one possible implementation, after coating one or both surfaces of the polyolefin layer with an aramid slurry, the aramid raw material is reacted by heating to generate aramid, thus obtaining an aramid preform layer. In some embodiments, the aramid in the aramid preform layer is cured by heat treatment. When the aramid slurry contains an organic pore-forming agent, the heating process also causes the organic pore-forming agent in the aramid to volatilize and overflow, forming pores in the aramid.

[0197] S22. Add ceramic material to the surface of the aramid preform layer, heat and dry it to form an aramid layer on the surface of the polyolefin layer, and form a mixture layer on the surface of the aramid layer.

[0198] In one possible implementation of this step, when the aramid preform is an incompletely cured preform, the composition of the ceramic material (including its physical state, components, type and content of additives), solid content, and its preparation or formation method are described in step S11 of the first embodiment above, and will not be repeated here for brevity. Alternatively, when the aramid preform is an incompletely cured preform, the first ceramic particles can be directly added to the surface of the incompletely cured preform, and the surface of the first ceramic particles is bound with a coupling agent. In this case, the first ceramic particles sink into the aramid preform, thereby achieving the mixing of the first ceramic particles and the aramid.

[0199] In this process, ceramic material is added to the surface of the aramid preform layer. The first ceramic particles in the ceramic material sink and become embedded in the aramid preform layer. During the heating and drying process, the aramid preform layer near the polyolefin layer solidifies to form an aramid layer; in the aramid preform layer away from the polyolefin layer, the embedded first ceramic particles are connected to the aramid by coupling agents on their surfaces. After heating and solidification, the first ceramic particles are fixed, forming a mixture layer of the first ceramic particles and aramid.

[0200] In one possible implementation, when the aramid in the aramid preform layer cures, the ceramic material is a mixed slurry containing ceramic and aramid, obtained by mixing raw materials containing ceramic particles and aramid. In some embodiments, in addition to ceramic particles and aramid, the mixed slurry also contains additives such as dispersants and thickeners, but is not limited thereto. In this case, the method of adding ceramic material to the surface of the aramid preform layer can be: coating the surface of the aramid preform layer with the aforementioned ceramic slurry. The coating method can be one of dip coating, spray coating, doctor blade coating, coating line bar coating, and micro-gravure roller coating. In this embodiment, the aramid in the aramid slurry and the aramid in the ceramic material can be the same or different.

[0201] The composite separator obtained in this application embodiment has a thermal shrinkage rate of <4%@150℃ / 1h due to the formation of a mixture layer of aramid and ceramic particles on the polyolefin base film. Simultaneously, the aramid layer acts as a protective layer, resulting in a membrane rupture temperature >200℃. Therefore, the composite separator significantly improves battery safety performance. Performance tests on the obtained composite separator revealed that: in the puncture strength test, all needle punctures passed at 90% SOC; and in the 150℃ thermal shrinkage rate test, the pass rate increased after heating at 150℃ for 60 minutes.

[0202] Thirdly, embodiments of this application provide an electrochemical device, including a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode, wherein the separator is a composite separator of the first aspect of embodiments of this application.

[0203] The electrochemical device provided in this application embodiment contains the above-mentioned composite separator, which has a low thermal shrinkage rate and a high membrane rupture temperature. This solves the problems of separator shrinkage and melting, reduces the risk of thermal runaway due to battery short circuit, and improves battery safety performance.

[0204] In some embodiments, at least one surface of the composite separator is provided with at least one polymer layer. The polymer layer can improve the interfacial adhesion between the composite separator and the electrode sheet, enhance the overall hardness and strength of the battery, and prevent cell deformation. In some embodiments, the polymer layer can be formed by heat shaping followed by activation. For example, after the polymer is formed on the surface of the composite separator, it is heat-treated at a pressure of 0.1–2.0 MPa and a temperature of 25°C–100°C for 20–300 min. In some embodiments, the pressure is 0.5–1.0 MPa, the temperature is 60°C–90°C, and the activation time is 60–150 min.

[0205] For example, the polymer layer is a material layer formed from at least one of PVDF, PMMA, dopamine, CMC, SBR, PTFE, and PVA; as a possible implementation of the electrochemical device of this application, the polymer layer is a polymer stack formed from at least two of PVDF, PMMA, dopamine, CMC, SBR, PTFE, and PVA, and the polymers constituting the polymer stack can be one or more of the above polymers. The above polymer materials can improve the bonding strength between the composite film containing the first aspect and the electrode sheet, maintaining the stability of the battery structure.

[0206] In some implementations, the electrochemical device is a lithium secondary battery, a potassium secondary battery, a sodium secondary battery, a zinc secondary battery, a magnesium secondary battery, or an aluminum secondary battery.

[0207] In some implementations, the electrochemical device has one or more of the following structures: a wound structure and a stacked structure.

[0208] In some implementations, the electrochemical device further includes a package, and one or more electrochemical device units are encapsulated within the package. The electrochemical device unit may be a battery cell comprising a positive electrode, a negative electrode, an electrolyte, and a composite separator.

[0209] The fourth aspect of this application provides an electronic device, including a housing and electronic components and an electrochemical device housed within the housing. The electrochemical device is the same as the electrochemical device of the third aspect of this application, and the electrochemical device is used to supply power to the electronic components.

[0210] In some implementations, the electronic device can be a mobile terminal, for example, a computer, mobile phone, tablet, or wearable product.

[0211] The fourth aspect of this application provides a mobile device that includes the electrochemical device of the third aspect.

[0212] In some implementation scenarios, the mobile device is a terminal product that requires a power source, such as a new energy vehicle, but it is not limited to new energy vehicles.

[0213] The following description is based on specific embodiments. It is worth noting that the polyolefin layer in the following embodiments is a porous polyolefin layer, and the H-HE7.0 um wet-process PE membrane produced by Chongqing Newmi Technology Co., Ltd. is selected. The parameters of this membrane are shown in Table 1.

[0214] Table 1

[0215]

[0216]

[0217] Example 1

[0218] A composite membrane, the preparation method of which includes:

[0219] (1) Preparation of ceramic slurry

[0220] a. After adding deionized water to the reactor, add 30 parts of silica particles and then 0.5 parts of silane coupling agent to obtain silane coupling agent modified ceramic particles.

[0221] b. Add 0.3 parts of polyethylene glycol to the above reactor, stir for 0.6 h and then grind for 1 h to obtain a uniform ceramic dispersion;

[0222] c. Add 0.5 parts of sodium carboxymethyl cellulose, 3 parts of polyvinylidene fluoride and 0.05 parts of polyether siloxane copolymer to the ceramic dispersion and stir to disperse for 1 hour to obtain a water-based high-temperature resistant ceramic slurry.

[0223] (2) Preparation of aramid slurry

[0224] a. Add N,N-dimethylacetamide solvent (DMAC) to the reactor, and then introduce p-phenylenediamine;

[0225] b. Lower the reactor temperature to about 0°C and stir. Add phthaloyl chloride and 2 wt.% silica particles, continue stirring, and add a strong alkali to make the pH of the synthesis solution neutral. Finally, a pale yellow liquid, namely aramid slurry, is obtained, in which the aramid content is 3.5 wt.%.

[0226] (3) Preparation of composite membrane

[0227] a. The water-based high-temperature resistant ceramic slurry prepared in step (1) is coated onto one side of a PE single-layer film with a thickness of 7μm by gravure roller coating, and the ceramic layer is obtained after drying.

[0228] b. The aramid slurry obtained in step (2) is sprayed onto one side of the ceramic layer by spraying. After coating, it is immersed in a plasticizing bath, which is N,N-dimethylacetamide. After drying, it is rolled up to obtain a composite membrane. The composite membrane includes an aramid layer, a mixed layer formed by ceramic particles and aramid, and a porous polyolefin layer, which are stacked in sequence.

[0229] In the composite membrane prepared in Example 1, the thickness of the aramid layer is about 2 μm, and the thickness of the mixture layer is about 2 μm.

[0230] Example 2

[0231] A composite separator, the preparation method of which differs from that of Example 1, lies in the preparation of the aramid slurry in the composite separator. Specifically, the preparation method of the aramid slurry is as follows:

[0232] a. Add N,N-dimethylacetamide solvent (DMAC) to the reactor, and then introduce m-phenylenediamine;

[0233] b. Lower the temperature of the reactor to about 0℃ and stir. Then add phthaloyl chloride and continue stirring. Add a strong base to neutralize the pH of the synthesis solution to obtain a pale yellow liquid, namely aramid slurry, in which the aramid content is 2.5 wt.%.

[0234] In the composite membrane prepared in Example 2, the thickness of the ceramic layer is 2 μm and the thickness of the aramid layer is 2 μm.

[0235] Example 3

[0236] A composite separator, the preparation method of which differs from that of Example 1, lies in the preparation of the aramid slurry in the composite separator. Specifically, the preparation method of the aramid slurry is as follows:

[0237] a) Barium sulfate nanoparticles are added to N,N-dimethylacetamide, lithium chloride is dissolved in N,N-dimethylacetamide, and then meta-aramid fibers are added. The mixture is heated and stirred to dissolve the meta-aramid fibers in N,N-dimethylacetamide to obtain a solution. In this step, lithium chloride is dissolved in the N,N-dimethylacetamide solvent and exists in a free state. During the heating and stirring process, lithium ions and chloride ions replace the hydrogen bonds between aramid molecules, causing the aramid molecules to separate and accelerating dissolution. The mass ratio of lithium chloride, N,N-dimethylacetamide, and meta-aramid fibers is (2-4):(70-75):(18-22), and the heating and stirring temperature is 80-100℃.

[0238] b. Add calcium hydroxide to neutralize the pH of the synthesis solution, and finally obtain a liquid, namely barium sulfate nanoparticle modified aramid slurry, in which the aramid percentage is about 4 wt.% and the barium sulfate content is about 5 wt.%.

[0239] In the composite membrane prepared in Example 3, the thickness of the mixture layer is 2 μm and the thickness of the aramid layer is 2 μm.

[0240] Example 4

[0241] A composite diaphragm, the preparation method of which differs from that of Example 1, lies in the preparation of the ceramic slurry in the composite diaphragm. Specifically, the preparation method of the ceramic slurry is as follows:

[0242] a. Add 40 parts of boehmite, 0.8 parts of silane coupling agent, and 0.51 parts of polyvinylpyrrolidone to 55.64 parts of deionized water, stir for 0.5 hours, and then grind for 1 hour to obtain a uniform ceramic dispersion.

[0243] b. Add 0.55 parts of sodium carboxymethyl cellulose, 3.26 parts of methacrylic acid-methyl methacrylate-maleic anhydride terpolymer, and 0.04 parts of sodium dodecyl sulfonate to the ceramic dispersion, stir at low speed and disperse for 1.5 hours to obtain an aqueous ceramic slurry.

[0244] In the composite membrane prepared in Example 4, the thickness of the mixture layer is 2 μm and the thickness of the aramid layer is 2 μm.

[0245] Example 5

[0246] A composite diaphragm, the preparation method of which differs from that of Example 1, lies in the preparation of the ceramic slurry in the composite diaphragm. Specifically, the preparation method of the ceramic slurry is as follows:

[0247] (1) Add 40 parts of alumina, 1 part of silane coupling agent and 0.51 parts of polyvinylpyrrolidone to 55.64 wt.% of deionized water, stir for 0.5 h, and then grind for 1 h to obtain a uniform ceramic dispersion, wherein the D50 of alumina is 0.2 μm.

[0248] (2) Add 0.55 parts of polytetrafluoroethylene, 3.26 parts of methacrylic acid-methyl methacrylate-maleic anhydride terpolymer and 0.04 parts of sodium dodecyl sulfonate to the ceramic dispersion, stir at low speed and disperse for 1.5 h to obtain water-based ceramic slurry.

[0249] In the composite membrane prepared in Example 5, the thickness of the mixture layer is 2 μm and the thickness of the aramid layer is 2 μm.

[0250] Example 6

[0251] A composite membrane is prepared in a manner different from that in Example 1, wherein the preparation method of the composite membrane is as follows:

[0252] a. The aramid slurry obtained in step (2) of Example 1 is coated onto one side of the polyolefin layer by spraying.

[0253] b. The ceramic slurry prepared in step (1) of Example 1 is sprayed onto the surface of the aramid coating by spraying.

[0254] After coating, it is immersed in a plasticizing bath, which is N,N-dimethylacetamide. After drying, it is wound up to obtain a composite membrane. The composite membrane includes a mixture layer formed by sequentially stacking ceramic particles and aramid, an aramid layer, and a porous polyolefin layer.

[0255] In the composite membrane prepared in Example 6, the thickness of the aramid layer is about 2 μm, and the thickness of the mixture layer is about 2 μm.

[0256] Example 7

[0257] A composite membrane is prepared in a manner different from that in Example 1, wherein the preparation method of the composite membrane is as follows:

[0258] a. The water-based high-temperature resistant ceramic slurry prepared in step (1) is coated on both sides of a PE single-layer film with a thickness of 7μm by gravure roller coating.

[0259] b. The aramid slurry obtained in step (2) is sprayed onto the surface of the ceramic layer by spraying. After coating, it is immersed in a plasticizing bath, which is N,N-dimethylacetamide. After drying, it is wound up to obtain a composite membrane. The composite membrane includes an aramid layer, a mixed layer formed by ceramic particles and aramid, and a porous polyolefin layer, which are stacked in sequence.

[0260] In the composite membrane prepared in Example 1, the thickness of the aramid layer is about 2 μm / side, and the thickness of the mixture layer is about 2 μm / side.

[0261] Comparative Example 1

[0262] A membrane, the preparation method of which includes:

[0263] (1) Preparation of aramid slurry

[0264] a. Add N,N-dimethylacetamide solvent (DMAC) to the reactor, and then introduce p-phenylenediamine;

[0265] b. Lower the reactor temperature to about 0°C and stir. Add phthaloyl chloride and 2 wt.% silica particles, continue stirring, and add a strong alkali to make the pH of the synthesis solution neutral. Finally, a pale yellow liquid, namely aramid slurry, is obtained, in which the aramid content is 3.5 wt.%.

[0266] (2) Preparation of the diaphragm

[0267] The prepared aramid slurry is coated onto one side of a 7μm thick PE single-layer film using a gravure roller coating method. After coating, the film is immersed in a plasticizing bath containing N,N-dimethylacetamide. After drying, the film is wound up to obtain a separator comprising sequentially stacked aramid layers and porous polyolefin layers.

[0268] In the diaphragm prepared in Comparative Example 1, the thickness of the aramid layer was 4 μm.

[0269] Comparative Example 2

[0270] A membrane, the preparation method of which includes:

[0271] (1) Preparation of ceramic slurry

[0272] a. After adding deionized water to the reactor, add 30 parts of silica particles and then 0.5 parts of silane coupling agent to obtain silane coupling agent modified ceramic particles.

[0273] b. Add 0.3 parts of polyethylene glycol to the above reactor, stir for 0.6 h and then grind for 1 h to obtain a uniform ceramic dispersion;

[0274] c. Add 0.5 parts of sodium carboxymethyl cellulose, 3 parts of polyvinylidene fluoride and 0.05 parts of polyether siloxane copolymer to the ceramic dispersion and stir to disperse for 1 hour to obtain a water-based high-temperature resistant ceramic slurry.

[0275] (2) Preparation of the diaphragm

[0276] The prepared ceramic slurry is coated onto one side of a 7μm thick PE monolayer film by gravure roller coating. After drying, a separator is obtained, which includes a ceramic layer and a porous polyolefin layer stacked sequentially.

[0277] In the diaphragm obtained in Comparative Example 2, the thickness of the ceramic layer is 4 μm.

[0278] Comparative Example 3

[0279] A membrane, the preparation method of which includes:

[0280] (1) Preparation of ceramic slurry

[0281] a. Add 40 wt.% boehmite and 0.51 wt.% polyvinylpyrrolidone to 55.64 wt.% deionized water, stir for 0.5 h, and then grind for 1 h to obtain a uniform ceramic dispersion.

[0282] b. Add 0.55 wt.% sodium carboxymethyl cellulose, 3.26 wt.% methacrylic acid-methyl methacrylate-maleic anhydride terpolymer, and 0.04 wt.% sodium dodecyl sulfonate to the ceramic dispersion, stir at low speed and disperse for 1.5 h to obtain an aqueous ceramic slurry.

[0283] (2) Preparation of the diaphragm

[0284] The prepared ceramic slurry is coated onto one side of a 7μm thick PE monolayer film by gravure roller coating. After drying, a separator is obtained, which includes a ceramic layer and a porous polyolefin layer stacked sequentially.

[0285] In the diaphragm obtained in Comparative Example 3, the thickness of the ceramic layer is 4 μm.

[0286] Comparative Example 4

[0287] A composite diaphragm, the preparation method of which differs from that of Example 1, lies in the preparation of the ceramic slurry in the composite diaphragm. Specifically, the preparation method of the ceramic slurry is as follows:

[0288] Preparation of ceramic slurry

[0289] a. Add 40 wt.% boehmite and 0.51 wt.% polyvinylpyrrolidone to 55.64 wt.% deionized water, stir for 0.5 h, and then grind for 1 h to obtain a uniform ceramic dispersion.

[0290] b. Add 0.55 wt.% sodium carboxymethyl cellulose, 3.26 wt.% methacrylic acid-methyl methacrylate-maleic anhydride terpolymer, and 0.04 wt.% sodium dodecyl sulfonate to the ceramic dispersion, stir at low speed and disperse for 1.5 h to obtain an aqueous ceramic slurry.

[0291] In the composite membrane prepared in Comparative Example 4, the thickness of the aramid layer is about 2 μm, and the thickness of the mixture layer is about 2 μm.

[0292] The composite membranes obtained in Examples 1-5 and the membranes obtained in Comparative Examples 1-3 were subjected to performance tests. The test results of the composite membranes obtained in Examples 1-5 are shown in Table 2 below, and the test results of the membranes obtained in Comparative Examples 1-3 are shown in Table 3 below.

[0293] Table 2

[0294]

[0295] Table 3

[0296]

[0297] As shown in Tables 1 and 2, the composite separators provided in Examples 1-7 of this application, after sequentially stacking ceramic particles / aramid layers and aramid layers on the surface of the porous polyolefin layer, can retain a low pore-closure temperature of approximately 140°C. Compared to the separator provided in Comparative Example 1, the composite films obtained in Examples 1-7 of this application exhibit significantly lower thermal shrinkage rates in both the mechanical direction and perpendicular to the mechanical direction, with thermal shrinkage rates all <4%@150°C / 1h. In contrast, the separator provided in Comparative Example 1, lacking the mixed layer formed by ceramic particles and aramid, has a higher thermal shrinkage rate. Compared to Comparative Examples 2-3, the rupture temperature of the composite films obtained in Examples 1-7 of this application is significantly higher. This indicates that the composite layer containing aramid layers and a mixed layer on the surface of the polyolefin layer in the embodiments of this application can improve the thermal shrinkage of the separator and increase the rupture temperature, thereby effectively improving the safety performance of the battery.

[0298] The composite membranes obtained in Examples 1-7 and the membranes obtained in Comparative Examples 1-3 were used to fabricate an electrochemical device. The fabrication method was as follows:

[0299] Positive electrode fabrication: PVDF binder is dissolved in NMP and dispersed to obtain a 7.0 wt.% PVDF adhesive solution. Then, carbon nanotube conductive liquid is added and uniformly dispersed. Finally, lithium cobalt oxide active material is added and stirred until uniformly mixed to form a positive electrode slurry. The positive electrode slurry is uniformly coated onto both sides of an aluminum foil using a coating device, and then dried in an oven to remove the NMP solvent. The coated electrode sheet is then cold-pressed, slited, and has tabs welded to form the positive electrode sheet. The mass ratio of the positive electrode material is: LCO:CNTs:PVDF = 98.8%:0.02%:1.0%.

[0300] Negative electrode sheet fabrication: The negative electrode is mixed using a kneading method. First, artificial graphite and SP are dry-mixed evenly. Then, 25 wt.% of pre-mixed CMC adhesive is added and kneaded again. Finally, the remaining CMC and deionized water are added and dispersed at high speed to form a mixed negative electrode slurry. After sieving, the slurry is evenly coated onto both sides of copper foil using a coating device. After drying in an oven, the electrode sheets are cold-pressed, slit, and have their tabs welded to form the negative electrode sheet. The mass ratio of the negative electrode materials is: graphite:SP:CMC:SBR = 96.8%:0.6%:1.2%:1.2%.

[0301] Separator fabrication: The surface of the battery separators of Examples 1-7 and Comparative Examples 1-3 above is then sprayed with a 0.5 μm PVDF or PMMA water-based adhesive layer.

[0302] The above-mentioned positive and negative electrode sheets and separator are wound together to form a bare cell with a capacity of 4.5Ah and an operating voltage range of 3.0-4.48V. The cell is then processed into a lithium-ion battery through processes such as encapsulation, baking, electrolyte injection, and formation.

[0303] The electrochemical devices containing the membranes prepared in Examples 1-7 and Comparative Examples 1-4 were subjected to performance tests, and the test results are shown in Tables 4 and 5, respectively:

[0304] Table 4

[0305]

[0306] Table 5

[0307] 90% SOC acupuncture 5 / 5 passed 3 / 5 passed 0 / 5 passed 3 / 5 passed 150℃, 1 hour hot box 0 / 5 passed 0 / 5 passed 3 / 5 passed 3 / 5 passed

[0308] As shown in Tables 4 and 5, when the batteries were subjected to a 90% SOC nail penetration test, the battery containing the composite separator of the present application passed all five tests, while the batteries containing the separators of Comparative Example 2 and Comparative Example 3 had a pass rate of 60% and 0%, respectively. This is attributed to the fact that the separators provided in Comparative Documents 2 and 3 do not contain an aramid layer, which caused an internal short circuit and heat generation during the nail penetration test. In contrast, the high heat resistance of the aramid layer in the composite separator of the present application prevents the separator from melting, suppresses further internal short circuit heating, and reduces the probability of battery overheating and combustion.

[0309] All batteries passed the heat treatment at 130°C for 30 minutes. However, when the batteries were heat-treated at 150°C for 60 minutes, the batteries containing the separators provided in Comparative Examples 1-3 did not achieve a 100% pass rate, and some even had a 0% pass rate. The reasons are as follows: Comparative Example 1 only contains an aramid layer, which is prone to curling at high temperatures, causing the battery separator to curl as well; Comparative Example 2 only contains a common ceramic coating, which collapsed and melted at 150°C, failing to effectively isolate the positive and negative electrodes, resulting in a short circuit and combustion; Comparative Example 3 only contains a high-temperature ceramic coating with a membrane breakage temperature of 180°C. After baking at 150°C for 1 hour, the separator strength was too low to effectively isolate the positive and negative electrodes, resulting in a short circuit and combustion.

[0310] It should be noted that the performance testing methods involved in the embodiments of this application are as follows:

[0311] (1) Film thickness (µm)

[0312] Method 1:

[0313] a. Sampling: Take a 1×10⁻⁶ sample from the diaphragm. 3 mm 2 Sample (the area of ​​the sample can be ≥1.5×10) 3 mm 2 The number of test points depends on the condition of the diaphragm (usually no less than 10 points).

[0314] b. Testing: The thickness was tested using a 1 / 20,000 thickness gauge at a temperature of 23±2℃.

[0315] c. Data processing: Measure the thickness at each test point and take the arithmetic mean.

[0316] Method 2:

[0317] a. Sampling: For products with a width < 200mm: Determine a point every 40mm ± 5mm along the longitudinal (MD) direction, with no less than 10 test points. The number of test points can be determined according to the width of the diaphragm. The measurement starting point should be no less than 20mm from the edge.

[0318] For products with a width ≥ 200mm: Determine a point every 80mm ± 5mm along the transverse (TD) direction, with a minimum of 10 test points. The number of test points can be determined based on the width of the diaphragm. The measurement starting point should be at least 20mm from the edge.

[0319] b. Testing: Each test point is tested using a thickness gauge at a temperature of 23±2℃. The diameter of the measuring surface is between 2.5mm and 10mm, and the load applied to the sample by the measuring surface should be between 0.5N and 1.0N.

[0320] c. Data processing: Measure the thickness at each test point and take the arithmetic mean.

[0321] (2) Porosity (%)

[0322] Method 1:

[0323] a. Sampling: Take a 1×10⁻⁶ sample from the diaphragm. 4 mm 2 sample.

[0324] b. Testing: Porosity was measured using the density method.

[0325] c. Data processing:

[0326] The overall porosity P of the sample can be calculated using the following formula:

[0327]

[0328] Where m can be the sample mass, ρ can be the true density of the sample material, and V can be the sample volume.

[0329] Method 2:

[0330] a. Sampling: Cut one rectangular sample using a 237×170mm template sampler. When cutting the sample, keep it as far away from the edge of the diaphragm as possible (e.g., more than 50mm from the edge of the diaphragm).

[0331] b. Testing: Porosity is measured using the density method, which involves measuring n (n can be greater than or equal to 9) points on the sample, which can be distributed in an equidistant lattice.

[0332] c. Data processing: Porosity P at each point i It can be calculated using the following formula:

[0333]

[0334] Where, m i For each point, ρ is the skeleton density of the sample (which can be calculated based on the material ratio), and V is the mass. i The total volume at each point (which can be calculated based on the length, width, and thickness of the sample);

[0335] The overall porosity P of the sample can be calculated using the following formula:

[0336]

[0337] Where m can be the sample mass, ρ can be the true density of the sample material, and V can be the sample volume.

[0338] (3) Breathability (s / 100cc)

[0339] Method 1:

[0340] a. Sampling: Take a sample with a diameter ≥28mm from the diaphragm.

[0341] b. Testing: The test shall be conducted in accordance with the method specified in standard JIS P8117-2009. Specifically, the pressure of the cylinder-driven pressure reducing valve shall be set to 0.25 MPa, the test pressure to 0.05 MPa, and the test standard shall be "JIS".

[0342] c. Data processing: Six samples were randomly cut from the full width of the diaphragm, and the air resistance value of each sample was recorded. The arithmetic mean of each sample was then calculated.

[0343] Method 2:

[0344] a. Sampling: Cut six square samples using a 100×100mm plate sampler. When cutting the samples, keep them as far away from the edge of the diaphragm as possible (e.g., more than 50mm from the edge of the diaphragm). Distribute each sample evenly on the diaphragm (i.e., divide the diaphragm into six zones across its full width, and cut one sample from each of these six zones).

[0345] b. Testing: The test shall be conducted in accordance with the method specified in standard JIS P8117-2009. Specifically, the pressure of the cylinder-driven pressure reducing valve shall be set to 0.25 MPa, the test pressure to 0.05 MPa, and the test standard shall be "JIS".

[0346] c. Data processing: Record the air resistance value of each sample and calculate the arithmetic mean of the air resistance values ​​of the six samples.

[0347] (4) Puncture strength (gf)

[0348] Method 1:

[0349] a. Sampling: Take a sample with a diameter ≥ 45 mm from the microporous membrane.

[0350] b. Testing: The sample is centered and fixed on the fixture. The test needle is a 1mm diameter spherical shape (made of ruby). Ensure the sample extends to or beyond the edge of the clamping plate in all directions, confirming that the sample is completely fixed to the annular fixture without slippage. During testing, the diaphragm is punctured. The machine speed is set to 300±10mm / min until the puncture bar completely breaks the sample. The puncture resistance is the maximum force recorded during the test.

[0351] c. Data processing: Six samples were randomly cut from the full width of the sample, and the puncture intensity value of each sample was recorded. The arithmetic mean of the puncture intensity values ​​of each sample was then calculated.

[0352] Method 2:

[0353] a. Sampling: Cut six rectangular samples using a 237×170mm plate sampler. When cutting the samples, keep them as far away from the edge of the diaphragm as possible (e.g., at least 50mm away from the edge of the diaphragm). Distribute each sample evenly on the diaphragm (i.e., divide the diaphragm into six zones across its full width, and cut one sample from each of these six zones).

[0354] b. Testing: The test shall be conducted according to the method specified in standard ASTM D4833-07. Specifically, this may include: using a spherical test needle with a diameter of 1 mm (made of sapphire); centering the sample on the fixture, ensuring that the sample extends to or exceeds the edge of the clamping plate in all directions, and confirming that the sample is completely fixed on the annular fixture without slippage; during the test, the machine speed is set to 300 ± 10 mm / min, and the diaphragm is punctured until the test needle completely breaks the sample; the puncture resistance is the maximum force recorded during the test.

[0355] c. Data processing: Record the puncture intensity of each sample and calculate the arithmetic mean of the puncture intensities of the six samples.

[0356] (5) Tensile strength and elongation (MPa and %)

[0357] Method 1:

[0358] a. Sampling: On the overall width sample, the diaphragm is cut along the MD and TD directions to obtain multiple strip samples with a length ≥ 50 mm and a width of approximately 15 ± 0.1 mm (for MD testing, the sample width can be along the TD direction of the diaphragm, and the sample length can be along the MD direction of the diaphragm; for TD testing, the sample width can be along the MD direction of the diaphragm, and the sample length can be along the TD direction of the diaphragm).

[0359] b. Testing: Tensioning is performed using a tensile testing machine with a clamp spacing of 100±5mm until the sample breaks. The tensile speed can be 100±1mm / min.

[0360] c. Data processing: Record the tensile strength and elongation of each sample separately.

[0361] Method 2:

[0362] a. Sampling: Cut six rectangular samples using a 237×170mm plate sampler. When cutting the samples, keep them as far away from the edge of the diaphragm as possible (e.g., at least 50mm from the edge). Distribute each sample evenly across the diaphragm (i.e., divide the entire width of the diaphragm into six zones along the MD and TD directions, and cut one sample from each of these six zones). Then, cut strip samples with a length ≥150mm and a width of 15±0.1mm using the sampler.

[0363] b. Testing: Measurements shall be performed according to the methods specified in GB / T1040.3-2006. Specifically, the clamp spacing can be 100±5mm, and the tensile speed can be 100±1mm / min.

[0364] c. Data processing: Record the tensile strength and elongation of each specimen, and calculate the arithmetic mean of the six specimens.

[0365] (6) Heat shrinkage rate at 150℃

[0366] a. Sampling: Six samples are randomly cut from the full width. The specific sampling for each sample may include: cutting 100 mm along the MD direction of the diaphragm; when the TD direction of the diaphragm is greater than 100 mm, the length of the test sample in the TD direction can be 100 mm; when the TD direction of the microporous membrane is less than 100 mm, the length of the test sample in the TD direction can be based on the actual length.

[0367] b. Testing: Mark the longitudinal and transverse dimensions of the sample, measure and record the longitudinal and transverse dimensions of each sample; place the sample flat in the paper sleeve layer, ensuring the sample is free from folds, wrinkles, or adhesions; place the paper sleeve containing the sample (e.g., 10 layers) flat in the middle of the constant temperature oven (door opening time not exceeding 3 seconds); heat the sample to 150°C using the electric heating constant temperature oven for 1 hour; remove the sample and cool it to room temperature, then measure the longitudinal and transverse lengths.

[0368] c. Data processing:

[0369] Calculate the thermal shrinkage rate of each sample:

[0370] T = (L0 - L) / L0 × 100%,

[0371] Where T can be the heat shrinkage rate of the sample (%), L0 can be the length of the sample before heating (mm), and L can be the length of the sample after heating (mm). Calculate the arithmetic mean of the heat shrinkage rates of the samples.

[0372] (7) Closed-cell temperature (°C)

[0373] The internal resistance method with temperature rise was used for testing. The diaphragm was placed in a stainless steel fixture or other similar fixture and an appropriate amount of electrolyte was injected. The fixture was then placed in an oven and heated at a certain rate. The resistance and temperature of the fixture were monitored at the same time. The temperature at which the resistance changed abruptly to 10 times the initial resistance was taken as the diaphragm's closed-cell temperature.

[0374] (8) Membrane rupture temperature (°C)

[0375] The rupture temperature was tested using a baking method. The diaphragm was placed in a 9*9cm fixture, which was then placed in an oven. The temperature was increased at a certain rate while monitoring whether the diaphragm ruptured. The rupture temperature of the diaphragm was recorded when the diaphragm ruptured as the temperature changed.

[0376] (9) Acupuncture test

[0377] a. Sampling: Take 5 power conversion system (pcs) batteries from each group and mark the center position of the cells.

[0378] b. Testing: At 25±3℃, charge the battery cell to the limiting voltage using a constant current of 0.7C, then charge it again under the limiting voltage constant voltage condition until the current decreases to 0.025C. Test within 12-24 hours. At 25±3℃, insert a steel nail into the center of the battery cell at a speed of 150mm / s until it penetrates completely. The steel nail should have a diameter of 2.45±0.06mm, a length of 45±2.5mm, and a tip length between 2mm and 4.9mm.

[0379] c. Data processing: If the steel nail does not catch fire or explode within 10 minutes during and after the puncture, it is considered a pass.

[0380] (10) 150℃ thermal shock test

[0381] a. Sampling: Take 5 batteries from each group.

[0382] b. Testing: At 25±3℃, charge the cell to the limit voltage with a constant current of 0.2C, and then charge it under the constant voltage condition of the limit voltage until the current decreases to 0.025C. Heat the battery from the initial temperature of 25±3℃ using convection or a circulating hot air chamber, with a temperature change rate of 5±2℃ / min; hold the temperature at 150±2℃ for 60min.

[0383] c. Data processing: Observe the experimental phenomena. If the experiment does not ignite or explode after heating, it is considered passed.

[0384] (11) Piercing test

[0385] After charging to 90% SOC using standard charging mode, test the battery within 12–24 hours. Then, place the battery in a 25°C explosion-proof chamber and insert a steel nail into the center of the cell at a speed of 150 mm / s until it is fully penetrated. Hold the nail in place for 10 minutes and then withdraw it. If the battery does not thermally run away, the test is passed, and the pass rate is recorded.

[0386] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A composite separator, characterized by, The invention includes a polyolefin layer, a composite layer bonded to one or both surfaces of the polyolefin layer, the composite layer including a mixture layer and an aramid layer bonded to one surface of the mixture layer, wherein the mixture layer and the aramid layer are both stacked with the polyolefin layer. The mixture layer includes aramid and first ceramic particles, the surface of which is bonded with a coupling agent; wherein the coupling agent contains inorganic-philic groups and organic-philic groups, and the coupling agent is connected to the first ceramic particles through the inorganic-philic groups and to the aramid through hydrogen bonds formed by the organic-philic groups. The mixture layer includes a first surface in contact with the aramid layer and a second surface away from the first surface. The aramid content in the mixture layer gradually increases along the direction from the second surface to the first surface. The mixture layer is formed by the aramid penetrating into the gaps between the first ceramic particles. The coupling agent is at least one silane coupling agent selected from vinylsilane, aminosilane, epoxysilane, mercaptosilane, and methacryloxysilane; the weight of the coupling agent is 0.3-2% of the total weight of the first ceramic particles; The composite diaphragm has a rupture temperature >240℃ and a thermal shrinkage rate <4%@150℃ / 1h.

2. The composite separator of claim 1, wherein Based on the total weight of the mixture layer as 100%, the weight percentage of aramid is 0.1-20%, and the weight percentage of the first ceramic particles is 80-99.9%.

3. The composite separator of any one of claims 1 to 2, wherein, Based on the total weight of the aramid layer being 100%, the weight percentage of the aramid is 50-100%.

4. The composite separator of claim 3, wherein The aramid layer also includes a second ceramic particle with a weight percentage of 0-50%.

5. The composite separator according to any one of claims 1 to 3, wherein The thickness of the mixture layer is 0.1-6 μm.

6. The composite separator of claim 5, wherein The thickness of the mixture layer ranges from 1 to 4 μm.

7. The composite diaphragm according to any one of claims 1 to 2, characterized in that, The thickness of the aramid layer is 0.1-6 μm.

8. The composite separator of claim 7, wherein The thickness of the aramid layer is 0.5-3 μm.

9. The composite separator of any one of claims 1 to 8, wherein, The aramid layer contains at least one of para-aramid and meta-aramid; and / or The aramid in the mixture layer is at least one of para-aramid and meta-aramid.

10. The composite separator of any one of claims 1 to 2, wherein The median particle size D50 of the first ceramic particles is 0.01–2.0 μm.

11. The composite separator of claim 4, wherein The median particle size D50 of the second ceramic particles is 0.1-1 μm.

12. The composite separator according to any one of claims 1 to 11, characterized in that, The thickness of the polyolefin layer is 0.2~20μm.

13. The composite separator of any one of claims 1 to 12, wherein In the composite layer, the mixture layer is bonded to the surface of the polyolefin layer, and the aramid layer is bonded to the side of the mixture layer opposite to the polyolefin layer.

14. The composite separator of any one of claims 1 to 13, wherein The composite layer comprises n layers formed by a mixture layer and an aramid layer, where n is an integer from 2 to 5.

15. An electrochemical device comprising a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode, characterized in that, The diaphragm is a composite diaphragm as described in any one of claims 1 to 14.

16. An electronic device comprising a housing and electronic components and an electrochemical device housed within the housing, characterized in that, The electrochemical device is the electrochemical device according to claim 15, and the electrochemical device is used to supply power to the electronic components.

17. The electronic device of claim 16, wherein, The electronic devices mentioned include computers, mobile phones, tablets, and wearable products.

18. A mobile device, comprising: The mobile device includes the electrochemical device as described in claim 17.

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