WO2023011293A1

WO2023011293A1 - Composite separator, electrochemical apparatus, electronic device, and mobile terminal

Info

Publication number: WO2023011293A1
Application number: PCT/CN2022/108337
Authority: WO
Inventors: 阳东方; 田雷雷; 李枝贤; 谢封超
Original assignee: 华为技术有限公司
Priority date: 2021-07-31
Filing date: 2022-07-27
Publication date: 2023-02-09
Also published as: CN115693024A

Abstract

The present application relates to the technical field of battery separators, and provides a composite separator, an electrochemical apparatus, an electronic device, and a mobile terminal. The composite separator comprises a polyolefin layer, a composite layer which is bonded to one side or both side surfaces of the polyolefin layer and comprises a mixture layer, and an aramid layer which is bonded to one side surface of the mixture layer, wherein both the mixture layer and the aramid layer are stacked with the polyolefin layer. The mixture layer comprises an aramid and first ceramic particles, and the surface of the first ceramic particles is bonded with a coupling agent, wherein the coupling agent contains an inorganophilic group and an organophilic group, and the coupling agent is linked to the surface of the first ceramic particles by means of the inorganophilic group, and is linked to the aramid by means of the organophilic group. The composite separator provided in the present application has a film-breaking temperature of greater than 240°C and a thermal shrinkage rate of less than 4%@150°C/1 h, and can effectively solve the problem of potential safety hazards of a battery caused by thermal runaway which occurs during battery short circuiting due to a thermal shrinkage- and melting-prone separator.

Description

Composite separators, electrochemical devices, electronic devices and mobile terminals

This application claims the priority of the Chinese patent application filed with the State Intellectual Property Office on July 31, 2021, with the application number 202110877240.X and the application name "composite separator, electrochemical device, electronic equipment and mobile terminal", all of which The contents are incorporated by reference in this application.

technical field

The application belongs to the technical field of battery separators, and in particular relates to a composite separator, an electrochemical device, an electronic device and a mobile terminal.

Background technique

With the development of electric vehicles, smart terminals and electronic mobile devices, lithium-ion batteries have become one of the most important devices in the electronics and new energy vehicle industries. The separator is used as a separator to separate the positive and negative electrodes of the battery. As one of the five main materials of lithium-ion batteries, the separator plays an important role in battery safety. The most commonly used diaphragm is polyethylene diaphragm, the heat shrinkage rate of the diaphragm is usually MD>10% (150°C/1h), TD>10% (150°C/1h); and the membrane rupture temperature of the diaphragm is usually <155 ℃. Therefore, when the battery works under high temperature conditions, the separator is heated and melts and shrinks severely. The damage of the diaphragm leads to direct contact between the positive and negative electrodes of the battery, which triggers a severe short circuit inside the battery and thermal runaway of the battery.

In order to improve the thermal stability of the diaphragm, the surface of the diaphragm is usually coated with a coating, which is usually an inorganic ceramic layer (silicon oxide, aluminum oxide, and magnesium oxide, etc.), an organic polymer viscous coating (PVDF, PMMA, etc.) or Organic high temperature resistant polymer coating (PI and aramid fiber layer, etc.). The inorganic ceramic layer and organic high-temperature-resistant polymer coating are used to improve the thermal stability of the separator, meet the reliability and safety of related products in high-temperature application scenarios, and prevent the battery from igniting, burning or even exploding. The organic polymer adhesive coating is used to improve the interface adhesion with the electrode sheet, improve the overall hardness and strength of the battery, prevent the deformation of the battery cell, and ensure the reliability and safety of the battery cell. However, when polymer materials such as aramid fibers are exposed to high temperatures, the motion units of the polymer chains change from the previous bond lengths and bond angles to chain segments, and the movement of the molecular chains is accelerated, causing the aramid fibers to curl up, resulting in high thermal shrinkage. The heat shrinkage rate of the coating reaches 6% (150°C/1h), which reduces the safety of the battery.

Contents of the invention

The purpose of this application is to provide a composite diaphragm and its preparation method, as well as electrochemical devices, electronic equipment and mobile terminals containing the above-mentioned composite diaphragm, aiming at solving the problem that the aramid layer on the surface of the diaphragm has a high thermal shrinkage rate and increases the short circuit in the battery. Risks, issues affecting battery safety performance.

In order to realize the above-mentioned application purpose, the technical scheme adopted in this application is as follows:

The first aspect of the present application provides a composite diaphragm, comprising a polyolefin layer, a composite layer bonded to one or both sides of the polyolefin layer, the composite layer including a mixture layer, and a composite layer bonded to one side of the mixture layer an aramid fiber layer on the surface, and both the mixture layer and the aramid fiber layer are laminated with the polyolefin layer;

The mixture layer includes aramid fibers and first ceramic particles, and a coupling agent is bound on the surface of the first ceramic particles; wherein, the coupling agent contains an inorganic group and an organophilic group, and the coupling agent passes through The inorganic-philic group is connected to the surface of the first ceramic particle, and is connected to the aramid fiber through the organophilic group.

The composite diaphragm provided by the application includes a composite layer arranged on one or both sides of the polyolefin layer, and the composite layer includes a mixture layer and an aramid fiber layer. Among them, the aramid fiber layer can withstand a high temperature of 200°C, so that the membrane rupture temperature of the composite diaphragm can be increased to make the membrane rupture temperature greater than 200°C. The battery with aramid layer in the diaphragm can withstand the high temperature of 200 ℃ without melting when it is subjected to thermal abuse and mechanical abuse, so as to effectively isolate the positive and negative electrodes of the battery and avoid direct contact between the positive and negative electrodes to cause severe Internal short circuit improves battery safety. However, the heat shrinkage rate of the aramid fiber layer is relatively high, which increases the risk of short circuit in the battery. On this basis, the present application introduces a mixture layer containing aramid fibers and first ceramic particles on the surface of the aramid fiber layer, and the surface of the first ceramic particles is bound with a coupling agent. Since the coupling agent contains inorganic and organophilic groups, it serves as a "molecular bridge" with one end connected to the surface of the first ceramic particle, and the other end connected to the aramid fiber in the mixture layer, thereby strengthening the connection between the first ceramic particle and the aramid fiber. The binding force between the fibers makes the aramid fiber act as a crosslinking agent to crosslink and fix the ceramic particles and form a continuous and stable film layer. Under the action of the coupling agent, the mixture layer has better structural stability, which is not only conducive to improving the structural stability of the composite diaphragm under high temperature conditions, but also the first ceramic particles play a role in the aramid molecular chain in the aramid layer. The role of rigid support can relieve the molecular bond curling of the polymer bond of aramid fiber at high temperature, thereby improving the heat shrinkage performance of the aramid fiber layer, so that the heat shrinkage rate of the composite diaphragm is <4%@150°C/1h (ie: put After the composite separator is heat-treated for 1 hour at a temperature of 150° C., its heat shrinkage rate is less than 4%). The battery containing the mixture layer can alleviate the risk of internal short circuit caused by the heat shrinkage of the separator at the head and tail of the cell when the composite separator is heated, thereby improving the safety of the battery.

In summary, the composite separator provided by this application has a membrane rupture temperature > 240°C and a thermal shrinkage rate < 4%@150°C/1h, which can effectively solve the problem of thermal runaway of the battery due to the thermal shrinkage and melting of the separator due to the short circuit of the battery, resulting in safety hazard issues.

As a possible implementation of the composite membrane of the present application, the coupling agent is a silane coupling agent. At this time, the silane coupling agent is bound to the surface of the first ceramic particle through the siloxane group. Because there are a large number of organophilic groups on the surface of the first ceramic particles combined with the coupling agent, the organophilic groups can form hydrogen bonds with the aramid molecules dispersed in the first ceramic particles, and the hydrogen bonds make the aramid fibers and the second ceramic particles A ceramic particle is closely combined to form a structurally stable mixture layer, and then the aramid fiber layer is stabilized by means of the first ceramic particle in the mixture layer.

As a possible implementation of the composite membrane of the present application, the silane coupling agent is selected from at least one of vinylsilane, aminosilane, epoxysilane, mercaptosilane and methacryloxysilane. The siloxane group in the above-mentioned silane coupling agent is combined on the surface of the first ceramic particle, so that the surface of the modified first ceramic particle forms a large number of terminal tentacles, these terminal tentacles can form hydrogen bonds with the aramid fibers, realize the connection between the aramid fibers and the first ceramic particles, and improve the binding force between the aramid fibers and the first ceramic particles.

As a possible implementation of the composite membrane of the present application, in the mixture layer, the weight of the coupling agent is 0.3-2% of the total weight of the first ceramic particles. When the content of the coupling agent is within the above range, it can effectively play the role of "molecular bridge" and improve the binding force between the first ceramic particle and the aramid fiber. In addition, when the content of the coupling agent is within the above range, the content of the coupling agent connected to the surface of the first ceramic particles is appropriate, and the formed mixture layer has better air permeability, so that the composite diaphragm can maintain good air permeability and improve the diaphragm. Affinity with electrolyte increases ionic conductivity. If the content of the coupling agent is too high, the air permeability of the composite membrane will be reduced.

As a possible implementation of the composite membrane of the present application, the mixture layer includes a first surface in contact with the aramid fiber layer and a second surface away from the first surface, along the second surface to the In the direction of the first surface, the aramid content in the mixture layer gradually increases. In this case, the side close to the aramid fiber layer has better structural stability, so that the mixture layer can effectively stabilize the aramid fiber layer through the first ceramic particles therein, reducing the heat shrinkage rate of the aramid fiber.

As a possible implementation of the composite diaphragm of the present application, based on the total weight of the mixture layer as 100%, the weight percentage of the aramid fiber is 0.1-20%, and the weight percentage of the first ceramic particles is Mineral content is 80 ~ 99.9%. In this case, a small amount of aramid fiber acts as a cross-linking agent to fix the granular first ceramic particles and form a continuous film layer; at the same time, because the aramid fiber undertakes the cross-linking effect in the separator particles, the aramid fiber can withstand 200°C The above high temperature keeps the mixture layer intact at a high temperature above 200°C, which increases the membrane rupture temperature of the mixture layer. On this basis, the first ceramic particles in the mixture layer play a rigid support role in the aramid molecular chain, which relieves the molecular bond curling of the aramid polymer bond in the aramid layer at high temperature, thereby improving the thermal stability of the composite diaphragm. Shrinkage performance, so that the heat shrinkage rate of the composite diaphragm is <4%@150°C/1h. When the composite diaphragm is heated, it can alleviate the risk of internal short circuit at the head and tail of the cell due to the heat shrinkage of the diaphragm, improving battery safety.

As a possible implementation of the composite membrane of the present application, the thickness of the mixture layer is 0.1-6um. In this case, the thickness of the mixture layer can achieve the effect of reducing the thermal shrinkage rate of the composite separator; moreover, since the thickness of the mixture layer is within a controllable range, the influence of the mixture layer on the energy density of the battery can be reduced.

As a possible implementation of the composite membrane of the present application, the thickness of the mixture layer is in the range of 1-4um. When the thickness of the mixture layer is within the above range, the effect of reducing the thermal shrinkage rate of the composite separator and the effect of reducing the mixture layer on the energy density of the battery can be better taken into account.

As a possible implementation of the composite separator of the present application, the aramid fiber in the mixture layer is at least one of para-aramid fiber and meta-aramid fiber. The aramid fibers mentioned above can achieve cross-linking of the first ceramic particles and increase the membrane rupture temperature of the mixture layer.

As a possible implementation of the composite membrane of the present application, the median diameter D50 of the first ceramic particles is 0.01-2.0 μm. In this case, the first ceramic particles have a suitable particle size and can form a dense and complete film layer under the crosslinking action of the aramid fiber.

As a possible implementation of the composite diaphragm of the present application, based on the total weight of the aramid layer as 100%, the weight percentage of the aramid fiber is 50-100%. When the weight percentage of the aramid fiber is more than 50%, the aramid fiber layer can maintain the characteristics of the aramid fiber material and effectively increase the membrane rupture temperature of the composite diaphragm.

In a possible implementation manner, based on the total weight of the aramid fiber layer as 100%, the weight percentage of the aramid fiber is 100%. At this time, the aramid fiber layer is composed of aramid fiber, which can improve the compound The effect of membrane rupture temperature.

In another possible implementation manner, based on the total weight of the aramid fiber layer being 100%, the weight percentage of the aramid fiber is between 50% and 100%, but not 100%. At this time, the aramid layer contains aramid and other materials. Other materials include porogens to impart porosity to the aramid layer.

As a possible implementation of the composite diaphragm of the present application, when the weight percentage of the aramid fiber is not 100%, the aramid fiber layer further includes second ceramic particles with a weight percentage of 0-50% . The porosity of the aramid fiber layer can be increased by adding the second ceramic particles with a weight percentage of 0-50% in the aramid fiber layer, so that the porosity of the aramid fiber layer is above 20%. Not only that, the second ceramic particles introduced into the aramid layer can improve the thermal stability of the aramid layer, improve the thermal shrinkage performance of the aramid layer, and finally reflect the improvement of the thermal shrinkage performance of the composite diaphragm.

As a possible implementation of the composite separator of the present application, the median diameter D50 of the second ceramic particles is 0.1-1 μm. In this case, the second ceramic particles play a pore-forming role to increase the porosity of the aramid fiber layer, and the median particle diameter D50 is in the above range, which can endow the aramid fiber layer with proper porosity and pore size.

As a possible implementation of the composite membrane of the present application, the thickness of the aramid fiber layer is 0.1-6um. In this case, the thickness of the aramid layer can not only achieve the effect of increasing the rupture temperature of the composite separator; moreover, since the thickness of the aramid layer is within a controllable range, the influence of the aramid layer on the energy density of the battery can be reduced.

As a possible implementation of the composite membrane of the present application, the thickness of the aramid fiber layer is 0.5-3um. When the thickness of the aramid fiber layer is within the above range, the effect of increasing the rupture temperature of the composite separator and reducing the influence of the aramid fiber layer on the energy density of the battery can be better taken into account.

As a possible implementation of the composite diaphragm of the present application, the aramid fiber in the aramid fiber layer is at least one of para-aramid fiber and meta-aramid fiber. In this case, the obtained aramid layer has excellent high temperature resistance, which can endow the composite separator with excellent membrane rupture performance, increase its membrane rupture temperature, and finally improve the safety performance of the battery using the composite separator.

As a possible implementation of the composite separator of the present application, the polyolefin layer has a thickness of 0.2-20 μm. Because the application forms a composite layer containing the above-mentioned aramid layer and the mixture layer on one surface of the polyolefin layer, which improves the film breaking temperature and thermal shrinkage performance of the polyolefin layer, therefore, the thickness of the polyolefin layer provided by the application It can be as low as 0.2 μm, and the polyolefin layer with a thickness of 0.2-20 μm can be used as the polyolefin layer of the separator matrix, which can effectively isolate the positive and negative electrodes of the battery.

As a possible implementation of the composite membrane of the present application, the mixture layer is bonded to one surface of the polyolefin layer, and the aramid layer is bonded to the surface of the mixture layer away from 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 rupture temperature of the composite diaphragm > 240°C; on the other hand On the one hand, the mixture layer is arranged between the aramid layer and the polyolefin layer, and at the same time provides rigid support for the polyolefin layer and the aramid layer, and relieves the thermal shrinkage of the composite diaphragm, thereby reducing the thermal shrinkage rate of the composite diaphragm. In addition, from the perspective of processing, the composite diaphragm can be made by first forming first ceramic particles on the surface of polyolefin, and then pouring aramid fibers on the surface of the first ceramic particles. The pores between the particles permeate downwards, and spread out on the surface of the first ceramic particles to realize the preparation of the mixture layer and the aramid fiber layer, and improve the process feasibility.

As a possible implementation of the composite membrane of the present application, the composite layer includes n laminated layers formed of a mixture layer and an aramid fiber layer, wherein n is an integer of 2-5. In the composite layer obtained in this case, the mixture layer and the aramid fiber layer are arranged alternately, thereby improving the performance stability of the composite layer.

The second aspect of the present application provides a method for preparing a composite diaphragm, comprising the following steps:

Using the first material to form a prefabricated film on one or both sides of the polyolefin layer;

adding a second material on the surface of the prefabricated film, drying, forming a first film on the surface of the polyolefin layer, and forming a second film on the surface of the first film;

Wherein, the first film is one of the mixture layer and the aramid layer, the second film is another layer of the mixture layer and the aramid layer, and the mixture layer includes aramid and the first ceramic particles, A coupling agent is bound on the surface of the first ceramic particle.

The preparation method of the composite separator provided by the application can sequentially prepare a mixture layer (or aramid layer) and an aramid layer (or mixture layer) on one or both sides of the polyolefin layer, wherein the first mixture layer A coupling agent is bound on the surface of the ceramic particles. Since the coupling agent contains inorganic and organophilic groups, after the second material is added to the surface of the prefabricated film, in the prefabricated film or the second material, the coupling agent bound to the surface of the first ceramic particle acts as a "molecular bridge" and The aramid fibers forming the mixture layer are connected, thereby enhancing the bonding force between the first ceramic particles and the aramid fibers, making the aramid fibers act as a crosslinking agent to crosslink and fix the ceramic particles, and form a continuous and stable mixture layer. Under the action of the coupling agent, the mixture layer has better structural stability, which is not only conducive to improving the structural stability of the composite diaphragm under high temperature conditions, but also the first ceramic particles play a role in the aramid molecular chain in the aramid layer. The role of rigid support can alleviate the molecular bond curling of the aramid polymer bond at high temperature, and then improve the thermal shrinkage performance of the adjacent layer, that is, the aramid layer, so that the thermal shrinkage rate of the composite diaphragm is <4%@150℃/ 1h. In this case, the prepared composite diaphragm can increase the rupture temperature of the diaphragm; at the same time, it can also reduce the thermal shrinkage rate of the diaphragm to achieve the effect of the thermal shrinkage rate <4%@150°C/1h. The composite film thus prepared can effectively improve the thermal stability of the separator and ensure the safety of the battery.

As a first possible implementation of the method for preparing the composite diaphragm of the present application, the first film is a mixture layer, and the second film is an aramid fiber layer. At this time, correspondingly, the first material is a material containing first ceramic particles, the prefabricated film is a ceramic layer; the second material is aramid fiber slurry. In this case, the preparation of the mixture layer and the aramid layer is realized by first forming the first ceramic particles on the surface of the polyolefin, and then pouring the aramid slurry on the surface of the first ceramic particles, which improves the process feasibility. Specifically, the first ceramic particles are spread on the surface of the polyolefin layer to form a ceramic layer, that is, a prefabricated film. At this time, the stability of the ceramic layer formed by laying ceramic particles is poor. When the aramid fiber slurry is poured on the surface of the ceramic layer, that is, the surface of the prefabricated film, the aramid fiber in the slurry will permeate downward along the pores between the first ceramic particles, and spread evenly around the surface of the first ceramic particles. The downward penetrating aramid fiber fills the pores between the first ceramic particles, and the aramid fiber acts as a cross-linking agent to fix the granular first ceramic particles; at the same time, the coupling agent combines with the aramid fiber through hydrogen bonds, so that the second A ceramic particle is cross-linked with the aramid fiber through a coupling agent, the first ceramic particle is fixed to form a film, and after crystallization and solidification, a mixture layer with a stable structure is finally formed.

As a possible implementation situation, the first material is ceramic slurry. By forming ceramic slurry on one or both surfaces of the polyolefin layer, a prefabricated film is formed on one or both surfaces of the polyolefin layer.

In some embodiments, the ceramic slurry is a slurry formed by dispersing the first ceramic particles with the coupling agent bound on the surface in a dispersion liquid. In this case, ceramic slurry is coated on one or both sides of the polyolefin layer, and after drying treatment, a prefabricated film formed of first ceramic particles is formed on one or both sides of the polyolefin layer, and the second A coupling agent is combined on the surface of ceramic particles.

In some embodiments, the ceramic slurry is a slurry containing a coupling agent, first ceramic particles and additives. In this case, ceramic slurry is coated on one or both sides of the polyolefin layer, and after drying treatment, a prefabricated film formed of first ceramic particles is formed on one or both sides of the polyolefin layer, and the second A coupling agent is combined on the surface of ceramic particles. Wherein, the auxiliary agent can be at least one of dispersant, thickener, binder and wetting agent. Among them, the dispersant is beneficial to improve the dispersibility of the first ceramic particles in the slurry; adding a wetting agent in the slurry can improve the wetting of the slurry on the polyolefin surface when the ceramic slurry is coated on the polyolefin surface. Wet and spreadability; thickener can increase the viscosity of the slurry; binder can bond the first ceramic particles after coating the ceramic particles on the polyolefin surface, and initially fix them on the polyolefin surface to form a ceramic layer , the prefabricated film.

In some embodiments, the preparation method of the ceramic slurry is as follows: dispersing the first ceramic particles, the coupling agent and the auxiliary agent in deionized water, and mixing them to obtain the ceramic slurry. Under the action of the auxiliary agent, the first ceramic particles disperse and form a slurry, which is beneficial for coating the surface of the polyolefin layer. The ceramic slurry is coated on the surface of the polyolefin layer, and after drying to remove the solvent, the ceramic layer can be formed, that is, the prefabricated film.

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

In the ceramic slurry formed in this case, the first ceramic particles and the coupling agent have better dispersion uniformity, which is conducive to the uniform combination of the coupling agent on the surface of the first ceramic particles, and then is conducive to entering the pores of the first ceramic particles The combination of the aramid fibers and the first ceramic particles; at the same time, the slurry has suitable viscosity and spreadability, which is beneficial to initially fix the first ceramic particles on the surface of the polyolefin layer.

In some embodiments, the coupling agent is a silane coupling agent. The silane coupling agent is combined on the surface of the first ceramic particles through the siloxane group, and there are a large number of organophilic groups at the other end of the silane coupling agent. When the second material containing aramid fiber is added to the surface of the prefabricated film, the organophilic group at the other end of the coupling agent forms a hydrogen bond with the aramid fiber molecule that enters the gap between the first ceramic particles, and the hydrogen bond makes the aramid fiber and the first ceramic particle The particles are closely combined, which enhances the bonding force between the reinforced ceramic particles and the aramid fiber, and finally forms a structurally stable mixture layer. In this case, through the rigid support of the first ceramic particles in the mixture layer, the effect of stabilizing the upper aramid fiber layer and reducing the heat shrinkage rate of the separator can be fully exerted. Exemplarily, the coupling agent is at least one of vinylsilane, aminosilane, epoxysilane, mercaptosilane and methacryloxysilane, but is not limited thereto. The above-mentioned silane coupling agent contains functional groups capable of forming hydrogen bonds with the aramid fibers, which is beneficial to realize the connection between the aramid fibers and the first ceramic particles, and improve the binding force between the aramid fibers and the first ceramic particles.

As a possible implementation situation, the preparation method of the ceramic slurry is:

Dispersing the first ceramic particles in deionized water, adding the silane coupling agent to prepare the first ceramic particles modified by the silane coupling agent;

Adding the dispersant to the first ceramic particles modified by the silane coupling agent, stirring and mixing, and grinding to obtain a ceramic dispersion;

Adding the thickener, the binder and the wetting agent into the ceramic dispersion, stirring and mixing to obtain the ceramic slurry.

After mixing the silane coupling agent and the first ceramic particles, add a dispersant for mixing treatment, so that the silane coupling agent and the first ceramic particles are evenly dispersed and then add other additives, which helps to improve the silane coupling agent and the first ceramic particles. The dispersion uniformity of the ceramic particles, thereby improving the distribution uniformity of the silane coupling agent on the surface of the first ceramic particles. In this case, when the second material containing aramid fiber is added on the surface of the prefabricated film, the aramid fiber enters the pores between the first ceramic particles, and with the help of the silane coupling agent uniformly distributed on the surface of the first ceramic particles, it is combined with the second material. The connection of one ceramic particle realizes the fixation of the first ceramic particle, and finally forms a mixture layer, that is, the first film.

As a second possible implementation of the preparation method of the composite diaphragm of the present 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 film is an aramid fiber layer. 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 prefabricated film; then ceramic materials are added to the surface of the prefabricated film and dried, and finally an aramid layer and a mixture layer are formed on the surface of the polyolefin layer. composite layer.

Wherein, the aramid fiber size is the size whose matrix material is aramid fiber. In a possible implementation manner, the aramid fiber size is a size made of aramid fiber. In another possible implementation manner, the aramid fiber slurry contains aramid fiber and additives. In these two possible implementation manners, after using the first material on one or both surfaces of the polyolefin layer, the aramid slurry is formed on one or both surfaces of the polyolefin layer. In some embodiments, the auxiliary agent includes a porogen.

As a possible implementation situation, the solid content of the aramid pulp is 1.5-10%. In this case, the aramid slurry has suitable viscosity and spreading properties, and the aramid fiber layer is formed on the surface of the substrate (ceramic layer or polyolefin layer).

As a possible implementation situation, the preparation method of the aramid pulp is:

Prepare an organic solution of phenylenediamine, lower the temperature to below 10° C., add phthaloyl chloride, add alkali to adjust the pH to neutral, and then add a pore-forming agent to prepare the aramid fiber slurry.

The method can directly prepare the aramid fiber slurry from raw materials, and the method is simple and has strong controllability in operation.

As a possible implementation situation, the coating includes one of dip coating, spray coating, doctor blade, coating wire bar and micro gravure roll coating.

As a possible implementation situation, the preparation method further includes: before the drying treatment, immersing the sample obtained after coating the second slurry into a plasticizing bath. Before drying, the sample obtained after coating the second slurry is immersed in a plasticizing bath, so that the aramid fiber is in a highly plastic state, so as to facilitate the stretching of the aramid fiber.

The third aspect of the present application provides an electrochemical device, including a positive electrode sheet, a negative electrode sheet, an electrolyte, and a diaphragm arranged between the positive electrode sheet and the negative electrode sheet, and the diaphragm is the one described in the first aspect of the present application. Composite diaphragm.

The electrochemical device provided by the present application has low thermal shrinkage rate and high membrane rupture temperature due to the above-mentioned composite separator, which can solve the problem of shrinkage and melting of the separator, reduce the risk of thermal runaway caused by short circuit of the battery, and further improve the safety performance of the battery.

As a possible implementation of the electrochemical device of the present 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, improve the overall hardness and strength of the battery, and prevent the deformation of the battery cell.

As a possible implementation of the electrochemical device of the present application, the polymer layer is a material layer formed by at least one of PVDF, PMMA, dopamine, CMC, SBR, PTFE and PVA; as the electrochemical device of the present application In a possible implementation situation, the polymer layer is a polymer laminate formed by at least two of PVDF, PMMA, dopamine, CMC, SBR, PTFE and PVA, and the polymer in the polymer laminate is composed, which can be One or more of the above polymers. The above-mentioned polymer material can improve the bonding strength between the composite film and the electrode sheet provided by the first aspect, and keep the battery structure stable.

As a possible implementation of the electrochemical device of the present 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.

As a possible implementation of the electrochemical device of the present application, the structure of the electrochemical device is one or more of a wound structure and a laminated structure.

As a possible implementation of the electrochemical device of the present application, the electrochemical device further includes an encapsulation case, and one or more electrochemical device units are encapsulated in the encapsulation case.

The fourth aspect of the present application provides an electronic device, including a housing, electronic components and electrochemical devices accommodated in the housing, the electrochemical device is the electrochemical device described in the third aspect of the present application, and the The electrochemical device is used for powering the electronic components.

As a possible implementation situation of the terminal of the present application, the terminal is a computer, a mobile phone, a tablet, or a wearable product.

The fifth aspect of the present application provides a mobile device, the mobile device includes the electrochemical device described in the third aspect.

Description of drawings

Fig. 1 is the first structural schematic diagram of the composite diaphragm provided by the embodiment of the present application;

Fig. 2 is a second structural schematic diagram of the composite diaphragm provided by the embodiment of the present application;

Fig. 3 is a kind of preparation process flowchart of the composite diaphragm provided in the embodiment of the present application;

Fig. 4 is a flow chart of another preparation process of the composite diaphragm provided in the embodiment of the present application.

Detailed ways

In order to make the technical problems, technical solutions and beneficial effects to be solved in the present application clearer, the present application will be further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described here are only used to explain the present application, and are not intended to limit the present application.

In this application, the term "and/or" describes the association relationship of associated objects, indicating that there may be three relationships, for example, A and/or B may mean: A exists alone, A and B exist simultaneously, and B exists alone Condition. Among them, A and B can be singular or plural. The character "/" generally indicates that the contextual objects are an "or" relationship.

In this application, "at least one" means one or more, and "multiple" 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 plural items. For example, "at least one item (unit) of a, b, or c", or "at least one item (unit) of a, b, and c" can mean: a, b, c, a-b( That is, a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

It should be understood that in various embodiments of the present application, the sequence numbers of the above-mentioned processes do not mean the order of execution, and some or all steps may be executed in parallel or sequentially, and the execution order of each process shall be based on its functions and The internal logic is determined and should not constitute any limitation to the implementation process of the embodiment of the present application.

Terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of this application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

The weight of the relevant components mentioned in the description of the embodiments of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of the various components. The scaling up or down of the content of the fraction is within the scope disclosed in the description of the embodiments of the present application. Specifically, the mass described in the description of the embodiments of the present application may be μg, mg, g, kg and other well-known mass units in the chemical industry.

The terms "first" and "second" are only used for descriptive purposes to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX can also be called the second XX, and similarly, the second XX can also be called the first XX. Thus, a feature defined as "first" and "second" may explicitly or implicitly include one or more of these features.

The term "MD" is the abbreviation of "Machine direction", which means the mechanical direction;

The term "TD" is the abbreviation of "Transverse direction", which means perpendicular to the machine direction;

The term "PE" is the abbreviation of "Polyethylene", which means polyethylene;

The term "DSC" is an abbreviation for "Differential scanning calorimetry", which means differential scanning calorimetry;

The term "SOC" is the abbreviation of "State of charge", which means the state of charge;

The term "PVDF" is an abbreviation for "polyvinylidenefluoride", which means polyvinylidene fluoride;

The term "PMMA" is an abbreviation for "polymethyl methacrylate", which means polymethyl methacrylate;

The term "SBR" is an abbreviation for "Styrene-butadiene", which means styrene-butadiene rubber;

The term "NMP" is the abbreviation of "N-Methyl-2-pyrrolidone", which means N-methylpyrrolidone, also known as 1-methyl 2-pyrrolidone;

The term "CNTs" is an abbreviation for "Carbon nanotubes", which means carbon nanotubes;

The term "CMC" is an abbreviation for "Carboxymethyl Cellulose", which means carboxymethyl cellulose;

The term "SP" is the abbreviation of "Super P", which means conductive carbon black;

The term "PP" is an abbreviation for "Polypropylene", which means polypropylene;

The term "PTFE" is an abbreviation for "Polytetrafluoroethylene", which means polytetrafluoroethylene;

The term "PVA" is an abbreviation for "Polyvinyl alcohol", which means polyvinyl alcohol.

The term "battery" is expressed as "Battery" in English, which refers to a device that utilizes the potential difference of two electrodes to generate a potential difference, thereby causing electrons to flow and generate current. The device can convert chemical energy into electrical energy.

The term "positive electrode" is expressed in English as "Cathode". In a primary battery, the positive electrode refers to the electrode where the current flows out or the potential is higher, and the positive electrode receives electrons for reduction; in the electrolytic cell, the positive electrode is the electrode connected to the positive electrode of the power supply, and loses electrons for oxidation.

The term "negative electrode" is expressed in English as "Anode". In the primary battery, the negative electrode refers to the electrode that the current flows into or the electrode with a lower potential. The negative electrode loses electrons for oxidation; in the electrolytic cell, the negative electrode is the electrode connected to the negative electrode of the power supply, and the electrons are obtained for reduction.

The term "electrolyte" is expressed as "Electrolyte" in English, which refers to the medium that provides ion exchange between the positive and negative electrodes of the battery.

The term "diaphragm" is expressed as "Separator" in English, which refers to the medium used to separate the positive and negative electrodes in the battery and prevent the positive and negative electrodes from being directly contacted and short-circuited. The basic characteristics of the separator are porosity (can provide channels for ion transmission) and electronic insulation (prevent leakage).

The term "heat abuse" is expressed as "Heat abuse" in English, which refers to: the abuse test of the battery cell in terms of heat (or high temperature), such as the hot box test (high temperature ≥ 130 degrees to bake the battery cell).

The term "mechanical abuse" is expressed in English as "Machenical abuse", which can refer to the mechanical abuse of the battery. Cells can be tested for mechanical abuse using needle penetration tests, impact tests, etc.

The English expression of the term "elongation" is "Elongation", which can also be called the elongation at break, which indicates the percentage of the length increment when the diaphragm is broken relative to the initial length. Specifically, a tensile test can be performed on the diaphragm under specific conditions, and when the diaphragm is just broken, the increase in the length of the diaphragm divided by the initial length of the diaphragm can be used to characterize the elongation. The larger the elongation value, the less likely the diaphragm will be broken and the better the elongation. The elongation can be divided into longitudinal (MD, ie along the long side of the separator) elongation and transverse (TD, perpendicular to MD, ie along the short side of the separator) elongation.

The term "tensile strength" is expressed in English as "Tensile strength", which indicates the critical strength value of the plastic deformation of the diaphragm, which can characterize the maximum bearing capacity of the diaphragm under uniform stretching conditions. Tensile strength can refer to the stress obtained by dividing the maximum load force of the diaphragm by the initial cross-sectional area of the diaphragm when the diaphragm is just pulled off. The tensile strength is divided into longitudinal (MD, ie along the long side direction of the separator) tensile strength and transverse direction (TD, perpendicular to MD, ie along the short side direction of the separator) tensile strength.

The term "puncture strength" is expressed in English as "Puncture strength", which can refer to the use of a spherical steel needle with a diameter of 1.0mm to pierce the diaphragm at a speed of 300±10mm/min, and the force required for the steel needle to penetrate the diaphragm is the diaphragm. puncture strength.

The English expression of the term "heat shrinkage rate" is "Heat shrinkage", which means that the diaphragm is in the longitudinal/transverse direction before and after heating (longitudinal MD, that is, along the long side direction of the diaphragm; transverse direction TD, perpendicular to MD, that is, along the short side direction of the diaphragm ) The rate of dimensional change in the direction. The test method of thermal shrinkage rate may include: measuring the size of the diaphragm in the longitudinal/transverse (MD/TD) direction; placing a diaphragm with a certain size in the longitudinal/transverse (MD/TD) direction in an incubator; Oven to a specific temperature; measure the dimension of the separator in the longitudinal/transverse (MD/TD) direction after heating.

The English expression of the term "air permeability" is "Gurley", which means the degree to which the membrane allows gas to pass through. The air permeability can be obtained by measuring the time required for a unit volume of gas (100cc) to pass through the membrane at a specific pressure (0.05MPa).

The English expression of the term "closed cell temperature" is "Obturator temperature", which means the temperature at which the diaphragm begins to melt and block some of the previously formed pores during the heating process.

The term "membrane rupture temperature" is expressed in English as "Rupture temperature", which means the temperature at which the diaphragm melts to a certain extent and ruptures to cause a partial or comprehensive short circuit.

In the battery, the separator is mainly used to prevent the short circuit of the positive and negative electrodes, which plays a key role in the safety of the battery. When the battery is subjected to mechanical and thermal abuse, the separator is prone to melting and thermal shrinkage in high-temperature scenes, resulting in a short circuit between the positive and negative electrodes and causing a safety hazard. In view of this, the present application provides a composite separator that can improve battery safety performance.

Specifically, the embodiment of the present application provides a composite diaphragm, including a polyolefin layer, a composite layer bonded to one side of the polyolefin layer, the composite layer includes a mixture layer, and an aramid layer bonded to one side of the mixture layer, and The mixture layer or the aramid fiber layer and the polyolefin layer are arranged on the surface of the polyolefin layer.

In the embodiment of the present application, the polyolefin layer, as the main functional layer of the composite separator, plays the role of separating the positive electrode and the negative electrode in the battery cell, preventing the positive and negative electrodes from directly contacting and short circuiting. Polyolefin has porous properties, so polyolefin is also called porous polyolefin, which can provide channels for ion transmission; at the same time, polyolefin has electronic insulation, which can prevent leakage. The polyolefin layer in the embodiment of the present application is also called a porous polyolefin layer.

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 made of one polyolefin material; in some embodiments, the polyolefin layer is made of a combination of two or more polyolefins. In this embodiment, the two or more polyolefins may be two or more different types of polyolefin materials. Exemplarily, the polyolefin materials of the polyolefin layer are polyethylene (PE) and polypropylene (PP) composition; It can also be two or more types of polyolefins that are the same but have different viscosity-average molecular weights. Exemplary, the polyolefin material of the polyolefin layer is a variety of polyethylenes with different viscosity-average molecular weights. combination.

In some embodiments, the polyolefin layer has a thickness of 0.2-20 μm. Since the embodiment of the present application forms a composite layer containing an aramid fiber layer and a mixture layer on one surface of the polyolefin layer, the film breaking temperature and thermal shrinkage performance of the polyolefin layer are improved, therefore, the polyolefin layer provided by the application The thickness can be as low as 0.2 μm, and the polyolefin layer with a thickness of 0.2-20 μm is used as the polyolefin layer of the separator matrix, which can effectively isolate the positive and negative electrodes of the battery. Exemplarily, the thickness of the polyolefin layer may 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, 11.0μm, 12.0μm, 13.0μm, 14.0μm, 15.0μm, 16.0μm, 17.0μm, 18.0μm, 19.0μm, 20.0μm. In some embodiments, the thickness of the polyolefin layer is 0.5-17um.

In the embodiment of the present application, a composite layer is provided on one or both sides of the polyolefin layer, the composite layer includes a mixture layer, and an aramid layer bonded to one side of the mixture layer, and both the mixture layer and the aramid layer are laminated with the polyolefin layer Arrangement, that is, the mixture layer and the aramid layer are arranged parallel to the polyolefin layer.

In one embodiment, a composite layer is formed on one surface of the polyolefin layer, and the other surface is left untreated (ie, a blank design is left). In this case, since the closed cell temperature of polyolefin is about 140°C, this characteristic enables the battery containing polyolefin separator to cut off the ion transport channel by itself (the micropores of polyolefin are closed) at the closed cell temperature. By keeping a blank design on one side of the polyolefin layer, the original closed-cell temperature characteristics of the polyolefin can be preserved, giving the battery better safety performance. In another embodiment, a composite layer is simultaneously formed on both sides of the polyolefin layer to increase the rupture temperature of the composite membrane and reduce its heat shrinkage rate.

Wherein, the limiting oxygen index of the aramid fiber material in the aramid fiber layer is greater than 28%, which belongs to the flame retardant fiber and has flame retardancy. Due to the flame-retardant properties of the aramid fiber material, the use of the aramid fiber layer as the protective layer of the polyolefin separator can increase the membrane rupture temperature of the separator, so that the membrane rupture temperature of the composite film can be greater than 200 ° C, so that when the battery is subjected to thermal and mechanical abuse , the composite separator can withstand high temperature > 200°C without melting, can effectively isolate the positive and negative electrodes of the battery, avoid direct contact between the positive and negative electrodes and cause severe internal short circuit, and improve battery safety.

In some embodiments, based on 100% of the total weight of the aramid layer, the aramid fiber content is 50-100% by weight. When the weight percentage of the aramid fiber is more than 50%, the characteristics of the aramid fiber material can be maintained, and the formed aramid fiber layer can effectively increase the membrane rupture temperature of the composite diaphragm. This embodiment includes two situations, respectively: the situation that the weight percentage of the aramid fiber is 100%, and the situation that the weight percentage of the aramid fiber is not 100%.

In the first implementation situation, based on the total weight of the aramid layer being 100%, the weight percentage of the aramid fiber is between 50% and 100%, but not 100%. At this time, the aramid layer contains aramid and other materials. Exemplarily, based on the total weight of the aramid layer as 100%, the weight percentage of the aramid fiber can be 50%, 55%, 50%, 55%, 50%, 55%, 50%, 55%, 50% %, 55%, 100% and other specific weight percentages.

In some embodiments, the other material includes a porogen to impart some porosity to the aramid layer. Wherein, the pore-forming agent is one or more of inorganic pore-forming agents. Exemplarily, the inorganic pore-forming agent is lithium chloride, sodium chloride, magnesium chloride, calcium carbonate, calcium chloride, and one or more.

In some embodiments, when the weight percentage of the aramid fiber is not 100%, the aramid fiber layer includes the second ceramic particles with a weight percentage of 0-50%, and the second ceramic particles serve as a pore-forming agent. The porosity of the aramid fiber layer can be increased by adding the second ceramic particles with a weight percentage of 0-50% in the aramid fiber layer, so that the porosity of the aramid fiber layer is above 20%. Not only that, the second ceramic particles introduced into the aramid layer can improve the thermal stability of the aramid layer, improve the thermal shrinkage performance of the aramid layer, and finally reflect the improvement of the thermal shrinkage performance of the composite diaphragm. In addition, while a small amount of second ceramic particles play a role in forming holes, the influence of the second ceramic particles on the performance of the aramid fiber layer is reduced. Exemplarily, based on the total weight of the aramid fiber 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% and other specific weight percentages.

The median diameter D50 of the second ceramic particles as the pore forming agent may be 0.01˜2 μm. In some embodiments, the median diameter D50 of the second ceramic particles is 0.1-1 μm. In this case, the second ceramic particles play a pore-forming role to increase the porosity of the aramid fiber layer, and the median particle diameter D50 is in the above range, which can give the aramid fiber layer suitable porosity and pore size, which is beneficial to obtain Aramid layer for better breathability and heat resistance. Exemplarily, the average median diameter D50 of the second ceramic particles may 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, 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2.0μm.

In some embodiments, the second ceramic particle is aluminum oxide, silicon dioxide, aluminum oxide, zirconium dioxide, magnesium oxide, zinc oxide, barium oxide, magnesium hydroxide, calcium oxide, boehmite, titanium dioxide, and sulfuric acid at least one of barium.

In the second implementation situation, the total weight of the aramid fiber layer is 100%, and the weight percentage of the aramid fiber is 100%. role. It should be understood that when the aramid fiber weight percentage in the aramid fiber layer is 100%, the aramid fiber layer also has a certain porosity, but the pore former is formed in the process of forming the aramid fiber layer or in the process of forming the aramid fiber layer. has since been eliminated. Exemplary, any one or more of methanol, ethanol, propanol, glycerol, polyethylene glycol, acetone, acetic acid, tetrahydrofuran, polyvinylpyrrolidone, ethyl acetate, petroleum ether, white oil, paraffin When waiting for an organic pore-forming agent, the pore-forming agent and aramid fiber are used as raw materials to form a prefabricated film. During the heating and forming process, the organic pore-forming agent volatilizes to form a pore structure in the aramid fiber layer.

In some embodiments, the thickness of the aramid layer is 0.1-6um. In this case, the thickness of the aramid fiber layer can achieve the effect of increasing the rupture temperature of the composite separator. Since the aramid material as a diaphragm material does not contribute capacity to the battery, when the aramid content is too high, the volume percentage in the battery will also increase, which will lower the energy density of the battery. When the thickness of the aramid layer is 0.1-6um, the thickness of the aramid layer is within a controllable range, which can reduce the influence of the aramid layer on the energy density of the battery. Exemplarily, the thickness of the aramid fiber layer can be 0.1um, 0.2um, 0.3um, 0.4um, 0.5um, 0.6um, 0.7um, 0.8um, 0.9um, 1.0um, 1.5um, 2.0um, 2.5um, 3.0um, 3.5um, 4.0um, 4.5um, 5.0um, 5.5um, 6.0um and other specific thicknesses.

In some embodiments, the thickness of the aramid layer is 0.5-3um. When the thickness of the aramid fiber layer is within the above range, the effect of increasing the rupture temperature of the composite separator and reducing the influence of the aramid fiber layer on the energy density of the battery can be better taken into account.

In some embodiments, the aramid in the aramid layer is at least one of para-aramid and meta-aramid. In this case, the obtained aramid layer has excellent high temperature resistance, which can endow the composite separator with excellent membrane rupture performance, increase its membrane rupture temperature, and finally improve the safety performance of the battery using the composite separator.

In the embodiment of the present application, the composite layer further includes a mixture layer, and the mixture layer includes aramid fibers and first ceramic particles. Wherein, a coupling agent is bound on the surface of the first ceramic particle. That is, the ceramic particles in the mixture layer are the first ceramic particles modified by the coupling agent. The coupling agent on the surface of the first ceramic particle contains an inorganic group and an organic group. Therefore, as a "molecular bridge", one end is connected to the surface of the first ceramic particle, and the other end is connected to the aramid fiber in the mixture layer, thereby strengthening The binding force between the first ceramic particles and the aramid fiber makes the aramid fiber act as a cross-linking agent to cross-link and fix the first ceramic particles and form a continuous and stable film layer. Under the action of the coupling agent, the mixture layer has better structural stability, which is not only conducive to improving the structural stability of the composite diaphragm under high temperature conditions, but also the first ceramic particles play a role in the aramid molecular chain in the aramid layer. It can play a rigid support role, alleviate the molecular bond curling of the aramid polymer bond at high temperature, reduce the thermal shrinkage of the aramid material, especially the aramid molecule in the aramid layer, and then improve the thermal shrinkage performance of the aramid layer. Make the thermal shrinkage rate of the composite diaphragm <4%@150°C/1h. In addition, the aramid fiber in this layer undertakes the crosslinking function in the ceramic particles, and the aramid fiber can withstand high temperatures above 200°C, so that the mixture layer continues to remain intact at high temperatures above 200°C, and the membrane rupture temperature of the layer is increased. The battery containing the mixture layer can alleviate the risk of internal short circuit caused by the heat shrinkage of the separator at the head and tail of the cell when the composite separator is heated, thereby improving the safety of the battery.

In some embodiments, the coupling agent is a silane coupling agent. At this time, the silane coupling agent is bound to the surface of the first ceramic particle through the siloxane group. There are a large number of organophilic groups on the surface of the first ceramic particle modified by the silane coupling agent, and the organophilic group can form a hydrogen bond with the aramid fiber molecular chain dispersed in the ceramic particle, and the hydrogen bond makes the aramid fiber and The first ceramic particles are closely combined to form a structurally stable mixture layer, and then the aramid fiber layer is stabilized by virtue of the rigid support of the ceramic particles in the mixture layer. That is, the silane coupling agent builds a "molecular bridge" between the ceramic particles and the aramid fiber interface to improve the bonding force between the ceramic particles and the aramid fiber.

Exemplarily, the silane coupling agent is selected from at least one of vinylsilane, aminosilane, epoxysilane, mercaptosilane and methacryloxysilane. Wherein, epoxy silane is also called epoxy silane crosslinking agent; mercapto silane refers to a silane coupling agent containing mercapto in the molecule, exemplary, such as 3-mercaptopropyltriethoxysilane; methacrylic Acyloxysilane refers to a silane coupling agent containing a methacryloxy group in its molecular structure, for example, methacryloxymethyltrimethoxysilane. The siloxane group in the above-mentioned silane coupling agent is combined on the surface of the first ceramic particles, so that a large number of vinyl groups, amino groups, epoxy groups, mercapto groups, acryloyloxy groups and the like are formed on the surface of the modified first ceramic particles. The terminal tentacles of the group can form hydrogen bonds with the aramid fiber, realize the connection between the aramid fiber and the first ceramic particle, and improve the binding force between the aramid fiber and the first ceramic particle.

In some embodiments, in the mixture layer, the weight of the coupling agent is 0.3-2% of the total weight of the first ceramic particles. When the content of the coupling agent is within the above range, it can effectively play the role of "molecular bridge" and improve the binding force between the first ceramic particle and the aramid fiber. In addition, when the content of the coupling agent is within the above range, the content of the coupling agent connected to the surface of the first ceramic particles is appropriate, and the formed mixture layer has better air permeability, so that the composite diaphragm can maintain good air permeability and improve the diaphragm. Affinity with electrolyte increases ionic conductivity. If the content of the coupling agent is too high, the air permeability of the composite membrane will be reduced. Exemplarily, the content of the coupling agent in the total weight of the 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% and other specific values.

In some embodiments, based on 100% of the total weight of the mixture layer, the weight percentage of the aramid fiber is 0.1-20%, and the weight percentage of the first ceramic particles is 80-99.9%. In this case, a small amount of aramid fiber acts as a cross-linking agent to fix the granular first ceramic particles and form a continuous film layer; at the same time, because the aramid fiber undertakes the cross-linking effect in the separator particles, the aramid fiber can withstand 200°C The above high temperature keeps the mixture layer intact at a high temperature above 200°C, which increases the membrane rupture temperature of the mixture layer. On this basis, the first ceramic particles in the mixture layer play a rigid support role in the aramid molecular chain, relieve the molecular bond curling of the aramid polymer bond in the aramid layer at high temperature, and maintain the structure of the aramid layer , thereby improving the thermal shrinkage performance of the composite diaphragm, so that the thermal shrinkage rate of the composite diaphragm is <4%@150°C/1h. When the composite diaphragm is heated, it can alleviate the risk of internal short circuit at the head and tail of the cell due to the heat shrinkage of the diaphragm, improving battery safety. Exemplarily, based on the total weight of the mixture layer as 100%, the weight percentage of aramid fiber 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. weight percent content.

In some embodiments, the aramid in the mixture layer is at least one of para-aramid and meta-aramid. The aramid fiber mentioned above can achieve cross-linking of the first ceramic particles by means of a coupling agent, fix the first ceramic particles to form a film, and increase the film rupture temperature of the mixture layer.

In some embodiments, the mixture layer is composed of a mixture group formed by the first ceramic particles and aramid fiber. In some embodiments, in addition to the first ceramic particles and the aramid fiber, the mixture layer also contains a small amount of additives. In some embodiments, the auxiliary agent can be selected from at least one of a dispersant, a thickener, a binder and a wetting agent. When the material containing the first ceramic particles is formed on the surface of the film layer, the dispersant is conducive to improving the dispersibility of the first ceramic particles in the material such as slurry; the wetting agent is conducive to improving the first ceramic particles in the polyolefin layer or The wettability and spreadability of the surface of the aramid layer; the thickener can form a ceramic slurry with a suitable viscosity, so that the first ceramic particles are formed on the surface of the polyolefin layer or the aramid layer; the binder can form the ceramic particles After the polyolefin surface, the first ceramic particles are bonded and initially fixed on the polyolefin surface.

Exemplary, the dispersant is one or more of nonionic dispersants such as polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, polyethylene oxide; exemplary, the thickener is sodium carboxymethyl cellulose , hydroxyethylcellulose, sodium alginate, hydroxypropylmethylcellulose and lithium hydroxymethylcellulose; exemplary, the binder is polyvinylidene fluoride, polytetrafluoroethylene, poly Amide, sodium carboxymethyl cellulose, styrene-butadiene rubber, acrylate, methacrylic acid-methyl/methyl acrylate-maleic anhydride terpolymer, methacrylic acid-methyl methacrylate-vinyl carbazole tripolymer At least one of meta-copolymers and polyimide derivatives; Exemplary, the wetting agent is polyether siloxane copolymer, Tween-90, fluoroalkyl ethoxy alcohol ether, fatty alcohol poly One or more of oxyethylene ether, sodium butylnaphthalene sulfonate, sodium isethionate, and sodium dodecyl sulfonate.

In some embodiments, the mixture layer has a thickness of 0.1-6 um. In this case, the thickness of the mixture layer can achieve the effect of reducing the thermal shrinkage rate of the composite separator. Since the first ceramic particles and aramid fiber in the mixture layer do not contribute capacity to the battery as separator materials, when the content of the first ceramic particles and aramid fiber is too much, the volume percentage in the battery will also increase, which will lower the battery capacity. Energy Density. When the thickness of the mixture layer is 0.1-6um, the thickness of the aramid fiber layer is within a controllable range, which can reduce the influence of the mixture layer on the energy density of the battery. Exemplarily, the thickness of the mixture layer can be 0.1um, 0.2um, 0.3um, 0.4um, 0.5um, 0.6um, 0.7um, 0.8um, 0.9um, 1.0um, 1.5um, 2.0um, 2.5um, 3.0um um, 3.5um, 4.0um, 4.5um, 5.0um, 5.5um, 6.0um and other specific thicknesses.

In some embodiments, the mixture layer has a thickness in the range of 1-4 um. When the thickness of the mixture layer is within the above range, the effect of reducing the thermal shrinkage rate of the composite separator and the effect of reducing the mixture layer on the energy density of the battery can be better taken into account.

In some embodiments, the median diameter D50 of the first ceramic particles is 0.01-2.0 μm. In this case, the first ceramic particles have a suitable particle size and can form a dense and complete film layer under the crosslinking action of the aramid fiber. Exemplarily, the average median diameter D50 of 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 , 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2.0μm.

On the basis of the above embodiments, the arrangement of the aramid fiber layer and the mixture layer in the composite layer of the embodiment of the present application includes two situations.

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 facing away from the polyolefin layer. That is, the mixture layer and the aramid fiber layer are sequentially laminated and bonded on at least one surface of the polyolefin layer.

In a possible implementation, a composite layer is formed on one side of the polyolefin layer, the mixture layer in the composite layer is bonded to one side of the polyolefin layer, and the aramid layer is bonded to the surface of the mixture layer away from the polyolefin layer . At this time, as shown in FIG. 1 , the composite separator 10 includes polyolefin 11 , a mixture layer 12 bonded to the surface of the polyolefin 11 , and an aramid layer 13 bonded to the surface of the mixture layer 12 away from the polyolefin 11 . In this case, on the one hand, the aramid fiber layer has better heat resistance, and as a surface layer protection layer, it can block the influence of high temperature on the polyolefin film layer, making the membrane rupture temperature of the composite diaphragm > 240 ° C; on the other hand On the one hand, the mixture layer is arranged between the aramid layer and the polyolefin layer, and at the same time provides rigid support for the polyolefin layer and the aramid layer, and relieves the thermal shrinkage of the composite diaphragm, thereby reducing the thermal shrinkage rate of the composite diaphragm. In addition, from the perspective of processing, the composite diaphragm can be made by first forming first ceramic particles on the surface of polyolefin, and then pouring aramid fibers on the surface of the first ceramic particles. The pores between the particles permeate downwards, and spread out on the surface of the first ceramic particles to realize the preparation of the mixture layer and the aramid fiber layer, and improve the process feasibility.

In a possible implementation, a composite layer is formed on both surfaces of the polyolefin layer, the mixture layer in the composite layer is bonded to both surfaces of the polyolefin layer, and the aramid layer is bonded to the surface of the mixture layer away from the polyolefin layer .

In the second embodiment, in the composite layer, the aramid fiber layer is bonded to at least one surface of the polyolefin layer, and the mixture layer is bonded to the surface of the aramid fiber layer facing away from the polyolefin layer. That is, the aramid fiber layer and the mixture layer are sequentially laminated and bonded on at least one surface of the polyolefin layer. The composite layer formed in this way can also increase the membrane rupture temperature of the composite diaphragm and reduce the thermal shrinkage performance. However, since the first ceramic particles are rigid particles, the mixture layer whose main component is the first ceramic particles forms a film on the surface of the aramid fiber layer. layer.

In a possible implementation manner, a composite layer is formed on one surface of the polyolefin layer, the aramid fiber layer is bonded to one side surface of the polyolefin layer, and the mixture layer is arranged on the side surface of the aramid fiber away from the polyolefin layer. At this time, as shown in FIG. 2 , the composite separator 10 includes polyolefin 11 , an aramid layer 13 bonded to the surface of the polyolefin 11 , and a mixture layer 12 bonded to the surface of the aramid layer 13 away from the polyolefin 11 . In other embodiments of this implementation situation, a composite layer is formed on one side of the polyolefin layer, the aramid fiber layer in the composite layer is bonded to one side surface of the polyolefin layer, and the mixture layer is arranged on a side where the aramid fiber is away from the polyolefin layer. side surface.

In a possible implementation manner, a composite layer is formed on both sides of the polyolefin layer, the aramid fiber layer in the composite layer is bonded to both sides of the polyolefin layer, and the mixture layer is bonded to the side of the aramid fiber layer away from the polyolefin layer surface.

In some embodiments, the composite layer includes n laminated layers formed by the mixture layer and the aramid fiber layer, wherein n is an integer of 2-5. In the composite layer obtained in this case, the mixture layer and the aramid fiber layer are alternately arranged to improve the performance stability of the composite layer. Exemplarily, n is 2, 3, 4 or 5. In some embodiments, n is 2 or 3.

The composite diaphragm provided in the examples of the present application can be prepared by the following method.

Correspondingly, in the second aspect, the embodiment of the present application provides a method for preparing a composite diaphragm, including the following steps:

S01. Using the first material to form a prefabricated film on one or both sides of the polyolefin layer;

S02. Adding the second material on the surface of the prefabricated film, heating and drying, forming a first film on the surface of the polyolefin layer, and forming a second film on the surface of the first film.

In the embodiment of the present application, the first film is one of the mixture layer and the aramid layer, the second film is the other layer of the mixture layer and the aramid layer, and the material of the mixture layer includes aramid and the first ceramic particles, A coupling agent is bound on the surface of the first ceramic particles.

The embodiment of the present application is divided into two implementation situations according to the types of the first film and the second film.

In a first embodiment, the first film is a mixture layer and the second film is an aramid layer. At this time, correspondingly, the first material is a ceramic material containing first ceramic particles, the prefabricated film is a ceramic layer formed by the first ceramic particles; the second material is aramid fiber slurry. In this case, by first forming the first ceramic particles on the surface of the polyolefin, and then pouring the aramid fiber slurry on the surface of the first ceramic particles, the preparation of the mixture layer and the aramid fiber layer is realized, and the process feasibility is improved. Specifically, the first ceramic particles are spread on the surface of the polyolefin layer to form a ceramic layer, that is, a prefabricated film. At this time, the stability of the ceramic layer formed by laying ceramic particles is poor. When the aramid fiber slurry is poured on the surface of the ceramic layer, that is, the surface of the prefabricated film, the aramid fiber in the slurry will permeate downward along the pores between the first ceramic particles, and spread evenly around the surface of the first ceramic particles. The downward penetrating aramid fiber will fill the pores between the first ceramic particles, and the aramid fiber will act as a crosslinking agent to fix the granular first ceramic particles; at the same time, the coupling agent will combine with the aramid fiber through hydrogen bonding, so that the The first ceramic particles are cross-linked with the aramid fiber through a coupling agent, the first ceramic particles are fixed to form a film, and after crystallization and solidification, a mixture layer with a stable structure is finally formed.

In this implementation situation, the preparation method of composite diaphragm, as shown in Figure 3, comprises the following steps:

S11. Using a ceramic material to form a ceramic layer on one or both sides of the polyolefin layer.

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

In some embodiments, the ceramic material is a ceramic slurry formed by dispersing the first ceramic particles with the coupling agent bound on the surface in the dispersion liquid. In this case, a ceramic slurry is coated on one or both sides of the polyolefin layer, and after drying to remove the solvent, a ceramic layer formed of first ceramic particles is formed on one or both sides of the polyolefin layer. , and the surface of the first ceramic particle is bound with a coupling agent. It should be understood that since the first ceramic particles are granular inorganic materials, in the ceramic layer formed by this method, the first ceramic particles are formed in granular form on the surface of the polyolefin layer, and the resulting ceramic layer has poor structural stability.

In some embodiments, the ceramic material is a ceramic slurry containing a coupling agent, first ceramic particles and additives. In this case, ceramic slurry is coated on one or both sides of the polyolefin layer, and after drying treatment, a ceramic layer formed of first ceramic particles is formed on one or both sides of the polyolefin layer, and the second A coupling agent is combined on the surface of ceramic particles. Wherein, the auxiliary agent can be at least one of dispersant, thickener, binder and wetting agent. Among them, the dispersant is beneficial to improve the dispersibility of the first ceramic particles in the slurry; adding a wetting agent in the slurry can improve the wetting of the slurry on the polyolefin surface when the ceramic slurry is coated on the polyolefin surface. wettability and spreadability; the thickener can increase the viscosity of the slurry; the binder can bond the first ceramic particles after the ceramic particles are coated on the polyolefin surface, and initially fix them on the polyolefin surface to form the first Ceramic particle film, that is, prefabricated film.

Exemplary, the thickener is at least one of sodium carboxymethylcellulose, hydroxyethylcellulose, sodium alginate, hydroxypropylmethylcellulose and lithium hydroxymethylcellulose; exemplary, viscose The binder is polyvinylidene fluoride, polytetrafluoroethylene, polyamide, sodium carboxymethyl cellulose, styrene-butadiene rubber, acrylate, methacrylic acid-methyl/methyl acrylate-maleic anhydride terpolymer, methyl At least one of acrylic acid-methyl methacrylate-vinyl carbazole terpolymer and polyimide derivatives; Exemplary, the wetting agent is polyether siloxane copolymer, Tween-90 , fluoroalkyl ethoxy alcohol ether, fatty alcohol polyoxyethylene ether, sodium butylnaphthalene sulfonate, sodium isethionate, sodium dodecylsulfonate; exemplary , the dispersant is one or more of non-ionic dispersants such as polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, and polyethylene oxide.

In some embodiments, the preparation method of the ceramic slurry is as follows: dispersing the first ceramic particles, the coupling agent and the auxiliary agent in deionized water, and mixing them to obtain the ceramic slurry. Under the action of the auxiliary agent, the first ceramic particles disperse and form a slurry, which is beneficial for coating the surface of the polyolefin layer. The ceramic slurry is coated on the surface of the polyolefin layer, and the ceramic layer can be formed after drying to remove the solvent. At this point, the ceramic layer is the prefabricated film.

In some embodiments, the coupling agent is a silane coupling agent. The silane coupling agent is combined on the surface of the first ceramic particle through the siloxane group. When the aramid slurry is added to the surface of the ceramic layer, the aramid slurry enters the pores of the ceramic layer, and the organophilic group at the other end of the coupling agent forms a hydrogen bond with the aramid molecule that enters the gap between the first ceramic particles. The effect makes the aramid fibers closely bond with the first ceramic particles, so that the first ceramic particles are fixed on the surface of the polyolefin layer to form a structurally stable mixture layer. Exemplarily, the coupling agent is at least one of vinylsilane, aminosilane, epoxysilane, mercaptosilane and methacryloxysilane.

As a possible implementation situation, the preparation method of ceramic slurry is:

Dispersing the first ceramic particles in deionized water, adding a silane coupling agent to prepare the first ceramic particles modified by the silane coupling agent;

Adding a dispersant to the first ceramic particles modified by a silane coupling agent, stirring and mixing, and grinding to obtain a ceramic dispersion;

Thickening agent, binding agent and wetting agent are added into the ceramic dispersion liquid, stirred and mixed to obtain ceramic slurry.

In this method, the silane coupling agent and the first ceramic particles are mixed, and then the dispersant is added for mixing treatment, so that the silane coupling agent and the first ceramic particles are uniformly dispersed, and then other additives are added, which helps to improve the silane coupling. The dispersion uniformity of the agent and the first ceramic particles, thereby improving the distribution uniformity of the silane coupling agent on the surface of the first ceramic particles. In this case, when the aramid fiber slurry is added on the surface of the ceramic layer, the aramid fiber enters the pores between the first ceramic particles and is connected to the first ceramic particles by means of the silane coupling agent uniformly distributed on the surface of the first ceramic particles , to achieve the immobilization of the first ceramic particles, and finally to form a structurally stable mixture layer, that is, the first film.

In some embodiments, the first ceramic particles are at least one of silicon dioxide, aluminum oxide, magnesium hydroxide, calcium oxide, boehmite, titanium dioxide, and barium sulfate. In some embodiments, the median diameter D50 of the first ceramic particles is 0.01-2.0 μm.

In a possible implementation, the method of using ceramic material to form a ceramic layer on one or both sides of the polyolefin layer is as follows: coating the above ceramic slurry on one or both sides of the polyolefin layer, A ceramic layer is formed. Wherein, the coating method is one of dip coating, spray coating, doctor blade, coating wire bar and micro gravure roll coating.

In a possible implementation manner, after the ceramic slurry is coated on one or both sides of the polyolefin layer, it is dried to remove the solvent in the ceramic slurry to form a ceramic layer. It should be understood that when the ceramic slurry does not contain additives, the solvent volatilizes after drying, the first ceramic particles are dispersed on the surface of the polyolefin layer, and the obtained ceramic layer cannot be firmly structured on the surface of the polyolefin. When the ceramic slurry contains a binder, the binder can bind the first ceramic particles, preliminarily fix the first ceramic particles on the surface of the polyolefin layer, and form a ceramic layer. The manner of the above drying treatment is not strictly limited, and the ceramic layer is obtained after drying.

S12. Adding aramid slurry on the surface of the ceramic layer, heating and drying to form a mixture layer on the surface of the polyolefin layer, and forming an aramid layer on the surface of the mixture layer.

In this step, the aramid fiber slurry is a slurry whose matrix material is aramid fiber. In a possible implementation manner, the aramid fiber size is a size made of aramid fiber. In another possible implementation manner, the aramid fiber slurry contains aramid fiber and additives.

In one possible implementation, the auxiliary agent includes a porogen. By adding a pore forming agent, a pore structure can be formed in the aramid fiber layer when the aramid fiber layer is prepared, and the porosity of the aramid fiber layer can be increased. In some embodiments, the pore-forming agent is one or more of inorganic pore-forming agents. Exemplarily, the inorganic pore-forming agent is lithium chloride, sodium chloride, magnesium chloride, calcium carbonate, calcium chloride, the second One or more of the ceramic particles.

In some embodiments, the porogen is a second ceramic particle. By adding the second ceramic particles in the aramid fiber slurry, the porosity of the aramid fiber layer can be increased, so that the porosity of the aramid fiber layer is above 20%. Not only that, the second ceramic particles introduced into the aramid layer can improve the thermal stability of the aramid layer, improve the thermal shrinkage performance of the aramid layer, and finally reflect the improvement of the thermal shrinkage performance of the composite diaphragm. In some embodiments, the second ceramic particles account for 0-50wt% of the total weight of the second ceramic particles and the aramid fibers, so as to impart proper porosity to the aramid fiber layer. At this time, while a small amount of second ceramic particles play a role in forming holes, the influence of the second ceramic particles on the performance of the aramid fiber layer is reduced.

The median diameter D50 of the second ceramic particles as the pore forming agent may be 0.01˜2 μm. In some embodiments, the median diameter D50 of the second ceramic particles is 0.1-1 μm. In this case, the second ceramic particles play a pore-forming role to increase the porosity of the aramid fiber layer, and the median particle diameter D50 is in the above range, which can give the aramid fiber layer suitable porosity and pore size, which is beneficial to obtain Aramid layer for better breathability and heat resistance.

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

As a possible implementation situation, the preparation method of aramid fiber slurry is:

Prepare an organic solution of phenylenediamine, lower the temperature to below 10°C, add phthaloyl chloride, add alkali to adjust the pH to neutral, and then add a pore-forming agent to prepare an aramid fiber slurry.

In some embodiments, the aramid pulp is at least one of para-aramid pulp and meta-aramid pulp. Exemplarily, the preparation method of aramid fiber slurry is as follows: configure an organic solution of phenylenediamine, lower the temperature to below 10°C, add phthaloyl chloride, add alkali to adjust the pH to neutral, and then add the second ceramic particles to obtain Aramid sizing. The method can directly prepare the aramid fiber slurry from raw materials, and the method is simple and has strong controllability in operation. Among them, phenylenediamine is p-phenylenediamine or m-phenylenediamine, and the organic solvent in the organic solution is N,N-dimethylacetamide, N-methylpyrrolidone, N,N-dimethylformamide or o- Any one or more of the dimethyl phthalates, the selection of the pore-forming agent is as above, and will not be repeated here.

In some embodiments, when preparing the aramid fiber slurry, additives that increase the solubility of the aramid fiber may also be added, for example, the additives are lithium chloride and calcium chloride. During the heating and stirring process, the lithium ions and chloride ions in lithium chloride replace the hydrogen bonds between the aramid molecules, so that the aramid molecules are separated and the aramid fibers are dissolved faster.

In some embodiments, in the preparation method of aramid fiber slurry, after adding phthaloyl chloride, stirring is continued to adjust the pH of the reaction solution to neutral. In some embodiments, a base such as a strong base is added to adjust the pH of the reaction solution. Exemplarily, the base may be sodium hydroxide, calcium hydroxide, potassium hydroxide and the like. Next, a pore forming agent is added to finally obtain a light yellow liquid, that is, aramid pulp.

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

In some embodiments, the solid content of the aramid pulp is 1.5-10%. In this case, the aramid slurry has suitable viscosity and spreading properties, and the aramid fiber layer is formed on the surface of the polyolefin layer.

After the aramid fiber slurry is added on the surface of the ceramic layer, the aramid fiber in the slurry will permeate downward along the pores between the first ceramic particles of the ceramic layer, and spread evenly around the surface of the first ceramic particles. The downward penetrating aramid fiber is distributed in the pores between the first ceramic particles, and the aramid fiber acts as a crosslinking agent to fix the granular first ceramic particle; at the same time, the coupling agent combines with the aramid fiber through hydrogen bonding, so that the first The ceramic particles are cross-linked with the aramid fiber through the coupling agent, the first ceramic particles are fixed, and after crystallization and solidification, a mixture layer with a stable structure is finally formed.

As a possible implementation, the method of adding the aramid slurry on the surface of the ceramic layer is to coat the aramid slurry on the surface of the ceramic layer. Wherein, the coating includes one of dip coating, spray coating, doctor blade, coating wire bar and micro gravure roll coating.

The aramid fiber slurry is added to the surface of the ceramic layer and then dried. During the drying process, on the one hand, the aramid fibers flowing into the ceramic layer are connected with the first ceramic particles under the action of a coupling agent. It is solidified in heating and drying, and the first ceramic particles are fixed on the surface of the polyolefin layer to form a mixture layer containing the first ceramic particles and aramid fibers. On the other hand, the aramid above the ceramic layer, that is, the aramid that has not flowed into the ceramic layer, solidifies into a film during the heating and drying process to form the aramid layer. In particular, when the aramid fiber slurry contains an organic pore-forming agent, the organic pore-forming agent volatilizes and overflows during the heating and drying process, forming a pore structure in the aramid fiber layer. Thus, a mixture layer is formed on the surface of the polyolefin, and an aramid fiber layer is formed on the surface of the mixture layer away from the polyolefin.

As a possible implementation situation, the preparation method of the composite diaphragm further includes: before the heating and drying treatment, immersing the sample obtained after coating the aramid fiber slurry into a plasticizing bath. Before drying, the sample obtained after coating the aramid slurry is immersed in a plasticizing bath, so that the formed aramid fiber is in a highly plastic state, so as to facilitate the stretching of the aramid fiber. Exemplarily, the plasticizing bath is N,N-dimethylacetamide, but not limited thereto. The samples immersed in the plasticizing bath were dried for the second time and then wound up to obtain a composite separator.

In a second embodiment, the first film is an aramid layer and the second film is a mixture layer. At this time, correspondingly, the first material is aramid fiber slurry, and the prefabricated film is aramid fiber prefabricated layer; the second material is a ceramic material containing the first ceramic particles.

In this implementation situation, the preparation method of composite diaphragm, as shown in Figure 4, comprises the following steps:

S21. Using aramid fiber slurry to form an aramid fiber prefabricated layer on one or both sides of the polyolefin layer.

In this step, an aramid fiber prefabricated layer is formed on one or both surfaces of the polyolefin layer by forming the aramid fiber slurry on one or both surfaces of the polyolefin layer.

Aramid pulp is a pulp whose base material is aramid fiber. The composition of aramid pulp (comprising the composition of aramid pulp, auxiliary agents such as the type of pore-forming agent), solid content and its preparation method or formation method refers to step S12 of the first implementation situation above, in order to save space , which will not be repeated here.

As a possible implementation situation, the method of using the aramid slurry on one or both sides of the polyolefin layer is to coat the aramid slurry on one or both sides of the polyolefin layer. Wherein, the coating includes one of dip coating, spray coating, doctor blade, coating wire bar and micro gravure roll coating.

As a possible implementation, after coating aramid slurry on one or both sides of the polyolefin layer, the fluidity of the slurry is reduced by heating or natural drying so that it can be fixed on the surface of the polyolefin layer, Aramid prefabricated layers are obtained. At this point, the aramid prefabricated layer is not fully cured. Among them, the way of heating can make aramid raw materials react to produce aramid.

As a possible implementation, after the aramid slurry is coated on one or both sides of the polyolefin layer, the aramid raw material is reacted by heating to form aramid, and the aramid prefabricated layer is obtained. In some embodiments, the aramid fibers in the aramid fiber preform layer are cured by heat treatment. When the aramid pulp contains an organic pore-forming agent, the heating process also causes the organic pore-forming agent in the aramid fiber to volatilize and overflow, forming pores in the aramid fiber.

S22. Adding ceramic materials on the surface of the aramid fiber prefabricated layer, heating and drying, forming an aramid fiber layer on the surface of the polyolefin layer, and forming a mixture layer on the surface of the aramid fiber layer.

In this step, in a possible implementation mode, when the aramid fiber prefabricated layer is an incompletely cured prefabricated layer, the composition of the ceramic material (including the state of matter of the ceramic material, the composition of the ceramic material, the type and content of the auxiliary agent) ), solid content and its preparation method or formation method refer to step S11 of the first implementation situation above, and in order to save space, details are not repeated here. Certainly, when the aramid fiber prefabricated layer is an incompletely cured prefabricated layer, the first ceramic particles can be directly added on the surface of the incompletely cured prefabricated layer, and the surface of the first ceramic particles is bonded with a coupling agent. In this case, the first ceramic particles sink toward the aramid fiber prefabricated layer, thereby realizing the mixing of the first ceramic particles and the aramid fiber.

In this case, ceramic material is added on the surface of the aramid fiber prefabricated layer, the first ceramic particles in the ceramic material sink, and the first ceramic particles are trapped in the aramid fiber prefabricated layer. During the heating and drying process, the aramid fiber prefabricated layer close to the polyolefin layer is cured to form an aramid fiber layer; the aramid fiber prefabricated layer far away from the polyolefin layer, the first ceramic particles trapped in it are combined with the aramid fiber by the coupling agent on its surface. connected and cured by heating, so as to fix the first ceramic particles and form a mixture layer of the first ceramic particles and aramid fibers.

In a possible implementation manner, when the aramid fibers in the aramid fiber prefabricated layer are solidified, the ceramic material is a mixed slurry containing ceramics and aramid fibers, which is obtained by mixing raw materials containing ceramic particles and aramid fibers. In some embodiments, in addition to ceramic particles and aramid fibers, the mixed slurry also contains auxiliary agents, such as dispersants, thickeners, etc., but is not limited thereto. At this time, the method for adding ceramic materials on the surface of the aramid fiber prefabricated layer may be: coating the above ceramic slurry on the surface of the aramid fiber prefabricated layer. Wherein, the coating method is one of dip coating, spray coating, doctor blade, coating wire bar and micro gravure roll coating. In this embodiment, the aramid fiber in the aramid fiber slurry and the aramid fiber in the ceramic material may be the same or different.

For the composite diaphragm obtained in the examples of the present application, since a mixture layer of aramid fiber and ceramic particles is formed on the polyolefin base film, the heat shrinkage rate of the composite diaphragm is <4%@150°C/1h; at the same time, the aramid fiber layer is used as a protective layer , so that the membrane rupture temperature of the composite separator is greater than 200° C., and the composite separator thus obtained can significantly improve the safety performance of the battery. The obtained composite diaphragm was tested for performance, and it was found that: when the puncture strength test was performed on the composite diaphragm, 90% SOC needles all passed; when the thermal shrinkage rate test was performed on the composite diaphragm at 150°C, the passing rate of heating at 150°C for 60 minutes increased.

In the third aspect, the embodiment of the present application provides an electrochemical device, including a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator arranged between the positive electrode sheet and the negative electrode sheet, and the separator is the composite separator according to the first aspect of the embodiment of the present application.

The electrochemical device provided in the embodiment of the present application contains the above-mentioned composite separator, which has a low thermal shrinkage rate and a high membrane rupture temperature, which can solve the problem of shrinkage and melting of the separator, reduce the risk of thermal runaway caused by short circuit of the battery, and improve the safety performance of the battery.

In some implementations, at least one surface of the composite membrane is provided with at least one polymer layer. The polymer layer can improve the interfacial adhesion between the composite separator and the electrode sheet, improve the overall hardness and strength of the battery, and prevent the deformation of the battery cell. In some embodiments, the polymer layer can be activated after shaping with heat. Exemplarily, after the polymer is formed on the surface of the composite membrane, heat treatment is performed at a pressure of 0.1-2.0 MPa and a temperature of 25° C.-100° C. for 20-300 minutes of activation. 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 minutes.

Exemplarily, the polymer layer is a material layer formed by at least one of PVDF, PMMA, dopamine, CMC, SBR, PTFE and PVA; as a possible implementation of the electrochemical device of the present application, the polymer layer is PVDF , PMMA, dopamine, CMC, SBR, PTFE and PVA formed by at least two polymer laminates, and the polymers that make up the polymer laminate can be one or more of the above polymers. The above-mentioned polymer material can improve the bonding strength between the composite film and the electrode sheet provided by the first aspect, and keep the battery structure stable.

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

In some implementation situations, the structure of the electrochemical device is one or more of a wound structure and a laminated structure.

In some implementations, the electrochemical device further includes a packaging case, and one or more electrochemical device units are packaged in the packaging case. Wherein, the electrochemical device unit may be an electric core including a positive electrode sheet, a negative electrode sheet, an electrolyte and a composite separator.

The fourth aspect of the present application provides an electronic device, including a housing, electronic components and electrochemical devices accommodated in the housing, the electrochemical device is the electrochemical device of the third aspect of the embodiment of the present application, and the electrochemical device is used for Provide power to electronic components.

In some implementation situations, the electronic device may be a mobile terminal. Exemplarily, the terminal is a computer, a mobile phone, a tablet, or a wearable product.

A fourth aspect of the present application provides a mobile device, which includes the electrochemical device of the third aspect.

In some implementation situations, the mobile device is a terminal product that needs to carry a power source, such as a new energy vehicle, but is not limited to a new energy vehicle.

The following will be described in conjunction with specific examples. It is worth noting that the polyolefin layer in the following examples is a porous polyolefin layer, and the H-HE7.0um wet-process PE film produced by Chongqing Newmi Technology Co., Ltd. is selected. The indicators are shown in Table 1.

Table 1

Example 1

A kind of composite diaphragm, its preparation method comprises:

(1) Preparation of ceramic slurry

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

b. Add 0.3 parts of polyethylene glycol into the above reactor, stir for 0.6 hours and then grind for 1 hour to obtain a uniform ceramic dispersion;

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

(2) Preparation of aramid fiber slurry

a, add N,N-dimethylacetamide solvent (DMAC) in the reactor, then introduce p-phenylenediamine;

b. Lower the temperature of the reactor to about 0°C and stir, add phthaloyl chloride and 2wt.% of silicon dioxide particles, continue to stir, add a strong base, make the pH of the synthetic solution to neutral, and finally obtain a light yellow The liquid is aramid fiber slurry, wherein the content of aramid fiber is 3.5wt.%.

(3) Preparation of composite diaphragm

a, the water-based high-temperature resistant ceramic slurry prepared in step (1) is coated on one side of a PE monolayer film with a thickness of 7 μm by gravure roll coating, and the ceramic layer is obtained after drying;

b. Spray the aramid slurry prepared in step (2) on one side of the ceramic layer by spraying. After coating, immerse in the plasticizing bath. The plasticizing bath is N,N-dimethyl ethyl alcohol After being dried, it is rolled up to obtain a composite diaphragm, which includes sequentially laminated aramid fiber layers, a mixed layer formed of ceramic particles and aramid fibers, and a porous polyolefin layer.

In the composite separator prepared in Example 1, the thickness of the aramid fiber layer is about 2um, and the thickness of the mixture layer is about 2um.

Example 2

A composite diaphragm, the difference between its preparation method and Example 1 lies in the preparation of the aramid slurry in the composite diaphragm, specifically, the preparation method of the aramid slurry is:

a, add N,N-dimethylacetamide solvent (DMAC) in the reactor, then introduce m-phenylenediamine;

b. Lower the temperature of the reactor to about 0°C and stir, then add phthaloyl chloride, continue to stir, add a strong base, make the pH of the synthesis solution neutral, and obtain a light yellow liquid, that is, aramid fiber slurry, in which aromatic The content of fiber is 2.5wt.%.

In the composite diaphragm prepared in Example 2, the thickness of the ceramic layer is 2um, and the thickness of the aramid fiber layer is 2um.

Example 3

a. Add barium sulfate nanoparticles into N,N-dimethylacetamide, dissolve lithium chloride in N,N-dimethylacetamide, add meta-aramid fiber, heat and stir to make the meta-position Aramid fibers are dissolved in N,N-dimethylacetamide to obtain a solution. In this step, lithium chloride is dissolved in 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 the aramid molecules, so that the aramid molecules are separated and the dissolution is accelerated. Wherein, the mass ratio of lithium chloride, N,N-dimethylacetamide and meta-aramid fiber is (2-4):(70-75):(18-22), and the heating and stirring temperature is 80-100 ℃.

b. Add calcium hydroxide to make the pH value of the synthetic solution neutral, and finally obtain a liquid, that is, a barium sulfate nanoparticle modified aramid fiber slurry, wherein the aramid fiber percentage is about 4wt.%, and the barium sulfate content is about 5wt. %.

In the composite separator prepared in Example 3, the thickness of the mixture layer is 2um, and the thickness of the aramid fiber layer is 2um.

Example 4

A kind of composite diaphragm, its preparation method differs from embodiment 1 in the preparation of the ceramic slurry in the composite diaphragm, specifically, the preparation method of the ceramic slurry is:

a. Add 40 parts of boehmite, 0.8 part of silane coupling agent, and 0.51 part of polyvinylpyrrolidone into 55.64 parts of deionized water, stir for 0.5 h, and grind for 1 h to obtain a uniform ceramic dispersion.

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 dodecylsulfonate to the ceramic dispersion, stir at a low speed, Disperse for 1.5h to obtain water-based ceramic-resistant slurry.

In the composite separator prepared in Example 4, the thickness of the mixture layer is 2um, and the thickness of the aramid fiber layer is 2um.

Example 5

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

(2) Add 0.55 parts of polytetrafluoroethylene, 3.26 parts of methacrylic acid-methyl methacrylate-maleic anhydride terpolymer, and 0.04 parts of sodium dodecylsulfonate to the ceramic dispersion, stir at low speed, and disperse After 1.5h, an aqueous ceramic slurry was obtained.

In the composite separator prepared in Example 5, the thickness of the mixture layer is 2um, and the thickness of the aramid fiber layer is 2um.

Example 6

A kind of composite diaphragm, its preparation method differs from embodiment 1 in that, the preparation method of composite diaphragm is:

a, by spraying the aramid slurry prepared in step (2) in Example 1, coated on one side of the polyolefin layer;

B, spray the ceramic slurry prepared in step (1) in Example 1 on the surface of the aramid fiber coating by spraying;

After coating, immerse in a plasticizing bath, the plasticizing bath is N,N-dimethylacetamide, and wind up after drying to obtain a composite diaphragm, which includes a mixture of ceramic particles and aramid fiber laminated in sequence layer, aramid layer, and porous polyolefin layer.

In the composite separator prepared in Example 6, the thickness of the aramid fiber layer is about 2um, and the thickness of the mixture layer is about 2um.

Example 7

a, the water-based high-temperature-resistant ceramic slurry prepared in step (1) is coated on both sides of a PE monolayer film with a thickness of 7 μm by gravure roll coating;

b. Spray the aramid slurry prepared in step (2) on the surface of the ceramic layer by spraying, after coating, immerse in the plasticizing bath, the plasticizing bath is N,N-dimethylacetamide After being dried, it is rolled up to obtain a composite diaphragm, which includes an aramid fiber layer laminated in sequence, a mixed layer formed of ceramic particles and aramid fiber, and a porous polyolefin layer.

In the composite diaphragm prepared in Example 1, the thickness of the aramid fiber layer is about 2um/side, and the thickness of the mixture layer is about 2um/side.

Comparative example 1

A diaphragm, its preparation method comprises:

(1) Preparation of aramid fiber slurry

(2) Preparation of diaphragm

The prepared aramid slurry was coated on one side surface of a PE monolayer film with a thickness of 7 μm by gravure roll coating. After coating, it was immersed in a plasticizing bath. The plasticizing bath was N, N-di Methyl acetamide, after being dried, is rolled to obtain a separator, which includes an aramid fiber layer and a porous polyolefin layer stacked in sequence.

In the separator prepared in Comparative Example 1, the thickness of the aramid fiber layer was 4um.

Comparative example 2

A diaphragm, its preparation method comprises:

(1) Preparation of ceramic slurry

(2) Preparation of diaphragm

The prepared ceramic slurry was coated on one side surface of a PE monolayer film with a thickness of 7 μm by gravure roll coating, and after drying, a separator was obtained, which included sequentially laminated ceramic layers and porous polyolefin layers.

In the separator obtained in Comparative Example 2, the thickness of the ceramic layer was 4um.

Comparative example 3

A diaphragm, its preparation method comprises:

(1) Preparation of ceramic slurry

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

b. Add 0.55wt.% sodium carboxymethyl cellulose, 3.26wt.% methacrylic acid-methyl methacrylate-maleic anhydride terpolymer, 0.04wt.% sodium dodecylsulfonate to the ceramic The dispersion liquid was stirred at a low speed and dispersed for 1.5 hours to obtain a water-based anti-ceramic slurry.

(2) Preparation of diaphragm

In the separator obtained in Comparative Example 3, the thickness of the ceramic layer was 4um.

Comparative example 4

Preparation of ceramic slurry

In the composite separator prepared in Comparative Example 4, the thickness of the aramid fiber layer is about 2um, and the thickness of the mixture layer is about 2um.

The composite membranes obtained in Examples 1-5 and the membranes obtained in Comparative Examples 1-3 are subjected to performance tests, and the test results of the composite films obtained in Examples 1-5 are shown in Table 2 below, and those obtained in Comparative Examples 1-3 The test results of the diaphragm are shown in Table 3 below:

Table 2

table 3

It can be seen from the data in Table 1 and Table 2 that the composite diaphragm provided in Examples 1-7 of the present application can retain a lower closed cell temperature after sequentially laminating ceramic particles/aramid layer and aramid layer on the surface of the porous polyolefin layer, The closed cell temperature is about 140°C. Compared with the diaphragm provided in Comparative Example 1, the composite films obtained in Examples 1-7 of the present application have significantly lower heat shrinkage rates in the machine direction and perpendicular to the machine direction, and the heat shrinkage rates are all <4%@150°C/1h; and The diaphragm provided in Comparative Example 1 does not contain a mixture layer formed of ceramic particles and aramid fiber, so the resulting diaphragm has a higher heat shrinkage rate. Compared with Comparative Examples 2-3, the membrane rupture temperature of the composite films obtained in Examples 1-7 of the present application was significantly increased. This shows that the composite layer including the aramid layer and the mixture layer provided on the surface of the polyolefin layer in the embodiment of the present application can improve the heat shrinkability of the separator and increase the membrane rupture temperature, thereby effectively improving the safety performance of the battery.

The composite separator obtained in Example 1-7 and the separator obtained in Comparative Example 1-3 are made into an electrochemical device, and the preparation method is as follows:

Production of positive electrode sheet: Dissolve the binder PVDF in NMP and disperse to obtain 7.0wt.% PVDF glue, then add carbon nanotube conductive liquid to disperse evenly, and finally add the active material lithium cobaltate and stir to form a positive electrode slurry. The cloth equipment evenly coats the positive electrode slurry on both sides of the aluminum foil, and dries in an oven to remove the NMP solvent. The coated pole piece is made into a positive pole piece after cold pressing, slitting, and tab welding processes. Wherein, the mass ratio of the positive electrode material is: LCO:CNTs:PVDF=98.8%:0.02%:1.0%;

Negative electrode sheet production: The negative electrode is mixed by kneading. First, dry mix artificial graphite and SP evenly, then add 25wt.% pre-mixed CMC glue for kneading and stirring, and finally add the remaining CMC and deionized water for high-speed mixing. Disperse to form a mixed negative electrode slurry. After the slurry is sieved, the coating equipment is used to evenly coat the negative electrode slurry on both sides of the copper foil, and the electrode piece after drying in the oven is made into the negative electrode piece through the processes of cold pressing, slitting, and tab welding. Wherein the mass proportion of negative electrode material is, graphite: SP: CMC: SBR=96.8%: 0.6%: 1.2%: 1.2%;

Fabrication of the diaphragm: The surface of the battery diaphragm of the above-mentioned Examples 1-7 and Comparative Examples 1-3 was sprayed with PVDF or PMMA water-based adhesive layers of 0.5um each.

The above-mentioned positive and negative pole pieces and the diaphragm are wound together to form a bare cell. The capacity of the cell is 4.5Ah, and the working voltage range is 3.0-4.48V. The cell is then packaged, baked, injected, and formed and other processes to make lithium-ion batteries.

Performance tests were performed on the electrochemical devices containing the diaphragms prepared in Examples 1-7 and Comparative Examples 1-4, and the test results are shown in Table 4 and Table 5 respectively:

Table 4

table 5

项目project	对比例1Comparative example 1	对比例2Comparative example 2	对比例3Comparative example 3	对比例4Comparative example 4
90％SOC针刺90% SOC acupuncture	5/5通过5/5 pass	3/5通过3/5 pass	0/5通过0/5 pass	3/5通过3/5 pass
150℃，1h热箱150℃, 1h hot box	0/5通过0/5 passed	0/5通过0/5 pass	3/5通过3/5 pass	3/5通过3/5 pass

It can be seen from Table 4 and Table 5 that when the 90% SOC needle test was performed on the above-mentioned batteries, the battery containing the composite separator of the embodiment of the present application passed all five tests, while the batteries containing the separators of Comparative Example 2 and Comparative Example 3 passed the test. The ratios are 60% and 0, which is attributed to the fact that the separators provided by Comparative Document 2 and Comparative Document 3 do not contain an aramid fiber layer, which leads to internal short-circuit heat generation inside the battery during the acupuncture test. In the composite separator of the embodiment of the present application, the high heat resistance of the aramid layer prevents the separator from melting, suppresses further internal short-circuit heating, and reduces the probability of battery heating and burning.

The above batteries were treated in a hot box at 130°C for 30 minutes, and all the batteries passed. However, when the above-mentioned battery was treated in a hot box at 150°C for 60 minutes, the pass rate of the battery containing the separator provided in Comparative Examples 1-3 could not reach 100%, or even 0, because: Comparative Example 1 only contained an aramid layer , Aramid fiber is prone to curling at high temperature, which causes the battery separator to curl easily at high temperature; while Comparative Example 2 only contains ordinary ceramic coating, which has collapsed and melted at 150°C, and cannot effectively isolate the positive and negative electrodes, and the battery will be short-circuited Combustion; Comparative Example 3 only contains high-temperature ceramic coating, and the membrane rupture temperature is 180°C; when baked at 150°C for 1 hour, the strength of the separator is low, and the positive and negative electrodes can no longer be effectively isolated, and the battery will short-circuit and burn.

It should be noted that the test method of the performance test involved in the embodiment of the present application is as follows:

(1) Film thickness (um)

method one:

a. Sampling: Take a sample of 1×10 ³ mm ² from the diaphragm (the area of the sample can be ≥1.5×10 ³ mm ² ), and the number of test points depends on the condition of the diaphragm (usually not less than 10 points).

b. Test: The test is carried out with a 10,000-degree thickness measuring instrument at a temperature of 23±2°C.

c. Data processing: the measured value of the thickness of each test point, and take the arithmetic mean value.

Method 2:

a. Sampling: For products with a width of less than 200mm: determine a point every 40mm±5mm along the longitudinal (MD) direction, the number of test points is not less than 10, and the number of test points can be determined according to the width of the diaphragm. less than 20mm;

For products with a width ≥ 200mm: determine a point every 80mm ± 5mm along the transverse (TD) direction, the number of test points is not less than 10, and the number of test points can be determined according to the width of the diaphragm.

b. Test: Test each test point with a thickness measuring instrument at a temperature of 23±2°C. The diameter of the measuring surface is between 2.5mm and 10mm, and the load applied to the sample on the measuring surface should be 0.5N～ between 1.0N.

(2) Porosity (%)

method one:

a. Sampling: Take a 1×10 ⁴ mm ² sample from the diaphragm.

b. Test: The porosity is measured by the density method.

c. Data processing:

The overall porosity P of the sample can be calculated by the following formula:

Wherein, m can be the mass of the sample, the skeleton density ρ can be the material true density of the sample, and V can be the volume of the sample.

Method 2:

a. Sampling: cut a rectangular sample with a 237×170mm plate sampler. When cutting samples, keep as far away from the edge of the diaphragm as possible (for example, more than 50mm from the edge of the diaphragm).

b. Test: The porosity is measured by the density method, including measuring n (n can be greater than or equal to 9) points of the sample, and the n points can be distributed in an equidistant lattice.

c. Data processing: the porosity _Pi of each point can be calculated by the following formula:

Among them, m _i is the mass of each point, ρ is the skeleton density of the sample (can be calculated according to the material ratio), V _i is the total volume of each point (can be calculated according to the length, width and thickness of the sample );

(3) Air permeability (s/100cc)

method one:

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

b. Test: Test according to the method specified in the standard JIS P8117-2009. Specifically include: setting the pressure of the cylinder-driven pressure reducing valve to 0.25MPa, the test pressure to 0.05MPa, and selecting "JIS" as the test standard.

c. Data processing: randomly cut 6 samples from the full width of the diaphragm, record the air resistance value of each sample respectively, and calculate the arithmetic mean value of each sample.

Method 2:

a. Sampling: Cut 6 square samples with a 100×100mm plate sampler. When cutting samples, keep as far away from the edge of the diaphragm as possible (for example, more than 50mm from the edge of the diaphragm). Each sample is evenly distributed on the membrane (that is, the full width of the membrane is evenly divided to obtain 6 areas, and one sample is cut in each area of the 6 areas).

c. Data processing: record the air resistance value of each sample separately, and calculate the arithmetic mean value of the air resistance values of these 6 samples.

(4) Puncture strength (gf)

method one:

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

b. Test: fix the sample on the fixture in the center, the test needle is spherical (made of ruby) with a diameter of 1mm, ensure that the sample extends to or exceeds the edge of the clamping disc in all directions, and confirm that the sample is completely fixed on the ring fixture on, no slippage. During the test, the diaphragm is punctured, and the speed of the machine is set at 300±10mm/min until the punctured ball completely breaks the sample, and the puncture resistance is the maximum force recorded during the test.

c. Data processing: randomly cut 6 samples from the full width, record the puncture strength values of each sample respectively, and calculate the arithmetic mean value of the puncture strength values of each sample.

Method 2:

a. Sampling: Cut 6 rectangular samples with a 237×170mm plate sampler. When cutting the sample, it should be as far away from the edge of the diaphragm as possible (for example, more than 50mm from the edge of the diaphragm). Each sample is evenly distributed on the membrane (that is, the full width of the membrane is evenly divided to obtain 6 areas, and one sample is cut in each area of the 6 areas).

b. Test: Test according to the method specified in the standard ASTMD4833-07. Specifically, it may include: the test needle is a spherical needle with a diameter of 1mm (the material is sapphire); fix the sample on the fixture in the center, ensure that the sample extends to or exceeds the edge of the clamping disc in all directions, and confirm that the sample is completely fixed in the ring There is no slippage on the fixture; during the test, the speed of the machine is set at 300±10mm/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.

c. Data processing: record the puncture strength of each sample separately, and calculate the arithmetic mean value of the puncture strength of these 6 samples.

(5) Tensile strength and elongation (Mpa and %)

method one:

a. Sampling: On the overall width sample, cut the diaphragm according to the MD and TD directions respectively, and obtain multiple strip-shaped samples with a length ≥ 50 mm and a width of about 15 ± 0.1 mm (for MD testing, the sample The width of the sample can be along the TD direction of the diaphragm, and the length of the sample can be along the MD direction of the diaphragm; for TD testing, the width of the sample can be along the MD direction of the diaphragm, and the length of the sample can be along the TD direction of the diaphragm).

b. Test: Use a stretching machine to stretch, the distance between the clamps can be 100±5mm, until the sample is broken, and the stretching speed can be 100±1mm/min.

c. Data processing: record the tensile strength and elongation of each sample respectively.

Method 2:

a. Sampling: Cut 6 rectangular samples with a 237×170mm plate sampler. When cutting the sample, it should be as far away from the edge of the diaphragm as possible (for example, more than 50mm from the edge of the diaphragm). Each sample is evenly distributed on the diaphragm (that is, along the MD and TD directions of the diaphragm, the entire width of the diaphragm is evenly separated to obtain 6 regions, and one sample is cut in each region of the 6 regions). Afterwards, a strip-shaped sample with a length ≥ 150 mm and a width 15 ± 0.1 mm is cut by a sampler.

b. Test: measure according to the method stipulated in GB/T1040.3-2006. Specifically include: the distance between the clamps can be 100±5mm, and the stretching speed can be 100±1mm/min.

c. Data processing: record the tensile strength and elongation of each sample separately, and calculate the arithmetic mean value of these 6 samples.

(6) Heat shrinkage rate at 150°C

a. Sampling: Randomly cut 6 samples from the full width. The specific sampling of each sample can include: cutting 100mm along the MD direction of the diaphragm; when the TD direction of the diaphragm is greater than 100mm, the length of the test sample in the TD direction can be 100mm; when the TD direction of the microporous membrane is less than 100mm , the length of the test sample in the TD direction can be based on actual conditions.

b. Test: Mark the vertical and horizontal marks of the sample, measure and record the vertical and horizontal dimensions of each sample; place the sample flat in the paper jacket layer, and the sample has no folding, wrinkling, adhesion, etc.; Put the paper sleeve with the sample (for example, 10 layers) into the middle of the constant temperature oven (for example, the opening time does not exceed 3s); heat the sample to 150°C in the electric thermostat for 1 hour; take it out After the sample was cooled to room temperature, the longitudinal and transverse lengths were measured.

c. Data processing:

Calculate the heat shrinkage of each sample:

T=(L ₀ -L)/L ₀ ×100%,

Wherein, T can be the thermal shrinkage rate (%) of the sample, L ₀ can be the length (mm) of the sample before heating, and L can be the length (mm) of the sample after heating. Calculate the arithmetic mean of the thermal shrinkage of the sample.

(7) Closed cell temperature (°C)

The temperature rise internal resistance method is used for testing. The diaphragm is placed in a stainless steel fixture or other similar fixtures and injected with an appropriate amount of electrolyte. The above fixture is placed in an oven, and the temperature is raised at a certain speed. At the same time, the resistance and temperature of the fixture are monitored. When the resistance value changes with the temperature to the initial resistance value The temperature corresponding to 10 times is the closed cell temperature of the diaphragm by default.

(8) Membrane rupture temperature (°C)

The membrane rupture temperature was measured by the baking method. Put the diaphragm in a 9*9cm fixture, put the above fixture in an oven, heat up at a certain speed, and monitor whether the diaphragm in the fixture is ruptured at the same time, when the diaphragm ruptures with the temperature change, record it as the rupture temperature of the diaphragm .

(9) Acupuncture test

a. Sampling: Take 5 power conversion system (pcs) batteries from each group, and mark the central position of the battery cells.

b. Test: At 25±3°C, charge the cell to the limit voltage according to a constant current of 0.7C, and then charge it under the constant voltage condition of the limit voltage until the current decreases to 0.025C, and test within 12-24h ;At 25±3°C, pierce the steel nail into the center of the cell at a speed of 150mm/s until it penetrates. The diameter of the steel nail is 2.45±0.06mm, the length is 45±2.5mm, and the length of the tip can be between 2mm and 4.9mm.

c. Data processing: During the puncture process and after the puncture, the steel nail does not catch fire or explode within 10 minutes, and it is judged as passed.

(10) 150°C Thermal Shock Test

a. Sampling: Take 5pcs batteries from each group.

b. Test: At 25±3°C, charge the cell to the limited voltage at a constant current of 0.2C, and then charge it at a constant voltage with the limited voltage until the current decreases to 0.025C, by means of convection or circulating hot air box, start heating the battery from the initial temperature of 25±3°C, and the temperature change rate can be 5±2°C/min; keep it for 60 minutes after raising the temperature to 150±2°C.

c. Data processing: Observe the experimental phenomenon, if there is no fire or explosion after heating up, it is judged as passed.

(11) Nail penetration test

After charging to 90% SOC in standard charging mode, test within 12-24 hours. Then put the battery in an explosion-proof box at 25°C, and pierce the steel nail into the center of the battery cell at a speed of 150mm/s until it penetrates, and then withdraw the needle after 10 minutes. If the battery is not thermally out of control, the test is passed, and the pass rate of the test is recorded.

The above are only preferred embodiments of the application, and are not intended to limit the application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the application should be included in the protection scope of the application. Inside.

Claims

A composite diaphragm, characterized in that it includes a polyolefin layer, a composite layer bonded to one side or both sides of the polyolefin layer, the composite layer includes a mixture layer, and a composite layer bonded to one side surface of the mixture layer an aramid layer, and both the mixture layer and the aramid layer are stacked with the polyolefin layer;

The mixture layer includes aramid fibers and first ceramic particles, and a coupling agent is bound on the surface of the first ceramic particles; wherein, the coupling agent contains an inorganic group and an organophilic group, and the coupling agent passes through The inorganic-philic group is connected with the first ceramic particles, and is connected with the aramid fiber through the organophilic group.
The composite diaphragm according to claim 1, wherein the coupling agent is a silane coupling agent.
The composite diaphragm according to claim 2, wherein the silane coupling agent is selected from at least one of vinylsilane, aminosilane, epoxysilane, mercaptosilane and methacryloxysilane.
The composite diaphragm according to claim 1, characterized in that, in the mixture layer, the weight of the coupling agent is 0.3-2% of the total weight of the first ceramic particles.
The composite diaphragm according to claim 1, characterized in that, based on the total weight of the mixture layer as 100%, the weight percentage of the aramid fiber is 0.1-20%, and the weight of the first ceramic particles The percentage content is 80～99.9%.
The composite membrane according to claim 1, wherein the mixture layer includes a first surface in contact with the aramid layer and a second surface facing away from the first surface, along the second surface to In the direction of the first surface, the aramid content in the mixture layer gradually increases.
The composite diaphragm according to any one of claims 1 to 6, characterized in that, based on 100% of the total weight of the aramid fiber layer, the weight percentage of the aramid fiber is 50-100%.
The composite diaphragm according to claim 7, wherein the aramid fiber layer further comprises second ceramic particles with a weight percentage of 0-50%.
The composite membrane according to any one of claims 1 to 6, characterized in that the thickness of the mixture layer is 0.1-6um.
The composite membrane according to claim 9, characterized in that, the thickness of the mixture layer is in the range of 1-4um.
The composite diaphragm according to any one of claims 1 to 6, characterized in that the thickness of the aramid fiber layer is 0.1-6um.
The composite diaphragm according to claim 10, characterized in that, the thickness of the aramid fiber layer is 0.5-3um.
The composite diaphragm according to any one of claims 1 to 12, wherein the aramid in the aramid layer is 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.
The composite diaphragm according to any one of claims 1 to 6, characterized in that the median diameter D50 of the first ceramic particles is 0.01-2.0 µm.
The composite diaphragm according to claim 8, characterized in that, the median diameter D50 of the second ceramic particles is 0.1-1 μm.
The composite separator according to any one of claims 1 to 15, characterized in that the thickness of the polyolefin layer is 0.2-20 μm.
The composite membrane according to any one of claims 1 to 16, 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 mixture layer The side surface facing away from the polyolefin layer.
The composite diaphragm according to any one of claims 1 to 17, characterized in that the composite layer comprises n laminated layers formed of a mixture layer and an aramid fiber layer, wherein n is an integer of 2-5.
An electrochemical device, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a diaphragm arranged between the positive electrode sheet and the negative electrode sheet, wherein the diaphragm is as described in any one of claims 1 to 18 The composite diaphragm described above.
An electronic device, comprising a housing, electronic components and electrochemical devices accommodated in the housing, characterized in that the electrochemical device is the electrochemical device according to claim 19, and the electrochemical device Used to supply power to the electronic components.
The electronic device according to claim 20, wherein the electronic device is a computer, a mobile phone, a tablet, or a wearable product.
A mobile device, characterized in that the mobile device comprises the electrochemical device according to claim 19.