阅读说明：本技术 一种隔膜及电池 (Diaphragm and battery ) 是由 王翔 彭冲 李俊义 徐延铭 于 2021-07-15 设计创作，主要内容包括：本申请公开了一种隔膜及电池,涉及锂离子电池技术领域。该隔膜包括：隔膜本体和涂覆于所述隔膜本体上的阻燃涂层；其中,所述阻燃涂层包括多孔碳材料和包裹所述多孔碳材料的聚合物；所述聚合物的熔点温度或者粘流温度低于所述隔膜的热失效临界温度。这样,当电池的温度较高时,包裹在多孔碳材料外层的聚合物会被高温熔化,使得多孔碳材料外露在电解液中,对电解液中分解出来的气体进行吸附,从而避免电池发生爆炸。因而,通过采用这种隔膜,不仅可以保障电池的性能,还可以提高电池的安全性。(The application discloses diaphragm and battery relates to lithium ion battery technical field. The diaphragm includes: the diaphragm comprises a diaphragm body and a flame-retardant coating coated on the diaphragm body; wherein the flame retardant coating comprises a porous carbon material and a polymer encapsulating the porous carbon material; the melting point temperature or viscous flow temperature of the polymer is below the thermal failure critical temperature of the separator. Like this, when the temperature of battery is higher, the polymer of parcel in the porous carbon material skin can be by high temperature melting for porous carbon material exposes in electrolyte, adsorbs the gas that decomposes out in the electrolyte, thereby avoids the battery to explode. Therefore, by using such a separator, not only can the performance of the battery be secured, but also the safety of the battery can be improved.)

1. A septum, comprising: the diaphragm comprises a diaphragm body and a flame-retardant coating coated on the diaphragm body;

wherein the flame retardant coating comprises a porous carbon material and a polymer encapsulating the porous carbon material;

the melting point temperature or viscous flow temperature of the polymer is below the thermal failure critical temperature of the separator.

2. The separator of claim 1, wherein the flame retardant coating is applied to a first surface and/or a second surface of the separator body, the first surface and the second surface being opposite sides of the separator body.

3. The separator of claim 1, wherein the flame retardant coating is applied at a thickness ranging from 1 micron to 8 microns.

4. The separator according to claim 1, wherein the porous carbon material is obtained by carbonizing a hypercrosslinked polymer, and the specific surface area of the porous carbon material is 3000m or more²And/g, wherein the hypercrosslinked polymer is at least one of benzene, pyridine and thiophene.

5. The separator according to claim 1, wherein the polymer is any one of polypropylene, polyethylene and silicon-based polymer, and the melting point temperature or viscous flow temperature of the polymer is in a range of 90 ℃ to 130 ℃.

6. A membrane according to any one of claims 1 to 5, characterized in that the preparation method of the membrane comprises:

adding a hypercrosslinked polymer into a potassium hydroxide solution, stirring, and carbonizing the stirred mixed solution to obtain the porous carbon material;

adding the polymer into a solvent, heating, and stirring after the polymer is dissolved to obtain a polymer solution, wherein the melting point temperature or viscous flow temperature of the polymer is lower than the thermal failure critical temperature of the diaphragm;

adding the porous carbon material into the polymer solution and stirring to obtain the flame-retardant coating;

and coating the flame-retardant coating on the diaphragm body to obtain the diaphragm.

7. The membrane of claim 6, wherein the solvent is xylene, toluene, or decalin.

8. The separator according to claim 6, wherein the ratio of the hypercrosslinked polymer to the potassium hydroxide solution is 1: 4.

9. A battery, comprising: a positive electrode sheet, a negative electrode sheet, and the separator according to any one of claims 1 to 8.

10. The battery according to claim 9, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, and the separator, the positive electrode sheet, and the negative electrode sheet are wound.

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to a diaphragm and a battery.

Background

The lithium ion battery has the advantages of high energy density, low self-discharge, no memory effect and the like, and is widely applied to the fields of mobile phones, flat plates, power industries and the like. When the lithium ion battery is abused in the using process, a large amount of gas can be decomposed from the electrolyte, and the battery is exploded. In order to solve the problem, in the prior art, a flame retardant is usually directly added into the electrolyte, and the flame retardant can release free radicals at high temperature to capture oxygen radicals generated by decomposition of the electrolyte, so that the problem of battery explosion is solved. However, in this way, the required amount of the flame retardant is large, which greatly increases the viscosity of the electrolyte, thereby causing the performance of the battery to be reduced.

Disclosure of Invention

The embodiment of the invention provides a diaphragm and a battery, and aims to solve the problem that the viscosity of an electrolyte is greatly improved and the performance of the battery is reduced in the conventional mode of directly adding a flame retardant into the electrolyte.

In a first aspect, embodiments of the present application provide a membrane, including: the diaphragm comprises a diaphragm body and a flame-retardant coating coated on the diaphragm body;

wherein the flame retardant coating comprises a porous carbon material and a polymer encapsulating the porous carbon material;

the melting point temperature or viscous flow temperature of the polymer is below the thermal failure critical temperature of the separator.

Optionally, the flame retardant coating is applied to a first surface and/or a second surface of the separator body, the first surface and the second surface being opposite sides of the separator body.

Optionally, the flame retardant coating layer has a coating thickness ranging from 1 micron to 8 microns.

Optionally, the porous carbon material is obtained by carbonizing a hypercrosslinked polymer, and the specific surface area of the porous carbon material is greater than or equal to 3000m²And/g, wherein the hypercrosslinked polymer is at least one of benzene, pyridine and thiophene.

Optionally, the polymer is any one of polypropylene, polyethylene and silicon polymers, and the melting point temperature or viscous flow temperature of the polymer ranges from 90 ℃ to 130 ℃.

Optionally, the preparation method of the separator comprises:

adding a hypercrosslinked polymer into a potassium hydroxide solution, stirring, and carbonizing the stirred mixed solution to obtain the porous carbon material;

adding the polymer into a solvent, heating, and stirring after the polymer is dissolved to obtain a polymer solution, wherein the melting point temperature or viscous flow temperature of the polymer is lower than the thermal failure critical temperature of the diaphragm;

adding the porous carbon material into the polymer solution and stirring to obtain the flame-retardant coating;

and coating the flame-retardant coating on the diaphragm body to obtain the diaphragm.

Alternatively, the solvent is xylene, toluene or decalin.

Optionally, the ratio of the hypercrosslinked polymer to the potassium hydroxide solution is 1: 4.

In a second aspect, an embodiment of the present application provides a battery, including: a positive electrode sheet, a negative electrode sheet, and a separator as described in the first aspect.

Optionally, the separator is located between the positive electrode sheet and the negative electrode sheet, and the separator, the positive electrode sheet and the negative electrode sheet are wound.

In an embodiment of the present application, the diaphragm includes: the diaphragm comprises a diaphragm body and a flame-retardant coating coated on the diaphragm body; wherein the flame retardant coating comprises a porous carbon material and a polymer encapsulating the porous carbon material; the melting point temperature or viscous flow temperature of the polymer is below the thermal failure critical temperature of the separator. Like this, when the temperature of battery is higher, the polymer of parcel in the porous carbon material skin can be by high temperature melting for porous carbon material exposes in electrolyte, adsorbs the gas that decomposes out in the electrolyte, thereby avoids the battery to explode. Therefore, by using such a separator, not only can the performance of the battery be secured, but also the safety of the battery can be improved.

Drawings

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

fig. 2 is a flowchart of a method for manufacturing a separator provided in an embodiment of the present application.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some, but not all, embodiments of the present application. Without conflict, the embodiments and features of the embodiments described below may be combined with each other. On the basis of the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without any creative effort belong to the protection scope of the present application.

The embodiment of the application provides a diaphragm. Referring to fig. 1, fig. 1 is a schematic structural diagram of a diaphragm provided in an embodiment of the present application. As shown in fig. 1, the diaphragm includes: a separator body 100 and a flame retardant coating 200 coated on the separator body 100;

wherein the flame retardant coating layer 200 comprises a porous carbon material and a polymer wrapping the porous carbon material;

the melting point temperature or viscous flow temperature of the polymer is below the critical temperature for thermal failure of the separator.

Specifically, the separator body 100 has a main function of separating a positive electrode sheet and a negative electrode sheet of a battery, preventing short circuit due to contact between the two electrodes, and a function of allowing electrolyte ions to pass therethrough. The material of the separator body 100 is electrically non-conductive, and the physical and chemical properties thereof have a great influence on the performance of the battery. The separator body 100 used differs depending on the type of battery. In the lithium ion battery system, since the electrolyte is an organic solvent, a material resistant to the organic solvent is required for the separator body 100. A polyolefin porous film having high strength and being thinned can be generally used as the separator body 100. The flame retardant coating 200 may include a porous carbon material and a polymer wrapping the porous carbon material, and is configured to melt the polymer when the temperature of the electrolyte is high, and expose the porous carbon material in the electrolyte to absorb gas generated by decomposition of the electrolyte, so that the flame retardant coating 200 may achieve effects of preventing combustion and avoiding explosion. Specifically, the porous carbon material herein can be obtained by carbonizing a hypercrosslinked polymer. The porous carbon material has a large number of micropore and mesoporous structures, has a high specific surface area and has strong gas adsorption capacity.

The thermal failure critical temperature of the separator is the critical temperature of the failure state reached by the separator under the condition of thermal shrinkage. That is, the thermal failure critical temperature of the separator is a temperature at which the separator shrinks by heat to a critical state where the positive electrode sheet and the negative electrode sheet are not completely separated. If the temperature in the battery reaches the thermal failure critical temperature of the diaphragm, the diaphragm can be seriously shrunk, and the positive plate and the negative plate in the battery are short-circuited to fail.

It is noted that the polymer in this application is a low melting point polymer such that the polymer reaches its melting point temperature or viscous flow temperature before the temperature within the cell reaches the critical temperature for thermal failure of the separator. The polymer may be a crystalline polymer, such as Polypropylene (PP), Polyethylene (PE), etc., or may be a non-crystalline polymer, such as a silicon-based polymer, etc. When the polymer in this application is a crystalline polymer, the melting point temperature corresponds to the temperature at which the crystalline polymer can be transformed from a solid state to a liquid state; when amorphous polymers are used as polymers in the present application, the viscous flow temperature corresponds to the temperature at which the amorphous polymer can be transformed from a high-elastic state to a viscous state.

In this embodiment, since the flame retardant coating 200 is coated on the separator body 100, when the temperature of the battery is high, the polymer wrapped on the outer layer of the porous carbon material is melted at high temperature, so that the porous carbon material is exposed in the electrolyte, and the decomposed gas in the electrolyte is adsorbed, thereby preventing the battery from exploding. Therefore, by using such a separator, not only can the performance of the battery be secured, but also the safety of the battery can be improved.

Further, the flame retardant coating layer 200 is applied to a first surface and/or a second surface of the separator body 100, the first surface and the second surface being opposite to each other of the separator body 100.

Specifically, the flame retardant coating 200 may be coated on one surface of the diaphragm body 100, such as a first surface or a second surface of the diaphragm body 100; it may also be coated on both surfaces of the diaphragm body 100, such as the first surface and the second surface of the diaphragm body 100, which is not particularly limited in this application. The first surface here may refer to one surface that is in contact with a positive electrode tab in the battery, and the second surface may refer to one surface that is in contact with a negative electrode tab in the battery.

In one embodiment, the flame retardant coating layer 200 may be coated on both the first surface and the second surface of the separator body 100, such that when the temperature inside the battery reaches the melting point temperature or the viscous flow temperature of the polymer, the flame retardant coating layer 200 on both sides of the separator body 100 may release the radical scavenger, so that the radical scavenger can be rapidly distributed at different positions of the electrolyte.

Further, the flame retardant coating layer 200 is applied at a thickness ranging from 1 to 8 micrometers.

It should be noted that the thicker the coating thickness of the flame retardant coating layer 200 is, the higher the content of the radical scavenger in the battery is, and the better the flame retardant effect is. But in order to ensure that the volume of the roll core structure in the battery is not influenced by the thickness of the diaphragm, the coating thickness of the flame-retardant coating layer 200 can be set within the range of 1-8 microns, so that the volume of the roll core structure is not greatly influenced by the diaphragm, and a better flame-retardant effect can be achieved.

Further, the porous carbon material is obtained by carbonizing a hypercrosslinked polymer, and the specific surface area of the porous carbon material is greater than or equal to 3000m²And/g, wherein the hypercrosslinked polymer is at least one of benzene, pyridine and thiophene.

In one embodiment, a hypercrosslinked polymer of any one or any combination of benzene, pyridine and thiophene can be selected and carbonized to obtain the porous carbon material. When the hypercrosslinked polymer comprises benzene, pyridine and thiophene, the proportion of benzene, pyridine and thiophene can be configured according to actual needs, and the application is not particularly limited. The porous carbon material prepared by carbonizing benzene, pyrrole and/or thiophene with ultrahigh crosslinking has a high specific surface area which can reach 3000m²More than/g, therefore, compared with the conventional porous material, the specific surface area is much larger, and the adsorption capacity to the gas decomposed in the electrolyte is stronger. In this embodiment, the porous carbon material prepared from the super-crosslinked polymer has a large number of micropores and mesoporous structures and high adsorption capacity. Can better adsorb the gas in the electrolyte, thereby playing a better role in flame retardance.

Further, the polymer is polypropylene, polyethylene or silicon polymer, and the melting point temperature or viscous flow temperature of the polymer ranges from 90 ℃ to 130 ℃.

In one embodiment, since the melting point temperature of polypropylene and polyethylene and the viscous flow temperature of silicon-based polymer are both low, typically in the range of 90 ℃ to 130 ℃, any one of polypropylene, polyethylene and silicon-based polymer can be selected as the polymer in the present application. Therefore, when the internal temperature of the battery reaches a temperature range of 90-130 ℃, the polymer can be melted, and the porous carbon material wrapped in the polymer can be exposed.

Referring to fig. 2, fig. 2 is a flowchart of a method for manufacturing a separator provided in an embodiment of the present application. The preparation method of the diaphragm comprises the following steps:

step 201, adding a hypercrosslinked polymer into a potassium hydroxide solution, stirring, and carbonizing the stirred mixed solution to obtain a porous carbon material;

step 202, adding a polymer into a solvent, heating, and stirring after the polymer is dissolved to obtain a polymer solution, wherein the melting point temperature or viscous flow temperature of the polymer is lower than the thermal failure critical temperature of the diaphragm;

step 203, adding a porous carbon material into the polymer solution and stirring to obtain a flame-retardant coating;

and 204, coating the flame-retardant coating on the diaphragm body to obtain the diaphragm.

The step 201 may be executed simultaneously with the step 202, may be executed prior to the step 202, or may be executed after the step 202, which is not limited in this application.

Specifically, the polymer may be a crystalline polymer, such as Polypropylene (PP), Polyethylene (PE), and the like, or may be an amorphous polymer, such as a silicon-based polymer, and the like. Adding the polymer into a solvent, heating the solvent to the melting point temperature or viscous flow temperature of the polymer, and fully stirring after the polymer is dissolved in the solvent to obtain a polymer solution.

The hypercrosslinked polymer may be obtained by carbonizing any one or a combination of any more of benzene, pyridine and thiophene, and the present application is not particularly limited. The above-mentioned hypercrosslinked polymer may be added to a potassium hydroxide solution and sufficiently stirred, and the stirred solution may be subjected to a carbonization treatment at a temperature of 700 ℃ and 1000 ℃, for example, at a temperature of 900 ℃, and then the remaining salt (i.e., solid potassium hydroxide) may be extracted, thereby obtaining a porous carbon material. Thus, the porous carbon material can be added into the polymer solution again to obtain the flame-retardant coating of the polymer-wrapped porous carbon material. And finally, coating the flame-retardant coating on the first surface and/or the second surface of the diaphragm body to obtain the diaphragm.

The diaphragm prepared by the preparation method of the embodiment can be used for wrapping the porous carbon material by the polymer and is positioned on the diaphragm body when the temperature of the battery is low, so that the electrolyte cannot be influenced; when the temperature of battery is higher, the polymer of parcel in the porous carbon material skin is by high temperature melting for the porous carbon material exposes in electrolyte, adsorbs the gas that electrolyte decomposition produced, thereby avoids the battery to explode. Therefore, by using such a separator, not only can the performance of the battery be secured, but also the safety of the battery can be improved.

Further, the solvent is xylene, toluene or decalin.

Specifically, any one of xylene, toluene and decalin can be selected as a solvent to participate in the preparation process of the polymer solution. The solvent has better solubility, so the solvent can be fully fused with the polymer to obtain a polymer solution.

Further, the ratio of the hypercrosslinked polymer to the potassium hydroxide solution was 1: 4.

Specifically, when the hypercrosslinked polymer is added to the potassium hydroxide solution, the ratio of the hypercrosslinked polymer to the potassium hydroxide solution can be made to be 1: 4. Therefore, a suitable alkaline environment can be provided for carbonization treatment of the hypercrosslinked polymer, so that the hypercrosslinked polymer can achieve a better carbonization effect.

In addition, this application embodiment also provides a battery, and this battery includes: positive plate, negative plate and the diaphragm.

Alternatively, the separator is located between the positive electrode sheet and the negative electrode sheet, and the separator, the positive electrode sheet and the negative electrode sheet are wound.

It should be noted that the specific embodiment of the battery is the same as the embodiment of the separator described above, and the same technical effects can be achieved, and are not described herein again.

The following examples are provided to further illustrate the advantageous effects of the present invention.

Example 1:

and winding the conventional separator (i.e. the separator body without the flame-retardant coating), the positive plate and the negative plate into a battery. The pass rate of the safety test was 40%.

Example 2:

a separator to be coated with a flame retardant coating layer prepared from a conventional porous material (the specific surface area of the conventional porous material is 2000 m)²Below/g), winding the positive plate and the negative plate into a battery. Safety surveyThe pass rate of the test was 60%. Example 3:

mixing ultrahigh cross-linked benzene and potassium hydroxide at a ratio of 1:4, heating at 900 deg.C, extracting residual salt, and drying to obtain porous carbon material with specific surface area of about 3000m²(ii)/g; heating and dissolving polypropylene by using dimethylbenzene, adding a porous carbon material after dissolving, and stirring to enable the polypropylene solution to uniformly wrap the porous carbon material to prepare a flame-retardant coating; and uniformly coating the flame-retardant coating on the first surface and the second surface of the diaphragm, wherein the coating thickness of the two surfaces is 1 mu m, preparing the final diaphragm, and winding the final diaphragm, the positive plate and the negative plate into a battery. The pass rate of the safety test was 80%.

Example 4:

mixing ultrahigh cross-linked benzene and potassium hydroxide at a ratio of 1:4, heating at 900 deg.C, extracting residual salt, and drying to obtain porous carbon material with specific surface area of about 3000m²(ii)/g; heating and dissolving polypropylene by using dimethylbenzene, adding a porous carbon material after dissolving, and stirring to enable the polypropylene solution to uniformly wrap the porous carbon material to prepare a flame-retardant coating; and uniformly coating the flame-retardant coating on the first surface and the second surface of the diaphragm, wherein the coating thickness of the two surfaces is 1.5 mu m, preparing the final diaphragm, and winding the final diaphragm, the positive plate and the negative plate into a battery. The pass rate of the safety test was 90%.

Example 5:

mixing ultrahigh cross-linked benzene and potassium hydroxide at a ratio of 1:4, heating at 900 deg.C, extracting residual salt, and drying to obtain porous carbon material with specific surface area of about 3000m²(ii)/g; heating and dissolving polypropylene by using dimethylbenzene, adding a porous carbon material after dissolving, and stirring to enable the polypropylene solution to uniformly wrap the porous carbon material to prepare a flame-retardant coating; and uniformly coating the flame-retardant coating on the first surface and the second surface of the diaphragm, wherein the coating thickness of the two surfaces is 2 microns, preparing the final diaphragm, and winding the final diaphragm, the positive plate and the negative plate into a battery. The pass rate of the safety test is 100%.

Example 6:

mixing ultra-high crosslinked pyrrole and potassium hydroxide at a ratio of 1:4, heating at 900 deg.C, extracting residual salt, and drying to obtain porous carbon material with specific surface area of about 4300m²(ii)/g; heating and dissolving polypropylene by using dimethylbenzene, adding a porous carbon material after dissolving, and stirring to enable the polypropylene solution to uniformly wrap the porous carbon material to prepare a flame-retardant coating; and uniformly coating the flame-retardant coating on the first surface and the second surface of the diaphragm, wherein the coating thickness of the two surfaces is 1.5 mu m, preparing the final diaphragm, and winding the final diaphragm, the positive plate and the negative plate into a battery. The pass rate of the safety test is 100%.

Example 7:

mixing ultrahigh cross-linked thiophene and potassium hydroxide at a ratio of 1:4, heating at 900 deg.C, extracting residual salt, and drying to obtain porous carbon material with specific surface area of about 3300m²(ii)/g; heating and dissolving polypropylene by using dimethylbenzene, adding a porous carbon material after dissolving, and stirring to enable the polypropylene solution to uniformly wrap the porous carbon material to prepare a flame-retardant coating; and uniformly coating the flame-retardant coating on the first surface and the second surface of the diaphragm, wherein the coating thickness of the two surfaces is 1.5 mu m, preparing the final diaphragm, and winding the final diaphragm, the positive plate and the negative plate into a battery. The pass rate of the safety test was 90%.

The safety tests of examples 1 to 7 described above, all of which were conducted at 130 ℃ for 1 hour after full charge storage, judged whether the battery ignited or whether it exploded.

As can be seen from the above examples 1 to 7, example 1 differs from examples 2, 3, 4, 5, 6 and 7 in that: example 1 employed a conventional separator, example 2 employed a separator coated with a conventional porous material, and examples 3 to 7 employed separators coated with a porous carbon coating prepared according to the present invention. By comparison, the safety test passing rate of the separator coated with the flame-retardant coating prepared by the invention is much higher than that of the conventional separator and the separator coated with the flame-retardant coating prepared by the conventional porous material.

The difference between examples 3 to 5 is that: the flame retardant coating layer was coated on both surfaces of the separator at a thickness of 1 μm in example 3, 1.5 μm in example 4, and 2 μm in example 5. By comparison, the thicker the coating thickness of the flame retardant coating layer is, the higher the safety of the battery is.

Example 4 differs from examples 6 and 7 in that: in example 4, a benzene hypercrosslinked polymer, in example 6, a pyrrole hypercrosslinked polymer, and in example 7, a thiophene hypercrosslinked polymer were selected. According to the comparison, the specific surface area of the porous carbon material obtained after carbonization is larger when pyrrole is selected as the super-crosslinked polymer than benzene or thiophene is selected as the super-crosslinked polymer, so that the adsorption capacity of the porous carbon material on gas decomposed by electrolyte is stronger under the condition of coating a flame-retardant coating with the same thickness, and therefore, the passing rate of a safety test when pyrrole is selected as the super-crosslinked polymer is high.

The embodiments described above are described with reference to the drawings, and various other forms and embodiments are possible without departing from the principles of the present application, so that the present application is not to be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. In the drawings, the size and relative sizes of components may be exaggerated for clarity. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. The terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, components, and/or components, but do not preclude the presence or addition of one or more other features, integers, components, and/or groups thereof. Unless otherwise indicated, a range of values, when stated, includes the upper and lower limits of the range and any subranges therebetween.

While the foregoing is directed to the preferred embodiment of the present application, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the principles of the disclosure and, therefore, the scope of the disclosure is to be defined by the appended claims.