CN115693024A

CN115693024A - Composite separator, electrochemical device, electronic apparatus, and mobile terminal

Info

Publication number: CN115693024A
Application number: CN202110877240.XA
Authority: CN
Inventors: 阳东方; 田雷雷; 李枝贤; 谢封超
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2021-07-31
Filing date: 2021-07-31
Publication date: 2023-02-03
Also published as: WO2023011293A1

Abstract

The application relates to the technical field of battery diaphragms and provides a composite diaphragm, an electrochemical device, electronic equipment and a mobile terminal. The composite diaphragm comprises a polyolefin layer and a composite layer combined on the surface of one side or two sides of the polyolefin layer, wherein the composite layer comprises a mixture layer and an aramid fiber layer combined on the surface of one side of the mixture layer, and the mixture layer and the aramid fiber layer are both stacked with the polyolefin layer; the mixture layer comprises aramid fibers and first ceramic particles, and a coupling agent is combined on the surfaces of the first ceramic particles; the coupling agent contains an inorganic group and an organic group, and is connected with the surface of the first ceramic particle through the inorganic group and is connected with the aramid fiber through the organic group. The application provides a compound diaphragm, rupture of membranes temperature > 240 ℃, and thermal shrinkage rate < 4% @150 ℃/1h can effectively solve the battery because the easy thermal shrinkage of diaphragm is with melting to lead to battery short circuit to take place thermal runaway, cause the problem of potential safety hazard.

Description

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

Technical Field

The application belongs to the technical field of battery diaphragms, and particularly relates to a composite diaphragm, an electrochemical device, electronic equipment and a mobile terminal.

Background

With the development of electric vehicles, intelligent terminals and electronic mobile devices, lithium ion batteries have become one of the most important devices in the industries of electronic products and new energy vehicles. The diaphragm is used as a separation component for separating the positive electrode and the negative electrode of the battery. As one of the five main materials of lithium ion batteries, separators play an important role in battery safety. The most commonly used separators at present are polyethylene separators, which typically have a thermal shrinkage of > 10% MD (150 ℃/1 h), TD > 10% (150 ℃/1 h); and the rupture temperature of the diaphragm is usually less than 155 ℃. Therefore, when the battery is operated under high temperature conditions, the separator is melted by heat and shrinks severely. The damage of the diaphragm causes the direct contact of the anode and the cathode of the battery, thereby promoting the serious short circuit inside the battery and causing thermal runaway of the battery.

In order to improve the thermal stability of the separator, the surface of the separator is usually coated with a coating, which is usually an inorganic ceramic layer (silicon oxide, aluminum oxide, magnesium oxide, and the like), an organic polymer adhesive coating (PVDF, PMMA, and the like), or an organic high temperature resistant polymer coating (PI, an aramid layer, and the like). The inorganic ceramic layer and the organic high-temperature-resistant polymer coating are used for improving the thermal stability of the diaphragm, meeting the reliability and safety of related products in high-temperature application scenes and preventing batteries from being ignited and even exploded. The organic polymer viscous coating is used for improving the interface cohesiveness with electrode plates, improving the integral hardness and strength of the battery, preventing the deformation of the battery cell and ensuring the reliability and safety of the battery cell. However, when a high-molecular material such as aramid fiber is at a high temperature, the movement unit of a high-molecular chain is changed into a chain segment from the previous bond length and bond angle, the movement of the molecular chain is accelerated, so that the aramid fiber molecule is curled, the thermal shrinkage is higher, the thermal shrinkage of the coating reaches 6% (150 ℃/1 h), and the safety of the battery is reduced.

Disclosure of Invention

The application aims to provide a composite diaphragm, a preparation method thereof, an electrochemical device, electronic equipment and a mobile terminal containing the composite diaphragm, and aims to solve the problems that the thermal shrinkage rate of an aramid fiber layer on the surface of the diaphragm is high, the risk of short circuit in a battery is increased, and the safety performance of the battery is influenced.

In order to achieve the purpose of the application, the technical scheme adopted by the application is as follows:

the first aspect of the present application provides a composite separator, including a polyolefin layer, a composite layer bonded to one or both surfaces of the polyolefin layer, the composite layer including a mixture layer, and an aramid layer bonded to one surface of the mixture layer, and both the mixture layer and the aramid layer being stacked on the polyolefin layer;

the mixture layer comprises aramid fibers and first ceramic particles, and a coupling agent is combined on the surfaces of the first ceramic particles; the coupling agent contains an organophilic group and an organophilic group, and is connected with the surface of the first ceramic particle through the organophilic group and is connected with the aramid fiber through the organophilic group.

The application provides a composite membrane, including setting up the composite bed on polyolefin layer one side or both sides surface, and the composite bed includes mixture layer and aramid fiber layer. The aramid fiber layer can resist the high temperature of 200 ℃, so that the film breaking temperature of the composite diaphragm can be increased to be more than 200 ℃. The battery with the diaphragm containing the aramid fiber layer can resist the high temperature of 200 ℃ and does not melt when being abused by heat and machinery, thereby effectively playing the role of isolating the positive electrode and the negative electrode of the battery, avoiding the violent internal short circuit caused by the direct contact of the positive electrode and the negative electrode and improving the safety of the battery. However, the aramid layer has a high thermal shrinkage rate, increasing the risk of short circuits in the battery. On the basis, the surface of the aramid fiber layer is provided with a mixture layer containing aramid fiber and first ceramic particles, and the surface of each first ceramic particle is combined with a coupling agent. Because the coupling agent contains an inorganic group and an organic group, one end of the coupling agent serving as a molecular bridge is connected with the surface of the first ceramic particle, and the other end of the coupling agent is connected with the aramid fiber in the mixture layer, so that the binding force between the first ceramic particle and the aramid fiber is enhanced, the aramid fiber serves as a crosslinking agent to crosslink and fix the ceramic particles, and a continuous and stable film layer is formed. Under the action of the coupling agent, the mixture layer has good structural stability, the structural stability of the composite diaphragm under the high-temperature condition is favorably improved, the first ceramic particles also play a role in rigidly supporting aramid fiber molecular chains in the aramid fiber layer, the molecular bond curling of the aramid fiber high-molecular bonds at high temperature is relieved, and the heat shrinkage performance of the aramid fiber layer is further improved, so that the heat shrinkage rate of the composite diaphragm is less than 4% @150 ℃/1h (namely, the heat shrinkage rate of the composite diaphragm is less than 4% after the composite diaphragm is subjected to heat treatment for 1 hour at the temperature of 150 ℃). The battery containing the mixture layer can relieve the risk of internal short circuit at the tail part of the battery core head due to the thermal shrinkage of the diaphragm when the composite diaphragm is heated, and the safety of the battery is improved.

In conclusion, the composite diaphragm provided by the application has the membrane rupture temperature of more than 240 ℃ and the thermal shrinkage rate of less than 4% @150 ℃/1h, and can effectively solve the problem of potential safety hazards caused by thermal runaway caused by the fact that the diaphragm is easy to thermally shrink and melt and the battery is short-circuited.

As one possible implementation of the composite separator of the present application, the coupling agent is a silane coupling agent. At this time, the silane coupling agent is bonded to the surface of the first ceramic particles through the siloxane group. Because there is a large amount of organophilic groups on the first ceramic particle surface that combines with coupling agent, this organophilic group can form the hydrogen bond with the aramid fiber molecule of dispersion in first ceramic particle, and the hydrogen bond effect makes aramid fiber and first ceramic particle closely combine to form stable in structure's mixture layer, and then with the help of the first ceramic particle in the mixture layer, stabilize the aramid fiber layer.

As one possible implementation of the composite separator of the present application, the silane coupling agent is selected from at least one of vinyl silane, amino silane, epoxy silane, mercapto silane, and methacryloxy silane. The siloxane group in the silane coupling agent is combined on the surface of the first ceramic particle, so that a large number of antennae with vinyl, amino, epoxy, sulfydryl, acryloxy and other terminals are formed on the surface of the modified first ceramic particle, the antennae at the terminals can form hydrogen bonds with the aramid fiber, the connection between the aramid fiber and the first ceramic particle is realized, and the binding force between the aramid fiber and the first ceramic particle is improved.

As one possible implementation of the composite separator of the present application, the weight of the coupling agent in the mixture layer is 0.3 to 2% of the total weight of the first ceramic particles. The content of the coupling agent is within the range, so that the function of a molecular bridge can be effectively exerted, and the binding force between the first ceramic particles and the aramid fiber is improved. 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 good air permeability, so that the composite separator can maintain good air permeability, the affinity of the separator with an electrolyte is improved, and the ionic conductivity is increased. If the content of the coupling agent is too high, the air permeability of the composite separator may be reduced.

As a possible implementation case of the composite membrane of the present application, the mixture layer includes a first surface in contact with the aramid layer and a second surface facing away from the first surface, and the aramid content in the mixture layer gradually increases along a direction from the second surface to the first surface. Under this condition, the one side that is close to the aramid fiber layer has better structural stability to make the mixture layer can be through the effective stable aramid fiber layer of first ceramic particle wherein, reduce the thermal shrinkage factor of aramid fiber.

As one possible embodiment of the composite separator of the present application, the weight percentage of the aramid fiber is 0.1 to 20% and the weight percentage of the first ceramic particles is 80 to 99.9% based on 100% of the total weight of the mixture layer. In this case, a small amount of aramid fiber as a crosslinking agent fixes the first ceramic particles in a granular form and forms a continuous film layer; meanwhile, the aramid fiber plays a role in crosslinking in the diaphragm particles and can resist the high temperature of more than 200 ℃, so that the mixture layer can be kept complete at the high temperature of more than 200 ℃, and the film breaking temperature of the mixture layer is improved. On the basis, the first ceramic particles in the mixture layer play a rigid supporting role in an aramid fiber molecular chain, and the molecular bond curling of an aramid fiber high-molecular bond in the aramid fiber layer at high temperature is relieved, so that the heat shrinkage performance of the composite diaphragm is improved, and the heat shrinkage rate of the composite diaphragm is less than 4% @150 ℃/1h. When the composite diaphragm is heated, the risk of internal short circuit at the tail of the electric core head caused by thermal contraction of the diaphragm can be relieved, and the safety of the battery is improved.

As a possible implementation of the composite separator of the present application, the thickness of the mixture layer is 0.1-6um. In this case, the thickness of the mixture layer may achieve the effect of reducing the thermal shrinkage of the composite separator; furthermore, since the thickness of the mixture layer is in 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 separator of the present application, the thickness of the mixture layer ranges from 1 to 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 both considered.

As one possible implementation case of the composite membrane of the present application, the aramid in the mixture layer is at least one of para-aramid and meta-aramid. The aramid fiber can realize the crosslinking of the first ceramic particles and improve the film breaking temperature of the mixture layer.

As one possible embodiment of the composite separator of the present application, the median diameter D50 of the first ceramic particles is 0.01 to 2.0 μm. In this case, the first ceramic particles have a suitable particle size and can form a compact and complete film layer under the crosslinking action of the aramid fibers.

As a possible implementation case of the composite membrane of the present application, the weight percentage of the aramid fiber is 50 to 100% based on the total weight of the aramid fiber layer as 100%. When the weight percentage of the aramid fiber is more than 50%, the aramid fiber layer can keep the characteristics of aramid fiber materials, and the film breaking temperature of the composite diaphragm is effectively improved.

In a possible implementation manner, the weight percentage of the aramid fiber is 100% based on 100% of the total weight of the aramid fiber layer, and at this time, the aramid fiber layer is made of aramid fiber, and plays a role in improving the film breaking temperature of the composite diaphragm.

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

As a possible implementation situation of the composite membrane, when the weight percentage of the aramid fiber is not 100%, the aramid fiber layer further includes 0 to 50% by weight of second ceramic particles. The second ceramic particles with the weight percentage of 0-50% are added into the aramid fiber layer, so that the porosity of the aramid fiber layer can be increased and is more than 20%. Moreover, the second ceramic particles introduced into the aramid fiber layer can improve the thermal stability of the aramid fiber layer and the thermal shrinkage performance of the aramid fiber layer, and finally the thermal shrinkage performance of the composite membrane is improved.

As one possible embodiment of the composite separator of the present application, the median diameter D50 of the second ceramic particles is 0.1 to 1 μm. In this case, the second ceramic particles exert a pore-forming action to increase the porosity of the aramid layer, and the median particle diameter D50 is in the above range, it is possible to impart appropriate porosity and pore size to the aramid layer.

As a possible implementation case of the composite membrane of the present application, the thickness of the aramid fiber layer is 0.1-6um. Under the condition, the thickness of the aramid fiber layer can achieve the effect of improving the film breaking temperature of the composite diaphragm; moreover, the thickness of the aramid fiber layer is in a controllable range, so that the influence of the aramid fiber layer on the energy density of the battery can be reduced.

As a possible implementation case 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 range, the effect of improving the film breaking temperature of the composite diaphragm and the influence of the aramid fiber layer on the energy density of the battery can be better considered.

As one possible implementation situation of the composite membrane of the present application, the aramid in the aramid layer is at least one of para-aramid and meta-aramid. The aramid fiber layer obtained under the condition has excellent high-temperature resistance, and can endow the composite diaphragm with excellent film breaking performance, so that the film breaking temperature is increased, and finally, the safety performance of a battery using the composite diaphragm is improved.

As one possible implementation of the composite separator of the present application, the thickness of the polyolefin layer is 0.2 to 20 μm. The composite layer containing the aramid fiber layer and the mixture layer is formed on the surface of one polyolefin layer, so that the film breaking temperature and the heat shrinkage performance of the polyolefin layer are improved, and therefore, the thickness of the polyolefin layer can be as low as 0.2 mu m, and the polyolefin layer with the thickness of 0.2-20 mu m serving as the diaphragm substrate can effectively isolate the positive electrode and the negative electrode of the battery.

As one possible implementation of the composite separator of the present application, the mixture layer is bonded to a surface of the polyolefin layer on one side, and the aramid layer is bonded to a surface of the mixture layer on a side facing away from the polyolefin layer. Under the condition, on one hand, the aramid fiber layer has better heat resistance, and can block the influence of high temperature on the polyolefin film layer by being used as a surface layer protective layer, so that the film breaking temperature of the composite diaphragm is more than 240 ℃; on the other hand, the mixture layer is arranged between the aramid fiber layer and the polyolefin layer, and simultaneously provides rigid support for the polyolefin layer and the aramid fiber layer, so that the thermal shrinkage of the composite diaphragm is relieved, and the thermal shrinkage of the composite diaphragm is reduced. In addition, from the process processing angle, the composite diaphragm can be prepared by forming first ceramic particles on the surfaces of polyolefin and then pouring aramid fibers on the surfaces of the first ceramic particles, wherein the poured aramid fibers downwards penetrate along pores among the first ceramic particles and are spread on the surfaces of the first ceramic particles, so that the preparation of a mixture layer and an aramid fiber layer is realized, and the process feasibility is improved.

As one possible implementation of the composite separator of the present application, the composite layer includes n stacked layers formed of a mixture layer and an aramid layer, where n is an integer of 2 to 5. In the composite layer obtained in this case, the mixture layer and the aramid layer are alternately arranged, so that the performance stability of the composite layer is improved.

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

forming a prefabricated film on one side or two sides of the polyolefin layer by adopting a first material;

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;

the first film is one of a mixture layer and an aramid layer, the second film is the other of the mixture layer and the aramid layer, the mixture layer comprises aramid and first ceramic particles, and a coupling agent is combined on the surfaces of the first ceramic particles.

According to the preparation method of the composite membrane, the mixture layer (or the aramid layer) and the aramid layer (or the mixture layer) can be sequentially prepared on the surface of one side or two sides of the polyolefin layer, wherein the coupling agent is combined on the surface of the first ceramic particle in the mixture layer. Because the coupling agent contains an inorganic group and an organic group, after the second material is added on the surface of the prefabricated film, the coupling agent combined on the surface of the first ceramic particle is connected with the aramid fiber forming the mixture layer as a molecular bridge in the prefabricated film or the second material, so that the bonding force between the first ceramic particle and the aramid fiber is enhanced, the aramid fiber is used as a cross-linking agent to cross-link and fix the ceramic particle, and a continuous and stable mixture layer is formed. Under the effect of the coupling agent, the mixture layer has good structural stability, the structural stability of the composite diaphragm under the high-temperature condition is favorably improved, the first ceramic particles also play a role in rigidly supporting aramid fiber molecular chains in the aramid fiber layer, the molecular bond curling of a high-molecular bond of the aramid fiber at high temperature is relieved, the thermal shrinkage performance of an adjacent layer, namely the aramid fiber layer, is further improved, and the thermal shrinkage rate of the composite diaphragm is less than 4% @150 ℃/1h. Under the condition, the prepared composite diaphragm can improve the diaphragm rupture temperature; meanwhile, the thermal shrinkage rate of the diaphragm can be reduced, and the effect that the thermal shrinkage rate is less than 4% @150 ℃/1h is achieved. The composite film prepared by the method can effectively improve the thermal stability of the diaphragm, and the safety of the battery is ensured.

As a first possible implementation manner of the preparation method of the composite membrane, 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, and the prefabricated film is a ceramic layer; the second material is aramid fiber slurry. Under the condition, the preparation of the mixture layer and the aramid layer is realized by forming the first ceramic particles on the surfaces of the polyolefin and then pouring the aramid slurry on the surfaces of the first ceramic particles, so that the process feasibility is improved. Specifically, the first ceramic particles are first spread on the surface of the polyolefin layer to form a ceramic layer, i.e., a prefabricated film. In this case, the ceramic layer formed by laying the ceramic particles is poor in stability. When the aramid fiber slurry is poured on the surface of the ceramic layer, namely the surface of the prefabricated film, the aramid fiber in the slurry can permeate downwards along the pores among the first ceramic particles and be evenly spread around the surface of the first ceramic particles. The aramid fiber which permeates downwards is filled in pores among the first ceramic particles, and the aramid fiber is used as a cross-linking agent to fix the granular first ceramic particles; meanwhile, the coupling agent is combined with the aramid fiber through hydrogen bonds, so that the first ceramic particles are crosslinked with the aramid fiber through the coupling agent, the first ceramic particles are fixed into a film, and after crystallization and solidification, a mixture layer with a stable structure is finally formed.

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

In some embodiments, the ceramic slurry is a slurry in which first ceramic particles having a coupling agent bonded to the surface thereof are dispersed in a dispersion liquid. In this case, a ceramic slurry is coated on one or both surfaces of the polyolefin layer, and a pre-formed film of first ceramic particles is formed on one or both surfaces of the polyolefin layer through a drying process, and a coupling agent is bonded to the surfaces of the first ceramic particles.

In some embodiments, the ceramic slurry is a slurry containing a coupling agent, first ceramic particles, and an auxiliary agent. In this case, a ceramic slurry is coated on one or both surfaces of the polyolefin layer, and a pre-formed film of first ceramic particles is formed on one or both surfaces of the polyolefin layer through a drying process, and a coupling agent is bonded to the surfaces of the first ceramic particles. Wherein, the auxiliary agent can be at least one of a dispersant, a thickening agent, a binder and a wetting agent. Wherein the dispersant is beneficial to improving the dispersibility of the first ceramic particles in the slurry; a wetting agent is added into the slurry, and when the ceramic slurry is coated on the surface of polyolefin, the wettability and the spreadability of the slurry on the surface of the polyolefin are improved; the thickening agent can improve the viscosity of the slurry; the binder can bind the first ceramic particles after the ceramic particles are coated on the surface of the polyolefin to be primarily fixed on the surface of the polyolefin to form a ceramic layer, i.e., a prefabricated film.

In some embodiments, the ceramic slurry is prepared by: and dispersing the first ceramic particles, the coupling agent and the auxiliary agent in deionized water, and mixing to obtain the ceramic slurry. Under the action of the auxiliary agent, the first ceramic particles are dispersed and form slurry, so that the first ceramic particles can be coated on the surface of the polyolefin layer. And coating the ceramic slurry on the surface of the polyolefin layer, and drying to remove the solvent to form a ceramic layer, namely a prefabricated film.

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

in the ceramic slurry formed under the condition, the first ceramic particles and the coupling agent have better dispersion uniformity, so that the coupling agent is favorably and uniformly combined on the surfaces of the first ceramic particles, and the aramid fibers entering the pores of the first ceramic particles are favorably combined with the first ceramic particles; meanwhile, the slurry has proper viscosity and spreadability, and is beneficial to initially fixing 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 bonded to the surface of the first ceramic particles through siloxane groups, and a large number of organophilic groups are present at the other end of the silane coupling agent. After a second material containing aramid fiber is added on the surface of the prefabricated film, the organophilic group at the other end of the coupling agent and the aramid fiber molecules entering the gaps of the first ceramic particles form hydrogen bonds, the aramid fiber and the first ceramic particles are tightly combined under the action of the hydrogen bonds, the binding force between the ceramic particles and the aramid fiber is enhanced, and finally a mixture layer with a stable structure is formed. In this case, the function of stabilizing the upper aramid layer and reducing the thermal shrinkage of the separator can be fully exerted by the rigid supporting function of the first ceramic particles in the mixture layer. Illustratively, the coupling agent is at least one of vinyl silane, amino silane, epoxy silane, mercapto silane, and methacryloxy silane, but is not limited thereto. The silane coupling agent contains a functional group capable of forming a hydrogen bond with the aramid fiber, so that the connection between the aramid fiber and the first ceramic particles is facilitated, and the binding force between the aramid fiber and the first ceramic particles is improved.

As a possible implementation case, the preparation method of the ceramic slurry comprises the following steps:

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

adding the dispersing agent into the silane coupling agent modified first ceramic particles, stirring and mixing, and then grinding to obtain a ceramic dispersion liquid;

and adding the thickening agent, the binder and the wetting agent into the ceramic dispersion liquid, and stirring and mixing to obtain the ceramic slurry.

The silane coupling agent and the first ceramic particles are mixed, then the dispersing agent is added for mixing treatment, so that the silane coupling agent and the first ceramic particles are uniformly dispersed, and then other auxiliary agents are added, which is beneficial to improving the dispersion uniformity of the silane coupling agent and the first ceramic particles, thereby improving the distribution uniformity of the silane coupling agent on the surfaces of the first ceramic particles. Under the condition, when a second material containing aramid fiber is added on the surface of the prefabricated film, the aramid fiber enters pores among the first ceramic particles, and is connected with the first ceramic particles by virtue of the silane coupling agent uniformly distributed on the surfaces of the first ceramic particles, so that the first ceramic particles are fixed, and finally, a mixture layer, namely the first film, is formed.

As a second possible implementation manner of the preparation method of the composite diaphragm, the first film is an aramid fiber layer, the second film is a mixture layer, the first material is aramid fiber slurry, and the second material is a ceramic material. In this case, the aramid pulp is coated on the surface of the polyolefin layer to form a prefabricated film; and then adding a ceramic material on the surface of the prefabricated film, drying, and finally forming a composite layer consisting of the aramid fiber layer and the mixture layer on the surface of the polyolefin layer.

The aramid fiber slurry is a slurry with aramid fiber as a base material. In one possible implementation, the aramid pulp is a pulp formed of aramid. In another possible implementation manner, the aramid pulp contains aramid and an auxiliary agent. In both possible implementations, the aramid pulp is formed on one or both surfaces of the polyolefin layer after the first material is applied to one or both surfaces of the polyolefin layer. In some embodiments, the adjuvant comprises a pore former.

As a possible implementation, the solid content of the aramid pulp is 1.5-10%. In this case, the aramid pulp has a suitable viscosity and spreading property, and forms an aramid layer on the surface of the base material (ceramic layer or polyolefin layer) evenly.

As a possible implementation situation, the preparation method of the aramid fiber slurry comprises the following steps:

preparing an organic solution of phenylenediamine, cooling to below 10 ℃, adding phthaloyl chloride, adding alkali to adjust the pH value to be neutral, and adding a pore-forming agent to prepare the aramid fiber slurry.

The method can be used for preparing the aramid fiber slurry directly from the raw materials, and is simple and high in operation controllability.

As a possible implementation, the coating comprises one of dip coating, spray coating, doctor blade, coating wire bar and micro-gravure coating.

As a possible implementation scenario, the preparation method further comprises: before the drying treatment, the sample obtained after the second slurry was applied was immersed in a plasticizing bath. Before drying, the sample coated with the second slurry is immersed in a plasticizing bath to enable the aramid fiber to be in a high-plasticity state, so that aramid fiber stretching is facilitated.

The third aspect of the present application provides an electrochemical device comprising a positive plate, a negative plate, an electrolyte and a separator disposed between the positive plate and the negative plate, wherein the separator is the composite separator of the first aspect of the present application.

The application provides an electrochemical device, owing to contain above-mentioned compound diaphragm, have low thermal shrinkage percentage and high rupture of membranes temperature, can solve diaphragm shrink and fused problem, reduce the risk that battery short circuit takes place thermal runaway, further improve the security performance of 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 interface cohesiveness between the composite diaphragm and the electrode plate, improve the integral hardness and strength of the battery, and prevent the deformation of the battery core.

As a possible implementation of the electrochemical device of the present application, the polymer layer is a material layer formed of 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 a polymer laminate formed by at least two of PVDF, PMMA, dopamine, CMC, SBR, PTFE and PVA, and the polymer in the polymer laminate may be one or more of the above polymers. The polymer material can improve the bonding strength between the composite film and the electrode plate, and the structure of the battery is kept stable.

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

The present application fourth aspect provides an electronic device, including the casing with accept electronic components and electrochemical device in the casing, electrochemical device is the electrochemical device of this application third aspect, just electrochemical device is used for electronic components supplies power.

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

A fifth aspect of the present application provides a mobile device containing the electrochemical device according to the third aspect.

Drawings

FIG. 1 is a schematic diagram of a first construction of a composite diaphragm provided in an embodiment of the present application;

FIG. 2 is a schematic diagram of a second structure of a composite diaphragm provided in an embodiment of the present application;

FIG. 3 is a flow chart of a process for preparing a composite separator as provided by an embodiment of the present application;

fig. 4 is a flow chart of another process for preparing a composite separator according to the embodiments of the present disclosure.

Detailed Description

In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly apparent, the present application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

In this application, the term "and/or" describes an association relationship of associated objects, which means that there may be three relationships, for example, a and/or B, which may mean: a is present alone, A and B are present simultaneously, and B is present alone. Wherein A and B can be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship.

In the present application, "at least one" means one or more, "a plurality" means two or more. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of the singular or plural items. For example, "at least one (a), b, or c", or "at least one (a), b, and c", may each represent: a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, wherein a, b, and c can be single or multiple respectively.

It should be understood that, in various embodiments of the present application, the sequence numbers of the above-mentioned processes do not mean the execution sequence, some or all of the steps may be executed in parallel or executed sequentially, and the execution sequence of each process should be determined by its function and inherent logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

The terminology used in the embodiments of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the examples of this application and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

The weight of the related components mentioned in the description of the embodiments of the present application may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, and therefore, the content of the related components is scaled up or down within the scope disclosed in the description of the embodiments of the present application as long as it is scaled up or down according to the description of the embodiments of the present application. Specifically, the mass described in the specification of the embodiments of the present application may be a mass unit known in the chemical industry field such as μ g, mg, g, kg, etc.

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

The term "MD" is an abbreviation for "Machine direction", indicating the Machine direction;

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

the term "PE" is an abbreviation for "Polyethylene," which means Polyethylene;

the term "DSC" is an abbreviation for "Differential scanning calorimetry";

the term "SOC" is an abbreviation for "State of charge", representing the State of charge;

the term "PVDF" is an abbreviation for "polyvinylidene fluoride," which refers to polyvinylidene fluoride;

the term "PMMA" is an abbreviation for "poly methyl methacrylate", which means polymethyl methacrylate;

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

the term "NMP" is an abbreviation for "N-Methyl-2-pyrrolidone", representing N-methylpyrrolidone, also known as 1-Methyl 2-pyrrolidone;

the term "CNTs" is an abbreviation for "Carbon nanotubes," meaning Carbon nanotubes;

the term "CMC" is an abbreviation of "Carboxymethyl Cellulose", representing Carboxymethyl Cellulose;

the term "SP" is an abbreviation for "Super P" and denotes conductive carbon black;

the term "PP" is an abbreviation for "Polypropylene" and denotes Polypropylene;

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

the term "PVA" is an abbreviation for "Polyvinyl alcohol" and denotes Polyvinyl alcohol.

The english expression of the term "Battery" is "Battery", meaning: the potential difference is generated by the difference of the potentials of the two electrodes, so that electrons flow, and a device for generating current can convert chemical energy into electric energy.

The term "positive electrode" is expressed in english as "Cathode". In the primary battery, the positive electrode refers to an electrode with current flowing out or higher potential, and electrons obtained by the positive electrode play a role in reduction; in the electrolytic cell, the positive electrode is an electrode connected with the positive electrode of a power supply, and electrons are lost to play an oxidation role.

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

The term "Electrolyte", expressed in english as "Electrolyte", refers to: a medium for ion exchange is provided between the positive and negative electrodes of the cell.

The term "membrane" is denoted "Separator" in english, and means: and the medium is used for separating the positive electrode and the negative electrode in the battery core and preventing the positive electrode and the negative electrode from being in direct contact with each other to cause short circuit. The basic properties of the separator are porosity (channels that provide ion transport) and electrical insulation (prevention of electrical leakage).

The term "thermal abuse," which is English-language for "Heat abuse," refers to: and (3) carrying out abuse test on the battery cell in the aspect of heat (or high temperature), such as a hot box test (the battery cell is baked at the high temperature of more than or equal to 130 ℃).

The english expression "mechanical abuse" of the term "mechanical abuse" may refer to the mechanical abuse of the electrical core. The cells may be tested for mechanical abuse using a needle test, impact test, or the like.

The english expression of the term "Elongation" is "Elongation", which may also be referred to as Elongation at break, and represents the percentage of the length increase at which the separator is stretch broken relative to the initial length. Specifically, the separator may be subjected to a tensile test under specific conditions, and the increase in the length of the separator divided by the initial length of the separator at the time the separator is just pulled apart may be used to characterize the elongation. A larger value of the elongation means that the separator is less likely to be pulled apart, and the elongation is better. The elongation may be divided into a machine direction (MD, i.e., in the long-side direction of the separator) elongation and a transverse direction (TD, perpendicular to the MD, i.e., in the short-side direction of the separator) elongation.

The english expression of the term "Tensile strength" denotes "Tensile strength," which denotes the critical strength value of the plastic deformation of the separator, and can characterize the maximum load-bearing capacity of the separator under uniform Tensile conditions. Tensile strength may refer to the stress resulting from dividing the maximum load force experienced by the membrane by the initial cross-sectional area of the membrane at the time the membrane is just pulled apart. The tensile strength is divided into a machine direction (MD, i.e., in the long-side direction of the separator) tensile strength and a transverse direction (TD, perpendicular to the MD, i.e., in the short-side direction of the separator) tensile strength.

The English expression of the term "Puncture strength" is "Puncture strength", which can mean that a spherical steel needle with the diameter of 1.0mm is used for puncturing the septum at the speed of 300 +/-10 mm/min, and the force required by the steel needle to penetrate the septum is the Puncture strength of the septum.

The term "Heat shrinkage" is expressed in english as "Heat shrinkage" and indicates the rate of change in the dimension of the separator in the longitudinal/transverse (machine direction MD, i.e., in the direction of the long side of the separator; transverse direction TD, perpendicular to MD, i.e., in the direction of the short side of the separator) direction before and after heating. The test method of the thermal shrinkage rate may include: measuring a dimension of the separator in a longitudinal/transverse (MD/TD) direction; placing a membrane having a dimension in a longitudinal/transverse (MD/TD) direction in an incubator; heating the incubator to a specific temperature; the dimension of the separator in the longitudinal/transverse (MD/TD) direction after heating was measured.

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

The english expression of the term "closed cell temperature" is "the" ovorator temperature "and refers to the temperature at which, during the heating process, the membrane begins to melt and block a portion of the pores that were previously formed.

The english expression of the term "Rupture temperature" is "Rupture temperature", and indicates a temperature at which the separator melts to some extent and ruptures, resulting in a local or global short circuit.

In the battery, the diaphragm is mainly used for preventing the short circuit of the positive electrode and the negative electrode, and plays a key role in the safety of the battery. When the battery is subjected to mechanical abuse and thermal abuse, the diaphragm is easy to melt and thermally contract under a high-temperature scene, so that the short circuit of the positive electrode and the negative electrode is caused, and further potential safety hazards are caused. In view of the above, the present application provides a composite separator that can improve the safety performance of a battery.

Specifically, the embodiment of the application provides a composite membrane, which comprises a polyolefin layer and a composite layer combined on one side surface of the polyolefin layer, wherein the composite layer comprises a mixture layer and an aramid layer combined on one side surface of the mixture layer, and the mixture layer or the aramid layer and the polyolefin layer are arranged on the surface of the polyolefin layer.

In the embodiment of the application, the polyolefin layer is used as a main functional layer of the composite diaphragm, and plays a role of separating the positive electrode and the negative electrode in the battery cell, so that the positive electrode and the negative electrode are prevented from being in direct contact with each other to cause short circuit. Polyolefins have porous properties, and therefore polyolefins are also called porous polyolefins, which provide channels for ion transport; meanwhile, polyolefin has electronic insulation and can prevent electric leakage. The polyolefin layer in the embodiments of the present application is also referred to as a porous polyolefin layer.

In some embodiments, the polyolefin material in the polyolefin layer may employ at least one of Polyethylene (PE), polypropylene (PP). In some embodiments, the polyolefin layer is prepared using a polyolefin material; in some embodiments, the polyolefin layer is made using a composition of two or more polyolefins. In this embodiment, the two or more polyolefins may be two or more different types of polyolefin materials, and the polyolefin material of the polyolefin layer is a combination of Polyethylene (PE) and polypropylene (PP); two or more polyolefins of the same type but having different viscosity average molecular weights are also possible, and the polyolefin material of the polyolefin layer is illustratively a composition of a plurality of polyethylenes having different viscosity average molecular weights.

In some embodiments, the polyolefin layer has a thickness of 0.2 to 20 μm. According to the embodiment of the application, the composite layer containing the aramid fiber layer and the mixture layer is formed on the surface of one polyolefin layer, so that the film breaking temperature and the heat shrinkage performance of the polyolefin layer are improved, and therefore, the thickness of the polyolefin layer provided by the application can be as low as 0.2 mu m, and the polyolefin layer with the thickness of 0.2-20 mu m can be used as the polyolefin layer of the diaphragm substrate, so that the positive electrode and the negative electrode of the battery can be effectively isolated. Illustratively, the polyolefin layer may have a thickness of 0.2 μm, 0.5 μm, 0.8 μm, 1.0 μm, 2.0 μm, 3.0 μm, 4.0 μm, 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm, 9.0 μm, 10.0 μm, 11.0 μm, 12.0 μm, 13.0 μm, 14.0 μm, 15.0 μm, 16.0 μm, 17.0 μm, 18.0 μm, 19.0 μm, 20.0 μm. In some embodiments, the polyolefin layer has a thickness of 0.5 to 17um.

This application embodiment sets up the composite bed on polyolefin layer one side or both sides surface, and the composite bed includes the mixture layer to and combine the aramid fiber layer at mixture layer one side surface, and mixture layer and aramid fiber layer all with the range upon range of setting on polyolefin layer, mixture layer and aramid fiber layer and polyolefin layer parallel arrangement promptly.

In one embodiment, the composite layer is formed on one surface of the polyolefin layer and the other surface is left untreated (i.e., blank design is retained). In this case, since the polyolefin has a closed cell temperature of about 140 ℃, this characteristic enables the cell containing the polyolefin separator to self-block ion transport channels (the micropores of the polyolefin are closed) around the closed cell temperature. The blank design is reserved on the surface of one side of the polyolefin layer, so that the original closed-cell temperature characteristic of the polyolefin can be reserved, and the battery has better safety performance. In another embodiment, the composite layers are formed on both surfaces of the polyolefin layer simultaneously to increase the rupture temperature and reduce the thermal shrinkage rate of the composite separator.

The aramid fiber material in the aramid fiber layer has a limit oxygen index of more than 28%, belongs to flame-retardant fiber and has flame retardance. The aramid fiber material has flame retardant property, and the aramid fiber layer is used as the protective layer of the polyolefin diaphragm, so that the diaphragm breaking temperature of the diaphragm can be increased, and the diaphragm breaking temperature of the composite film is higher than 200 ℃, so that the composite diaphragm can resist the high temperature of higher than 200 ℃ and cannot melt when the battery is abused by heat and machinery, the positive electrode and the negative electrode of the battery can be effectively isolated, the severe internal short circuit caused by the direct contact of the positive electrode and the negative electrode is avoided, and the safety of the battery is improved.

In some embodiments, the weight percentage of aramid fiber is 50 to 100% based on the total weight of the aramid fiber layer being 100%. When the weight percentage of the aramid fiber is more than 50%, the characteristics of the aramid fiber material can be kept, and the formed aramid fiber layer can effectively improve the film breaking temperature of the composite diaphragm. This embodiment includes two cases, respectively: the case where the weight percentage of the aramid fiber is 100%, and the case where the weight percentage of the aramid fiber is not 100%.

In a first embodiment, the weight percentage of aramid fiber is between 50% and 100%, and not 100%, based on 100% of the total weight of the aramid fiber layer. At this time, the aramid layer contains aramid and other materials. Illustratively, the weight percentage of the aramid fiber may be 50%, 55%, 50%, 55%, 100%, etc. based on the total weight of the aramid fiber layer being 100%.

In some embodiments, the other material includes a pore former to impart a certain porosity to the aramid layer. Wherein the pore former is one or more of inorganic pore formers, illustratively one or more of lithium chloride, sodium chloride, magnesium chloride, calcium carbonate, calcium chloride, second ceramic particles.

In some embodiments, when the weight percentage of the aramid fiber is not 100%, the aramid fiber layer includes 0 to 50% by weight of second ceramic particles, and the second ceramic particles serve as a pore-forming agent. The second ceramic particles with the weight percentage of 0-50% are added into the aramid fiber layer, so that the porosity of the aramid fiber layer can be increased and is more than 20%. Moreover, the second ceramic particles introduced into the aramid fiber layer can improve the thermal stability of the aramid fiber layer and the thermal shrinkage performance of the aramid fiber layer, and finally the thermal shrinkage performance of the composite membrane is improved. In addition, when a small amount of second ceramic particles play a pore-forming role, the influence of the second ceramic particles on the performance of the aramid layer is reduced. For example, the weight percentage of the second ceramic particles may be 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc. based on the total weight of the aramid layer being 100%.

The median particle diameter D50 of the second ceramic particles as pore former may be 0.01 to 2 μm. In some embodiments, the median particle diameter D50 of the second ceramic particles is from 0.1 to 1 μm. Under the condition, 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 range, so that the aramid fiber layer can be endowed with proper porosity and pore size, and the aramid fiber layer with better air permeability and heat resistance can be obtained. Illustratively, the average median particle diameter D50 of the second ceramic particles may be 0.01. Mu.m, 0.02. Mu.m, 0.05. Mu.m, 0.08. Mu.m, 0.1. Mu.m, 0.2. Mu.m, 0.3. Mu.m, 0.4. Mu.m, 0.5. Mu.m, 0.6. Mu.m, 0.7. Mu.m, 0.8. Mu.m, 0.9. Mu.m, 1.0. Mu.m, 1.1. Mu.m, 1.2. Mu.m, 1.3. Mu.m, 1.4. Mu.m, 1.5. Mu.m, 1.6. Mu.m, 1.7. Mu.m, 1.8. Mu.m, 1.9. Mu.m, 2.0. Mu.m.

In some embodiments, the second ceramic particles are at least one of alumina, silica, alumina, zirconia, magnesia, zinc oxide, barium oxide, magnesium hydroxide, calcium oxide, boehmite, titania, and barium sulfate.

In a second implementation case, the weight percentage of the aramid fiber is 100% based on 100% of the total weight of the aramid fiber layer, and in this case, the aramid fiber layer is made of the aramid fiber and plays a role in increasing the film breaking temperature of the composite diaphragm. It should be understood that when the weight percentage of aramid in the aramid layer is 100%, the aramid layer also has a certain porosity, except that the pore former has been eliminated during or after the formation of the aramid layer. Illustratively, when organic pore-forming agents such as any one or more of methanol, ethanol, propanol, glycerol, polyethylene glycol, acetone, acetic acid, tetrahydrofuran, polyvinylpyrrolidone, ethyl acetate, petroleum ether, white oil and paraffin are used, the pore-forming agents and the aramid fibers are used as raw materials to form a prefabricated film, and the organic pore-forming agents volatilize during the heating forming process to form a pore structure in the aramid fiber layer.

In some embodiments, the aramid layer has a thickness of 0.1 to 6um. In this case, the thickness of the aramid fiber layer can achieve the effect of increasing the film breaking temperature of the composite diaphragm. Since the aramid material does not contribute to the capacity of the battery as the separator material, when the aramid content is excessive, the volume percentage of the aramid material in the battery is increased, and the energy density of the battery is lowered. When the thickness of the aramid fiber layer is 0.1-6um, the thickness of the aramid fiber layer is in a controllable range, and the influence of the aramid fiber layer on the energy density of the battery can be reduced. Illustratively, the thickness of the aramid layer may be a specific thickness such as 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, 6.0 um.

In some embodiments, the aramid layer has a thickness of 0.5-3um. When the thickness of the aramid fiber layer is within the range, the effect of improving the film breaking temperature of the composite diaphragm and the influence of the aramid fiber layer on the energy density of the battery can be better considered.

In some embodiments, the aramid in the aramid layer is at least one of para-aramid and meta-aramid. The aramid fiber layer obtained under the condition has excellent high-temperature resistance, and can endow the composite diaphragm with excellent film breaking performance, so that the film breaking temperature is increased, and finally, the safety performance of a battery using the composite diaphragm is improved.

In an embodiment of the present application, the composite layer further includes a mixture layer including aramid fibers and first ceramic particles. Wherein the surface of the first ceramic particle is bonded with a coupling agent. Namely, the ceramic particles of 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, so that one end of the coupling agent serving as a molecular bridge is connected with the surface of the first ceramic particle, and the other end of the coupling agent is connected with the aramid fiber in the mixture layer, so that the binding force between the first ceramic particle and the aramid fiber is enhanced, the aramid fiber serves as a crosslinking agent to crosslink and fix the first ceramic particle, and a continuous and stable film layer is formed. Under the effect of the coupling agent, the mixture layer has good structural stability, the structural stability of the composite diaphragm under the high-temperature condition is favorably improved, the first ceramic particles also play a role in rigid support of aramid fiber molecular chains in the aramid fiber layer, the molecular bond curling of high-molecular bonds of the aramid fiber at high temperature is relieved, the thermal shrinkage influence of aramid fiber materials, particularly aramid fiber molecules in the aramid fiber layer is reduced, the thermal shrinkage performance of the aramid fiber layer is further improved, and the thermal shrinkage rate of the composite diaphragm is smaller than 4% @150 ℃/1h. In addition, the aramid fiber of the layer plays a role in cross-linking the ceramic particles, and the aramid fiber can resist the high temperature of more than 200 ℃, so that the mixture layer can continuously keep complete at the high temperature of more than 200 ℃, and the film breaking temperature of the layer is improved. The battery containing the mixture layer can relieve the risk of internal short circuit at the tail part of the battery core head due to the thermal shrinkage of the diaphragm when the composite diaphragm is heated, and the safety of the battery is improved.

In some embodiments, the coupling agent is a silane coupling agent. At this time, the silane coupling agent is bonded to the surface of the first ceramic particles through the siloxane group. There are a large amount of organophilic groups on the first ceramic particle surface through silane coupling agent modification, and this organophilic group can form the hydrogen bond effect with the aramid fiber molecular chain of dispersion in ceramic particle, and the hydrogen bond effect makes aramid fiber and first ceramic particle closely combine to form stable in structure's mixture layer, and then stabilizes the aramid fiber layer with the help of ceramic particle's rigid support effect in the mixture layer. Namely, the silane coupling agent can be used for erecting a 'molecular bridge' between the ceramic particles and the aramid fiber interface and improving the binding force between the ceramic particles and the aramid fiber.

Illustratively, the silane coupling agent is selected from at least one of vinyl silane, amino silane, epoxy silane, mercapto silane, and methacryloxy silane. Wherein, the epoxy silane is also called epoxy silane cross-linking agent; mercaptosilane refers to a silane coupling agent containing a mercapto group in the molecule, such as, for example, 3-mercaptopropyltriethoxysilane; methacryloxy silane refers to a silane coupling agent having a methacryloxy group in the molecular structure, and is exemplified by methacryloxy methyltrimethoxy silane. The siloxane group in the silane coupling agent is combined on the surface of the first ceramic particle, so that a large number of terminal antennae with vinyl, amino, epoxy, sulfydryl, acryloxy and other groups are formed on the surface of the modified first ceramic particle, the terminal antennae can form hydrogen bonds with the aramid fiber, the connection between the aramid fiber and the first ceramic particle is realized, and the binding force between the aramid fiber and the first ceramic particle is improved.

In some embodiments, the weight of the coupling agent in the mixture layer is 0.3 to 2% of the total weight of the first ceramic particles. The content of the coupling agent is within the range, so that the function of a molecular bridge can be effectively exerted, and the binding force between the first ceramic particles and the aramid fiber is improved. 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 good air permeability, so that the composite separator can maintain good air permeability, the affinity of the separator with an electrolyte is improved, and the ionic conductivity is increased. If the content of the coupling agent is too high, the air permeability of the composite separator may be reduced. Illustratively, the coupling agent is present in an amount of 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2.0wt%, etc., based on the total weight of the ceramic particles.

In some embodiments, the aramid fiber is present in an amount of 0.1 to 20% by weight and the first ceramic particles are present in an amount of 80 to 99.9% by weight, based on 100% by weight of the total mixture layer. In this case, a small amount of aramid fiber as a cross-linking agent fixes the first ceramic particles in a granular form and forms a continuous film layer; meanwhile, the aramid fiber plays a role in crosslinking in the diaphragm particles and can resist the high temperature of more than 200 ℃, so that the mixture layer can be kept complete at the high temperature of more than 200 ℃, and the film breaking temperature of the mixture layer is improved. On the basis, the first ceramic particles in the mixture layer play a rigid supporting role in an aramid fiber molecular chain, the molecular bond curling of an aramid fiber high-molecular bond in the aramid fiber layer at high temperature is relieved, and the structure of the aramid fiber layer is maintained, so that the heat shrinkage performance of the composite diaphragm is improved, and the heat shrinkage rate of the composite diaphragm is less than 4% @150 ℃/1h. When the composite diaphragm is heated, the risk of internal short circuit at the tail of the electric core head caused by thermal contraction of the diaphragm can be relieved, and the safety of the battery is improved. Illustratively, the weight percent aramid fiber may be present in specific weight percentages of 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., based on the total weight of the mixture layer taken as 100%.

In some embodiments, the aramid in the mixture layer is at least one of para-aramid and meta-aramid. The aramid fibers can realize crosslinking of the first ceramic particles by means of the coupling agent, fix the first ceramic particles into a film and improve the film breaking temperature of the mixture layer.

In some embodiments, the mixture layer is composed of a mixture group formed of the first ceramic particles and the aramid. In some embodiments, the mixture layer contains a minor amount of an additive in addition to the first ceramic particles and the aramid. In some embodiments, the adjuvant may be selected from at least one of a dispersant, a thickener, a binder, and a wetting agent. When a material containing the first ceramic particles is formed on the surface of the film layer, the dispersant is beneficial to improving the dispersibility of the first ceramic particles in the material such as slurry; the wetting agent is beneficial to improving the wettability and the spreadability of the first ceramic particles on the surface of the polyolefin layer or the aramid fiber layer; the thickening agent can form ceramic slurry with proper viscosity, so that the first ceramic particles are formed on the surface of the polyolefin layer or the aramid fiber layer; the binder may bind and preliminarily fix the first ceramic particles to the polyolefin surface after the ceramic particles are formed on the polyolefin surface.

Illustratively, the dispersant is one or more of nonionic dispersants such as polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol and polyethylene oxide; illustratively, the thickener is at least one of sodium carboxymethylcellulose, hydroxyethylcellulose, sodium alginate, hydroxypropylmethylcellulose, and lithium hydroxymethylcellulose; illustratively, the binder is at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyamide, sodium carboxymethylcellulose, styrene-butadiene rubber, acrylate, methacrylic acid-methyl/methyl acrylate-maleic anhydride terpolymer, methacrylic acid-methyl methacrylate-vinylcarbazole terpolymer, and polyimide derivative; illustratively, the wetting agent is one or more of polyether siloxane copolymer, tween-90, fluorinated alkyl ethoxy alcohol ether, fatty alcohol polyoxyethylene ether, sodium butyl naphthalene sulfonate, sodium hydroxyethyl sulfonate and sodium dodecyl sulfonate.

In some embodiments, the thickness of the mixture layer is 0.1-6um. In this case, the thickness of the mixture layer may achieve an effect of reducing the thermal shrinkage of the composite separator. Since the first ceramic particles and the aramid fibers in the mixture layer do not contribute to the capacity of the battery as the separator material, when the content of the first ceramic particles and the aramid fibers is too large, the volume percentage occupied in the battery is also increased, which may lower the energy density of the battery. When the thickness of the mixture layer is 0.1-6um, the thickness of the aramid fiber layer is in a controllable range, and the influence of the mixture layer on the energy density of the battery can be reduced. Illustratively, the thickness of the mixture layer can be a specific thickness such as 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, 6.0 um.

In some embodiments, the thickness of the mixture layer ranges from 1-4um. When the thickness of the mixture layer is within the above range, the effect of reducing the thermal shrinkage of the composite separator and the effect of reducing the influence of the mixture layer on the energy density of the battery can be better both considered.

In some embodiments, the first ceramic particles have a median particle diameter D50 of 0.01 to 2.0 μm. In this case, the first ceramic particles have a suitable particle size, and can form a compact and complete film layer under the crosslinking action of the aramid fiber. Illustratively, the average median particle diameter D50 of the ceramic particles may be 0.01. Mu.m, 0.02. Mu.m, 0.05. Mu.m, 0.08. Mu.m, 0.1. Mu.m, 0.2. Mu.m, 0.3. Mu.m, 0.4. Mu.m, 0.5. Mu.m, 0.6. Mu.m, 0.7. Mu.m, 0.8. Mu.m, 0.9. Mu.m, 1.0. Mu.m, 1.1. Mu.m, 1.2. Mu.m, 1.3. Mu.m, 1.4. Mu.m, 1.5. Mu.m, 1.6. Mu.m, 1.7. Mu.m, 1.8. Mu.m, 1.9. Mu.m, 2.0. Mu.m.

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

In a first embodiment, the composite layer has a mixture layer bonded to at least one surface of the polyolefin layer and an aramid layer bonded to a surface of the mixture layer facing away from the polyolefin layer. Namely, the mixture layer and the aramid layer are sequentially laminated and combined on at least one surface of the polyolefin layer.

In one possible embodiment, the polyolefin layer has a surface on one side forming a composite layer, the mixture layer of the composite layer being bonded to the polyolefin layer on one side, and the aramid layer being bonded to the mixture layer on the side facing away from the polyolefin layer. At this time, as shown in fig. 1, the composite separator 10 includes a polyolefin 11, a mixture layer 12 bonded to a surface of the polyolefin 11, and an aramid layer 13 bonded to a surface of the mixture layer 12 facing away from the polyolefin 11. Under the condition, on one hand, the aramid fiber layer has better heat resistance, and can block the influence of high temperature on the polyolefin film layer by being used as a surface layer protective layer, so that the film breaking temperature of the composite diaphragm is more than 240 ℃; on the other hand, the mixture layer is arranged between the aramid fiber layer and the polyolefin layer, and simultaneously provides rigid support for the polyolefin layer and the aramid fiber layer, so that the thermal shrinkage of the composite diaphragm is relieved, and the thermal shrinkage rate of the composite diaphragm is reduced. In addition, from the process processing angle, the composite diaphragm can be prepared by forming first ceramic particles on the surfaces of polyolefin and then pouring aramid fibers on the surfaces of the first ceramic particles, the poured aramid fibers penetrate downwards along pores among the first ceramic particles and are spread around the surfaces of the first ceramic particles, the preparation of a mixture layer and an aramid fiber layer is realized, and the process feasibility is improved.

In one possible embodiment, the polyolefin layer is formed on both side surfaces thereof as a composite layer, the mixture layer of the composite layer being bonded to both side surfaces of the polyolefin layer, and the aramid layer being bonded to a side surface of the mixture layer facing away from the polyolefin layer.

In a second embodiment, the aramid layer is bonded to at least one surface of the polyolefin layer and the mixture layer is bonded to a surface of the aramid layer facing away from the polyolefin layer. Namely, the aramid fiber layer and the mixture layer are sequentially laminated and combined on at least one side surface of the polyolefin layer. The composite layer formed in the mode can also improve the film breaking temperature of the composite diaphragm and reduce the thermal shrinkage performance. However, since the first ceramic particles are rigid particles, the mixture layer mainly composed of the first ceramic particles is inferior to a mixture layer obtained by directly casting aramid fibers on the surfaces of the first ceramic particles in the film formation on the surface of the aramid fiber layer.

In one possible implementation, the polyolefin layer has a side surface formed into a composite layer, the aramid fiber layer is bonded to the polyolefin layer, and the mixture layer is disposed on the side surface of the aramid fiber layer facing away from the polyolefin layer. At this time, as shown in fig. 2, the composite separator 10 includes a polyolefin 11, an aramid layer 13 bonded to a surface of the polyolefin 11, and a mixture layer 12 bonded to a surface of the aramid layer 13 facing away from the polyolefin 11. In other embodiments of this embodiment, the polyolefin layer has a side surface forming a composite layer, the aramid layer of the composite layer is bonded to the polyolefin layer, and the mixture layer is disposed on a side surface of the aramid layer facing away from the polyolefin layer.

In one possible implementation mode, the polyolefin layer is provided with a composite layer on two side surfaces, the aramid fiber layer in the composite layer is combined on the two side surfaces of the polyolefin layer, and the mixture layer is combined on the side surface of the aramid fiber layer, which is far away from the polyolefin layer.

In some embodiments, the composite layer comprises n laminates of the mixture layer and the aramid layer, wherein n is an integer from 2 to 5. In the composite layer obtained under the condition, the mixture layer and the aramid fiber layer are alternately arranged, so that the performance stability of the composite layer is improved. Illustratively, n is 2, 3, 4, or 5. In some embodiments, n is 2 or 3.

The composite membrane provided by the embodiment of the application can be prepared by the following method.

Correspondingly, in a second aspect, embodiments of the present application provide a method for preparing a composite separator, including the following steps:

s01, forming a prefabricated film on the surface of one side or two sides of the polyolefin layer by adopting a first material;

s02, adding a second material on the surface of the prefabricated film, heating and drying to form 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 application, the first film is one of the mixture layer and the aramid fiber layer, the second film is the other one of the mixture layer and the aramid fiber layer, the material of the mixture layer comprises aramid fiber and first ceramic particles, and the surface of each first ceramic particle is combined with a coupling agent.

The embodiment of the present application is divided into two implementation cases 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 the moment, correspondingly, the first material is a ceramic material containing first ceramic particles, and the prefabricated film is a ceramic layer formed by the first ceramic particles; the second material is aramid fiber slurry. Under the condition, the preparation of the mixture layer and the aramid fiber layer is realized by forming the first ceramic particles on the surfaces of the polyolefin and pouring the aramid fiber slurry on the surfaces of the first ceramic particles, so that the process feasibility is improved. Specifically, the first ceramic particles are first spread on the surface of the polyolefin layer to form a ceramic layer, i.e., a prefabricated film. In this case, the ceramic layer formed by laying the ceramic particles is poor in stability. When the aramid pulp is poured on the surface of the ceramic layer, namely the surface of the prefabricated film, the aramid in the pulp can downwards permeate along the pores among the first ceramic particles and be evenly spread on the surface of the first ceramic particles all around. The downward-penetrating aramid fibers can be filled in pores among the first ceramic particles, and the aramid fibers are used as a cross-linking agent to fix the granular first ceramic particles; meanwhile, the coupling agent is combined with the aramid fiber through hydrogen bonds, so that the first ceramic particles are crosslinked with the aramid fiber through the coupling agent, the first ceramic particles are fixed into a film, and after crystallization and solidification, a mixture layer with a stable structure is finally formed.

In this embodiment, the method for manufacturing the composite separator, as shown in fig. 3, includes the steps of:

s11, forming a ceramic layer on the surface of one side or two sides of the polyolefin layer by adopting a ceramic material.

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 first ceramic particles having a coupling agent bound to the surface thereof in a dispersion liquid. In this case, a ceramic slurry is coated on one or both surfaces of the polyolefin layer, and after a drying process to remove a solvent, a ceramic layer formed of first ceramic particles is formed on one or both surfaces of the polyolefin layer, and a coupling agent is bonded to the surfaces of the first ceramic particles. It is understood that, since the first ceramic particles are inorganic materials in a particle form, the ceramic layer formed by the method has the first ceramic particles formed in a particle form on the surface of the polyolefin layer, and the resulting ceramic layer has poor structural stability.

In some embodiments, the ceramic mass is a ceramic slurry comprising a coupling agent, first ceramic particles, and an auxiliary agent. In this case, a ceramic slurry is coated on one or both surfaces of the polyolefin layer, and a ceramic layer formed of first ceramic particles is formed on one or both surfaces of the polyolefin layer through a drying process, and a coupling agent is bonded to the surfaces of the first ceramic particles. Wherein, the auxiliary agent can be at least one of a dispersant, a thickening agent, a binder and a wetting agent. Wherein the dispersant is beneficial to improving the dispersibility of the first ceramic particles in the slurry; a wetting agent is added into the slurry, and when the ceramic slurry is coated on the surface of polyolefin, the wettability and the spreadability of the slurry on the surface of the polyolefin are improved; the thickening agent can improve the viscosity of the slurry; the binder can bind the first ceramic particles after the ceramic particles are coated on the surface of the polyolefin, and fix the first ceramic particles on the surface of the polyolefin primarily to form a first ceramic particle film, i.e., a prefabricated film.

Illustratively, the thickener is at least one of sodium carboxymethylcellulose, hydroxyethylcellulose, sodium alginate, hydroxypropylmethylcellulose, and lithium hydroxymethylcellulose; illustratively, the binder is at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyamide, sodium carboxymethylcellulose, styrene-butadiene rubber, acrylate, methacrylic acid-methyl/methyl acrylate-maleic anhydride terpolymer, methacrylic acid-methyl methacrylate-vinylcarbazole terpolymer, and polyimide derivative; illustratively, the wetting agent is one or more of polyether siloxane copolymer, tween-90, fluorinated alkyl ethoxy alcohol ether, fatty alcohol-polyoxyethylene ether, sodium butyl naphthalene sulfonate, sodium hydroxyethyl sulfonate and sodium dodecyl sulfonate; illustratively, the dispersant is one or more of nonionic dispersants such as polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol and polyethylene oxide.

In some embodiments, the ceramic slurry is prepared by: and dispersing the first ceramic particles, the coupling agent and the auxiliary agent in deionized water, and mixing to obtain the ceramic slurry. Under the action of the auxiliary agent, the first ceramic particles are dispersed and form slurry, so that the first ceramic particles can be coated on the surface of the polyolefin layer. And coating the ceramic slurry on the surface of the polyolefin layer, and drying to remove the solvent to form the ceramic layer. At this time, the ceramic layer is a prefabricated film.

In some embodiments, the coupling agent is a silane coupling agent. The silane coupling agent is bonded to the surface of the first ceramic particles through a siloxane group. After the aramid fiber sizing agent is added to the surface of the ceramic layer, the aramid fiber sizing agent enters pores of the ceramic layer, an organophilic group at the other end of the coupling agent forms a hydrogen bond with aramid fiber molecules entering gaps of the first ceramic particles, and the aramid fiber and the first ceramic particles are tightly combined under the action of the hydrogen bond, so that the first ceramic particles are fixed on the surface of the polyolefin layer to form a mixture layer with a stable structure. Illustratively, the coupling agent is at least one of a vinyl silane, an amino silane, an epoxy silane, a mercapto silane, and a methacryloxy silane.

As a possible implementation, the preparation method of the ceramic slurry comprises the following steps:

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

adding a dispersing agent into the first ceramic particles modified by the silane coupling agent, stirring and mixing, and then grinding to obtain a ceramic dispersion liquid;

and adding a thickening agent, a binder and a wetting agent into the ceramic dispersion liquid, and stirring and mixing to obtain the ceramic slurry.

According to the method, the silane coupling agent and the first ceramic particles are mixed, then the dispersing agent is added for mixing treatment, so that the silane coupling agent and the first ceramic particles are uniformly dispersed, and then other auxiliary agents are added, so that the improvement of the dispersion uniformity of the silane coupling agent and the first ceramic particles is facilitated, and the distribution uniformity of the silane coupling agent on the surfaces of the first ceramic particles is improved. Under the condition, when aramid pulp is added on the surface of the ceramic layer, aramid enters pores among the first ceramic particles, and is connected with the first ceramic particles by virtue of the silane coupling agent uniformly distributed on the surfaces of the first ceramic particles, so that the first ceramic particles are fixed, and finally, a mixture layer with a stable structure, namely a first film, is formed.

In some embodiments, the first ceramic particles are at least one of silica, alumina, magnesium hydroxide, calcium oxide, boehmite, titania, and barium sulfate. In some embodiments, the first ceramic particles have a median particle diameter D50 of 0.01 to 2.0 μm.

In one possible implementation, the method for forming the ceramic layer on one or both surfaces of the polyolefin layer by using the ceramic material comprises the following steps: and coating the ceramic slurry on one or both surfaces of the polyolefin layer to form a ceramic layer. Wherein, the coating mode is one of dip coating, spray coating, a scraper, a coating wire rod and micro-concave roller coating.

In one possible implementation, the ceramic slurry is coated on one or both surfaces of the polyolefin layer, and then dried to remove the solvent from the ceramic slurry, thereby forming the ceramic layer. It is understood that, when the ceramic slurry does not contain an auxiliary agent, the solvent is volatilized after the drying process, the first ceramic particles are dispersed on the surface of the polyolefin layer, and the resulting ceramic layer cannot be firmly structured on the surface of the polyolefin. When the ceramic slurry contains the binder, the binder can bind the first ceramic particles, and the first ceramic particles are preliminarily fixed on the surface of the polyolefin layer to form the ceramic layer. The manner of the drying treatment is not particularly limited, and a ceramic layer is obtained after drying.

S12, adding aramid pulp 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 the step, the aramid fiber slurry is a slurry with the aramid fiber as a base material. In one possible implementation, the aramid pulp is a pulp formed of aramid. In another possible implementation manner, the aramid pulp contains aramid and an auxiliary agent.

In one possible implementation, the auxiliary agent includes a pore former. Through adding the pore-forming agent, can form pore structure in the aramid fiber layer when preparing the aramid fiber layer, improve the porosity on aramid fiber layer. In some embodiments, the pore former is one or more of an inorganic pore former, illustratively one or more of lithium chloride, sodium chloride, magnesium chloride, calcium carbonate, calcium chloride, second ceramic particles.

In some embodiments, the pore former is a second ceramic particle. The second ceramic particles are added into the aramid fiber slurry, so that the porosity of the aramid fiber layer can be increased and is more than 20%. Moreover, the second ceramic particles introduced into the aramid fiber layer can improve the thermal stability of the aramid fiber layer and improve the thermal shrinkage performance of the aramid fiber layer, and finally the thermal shrinkage performance of the composite membrane is improved. In some embodiments, the second ceramic particles comprise 0 to 50wt% of the total weight of the second ceramic particles and the aramid, thereby imparting suitable porosity to the aramid layer. At the moment, a small amount of second ceramic particles play a pore-forming role, and meanwhile, the influence of the second ceramic particles on the performance of the aramid layer is reduced.

The median particle diameter D50 of the second ceramic particles as pore former may be 0.01 to 2 μm. In some embodiments, the median particle diameter D50 of the second ceramic particles is from 0.1 to 1 μm. Under the condition, the second ceramic particles play a pore-forming role to increase the porosity of the aramid fiber layer, and the median diameter D50 is in the range, so that the aramid fiber layer can be endowed with proper porosity and pore size, and the aramid fiber layer with better air permeability and heat resistance can be obtained.

In some embodiments, the pore former is an organic pore former that volatilizes during thermoforming of the aramid layer to form micropores in the aramid layer. Illustratively, the organic pore former is selected from any one or more of methanol, ethanol, propanol, glycerol, polyethylene glycol, acetone, acetic acid, tetrahydrofuran, polyvinylpyrrolidone, ethyl acetate, petroleum ether, white oil, and paraffin.

As a possible implementation case, the preparation method of the aramid fiber slurry comprises the following steps:

In some embodiments, the aramid pulp is at least one of para-aramid pulp, meta-aramid pulp. The preparation method of the aramid pulp comprises the following steps: preparing an organic solution of phenylenediamine, cooling to below 10 ℃, adding phthaloyl chloride, adding alkali to adjust the pH value to be neutral, and adding second ceramic particles to prepare aramid slurry. The method can be used for preparing the aramid fiber slurry directly from the raw materials, and is simple and high in operation controllability. Wherein, the phenylenediamine is p-phenylenediamine or m-phenylenediamine, the organic solvent in the organic solution is one or more of N, N-dimethylacetamide, N-methylpyrrolidone, N-dimethylformamide or dimethyl phthalate, and the selection of the pore-forming agent is as above, which is not repeated herein.

In some embodiments, an auxiliary agent for increasing the solubility of the aramid fiber can be added in the preparation of the aramid fiber slurry, and the auxiliary agent is lithium chloride or calcium chloride. In the heating and stirring process, lithium ions and chloride ions in the lithium chloride replace hydrogen bonds between aramid fiber molecules, so that the aramid fiber molecules are separated, and the dissolving of the aramid fiber is accelerated.

In some embodiments, the aramid slurry is prepared by adding phthaloyl chloride followed by continuous stirring 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. Illustratively, the base may be sodium hydroxide, calcium hydroxide, potassium hydroxide, or the like. And then, adding a pore-forming agent to finally obtain a light yellow liquid, namely aramid fiber slurry.

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

In some embodiments, the solids content of the aramid pulp is 1.5-10%. In this case, the aramid pulp has appropriate viscosity and spreading property, and forms an aramid layer on the surface of the polyolefin layer evenly.

After the aramid fiber slurry is added to the surface of the ceramic layer, aramid fibers in the slurry can permeate downwards along pores among the first ceramic particles of the ceramic layer and are evenly spread on the surface of the first ceramic particles all around. Downward-penetrating aramid fibers are distributed in pores among the first ceramic particles, and the aramid fibers are used as a cross-linking agent to fix the granular first ceramic particles; meanwhile, the coupling agent is combined with the aramid fiber through hydrogen bonds, so that the first ceramic particles are crosslinked 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 case, the aramid pulp is added on the surface of the ceramic layer by coating the aramid pulp on the surface of the ceramic layer. Wherein the coating comprises one of dip coating, spray coating, doctor blade, coating wire rod and micro-gravure coating.

And adding aramid fiber slurry on the surface of the ceramic layer, and then drying, wherein in the drying process, on one hand, the aramid fiber flowing into the ceramic layer is connected with the first ceramic particles under the action of the coupling agent. And solidifying in heating and drying to fix the first ceramic particles on the surface of the polyolefin layer to form a mixture layer containing the first ceramic particles and the aramid fibers. On the other hand, the aramid fiber above the ceramic layer, i.e., the aramid fiber that does not flow into the ceramic layer, is cured to form a film in the heating and drying process, thereby forming an aramid fiber layer. Particularly, when the aramid fiber slurry contains the organic pore-forming agent, the organic pore-forming agent is volatilized and overflows in the heating and drying process, and a pore structure is formed in the aramid fiber layer. Thereby, a mixture layer is formed on the surface of the polyolefin and an aramid layer is formed on the surface of the mixture layer facing away from the polyolefin.

As a possible implementation scenario, the method for preparing the composite separator further includes: the sample obtained after coating the aramid slurry was immersed in a plasticizing bath before the heat-drying treatment. Before drying, a sample coated with aramid pulp is immersed in a plasticizing bath, so that the formed aramid fiber is in a high-plasticity state, and aramid fiber stretching is facilitated. Illustratively, the plasticizing bath is N, N-dimethylacetamide, without limitation. And carrying out secondary drying on the sample immersed in the plasticizing bath, and then rolling to finally obtain the composite diaphragm.

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

In this embodiment, the method for manufacturing the composite separator, as shown in fig. 4, includes the steps of:

s21, aramid fiber slurry is adopted to form aramid fiber prefabricated layers on the surfaces of one side or two sides of the polyolefin layer.

In the step, aramid pulp is formed on one side or two side surfaces of the polyolefin layer, and aramid prefabricated layers are formed on one side or two side surfaces of the polyolefin layer.

The aramid fiber slurry is a slurry with aramid fiber as a base material. The composition of the aramid pulp (including the components of the aramid pulp, the type of the assistant, such as the pore former component), the solid content, and the preparation method or formation method thereof refer to step S12 of the above first embodiment, and are not repeated herein for the sake of brevity.

As a possible implementation, the aramid pulp is applied to one or both surfaces of the polyolefin layer by coating the aramid pulp on one or both surfaces of the polyolefin layer. Wherein the coating comprises one of dip coating, spray coating, doctor blade, coating wire rod and micro-gravure coating.

As a possible implementation case, after the aramid pulp is coated on one side or both sides of the polyolefin layer, the fluidity of the pulp is reduced by heating or natural drying so that it can be fixed on the surface of the polyolefin layer, thereby obtaining the aramid preform layer. At this time, the aramid preform layer is not completely cured. Wherein, the heating mode can make the aramid fiber raw material react to generate the aramid fiber.

As a possible implementation, after coating aramid pulp on one or both surfaces of the polyolefin layer, the aramid raw material is reacted by heating to generate aramid, and the aramid preform layer is obtained. In some embodiments, the aramid fibers in the aramid preform layer are cured by a heating process. When the aramid fiber slurry contains the organic pore-forming agent, the heating process also enables the organic pore-forming agent in the aramid fiber to volatilize and overflow, and pores are formed in the aramid fiber.

S22, adding a ceramic material on the surface of the aramid fiber prefabricated layer, heating and drying to form 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 manner, when the aramid fiber prefabricated layer is an incompletely cured prefabricated layer, the composition (including the material state of the ceramic material, the composition components of the ceramic material, the type and content of the auxiliary agent), the solid content, and the preparation method or the forming method thereof refer to step S11 of the above first implementation case, and are not described herein again for saving space. Of course, when the aramid fiber prefabricated layer is an incompletely cured prefabricated layer, the first ceramic particles can be directly added to the surface of the incompletely cured prefabricated layer, and the surface of the first ceramic particles is combined with the coupling agent. In this case, the first ceramic particles sink down to the aramid preform layer, thereby achieving mixing of the first ceramic particles and the aramid.

Under the condition, the 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 sink into the aramid fiber prefabricated layer. In the heating and drying process, the aramid fiber prefabricated layer close to the polyolefin layer is solidified to form an aramid fiber layer; the aramid fiber prefabricated layer far away from the polyolefin layer is characterized in that the sunk first ceramic particles are connected with aramid fiber by virtue of a coupling agent on the surface of the aramid fiber prefabricated layer, and the aramid fiber prefabricated layer is heated and cured to fix the first ceramic particles to form a mixture layer of the first ceramic particles and the aramid fiber.

In one possible implementation mode, when the aramid fiber in the aramid fiber prefabricated layer is solidified, the ceramic material is mixed slurry containing ceramic and aramid fiber, and the ceramic material is obtained by mixing raw materials containing ceramic particles and aramid fiber. In some embodiments, the mixed slurry may contain an auxiliary agent such as a dispersant, a thickener, etc., in addition to the ceramic particles and the aramid fibers, without being limited thereto. At this time, the method for adding the ceramic material on the surface of the aramid fiber prefabricated layer may be as follows: and coating the ceramic slurry on the surface of the aramid fiber prefabricated layer. Wherein, the coating mode is one of dip coating, spray coating, a scraper, a coating wire rod and micro-concave roller coating. In this embodiment, the aramid fiber in the aramid fiber slurry may be the same as or different from the aramid fiber in the ceramic material.

According to the composite diaphragm obtained in the embodiment of the application, the mixture layer of aramid fiber and ceramic particles is formed on the polyolefin base film, so that the thermal shrinkage rate of the composite diaphragm is less than 4% @150 ℃/1h; meanwhile, the aramid fiber layer is used as a protective layer, so that the film breaking temperature of the composite diaphragm is higher than 200 ℃, and the safety performance of the battery can be remarkably improved by the obtained composite diaphragm. The obtained composite diaphragm is subjected to performance test, and the following results are found: when the composite membrane is subjected to puncture strength test, 90% of SOC acupuncture is passed; when the composite diaphragm is subjected to a 150 ℃ thermal shrinkage test, the pass rate of heating at 150 ℃ for 60min is improved.

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

The electrochemical device provided by the embodiment of the application has low thermal shrinkage and high film breaking temperature due to the composite diaphragm, can solve the problems of diaphragm shrinkage and melting, reduces the risk of thermal runaway caused by battery short circuit, and improves the safety performance of the battery.

In some implementations, at least one surface of the composite separator is provided with at least one polymer layer. The polymer layer can improve the interface cohesiveness between the composite diaphragm and the electrode plate, improve the integral hardness and strength of the battery, and prevent the deformation of the battery core. In some embodiments, the polymer layer may be activated after shaping by heating. Illustratively, after the polymer is formed on the surface of the composite diaphragm, the composite diaphragm is heated and activated for 20-300 min under the conditions that the pressure is 0.1-2.0 Mpa and the temperature is 25-100 ℃. In some embodiments, the pressure is 0.5 to 1.0MPa, the temperature is 60 to 90 ℃, and the activation time is 60 to 150min.

Illustratively, the polymer layer is a material layer formed of 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 a polymer laminate formed by at least two of PVDF, PMMA, dopamine, CMC, SBR, PTFE and PVA, and the polymer in the polymer laminate may be one or more of the above polymers. The polymer material can improve the bonding strength between the composite film and the electrode plate, and the structure of the battery is kept stable.

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

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

In some implementations, the electrochemical device further includes an enclosure, and the one or more electrochemical device cells are enclosed within the enclosure. The electrochemical device unit may be a battery cell 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, which includes a housing, and an electronic component and an electrochemical device that are housed in the housing, where the electrochemical device is the electrochemical device according to the third aspect of the present application, and the electrochemical device is configured to supply power to the electronic component.

In some implementations, the electronic device may be a mobile terminal, illustratively a computer, a mobile phone, a tablet, a wearable product.

A fourth aspect of the present application provides a mobile device comprising the electrochemical device of the third aspect.

In some implementations, the mobile device is an end product such as a new energy vehicle that needs to be equipped with a power supply, but is not limited to the new energy vehicle.

In the following description, the specific examples are described, and it is noted that the polyolefin layer in the following examples is a porous polyolefin layer, and H-HE7.0 um wet PE film manufactured by ny technologies gmbh, chongqing, is selected, and the index of the separator is shown in table 1.

TABLE 1

Example 1

A composite separator, the method of making comprising:

(1) Preparation of ceramic slurry

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

b. adding 0.3 part of polyethylene glycol into the reactor, stirring for 0.6h, and then grinding for 1h to obtain uniform ceramic dispersion liquid;

c. and adding 0.5 part of sodium carboxymethylcellulose, 3 parts of polyvinylidene fluoride and 0.05 part of polyether siloxane copolymer into the ceramic dispersion liquid, and stirring and dispersing for 1 hour to obtain the water-based high-temperature-resistant ceramic slurry.

(2) Preparation of aramid pulp

a. Adding N, N-Dimethylacetamide (DMAC) solvent into a reactor, and introducing p-phenylenediamine;

b. cooling the temperature of the reactor to about 0 ℃ and stirring, adding phthaloyl chloride and 2wt.% of silicon dioxide particles, continuously stirring, adding strong base to enable the pH value of the synthetic solution to be neutral, and finally obtaining light yellow liquid, namely aramid fiber slurry, wherein the aramid fiber content is 3.5wt.%.

(3) Preparation of composite separator

a. Coating the water-based high-temperature-resistant ceramic slurry prepared in the step (1) on one side of a PE single-layer film with the thickness of 7 mu m in a gravure roll coating mode, and drying to obtain a ceramic layer;

b. spraying the aramid fiber slurry prepared in the step (2) on one side of a ceramic layer in a spraying mode, immersing the coated aramid fiber slurry into a plasticizing bath which is N, N-dimethylacetamide after coating, and rolling the coated aramid fiber slurry after drying to obtain the composite diaphragm, wherein the composite diaphragm comprises an aramid fiber layer, a mixed layer formed by ceramic particles and aramid fibers and a porous polyolefin layer which are sequentially stacked.

The composite separator prepared in example 1 had a thickness of the aramid layer of about 2um and a thickness of the mixture layer of about 2um.

Example 2

The preparation method of the composite diaphragm is different from that of the composite diaphragm in the embodiment 1 in the preparation of aramid pulp, and specifically, the preparation method of the aramid pulp comprises the following steps:

a. adding N, N-Dimethylacetamide (DMAC) solvent into a reactor, and introducing m-phenylenediamine;

b. cooling the temperature of the reactor to about 0 ℃, stirring, adding phthaloyl chloride, continuously stirring, adding strong base to enable the pH value of the synthetic solution to be neutral, and obtaining light yellow liquid, namely aramid fiber slurry, wherein the content of the aramid fiber is 2.5wt.%.

In the composite separator prepared in example 2, the thickness of the ceramic layer was 2um, and the thickness of the aramid layer was 2um.

Example 3

a. adding barium sulfate nanoparticles into N, N-dimethylacetamide, dissolving lithium chloride into the N, N-dimethylacetamide, adding meta-aramid fiber, and heating and stirring to dissolve the meta-aramid fiber in the N, N-dimethylacetamide to obtain a solution. In this step, lithium chloride is dissolved in an N, N-dimethylacetamide solvent and exists in a free state. In the heating and stirring process, the lithium ions and the chloride ions replace hydrogen bonds between aramid fiber molecules, so that the aramid fiber molecules are separated, and the dissolution is accelerated. Wherein the mass ratio of the lithium chloride to the N, N-dimethylacetamide to the meta-aramid fiber is (2-4): (70-75): (18-22), and the heating and stirring temperature is 80-100 ℃.

b. And adding calcium hydroxide to enable the pH value of the synthetic solution to be neutral, and finally obtaining liquid, namely the barium sulfate nanoparticle modified aramid fiber slurry, wherein the percentage content of aramid fiber is about 4wt%, and the content of barium sulfate is about 5 wt%.

In the composite separator prepared in example 3, the thickness of the mixture layer was 2um, and the thickness of the aramid layer was 2um.

Example 4

The preparation method of the composite diaphragm is different from that of the composite diaphragm in the embodiment 1 in the preparation of ceramic slurry, and specifically, the preparation method of the ceramic slurry comprises the following steps:

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

b. Adding 0.55 part of sodium carboxymethylcellulose, 3.26 parts of methacrylic acid-methyl methacrylate-maleic anhydride terpolymer and 0.04 part of sodium dodecyl sulfate into the ceramic dispersion liquid, stirring at low speed, and dispersing for 1.5h to obtain the water-based ceramic-resistant slurry.

In the composite separator obtained in example 4, the thickness of the mixture layer was 2um, and the thickness of the aramid layer was 2um.

Example 5

(1) Adding 40 parts of alumina, 1 part of silane coupling agent and 0.51 part of polyvinylpyrrolidone into 55.64wt.% of deionized water, stirring for 0.5h, and grinding for 1h to obtain a uniform ceramic dispersion liquid, wherein the D50 of the alumina is 0.2um.

(2) Adding 0.55 part of polytetrafluoroethylene, 3.26 parts of methacrylic acid-methyl methacrylate-maleic anhydride terpolymer and 0.04 part of sodium dodecyl sulfate into the ceramic dispersion liquid, stirring at low speed, and dispersing for 1.5 hours to obtain the water-based ceramic slurry.

In the composite separator obtained in example 5, the thickness of the mixture layer was 2um, and the thickness of the aramid layer was 2um.

Example 6

A method for manufacturing a composite separator, which is different from embodiment 1, includes:

a. coating the aramid slurry prepared in the step (2) in the example 1 on one side of the polyolefin layer in a spraying manner;

b. the ceramic slurry prepared in the step (1) in the example 1 is sprayed on the surface of the aramid coating by a spraying mode

And after coating, immersing the membrane into a plasticizing bath, wherein the plasticizing bath is N, N-dimethylacetamide, drying and rolling to obtain the composite membrane, and the composite membrane comprises a mixture layer formed by sequentially laminating ceramic particles and aramid fibers, an aramid fiber layer and a porous polyolefin layer.

Example 6 produced a composite separator in which the aramid layer was about 2um thick and the mixture layer was about 2um thick.

Example 7

a. coating the water-based high-temperature-resistant ceramic slurry prepared in the step (1) on two sides of a PE single-layer film with the thickness of 7 mu m in a gravure roll coating mode;

b. spraying the aramid fiber slurry prepared in the step (2) on the surface of the ceramic layer in a spraying mode, immersing the coated aramid fiber slurry into a plasticizing bath which is N, N-dimethylacetamide after coating, and rolling the coated aramid fiber slurry after drying to obtain the composite diaphragm, wherein the composite diaphragm comprises an aramid fiber layer, a mixed layer formed by ceramic particles and aramid fibers and a porous polyolefin layer which are sequentially stacked.

The composite separator prepared in example 1 had a thickness of the aramid layer of about 2 um/side and a thickness of the mixture layer of about 2 um/side.

Comparative example 1

A separator, the method of making comprising:

(1) Preparation of aramid pulp

(2) Preparation of the separator

Coating the prepared aramid pulp on one side surface of a PE single-layer film with the thickness of 7 mu m in a gravure roll coating mode, immersing the coated aramid pulp into a plasticizing bath which is N, N-dimethylacetamide after coating, drying and rolling to obtain the diaphragm, wherein the diaphragm comprises an aramid layer and a porous polyolefin layer which are sequentially laminated.

In the separator prepared in comparative example 1, the thickness of the aramid layer was 4um.

Comparative example 2

A separator, the method of making comprising:

(1) Preparation of ceramic slurry

(2) Preparation of the separator

The prepared ceramic slurry was coated on one side surface of a PE single layer film having a thickness of 7 μm by a gravure roll coating method, and dried to obtain a separator including a ceramic layer and a porous polyolefin layer, which were sequentially laminated.

The separator obtained in comparative example 2 had a ceramic layer thickness of 4um.

Comparative example 3

A separator, the method of making comprising:

(1) Preparation of ceramic slurry

a. 40wt.% of boehmite and 0.51wt.% of polyvinylpyrrolidone were added to 55.64wt.% of deionized water, stirred for 0.5h, and milled for 1h to obtain a homogeneous ceramic dispersion.

b. Adding 0.55wt.% of sodium carboxymethylcellulose, 3.26wt.% of methacrylic acid-methyl methacrylate-maleic anhydride terpolymer and 0.04wt.% of sodium dodecyl sulfate into the ceramic dispersion, stirring at low speed, and dispersing for 1.5h to obtain the water-based ceramic-resistant slurry.

(2) Preparation of the separator

The separator obtained in comparative example 3 had a ceramic layer thickness of 4um.

Comparative example 4

preparation of ceramic slurry

In the composite separator prepared in comparative example 4, the thickness of the aramid layer was about 2um, and the thickness of the mixture layer was about 2um.

The composite separators obtained in examples 1 to 5 and the separators obtained in comparative examples 1 to 3 were subjected to performance tests, and the test results of the composite films obtained in examples 1 to 5 are shown in table 2 below, and the test results of the separators obtained in comparative examples 1 to 3 are shown in table 3 below:

TABLE 2

TABLE 3

As can be seen from data in tables 1 and 2, the composite membranes provided in examples 1 to 7 of the present application can retain a low closed-cell temperature, which is about 140 ℃, after the ceramic particle/aramid fiber layer and the aramid fiber layer are sequentially stacked on the surface of the porous polyolefin layer. Compared with the diaphragm provided by the comparative example 1, the composite films obtained in the examples 1 to 7 of the present application have obviously reduced thermal shrinkage rates in the mechanical direction and the direction perpendicular to the mechanical direction, wherein the thermal shrinkage rates are both less than 4% @150 ℃/1h; in contrast, the separator provided in comparative example 1 has a high thermal shrinkage rate because it does not contain a mixture layer formed of ceramic particles and aramid. Compared with comparative examples 2-3, the film breaking temperature of the composite films obtained in examples 1-7 of the application is obviously improved. This shows that the composite layer including the aramid fiber layer and the mixture layer disposed on the surface of the polyolefin layer according to the embodiment of the present invention can improve the heat shrinkage of the separator, increase the film rupture temperature, and thus can effectively improve the safety performance of the battery.

The composite separators obtained in examples 1 to 7 and the separators obtained in comparative examples 1 to 3 were used to fabricate electrochemical devices by the following method:

manufacturing a positive pole piece: dissolving a binder PVDF in NMP for dispersion to obtain 7.0wt.% PVDF glue solution, then adding a carbon nano tube conductive solution for uniform dispersion, finally adding an active material lithium cobaltate, uniformly stirring and mixing to obtain anode slurry, uniformly coating the anode slurry on two surfaces of an aluminum foil by adopting coating equipment, and drying by using an oven to remove the NMP solvent. And (3) carrying out cold pressing, splitting and tab welding on the coated pole piece to prepare the positive pole piece. The anode material comprises the following components in percentage by mass: LCO, CNTs, PVDF, 98.8, 0.02, 1.0;

manufacturing a negative pole piece: mixing the artificial graphite and the SP in a kneading mode, mixing the artificial graphite and the SP uniformly in a dry mode, adding 25wt.% of pre-stirred CMC glue solution, kneading and stirring, and finally adding the rest CMC and deionized water to perform high-speed dispersion to obtain mixed negative electrode slurry. And after the slurry is sieved, the negative slurry is uniformly coated on two sides of the copper foil by adopting coating equipment, and the pole piece dried by the oven is subjected to cold pressing, splitting and tab welding to prepare the negative pole piece. The negative electrode material comprises the following components, by mass, graphite, SP, CMC, SBR =96.8%, 0.6%, 1.2%;

manufacturing a diaphragm: the surfaces of the battery separators of the above examples 1 to 7 and comparative examples 1 to 3 were sprayed with 0.5um each of PVDF or PMMA aqueous adhesive layers.

And winding the positive and negative pole pieces and the diaphragm together to prepare a bare cell, wherein the capacity of the cell is 4.5Ah, the working voltage range is 3.0-4.48V, and the cell is subjected to processes of packaging, baking, liquid injection, formation and the like to prepare the lithium ion battery.

The electrochemical devices comprising the separators prepared in examples 1 to 7 and comparative examples 1 to 4 were subjected to performance tests, the results of which are shown in tables 4 and 5, respectively:

TABLE 4

TABLE 5

Item	Comparative example 1	Comparative example 2	Comparative example 3	Comparative example 4
					90% SOC needling	5/5 through	3/5 through	0/5 through	3/5 through
150 ℃ 1h hot box	0/5 through	0/5 through	3/5 through	3/5 through

As can be seen from tables 4 and 5, the batteries containing the composite separators according to the examples of the present application all passed five times of the 90-degree soc puncture test on the above batteries, while the batteries containing the separators according to comparative examples 2 and 3 had test passing rates of 60% and 0, which was attributed to the fact that the separators provided in comparative documents 2 and 3 did not contain an aramid layer, resulting in heat generation from internal short circuits inside the batteries during the puncture test. In the composite diaphragm, the aramid fiber layer has high heat-resisting property, so that the diaphragm is prevented from melting, further internal short-circuit heating is inhibited, and the probability of heating and burning of the battery is reduced.

The cells were subjected to a hot box treatment at 130 ℃ for 30min, and all cells were passed. However, when the above-mentioned battery was subjected to a hot box treatment at 150 ℃ for 60min, the batteries including the separators provided in comparative examples 1 to 3 could not achieve a pass rate of 100%, or even 0, because: the comparative example 1 only contains an aramid fiber layer, and the aramid fiber is easy to curl at high temperature, so that the battery diaphragm is easy to curl at high temperature; the comparative example 2 only contains a common ceramic coating, the layer collapses and melts at 150 ℃, the anode and the cathode cannot be effectively isolated, and the battery can be burnt in a short circuit manner; comparative example 3 contains only a high temperature ceramic coating, and the film breaking temperature is 180 ℃; when the battery is baked at 150 ℃ for 1 hour, the strength of the diaphragm is low, the positive electrode and the negative electrode cannot be effectively isolated, and the battery can be short-circuited and burnt.

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

(1) Film thickness (um)

The first method is as follows:

a. sampling: taking 1X 10 from the diaphragm ³ mm ² Sample (sample area can be more than or equal to 1.5 multiplied by 10) ³ mm ² ) The number of test points depends on the diaphragm (usually not less than 10 points).

b. And (3) testing: the test was carried out by means of a ten-thousandth thickness measuring instrument at a temperature of 23. + -. 2 ℃.

c. Data processing: and (4) measuring the thickness of each test point and taking the arithmetic mean value.

The second method comprises the following steps:

a. sampling: for products with width < 200 mm: determining a point every 40mm +/-5 mm along the longitudinal direction (MD), wherein the number of the test points is not less than 10, the number of the test points can be determined according to the width of the diaphragm, and the distance between the measurement starting point and the edge part is not less than 20mm;

for products with width larger than or equal to 200 mm: and determining a point every 80mm +/-5 mm along the Transverse Direction (TD), wherein the number of the test points is not less than 10, the number of the test points can be determined according to the width of the diaphragm, and the distance from the measurement starting point to the edge part is not less than 20mm.

b. And (3) testing: each test point is tested by a thickness measuring instrument under the condition that the temperature is 23 +/-2 ℃, the diameter of a measuring surface is between 2.5mm and 10mm, and the load applied to the test sample by the measuring surface is between 0.5N and 1.0N.

(2) Porosity (%)

The first method is as follows:

a. sampling: taking 1X 10 from the diaphragm ⁴ mm ² And (4) sampling.

b. And (3) testing: porosity was measured by density method.

c. Data processing:

the porosity P of the sample as a whole can be calculated by the following formula:

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

The second method comprises the following steps:

a. sampling: rectangular specimens 1 are cut out by means of a 237X 170mm template sampler. The samples are cut as far away as possible from the edge of the membrane (e.g., more than 50mm from the edge of the membrane).

b. And (3) testing: the porosity is measured by densitometry, which involves measuring n (n may be, for example, 9 or more) points of the sample, which may be distributed in an equidistant lattice.

c. Data processing: porosity P of each dot _i Can be calculated by the following formula:

wherein m is _i Rho is the skeleton density of the sample (which can be calculated according to the material proportion) for the mass of each point, V _i The total volume of each point (which can be calculated according to the length, width and thickness of the sample);

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

(3) Air permeability (s/100 cc)

The first method is as follows:

a. sampling: a sample with the diameter of more than or equal to 28mm is cut from the diaphragm.

b. And (3) testing: the test was carried out according to the method specified in JIS P8117-2009. The method specifically comprises the following steps: setting the pressure of the cylinder driving pressure reducing valve to be 0.25MPa, testing the pressure to be 0.05MPa, and selecting JIS according to the testing standard.

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

The second method comprises the following steps:

a. sampling: 6 square specimens were cut out by means of a 100X 100mm template sampler. The samples are cut as far away as possible from the edge of the membrane (e.g., more than 50mm from the edge of the membrane). Each sample was evenly distributed on the membrane (i.e. the full width of the membrane was averaged to give 6 zones, and 1 sample was cut in each of these 6 zones).

b. And (3) testing: the test was carried out according to the method specified in JIS P8117-2009. The method specifically comprises the following steps: setting the pressure of a cylinder driving pressure reducing valve to be 0.25MPa, testing the pressure to be 0.05MPa, and selecting JIS as a testing standard.

c. Data processing: the air resistance value of each sample is recorded separately, and the arithmetic mean of the air resistance values of the 6 samples is calculated.

(4) Puncture Strength (gf)

The first method is as follows:

a. sampling: and intercepting a sample with the diameter of more than or equal to 45mm from the microporous membrane.

b. And (3) testing: fix the sample on anchor clamps centrally, the test needle is the sphere (the material is ruby) of diameter 1mm, ensures that the sample extends to or surpasses the edge of clamping disk in all directions, confirms that the sample is fixed in on the cyclic annular anchor clamps completely, does not have the phenomenon of skidding. During the test, the membrane was punctured and the machine speed was set at 300 ± 10mm/min until the puncture bat completely ruptured the specimen and the puncture resistance was the maximum force recorded during the test.

c. Data processing: and randomly cutting 6 samples in full width, respectively recording the puncture strength values of the samples, and calculating the arithmetic mean value of the puncture strength values of the samples.

The second method comprises the following steps:

a. sampling: rectangular test specimens of 6 size were cut out by means of a 237X 170mm template sampler. The sample is cut as far away as possible from the edge of the membrane (e.g., more than 50mm from the edge of the membrane). Each sample was evenly distributed on the membrane (i.e. the full width of the membrane was averaged to give 6 zones, and 1 sample was cut in each of these 6 zones).

b. And (3) testing: the test was carried out according to the method specified in the standard ASTM D4833-07. The method specifically comprises the following steps: the test needle head is a spherical needle head with the diameter of 1mm (made of sapphire); fixing the sample on a clamp in the middle, ensuring that the sample extends to or exceeds the edge of a clamping disc in each direction, and confirming that the sample is completely fixed on the annular clamp without slipping; during testing, the speed of the machine is set to be 300 +/-10 mm/min, and the diaphragm is punctured until the test needle head completely breaks the sample; puncture resistance is the maximum force recorded during the test.

c. Data processing: the puncture strength of each sample was recorded separately and the arithmetic mean of the puncture strengths of these 6 samples was calculated.

(5) Tensile Strength and elongation (% MPa)

The first method is as follows:

a. sampling: on the whole width sample, the diaphragm is cut according to the MD direction and the TD direction respectively to obtain a plurality of strip-shaped samples with the length being more than or equal to 50mm and the width being about 15 +/-0.1 mm (when the MD is tested, the width of the sample can be along the TD direction of the diaphragm, the length of the sample can be along the MD direction of the diaphragm, and when the TD is tested, 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. And (3) testing: and (3) stretching by using a stretcher, wherein the distance between the clamps can be 100 +/-5 mm until the sample is pulled apart, and the stretching speed can be 100 +/-1 mm/min.

c. Data processing: the tensile strength and elongation of each sample were recorded separately.

The second method comprises the following steps:

a. sampling: rectangular test specimens of 6 size were cut out by means of a 237X 170mm template sampler. The sample is cut as far away as possible from the edge of the membrane (e.g., more than 50mm from the edge of the membrane). Each sample was uniformly distributed on the separator (i.e., the full width of the separator was divided equally in the MD, TD directions of the separator to give 6 zones, and 1 sample was cut out in each of the 6 zones). And then, cutting a strip sample with the length of more than or equal to 150mm and the width of 15 +/-0.1 mm by using a sampling instrument.

b. And (3) testing: the measurement was carried out according to the method specified in GB/T1040.3-2006. The method specifically comprises the following steps: the distance between the clamps can be 100 +/-5 mm, and the stretching speed can be 100 +/-1 mm/min.

c. Data processing: the tensile strength, elongation of each specimen were recorded separately and the arithmetic mean of the 6 specimens was calculated.

(6) Thermal shrinkage at 150 DEG C

a. Sampling: 6 specimens were randomly cut out over the full width. The specific sampling of each sample may include: cutting 100mm along the MD direction of the diaphragm; when the TD direction of the separator is greater than 100mm, the length of the test sample in the TD direction may be 100mm; when the TD direction of the microporous membrane is less than 100mm, the length of the test sample in the TD direction may be practically defined.

b. And (3) testing: marking the longitudinal and transverse marks of the sample, and measuring and recording the longitudinal and transverse dimensions of each sample; the sample is flatly placed in the paper jacket layer, and the sample has no folding, wrinkling, adhesion and other conditions; placing a paper sleeve (the number of layers can be 10 for example) clamping a sample into the middle of a constant-temperature oven flatly (the door opening time is not more than 3s for example); heating the sample to 150 ℃ by an electric heating thermostat for 1h; the sample was taken out and cooled to room temperature, and the longitudinal length and the transverse length were measured.

c. Data processing:

calculate the heat shrinkage for each sample:

T＝(L ₀ -L)/L ₀ ×100％，

wherein T may be a sample thermal shrinkage (%) or L ₀ May be the length (mm) of the sample before heating, and L may be the length (mm) of the sample after heating. The arithmetic mean of the sample heat shrinkage was calculated.

(7) Closed cell temperature (. Degree. C.)

And testing by adopting a temperature rise internal resistance method. The diaphragm is placed in a stainless steel clamp or other similar clamps, a proper amount of electrolyte is injected into the stainless steel clamp or other similar clamps, the clamps are placed in an oven, the temperature is raised at a certain speed, meanwhile, the resistance value and the temperature of the clamps are monitored, and when the resistance value suddenly changes to 10 times of the initial resistance value along with the temperature, the corresponding temperature is defaulted to be the closed pore temperature of the diaphragm.

(8) Temperature of film breaking (. Degree. C.)

And testing the film breaking temperature by adopting a baking method. And (3) placing the diaphragm in a 9 x 9cm clamp, placing the clamp in an oven, raising the temperature at a certain speed, monitoring whether the diaphragm in the clamp breaks or not, and recording the diaphragm breaking temperature of the diaphragm when the diaphragm breaks along with the temperature change.

(9) Needle stick test

a. Sampling: each group took 5 power conversion system (pcs) batteries and marked the center of the cell.

b. And (3) testing: charging the battery cell to a limit voltage at 25 +/-3 ℃ according to a constant current of 0.7 ℃, then charging under a constant voltage condition of the limit voltage until the current is reduced to 0.025 ℃, and testing within 12-24 h; the steel nail was pierced into the central portion of the cell at a rate of 150mm/s at 25 ± 3 ℃ until penetration. The diameter of the steel nail is 2.45 +/-0.06 mm, the length of the steel nail is 45 +/-2.5 mm, and the length of the tip can be between 2mm and 4.9 mm.

c. Data processing: and (4) keeping the steel nail not to catch fire or explode within 10min in the puncturing process and after puncturing is finished, and judging that the steel nail passes the puncturing judgment.

(10) Thermal shock test at 150 ℃

a. Sampling: 5pcs of cells were used for each group.

b. And (3) testing: at 25 +/-3 ℃, charging the battery core to a limiting voltage according to a constant current of 0.2 ℃, then charging to a current reduction of 0.025 ℃ under the constant voltage condition of the limiting voltage, heating the battery from an initial temperature of 25 +/-3 ℃ by a convection mode or a circulating hot air box, wherein the temperature change rate can be 5 +/-2 ℃/min; heating to 150 + -2 deg.C, and maintaining for 60min.

c. Data processing: and observing an experimental phenomenon, and judging that the temperature is passed without fire or explosion after the temperature is raised.

(11) Nail penetration test

The standard charge mode was charged to 90% SOC and then tested for 12-24 h. Then the battery is placed in an explosion-proof box at 25 ℃, a steel nail is punctured into the central part of the battery core at the speed of 150mm/s until the battery core penetrates through the explosion-proof box, and the needle is withdrawn after the battery core is kept for 10 min. And if the battery is not in thermal runaway, the test is passed, and the test passing rate is recorded.

The present application is intended to cover various modifications, equivalent arrangements, and adaptations of the present application without departing from the spirit and scope of the present application.

Claims

1. A composite separator, comprising a polyolefin layer, a composite layer bonded to one or both surfaces of the polyolefin layer, the composite layer comprising a mixture layer and an aramid layer bonded to one surface of the mixture layer, wherein the mixture layer and the aramid layer are laminated to the polyolefin layer;

the mixture layer comprises aramid fibers and first ceramic particles, and a coupling agent is bonded on the surfaces of the first ceramic particles; the coupling agent contains an organophilic group and an organophilic group, and is connected with the first ceramic particles through the organophilic group and is connected with the aramid through the organophilic group.

2. The composite membrane of claim 1, wherein the coupling agent is a silane coupling agent.

3. The composite separator of claim 2, wherein said silane coupling agent is selected from at least one of vinyl silane, amino silane, epoxy silane, mercapto silane, and methacryloxy silane.

4. The composite separator according to claim 1, wherein the weight of the coupling agent in the mixture layer is 0.3 to 2% of the total weight of the first ceramic particles.

5. The composite separator of claim 1, wherein the weight percent of the aramid fiber is 0.1-20% and the weight percent of the first ceramic particles is 80-99.9% based on 100% of the total weight of the mixture layer.

6. The composite membrane of claim 1, wherein the mixture layer comprises a first surface in contact with the aramid layer and a second surface facing away from the first surface, the aramid content in the mixture layer increasing in a direction from the second surface to the first surface.

7. The composite membrane of any one of claims 1 to 6, wherein the weight percentage of the aramid fiber is 50 to 100% based on 100% of the total weight of the aramid fiber layer.

8. The composite membrane of claim 7, wherein the aramid layer further comprises 0 to 50 weight percent of second ceramic particles.

9. The composite separator of any of claims 1 to 6, wherein the thickness of the mixture layer is 0.1-6um.

10. The composite separator of claim 9, wherein the mixture layer has a thickness in the range of 1-4um.

11. The composite membrane of any one of claims 1 to 6 wherein the aramid layer has a thickness of 0.1-6um.

12. The composite membrane of claim 10, wherein the aramid layer has a thickness of 0.5-3um.

13. The composite membrane of 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 fiber in the mixture layer is at least one of para-aramid fiber and meta-aramid fiber.

14. The composite separator according to any one of claims 1 to 6, wherein the median particle diameter D50 of the first ceramic particles is 0.01 to 2.0 μm.

15. The composite membrane according to claim 8, wherein the second ceramic particles have a median particle diameter D50 of 0.1 to 1 μ ι η.

16. The composite separator according to any one of claims 1 to 15, wherein the polyolefin layer has a thickness of 0.2 to 20 μm.

17. The composite membrane of any one of claims 1 to 16 wherein said mixture layer is bonded to a surface of said polyolefin layer and said aramid layer is bonded to a surface of said mixture layer on a side thereof facing away from said polyolefin layer.

18. The composite membrane of any one of claims 1 to 17, wherein the composite layer comprises n laminated layers of the mixture layer and the aramid layer, wherein n is an integer of 2 to 5.

19. An electrochemical device comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator provided between the positive electrode sheet and the negative electrode sheet, characterized in that the separator is a composite separator according to any one of claims 1 to 18.

20. An electronic device comprising a housing, and an electronic component and an electrochemical device housed in the housing, wherein the electrochemical device is the electrochemical device of claim 19, and the electrochemical device is configured to supply power to the electronic component.

21. The electronic device of claim 20, wherein the electronic device is a computer, a mobile phone, a tablet, a wearable product.

22. A mobile device comprising the electrochemical device of claim 19.