CN116683118A

CN116683118A - Para-aramid dissolution system and application thereof, aramid diaphragm and preparation method thereof, and aramid ceramic composite diaphragm and preparation method thereof

Info

Publication number: CN116683118A
Application number: CN202310664318.9A
Authority: CN
Inventors: 曹大为; 周广盖; 蒋广翔; 陈永乐; 廖晨博; 马芸; 孙照伟; 李文强; 庄志; 程跃
Original assignee: Shanghai Energy New Materials Technology Co Ltd
Current assignee: Shanghai Energy New Materials Technology Co Ltd
Priority date: 2022-08-29
Filing date: 2023-06-06
Publication date: 2023-09-01
Also published as: CN115663394A

Abstract

The embodiment of the application provides a dissolving system of para-aramid fiber and application thereof, an aramid fiber diaphragm and a preparation method thereof, an aramid fiber ceramic composite diaphragm and a preparation method thereof, wherein the dissolving system of para-aramid fiber comprises a proton donor, a solvent and a cosolvent, the solvent comprises an aprotic strong polar solvent, and the cosolvent comprises strong alkali. The application of the dissolving system of the para-aramid in dissolving the para-aramid can solve the problems of large dissolving damage and long dissolving time. In some preparation methods, a dissolving system containing strong alkali is adopted to dissolve para-aramid fiber, a porous membrane layer is formed under the condition of containing PVDF, and PVDF and strong alkali can react to form a porous structure with three-dimensional stereo, so that the bonding performance is improved through PVDF, and meanwhile, better air permeability can be maintained compared with that of directly coating PVDF; the PVDF is controlled to be used in a lower specific range, so that island distribution of PVDF can be formed, and the air permeability can be better improved.

Description

Para-aramid dissolution system and application thereof, aramid diaphragm and preparation method thereof, and aramid ceramic composite diaphragm and preparation method thereof

Cross reference

The present application claims priority from chinese patent application (2022110397163) filed on the year 2022, month 08 and 29, which is incorporated herein by reference in its entirety.

Technical Field

The application relates to the technical field of aramid fiber dissolution, in particular to a para-aramid fiber dissolution system and application thereof, an aramid fiber diaphragm and a preparation method thereof, and an aramid fiber ceramic composite diaphragm and a preparation method thereof.

Background

Para-aramid fiber is usually dissolved in the spinning, chemical modification and processing processes, and then can be subjected to the next reaction or process. So how to obtain a simple and efficient method for dissolving para-aramid is extremely important.

For the dissolution of para-aramid, the most commonly used dissolution method at present is concentrated sulfuric acid dissolution, but the concentrated sulfuric acid has extremely strong corrosiveness, and the method has direct or potential damage to equipment and production personnel. Another method of the present application is to use aprotic highly polar solvents in combination with salts as co-solvents for dissolution, but such dissolution methods generally require a long dissolution time.

In addition, the aramid separator generally has no adhesive property, cannot meet the process requirements of soft-pack batteries and square-shell batteries, and can be used for cylindrical batteries. In order to improve the adhesive property, an adhesive layer is generally added to the surface of the aramid separator, but this approach generally results in a serious decrease in the air permeability of the aramid separator.

Disclosure of Invention

The application aims to provide a dissolving system of para-aramid fiber and application thereof, an aramid fiber diaphragm and a preparation method thereof, an aramid fiber ceramic composite diaphragm and a preparation method thereof, and in some embodiments, the problems of large dissolving damage and long dissolving time can be solved; in some embodiments, the adhesion properties of the aramid separator can be improved while maintaining good breathability.

Embodiments of the present application are implemented as follows:

in a first aspect, embodiments of the present application provide a solution system for para-aramid fiber, including a proton donor, a solvent, and a cosolvent, where the solvent includes an aprotic strongly polar solvent, and the cosolvent includes a strong base.

In a second aspect, an embodiment of the present application provides an application of the dissolution system of para-aramid according to the embodiment of the first aspect in dissolving para-aramid, including: and dissolving the para-aramid in a dissolving system of the para-aramid.

In a third aspect, an embodiment of the present application provides a method for preparing an aramid separator, including: the dissolved para-aramid slurry formed by the application of the above second aspect embodiment is coated on at least one side surface of the porous base film.

In a fourth aspect, an embodiment of the present application provides an aramid separator, which is made by the method for preparing an aramid separator according to the embodiment of the third aspect.

In a fifth aspect, an embodiment of the present application provides a method for preparing an aramid ceramic composite separator, including: mixing the ceramic slurry with the dissolved para-aramid slurry formed by the application of the embodiment of the second aspect to obtain an aramid ceramic composite slurry; and coating the aramid ceramic composite slurry on at least one side surface of the base film.

In a sixth aspect, an embodiment of the present application provides an aramid ceramic composite separator, which is made by the method for preparing an aramid ceramic composite separator according to the fifth aspect.

In a seventh aspect, an embodiment of the present application provides a method for preparing an aramid separator, including: dissolving para-aramid in a para-aramid dissolving system to form dissolved para-aramid slurry; wherein, the dissolving system of para-aramid comprises strong alkali; coating para-aramid pulp on at least one side surface of a base film, and forming a para-aramid porous film layer by the para-aramid pulp under a PVDF-containing system; wherein PVDF is distributed in the para-aramid porous membrane layer.

In an eighth aspect, an embodiment of the present application provides an aramid separator, which is made by the method for preparing an aramid separator according to the seventh aspect; the aramid membrane comprises a base membrane and a para-aramid porous membrane layer positioned on at least one side surface of the base membrane, wherein PVDF is distributed in the para-aramid porous membrane layer.

The para-aramid dissolution system and application thereof, the aramid diaphragm and the preparation method thereof, and the aramid ceramic composite diaphragm and the preparation method thereof provided by the embodiment of the application have the beneficial effects that:

in the dissolving system of para-aramid, the speed of dissolving para-aramid can be effectively improved by the combined action of strong alkali, proton donor and aprotic strong polar solvent, and the quick dissolving of para-aramid can be realized at normal temperature. Wherein, by selecting the aprotic strong polar solvent with specific combination, the speed of dissolving para-aramid at normal temperature can be further improved remarkably.

The dissolving system of para-aramid fiber does not contain concentrated sulfuric acid, does not need to be heated in the dissolving process, has convenient operation and simple equipment requirement, and has little damage to equipment and production personnel.

In the solution system of para-aramid, the kind of the solvent is not limited to a specific one, and the solvent selectivity is wide.

In some preparation methods of aramid fiber membranes, the heat resistance of the membrane can be improved due to the introduction of aramid fiber and PVDF into the membrane. PVDF is added into the aramid fiber diaphragm, so that the bonding performance of the diaphragm can be improved by the PVDF; in the hot pressing process of the soft package battery and the square shell battery, PVDF can be softened and an adhesive effect is provided, so that the aramid fiber diaphragm can be widely applied. PVDF also has good liquid absorption and retention capacity, and the introduction of PVDF can also improve the liquid absorption and retention capacity of the diaphragm.

And the solution system containing strong alkali is adopted to dissolve the para-aramid, and a para-aramid porous membrane layer is formed under the condition of containing PVDF, so that the PVDF and the strong alkali can react to remove one HF and form double bonds, the charge balance in the original para-aramid is broken, and thus, the composite gel of the aramid and the PVDF is formed, and has a three-dimensional loose porous structure. Furthermore, the consumption of PVDF is controlled in a lower specific range, and when the PVDF has certain promotion effects on the adhesive property, heat resistance, liquid absorption and retention capacity and the like of the diaphragm, discontinuous island-shaped distribution can be formed by the PVDF with lower consumption in the drying shrinkage process, thereby being beneficial to further improving the air permeability of the diaphragm, and the PVDF with island-shaped distribution can better exert the liquid absorption and retention capacity.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic diagram of a dissolving process of para-aramid fibers provided by the application;

FIG. 2 is a graph showing the dissolution state of the para-aramid dissolution system according to some examples and comparative examples of the present application in different time periods when the para-aramid is dissolved;

FIG. 3 is an SEM image of an aramid ceramic composite separator prepared in preparation example 1 of the present application;

FIG. 4 is an SEM image of an aramid ceramic composite separator prepared in preparation example 2 of the present application;

FIG. 5 is an SEM image of an aramid ceramic composite separator prepared in preparation example 3 of the application;

FIG. 6 is a schematic diagram of a mechanism for forming a para-aramid porous membrane layer from a para-aramid slurry in a PVDF-containing system according to the present application;

FIG. 7 is an SEM image of a para-aramid porous film layer of the surface of the aramid separator prepared in preparation example 5 of the present application;

FIG. 8 is an SEM image of a para-aramid porous film layer of the surface of the aramid separator prepared in preparation example 8 of the present application;

FIG. 9 is an SEM image of a para-aramid porous film layer of the surface of the aramid separator prepared in preparation example 9 of the present application;

FIG. 10 is an SEM image of a para-aramid porous film layer of the surface of the aramid separator prepared in preparation example 10 of the application;

FIG. 11 is an SEM image of a para-aramid porous film layer of the surface of an aramid separator prepared in preparation example 11 of the present application.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions of the embodiments of the present application will be clearly and completely described below. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.

In the description of the present application, unless otherwise indicated, "plural" in "one or more" means two or more; the range of "value a to value b" includes both ends "a" and "b", and "unit of measure" in "value a to value b+ unit of measure" represents "unit of measure" of both "value a" and "value b".

For a solvent system capable of dissolving, the dissolution rate can be generally improved by auxiliary means such as heating, stirring, shaking and the like. The applicant has noted that in some current designs, the dissolution rate is increased by heat treatment when the dissolution of the aramid fibers is performed. However, in a system for dissolving aramid fiber, a heating method is easy to cause adverse effects such as volatilization of an organic solvent, consumption of more energy, easy combustion and explosion of a high-temperature solvent, and the like.

The applicant also noted that when the dissolution of the aramid fiber is performed, strong base is adopted to be matched with DMSO (dimethyl sulfoxide) for dissolution, hydrogen bonds among different molecular chains in the para-aramid fiber are easy to break under the action of the strong base, and amide bonds in the molecular chains are easy to hydrolyze under the action of the strong base, so that the para-aramid fiber is easy to be rapidly dissolved. However, in some current protocol designs, the system is limited to use with DMSO for efficient dissolution and single solvent selectivity.

Based on the above, the inventor further researches and discovers that in a dissolution system, by adopting the combination of strong alkali, proton donor and aprotic strong polar solvent, the solvent is not limited to DMSO, the speed of dissolving para-aramid can be effectively improved, and the quick dissolution of para-aramid can be realized at normal temperature.

The para-aramid dissolution system and application thereof, the aramid diaphragm and preparation method thereof, and the aramid ceramic composite diaphragm and preparation method thereof of the application are specifically described below with reference to specific embodiments.

Aramid fibers are short for aromatic polyamide fibers, which are generally classified into para-aramid, meta-aramid, and heterocyclic aramid. Because most of the heterocyclic aramid fibers are obtained by copolymerizing para-aramid fibers with other monomers, the heterocyclic aramid fibers are classified into para-aramid fibers in the application.

The mechanism of dissolving para-aramid in the dissolving system of para-aramid provided by the embodiment of the application is shown in fig. 1, and the dissolving system is mainly divided into two steps, wherein in the first step, hydrogen bonds among different molecular chains in the para-aramid are broken under the action of strong alkali, the acting force among the molecular chains is weakened, and finally nanofibers are obtained under the synergistic effects of electrostatic repulsion, pi-pi conjugated effect and the like; and secondly, performing hydrolysis reaction on amide bonds in a molecular chain under the action of strong alkali to obtain para-aramid nanofibers with lower molecular weight.

The solution system of the para-aramid fiber provided by the application can be prepared according to a specific feeding sequence, and is exemplified by a solution system of the para-aramid fiber, wherein a cosolvent is dissolved in a proton donor to form a uniform solution, the solvent is mixed when the solvent contains two or more components, and then the uniform solution containing the cosolvent and the proton donor is dropwise added into the solvent under the condition of stirring, so that the solution system of the para-aramid fiber is obtained.

Regarding proton donors:

in the present application, proton donor means a proton donor capable of providing H ⁺ In some possible embodiments, the proton donor is water or an organic protic acid. Wherein the organic protic acid may be selected from organic sulfonic acids such as, but not limited to, one or more of methanesulfonic acid, trifluoromethanesulfonic acid, p-toluenesulfonic acid, and dodecylbenzenesulfonic acid.

In the solution system of the para-aramid fiber provided by the application, the proton donor is matched with the solvent according to a proper mass ratio, so that the solution system is favorable for better and rapidly dissolving the para-aramid fiber at normal temperature.

As an example, the mass ratio of proton donor to solvent is (0.01-10): 100, for example, but not limited to, 0.01: 100. 0.1: 100. 1: 100. 2: 100. 5: 100. 8:100 and 10:100, or a range value between any two.

Regarding the solvent:

in the present application, the aprotic highly polar solvent refers to an aprotic polar solvent having a strong polarity, and in some possible embodiments, the aprotic highly polar solvent includes one or more of DMAc (N, N-dimethylformamide), DMF (N, N-dimethylacetamide), NMP (N-methylpyrrolidone), and DMSO (dimethylsulfoxide).

In the solution system of para-aramid provided by the application, the solvent comprises an aprotic strong polar solvent, which means that: the solvent may be composed entirely of aprotic strongly polar solvents, wherein the types of aprotic strongly polar solvents may be one or more; the dissolution may also consist of aprotic strongly polar solvents and other types of solvents, where the other types of solvents are optionally polar solvents, for example aprotic polar solvents having a slightly lower polarity than the aprotic strongly polar solvents, and for example protic polar solvents.

As a first example, the solvent consists of an aprotic strongly polar solvent.

The research shows that DMAc, DMF and NMP are independently adopted as solvents, so that the solution system of the para-aramid provided by the application can better and rapidly dissolve the para-aramid at normal temperature.

Based on this, optionally, in the first example, the solvent is composed of one of DMAc, DMF, and NMP.

As a second example, the solvent consists of two aprotic strongly polar solvents.

The research shows that when two non-proton type strong polar solvents are mixed to be used as solvents, DMAc, DMF and NMP are used as main components, DMSO is used as a secondary component, so that the solution system of the para-aramid provided by the application can better and rapidly dissolve the para-aramid at normal temperature.

Based on this, alternatively, in the second example, the solvent is composed of DMSO and one of DMAc, DMF and NMP, and the mass ratio of DMSO in the solvent, wt1, satisfies 0.1% to wt1 < 50%.

Further research shows that especially under the condition that DMAc and DMSO are mixed as solvents, DMAc and DMSO are controlled according to a specific proportion, so that the speed of dissolving para-aramid at normal temperature can be remarkably improved, and the dissolving system of the para-aramid provided by the application can completely dissolve the para-aramid at normal temperature for 60 min.

Based on this, further, in the second example, the solvent is composed of DMAc and DMSO, and in the solvent, the mass ratio wt1 of DMSO satisfies wt 1.ltoreq.5%, wt1 is, for example, but not limited to, any one point value or a range value between any two of 1%, 2%, 3%, 4% and 5%.

As a third example, the solvent includes an aprotic strongly polar solvent and an aprotic polar solvent, the aprotic polar solvent including one or more of methanol, ethanol, and acetone; in the solvent, the mass ratio of the aprotic strong polar solvent is 80-99.9%.

In a third example, the mass fraction of the aprotic strongly polar solvent is, for example, but not limited to, any one point value or range value between any two of 80%, 85%, 90%, 95%, 99% and 99.9%.

As a fourth example, the solvent includes an aprotic strongly polar solvent and water; in the solvent, the mass ratio of the aprotic strong polar solvent is 90-99.99%.

In a fourth example, the mass fraction of the aprotic strongly polar solvent is, for example, but not limited to, any one point value or range value between any two of 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% and 99%.

Regarding the co-solvent:

in the present application, strong bases used in cosolvents refer to the well-defined strong bases that are basic and include, in some possible embodiments, naH, KH, t-BuOK, KOH, naOH and C ₂ H ₅ One or more of ONa.

Optionally, the cosolvent further comprises a basic salt, a baseSalts include LiCl, naCl, KCl and CaCl ₂ One or more of the following.

The applicant researches find that under the condition that the cosolvent comprises strong alkali and basic salt, the strong alkali is used as the main component of the cosolvent, so that the dissolving system is favorable for better and rapidly dissolving the para-aramid at normal temperature.

By way of example, the molar ratio of the basic salt in the co-solvent, wn1, satisfies 1% to 50% of wn1, where wn1 is, for example, but not limited to, any one point value or range value between any two of 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% and 50%.

By way of example, the dissolution system of para-aramid of the above embodiments has application in dissolving para-aramid, such as, but not limited to, for the preparation of body armor, tires, brake pads, cables, battery separator coatings, and the like.

In the application, when the para-aramid is dissolved by adopting a dissolution system of the para-aramid, the temperature condition can be any temperature from room temperature to the melting point of the main component of the solvent.

According to research, the solution system of the para-aramid provided by the application can be used for rapidly dissolving the para-aramid at normal temperature, and can be used for realizing complete dissolution of the para-aramid in 12 hours.

Based on this, as an example, the dissolution treatment is performed at room temperature, and the time of the dissolution treatment is 12 hours or less.

In the technical scheme of the room temperature dissolution of the present application, auxiliary means such as stirring and shaking may be adopted in order to reasonably increase the dissolution rate.

Based on this, as an example, during the dissolution process, stirring by a stirring paddle, magnetic stirring, or ultrasonic vibration is accompanied.

In some possible embodiments, the para-aramid is selected from one of Kevlar para-aramid of DuPont, twaron para-aramid of Japan Diman, technophora para-aramid of Shandong Tai and Technora Heteropoly-aramid of Japan Diman, homo-polyamide containing a paraphenylene terephthalamide structure, and co-polyamide containing a paraphenylene terephthalamide structure. Among them, the homopolyamide containing the paraphenylene terephthalamide structure and the copolyamide containing the paraphenylene terephthalamide structure may be manufactured or homemade by commercial manufacturers currently on the market.

The research shows that the solution system of the para-aramid fiber provided by the application can be used for effectively dissolving the para-aramid fiber at room temperature when being applied to dissolving the para-aramid fiber.

In the present application, the morphology of the para-aramid of the above-mentioned kind used is not limited, and the morphology of the para-aramid includes, for example, one or more of pulp, long fiber and short fiber, for example, one of them.

The coating method is not limited, and is, for example, but not limited to, extrusion coating, gravure coating, bar coating, dip coating, and the like.

The material of the porous base film may be selected as desired, and in some possible embodiments the material of the porous base film comprises one or more of polyethylene terephthalate, polybutylene terephthalate, polyether, polyacetal, polyamide, polycarbonate, polyimide, high density polyethylene, low density polyethylene, linear low density polyethylene, ultra-high molecular weight polypropylene, and non-woven fabric.

The mixture ratio of the para-aramid pulp and the ceramic pulp can be prepared according to the requirement, and in some possible embodiments, the volume ratio of the para-aramid pulp to the ceramic pulp is (2-4): (1-3), such as but not limited to any one point value or range value between any two of 2:1, 3:1, 4:1, 2:2, 3:2, 2:3, and 4:3.

Regarding the ceramic slurry, as an example of an aspect, the solvent of the ceramic slurry is an organic solvent or a mixed solution of an organic solvent and water, the mass ratio of the organic solvent in the mixed solution of the organic solvent and water is equal to or more than 50%, and the organic solvent includes one or more of DMAc, NMP, DMSO and acetone.

Regarding the ceramic slurry, as an example of another aspect, the material of the ceramic in the ceramic slurry includes one or more of alumina, boehmite, barium sulfate, zirconia, and silica.

Regarding the ceramic slurry, as an example of yet another aspect, the mass ratio of ceramic to solvent in the ceramic slurry is (0.02-5): 1, such as, but not limited to, any one point value or range value between any two of 0.02:1, 0.05:1, 0.1:1, 0.5:1, 1:1, 2:1, 3:1, 4:1, and 5:1.

As for the base film, as one example, the material of the base film includes one or more of polyolefin and nonwoven fabric.

The para-aramid is dissolved in the dissolution system of the para-aramid after dissolution treatment, and the dissolution system of the para-aramid are mixed together, so that the dissolved para-aramid slurry comprises the dissolution system of the para-aramid and the dissolved micromolecule para-aramid.

In the solution system of para-aramid, strong base refers to a conventionally defined strong base, and its kind is not limited, and for example, reference may be made to the embodiment of the first aspect. In addition, specific solvents and/or other solutes can be added into the solution system of para-aramid fiber according to the requirement, and the specific composition of the solution system can be, for example, the embodiment of the first aspect, for example, the solution system uses aprotic strongly polar solvent as main solvent (the mass ratio in the solvent is more than 50%), for example, H can be included ₂ Proton donor such as O [ mass ratio of proton donor to solvent is (0.01-20): 100)]Also, for example, liCl, naCl, KCl, caCl can be included ₂ And the like.

The manner of applying the para-aramid slurry to the base film is not limited, and examples include, but are not limited to, extrusion coating, gravure roll coating, wire bar coating, dip coating, and the like.

The para-aramid is not limited in kind, see the embodiment of the first aspect.

The type of the base film is not limited, and is, for example, a polyolefin separator or a nonwoven fabric. In particular, see for example embodiments of the third aspect.

The manner of forming the para-aramid porous film layer in the PVDF-containing system is not limited, and is, for example, but not limited to, a thermally induced phase separation method, a non-solvent induced phase separation method, a vapor induced phase separation method, and the like.

It is understood that in the process of preparing an aramid separator, a pretreatment step and a post-treatment step may be performed as needed in addition to the above-mentioned steps. Wherein the pretreatment step comprises unreeling the base film, the post-treatment step comprises drying and reeling, and the drying comprises a first section of drying and a second section of drying which are sequentially carried out.

According to the preparation method of the aramid fiber diaphragm provided by the embodiment of the seventh aspect of the application, as the aramid fiber and PVDF are introduced into the diaphragm, the heat resistance of the diaphragm can be improved. PVDF is added into the aramid fiber diaphragm, so that the bonding performance of the diaphragm can be improved by the PVDF; in the hot pressing process of the soft package battery and the square shell battery, PVDF can be softened and an adhesive effect is provided, so that the aramid fiber diaphragm can be widely applied. PVDF also has good liquid absorption and retention capacity, and the introduction of PVDF can also improve the liquid absorption and retention capacity of the diaphragm.

And the solution system containing strong alkali is adopted to dissolve the para-aramid, and a para-aramid porous membrane layer is formed under the condition of containing PVDF, so that the PVDF and the strong alkali can react to remove one HF and form double bonds, the charge balance in the original para-aramid is broken, and thus, the composite gel of the aramid and the PVDF is formed, and has a three-dimensional loose porous structure.

In some possible embodiments, the process of forming the para-aramid slurry into a para-aramid porous membrane layer under a PVDF-containing system is performed using a non-solvent induced phase separation method.

In the embodiment, a non-solvent induced phase separation method is adopted to enable the para-aramid slurry to form a para-aramid porous membrane layer under a system containing PVDF, the PVDF can be dissolved in a coagulating liquid, the operation is convenient, the process requirement is low, and the PVDF can be fully contacted and reacted with an aramid coating.

Referring to fig. 6, a non-solvent induced phase separation process is exemplified which illustrates the mechanism of permeation enhancement of aramid nanofiber coatings by PVDF-containing coagulation baths. As can be seen from fig. 6, the aramid coating initially assumes a charge-balanced state,in a coagulation bath containing PVDF, the PVDF consumes OH ^- So that the charges repel each other, eventually forming a porous grid.

In the embodiment of the application, in the process of forming the para-aramid porous film layer by the non-solvent induced phase separation method, at least one section of coagulating bath containing PVDF is passed, and other sections of coagulating bath can be further included.

In some possible embodiments, the process of forming a para-aramid slurry into a para-aramid porous film layer under a PVDF-containing system comprises: performing first-stage solidification in the first-stage solidification liquid, and then performing second-stage solidification in the second-stage solidification liquid; wherein the first section of solidification liquid comprises a strong polar solvent and PVDF, and the second section of solidification liquid is water.

The type of strongly polar solvent is not limited, for example, but not limited to, including one or more of DMF, DMAc, and DMSO.

In some possible embodiments, the PVDF has a mass ratio in the first stage coagulation liquid of 0.5% to 1.5% so that the PVDF is island-like distributed in the porous membrane layer.

As an example, the mass fraction of PVDF in the first stage coagulation liquid is, for example, but not limited to, any one point value or a range value between any two of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4% and 1.5%.

In the embodiment, when PVDF has a certain improving effect on the bonding performance, heat resistance, liquid absorption and retention capacity and the like of the diaphragm, the PVDF with lower dosage can form discontinuous island-shaped distribution in the drying and shrinking process, which is beneficial to further improving the air permeability of the diaphragm, and the island-shaped distribution enables gaps to exist among PVDF points, and the gaps can contain electrolyte, so that the PVDF with island-shaped distribution can better exert the liquid absorption and retention capacity. If the dosage of PVDF is too low, the PVDF has small promotion effects on the adhesive property, heat resistance, liquid absorption and retention capacity and the like of the diaphragm; if the amount of PVDF is too high, island-shaped PVDF is not easily controlled and continuous PVDF is easily formed.

In some possible embodiments, the mass fraction of the strongly polar solvent in the first-stage coagulation liquid is greater than or equal to 50%.

In some exemplary embodiments, the mass ratio of the strongly polar solvent in the first-stage coagulation liquid is greater than or equal to 70%, and the strongly polar solvent comprises DMAC.

In some possible embodiments, the first stage of solidification takes from 1s to 60s and/or the second stage of solidification takes from 1s to 60s.

The time of the first and second stage solidification is, for example, but not limited to, any one point value or a range value between any two of 1s, 5s, 10s, 15s, 20s, 25s, 30s, 35, 40s, 45s, 50s, 55s and 60s, respectively.

In this embodiment, each coagulation stage has a proper coagulation time, and the efficiency and effect of the coagulation bath can be well considered.

In some possible embodiments, a solution system of para-aramid as in the example of the first aspect described above is employed.

It will be appreciated that in the embodiment of the seventh aspect, the solvent system for para-aramid is a solvent system containing a solvent capable of dissolving para-aramid, but the kind of solvent is not limited and may be selected as required. In some exemplary embodiments, the dissolution system based on the para-aramid of the first aspect embodiment is selected with reference to solvent requirements therein.

Optionally, the process of dissolving the para-aramid in the dissolution system of the para-aramid has a mass ratio of the co-solvent to the para-aramid of (50-300): 100, for example, but not limited to, any one point value or a range value between any two points of 50:100, 100:100, 150:100, 200:100, 250:100 and 300:100.

In the embodiment, the cosolvent and the para-aramid fiber have proper mass ratio, so that the cosolvent and the para-aramid fiber with proper ratio in a dissolution system of the para-aramid fiber are ensured, and when the para-aramid fiber porous membrane layer is further formed under a system containing PVDF with proper content, the cosolvent, the para-aramid fiber and the PVDF have proper ratio, and the para-aramid fiber porous membrane layer which is distributed in an island shape and has a three-dimensional loose porous structure can be better formed.

The dissolution system of para-aramid according to the embodiment of the first aspect, wherein the cosolvent comprises a strong base, and optionally LiCl, naCl, KCl and CaCl ₂₊ An isobasic salt, that is, when the cosolvent comprises only a strong base, the mass ratio of the cosolvent to the para-aramid, i.e., the mass ratio of the strong base to the para-aramid; when the cosolvent comprises strong base and basic salt, the mass ratio of the cosolvent to the para-aramid fiber is that of the total amount of the strong base and the basic salt to the para-aramid fiber.

In the seventh embodiment of the present application, other reinforcing components, adhesive components, and the like may be added to the para-aramid slurry as necessary.

As an example, before the process of coating the para-aramid slurry on at least one side surface of the base film, further comprising: mixing the ceramic slurry with para-aramid slurry.

That is, in the case of applying the slurry, the slurry contains ceramic particles in addition to the dissolved para-aramid fibers, and thus the para-aramid porous film layer is formed as a composite system of the para-aramid fibers and the ceramic particles.

Regarding the above embodiments, the aramid pulp and the ceramic pulp, the composition of the ceramic pulp, etc. may refer to the embodiments provided in the fifth aspect, and will not be described herein.

In some possible embodiments, PVDF is distributed in islands in the porous membrane layer.

In the embodiment of the application, PVDF is distributed in an island shape, which means that PVDF agglomerates are distributed in a discontinuous dispersion mode, and PVDF agglomerates are not directly connected.

The features and capabilities of the present application are described in further detail below in connection with the examples.

Example 1

0.2g of LiCl and 0.1g of KOH were weighed, poured into 1g of water, and magnetically stirred for 5 minutes to obtain an aqueous solution in which LiCl and KOH were dissolved. Then slowly dripping the solution into 25g of DMAc, and stirring magnetically during the dripping process to obtain a solution system of para-aramid.

0.5g of Technora short fiber was added to the above solution, magnetically stirred at room temperature for 24 hours, and after the agglomerated fiber macroparticles were filtered off, a pale yellow solution was obtained.

Example 2

0.2g of LiCl and 0.5g of KOH were weighed, poured into 1g of water, and magnetically stirred for 5 minutes to obtain an aqueous solution in which LiCl and KOH were dissolved. Then slowly dripping the solution into 25g of DMAc, and stirring magnetically during the dripping process to obtain a solution system of para-aramid.

0.5g of Technora short fiber is added into the solution, and the solution is magnetically stirred for 1.5 hours at normal temperature, and the agglomerated fiber large particles are filtered to obtain a dark green solution.

Example 3

0.75g of KOH was weighed out and poured into 1g of water to obtain an aqueous solution in which KOH was dissolved. Then slowly dripping the solution into 25g of DMAc, and stirring magnetically during the dripping process to obtain a solution system of para-aramid.

0.5g of Technora short fiber is added into the solution, and the solution is magnetically stirred for 2 hours at normal temperature, and the agglomerated fiber large particles are filtered to obtain a dark red solution.

Example 4

0.75g of KOH was weighed out and poured into 1g of water to obtain an aqueous solution in which KOH was dissolved. Then slowly dripping the solution into a mixed solvent of 24g of DMAc and 1g of DMSO, and carrying out magnetic stirring in the dripping process to obtain a para-aramid dissolution system.

0.5g of Technora short fiber is added into the solution, and the solution is magnetically stirred for 1 hour at normal temperature, and the agglomerated fiber macroparticles are filtered to obtain a dark red solution.

Example 5

0.75g of KOH was weighed out and poured into 1g of water to obtain an aqueous solution in which KOH was dissolved. Then, the solution is slowly added into a mixed solvent of 20g of DMAc and 5g of DMSO in a dropwise manner, and magnetic stirring is carried out in the dropwise manner, so that a para-aramid dissolution system is obtained.

0.5g of Technora staple was added to the above solution, magnetically stirred at room temperature for 12 hours, and after filtering off agglomerated large fiber particles, a dark red solution was obtained, but slightly lighter in color than in example 4.

Example 6

0.75g of KOH was weighed out and poured into 2g of water to obtain an aqueous solution in which KOH was dissolved. Then slowly dripping the solution into 25g of DMAc solvent, and stirring magnetically during the dripping process to obtain a solution system of para-aramid.

0.5g of Technora short fiber was added to the above solution, and the solution was magnetically stirred at room temperature for 90 minutes, and insoluble KOH was filtered off to obtain a pale red solution.

Example 7

0.75g of KOH was weighed out and poured into 5g of water to obtain an aqueous solution in which KOH was dissolved. Then slowly dripping the solution into 25g of DMAc solvent, and stirring magnetically during the dripping process to obtain a solution system of para-aramid.

To the above solution, 0.5g of Technora short fiber was added, and the solution was magnetically stirred at room temperature for 2 days, and was not completely dissolved.

Example 8

0.75g of KOH was weighed out and poured into 10g of water to obtain an aqueous solution in which KOH was dissolved. Then slowly dripping the solution into 25g of DMAc solvent, and stirring magnetically during the dripping process to obtain a solution system of para-aramid.

Comparative example 1

0.2g of LiCl was weighed out, poured into 1g of water, and magnetically stirred for 5 minutes to obtain an aqueous solution in which LiCl was dissolved. Then slowly dripping the solution into 25g of DMAc, and stirring magnetically during the dripping process to obtain a solution system of para-aramid.

To the above solution, 0.5g of Technora short fiber was added, and magnetically stirred at room temperature for 12 hours to obtain a pale white solution.

Comparative example 2

0.75g KOH was weighed and added to 25g DMAc solvent, and the solution system of para-aramid was obtained with magnetic stirring during the dropping, but it was found that KOH was not completely dissolved in DMAc solvent during the dropping.

0.5g of Technora short fiber was added to the above solution, and the solution was magnetically stirred at room temperature for 150 minutes, and insoluble KOH was filtered off to obtain a pale red solution.

The dissolution conditions of the para-aramid dissolution systems provided in examples and comparative examples were observed for different time periods when the para-aramid was dissolved, and the results are shown in fig. 2.

In the present application, some experimental conditions in each example and comparative example were collated for convenience of comparison, as shown in table 1. Meanwhile, the dissolution time of the para-aramid dissolved at normal temperature was measured to obtain the dissolution rate of the para-aramid, and the results are shown in table 1. Wherein, complete dissolution means that a uniform solution is obtained (a small amount of agglomerates can be removed by filtration); for experiments in which only KOH was used as a cosolvent, the color of the solution was changed to dark red as a judgment index. The dissolution time is the time taken from the addition of the cosolvent until a homogeneous solution is obtained after complete dissolution of the para-aramid.

TABLE 1 dissolution conditions and dissolution time of examples and comparative examples

As can be seen from fig. 2 and table 1:

comparative example 1 was conducted using dmac+licl+h ₂ O is dissolved in a system with dissolution time of 24 hours or more; examples 1 to 3, in which a suitable amount of KOH was added to the cosolvent or a suitable amount of KOH was directly used instead of LiCl, showed a significant reduction in dissolution time, and in particular, in examples 2 and 3, the dissolution time was reduced to 90 to 120 minutes, indicating a significant increase in dissolution rate.

Example 4 and example 5 based on example 3, the solvent adopts a mixed system of DMAc and DMSO, the dissolution time can be kept within 12 hours, and the dissolution speed is improved to a certain extent compared with comparative example 1. In the embodiment 4, the DMAc+DMSO has a proper mass ratio, the mass ratio of the DMAc in the solvent is about 95%, the mass ratio of the DMSO in the solvent is about 5%, and the dissolution of the para-aramid can be completed within 60 minutes, so that the dissolution speed is remarkably improved.

In examples 6 to 8 and comparative example 2, the amount of the proton donor added was adjusted in the case of DMAc as a solvent, compared with example 3. In comparative example 2, no proton donor was added, and the dissolution time was increased. When proton donor H is added in example 6 ₂ When O is 2g, the dissolution time is improved to about 90min as compared with example 3. Proton donor H as in examples 7 and 8 ₂ When the amount of O added reaches 5g and 10g, the concentration of DMAc in the solvent is diluted by the addition of water, so that the para-aramid cannot be completely dissolved well.

Some examples of applications of the dissolution system of para-aramid of the present application are provided below.

Preparation example 1

0.75g KOH was weighed and placed in a 100ml beaker, and 1g deionized water was added dropwise so that it was sufficiently dissolved, to obtain an aqueous solution of KOH. The aqueous solution of KOH was then slowly added dropwise to a mixed solution of 24g of DMAc+1g of DMSO to give a solution containing KOH+DMSO+DMAc, with rapid magnetic stirring during the addition. Then adding 0.5g of Technora short fiber into the solution under stirring, stirring at normal temperature, and obtaining uniform dark red solution, namely para-aramid pulp, within 1 hour.

12g of alumina was weighed and uniformly dispersed in 84g of DMAc under high-speed stirring, and after stirring at high speed for 1 hour, ultrasonic dispersion was performed for 1 minute to obtain a uniform slurry, i.e., a ceramic slurry.

Preparing the prepared para-aramid fiber slurry and ceramic slurry into aramid fiber ceramic composite slurry according to the volume ratio of 4:1, wherein the preparation process is accompanied by high-speed stirring or ultrasonic dispersion. The aramid ceramic composite slurry is coated by using a small experimental coater, the aramid ceramic composite slurry is uniformly coated on a polyolefin-based film, and then the coated film is immersed in a coagulating bath of the first stage, wherein the extracting solution in the coagulating bath of the first stage is 90% DMAc+10% ethanol, and the extracting time is 15s. Then immersing the mixture in a water tank of the second stage, wherein the extraction liquid in the water tank of the second stage is water, and the extraction time is 15s. The residual moisture on the surface was slightly wiped off, and then dried in an oven at 50 ℃ to obtain an aramid ceramic composite membrane, and an SEM surface photograph was taken to obtain an SEM thereof as shown in fig. 3.

Preparation example 2

0.75g KOH was weighed and placed in a 100ml beaker, and 1g deionized water was added dropwise so that it was sufficiently dissolved, to obtain an aqueous solution of KOH. The aqueous solution of KOH was then slowly added dropwise to a mixed solution of 24g of DMAc+1g of DMSO to give a solution containing KOH+DMSO+DMAc. Rapid magnetic stirring was accompanied during the dropping process. Then adding 0.5g of Technora short fiber into the solution under stirring, stirring at normal temperature, and obtaining uniform dark red solution, namely para-aramid pulp, within 1 hour.

Preparing the prepared para-aramid fiber slurry and ceramic slurry into aramid fiber ceramic composite slurry according to the volume ratio of 3:2, wherein the preparation process is accompanied by high-speed stirring or ultrasonic dispersion. The aramid ceramic composite slurry is uniformly coated on a polyolefin-based film by using a small experimental coater, and then the coated film is immersed in a coagulating bath of the first stage, wherein the extracting solution in the coagulating bath of the first stage is 90% DMAc+10% ethanol, and the extracting time is 15s. Then immersing the mixture in a water tank of the second stage, wherein the extraction liquid in the water tank of the second stage is water, and the extraction time is 15s. The residual moisture on the surface was slightly wiped off, and then dried in an oven at 50 ℃ to obtain an aramid ceramic composite membrane, and an SEM surface photograph was taken to obtain an SEM thereof as shown in fig. 4.

Preparation example 3

0.75g KOH was weighed and placed in a 100ml beaker, and 1g deionized water was added dropwise so that it was sufficiently dissolved, to obtain an aqueous solution of KOH. Then, it was slowly dropped into a mixed solution containing 24g of DMAc+1g of DMSO to obtain a solution containing KOH+DMSO+DMAc. Rapid magnetic stirring was accompanied during the dropping process. Then adding 0.5g of Technora short fiber into the solution under the condition of stirring, stirring at normal temperature, and obtaining uniform dark red solution, namely para-aramid pulp, within 1 hour.

Preparing the prepared para-aramid fiber slurry and ceramic slurry into aramid fiber ceramic composite slurry according to the volume ratio of 2:3, wherein the preparation process is accompanied by high-speed stirring or ultrasonic dispersion. The aramid ceramic composite slurry is coated by using a small experimental coater, the aramid ceramic composite slurry is uniformly coated on a polyolefin-based film, and then the coated film is immersed in a coagulating bath of the first stage, wherein the extracting solution in the coagulating bath of the first stage is 90% DMAc+10% ethanol, and the extracting time is 15s. Then immersing the mixture in a water tank of the second stage, wherein the extraction liquid in the water tank of the second stage is water, and the extraction time is 15s. The residual moisture on the surface was slightly wiped off, and then dried in an oven at 50 ℃ to obtain an aramid ceramic composite membrane, and an SEM surface photograph was taken to obtain an SEM thereof as shown in fig. 5.

Preparation example 4

The aramid ceramic composite slurry is coated by using a small experimental coater, the aramid ceramic composite slurry is uniformly coated on a polyolefin-based film, and then the coated film is immersed in a coagulating bath of the first stage, wherein the extracting solution in the coagulating bath of the first stage is 90% DMAc+10% ethanol, and the extracting time is 15s. Then immersing the mixture in a water tank of the second stage, wherein the extraction liquid in the water tank of the second stage is water, and the extraction time is 15s. The residual moisture on the surface was slightly wiped off, and then dried in an oven at 50 ℃ to obtain an aramid coated separator.

The performance parameters of the aramid fiber separator and the aramid fiber ceramic composite separator prepared in preparation examples 1 to 4 were characterized, and the results are shown in table 2.

TABLE 2 Performance parameters of aramid ceramic composite diaphragm

The testing method comprises the following steps:

(1) Breathable

The air permeability value of the lithium battery diaphragm is tested by adopting a Wang Yan battery diaphragm air permeability tester. The test conditions were: the intake pressure was 0.25MPa, the measurement pressure was 0.05MPa, and the measurement time was 5s.

(2) Needling strength

The instrument is a KES-G5 puncture tester, and is used for testing according to the GBT 36363-2018 needle strength method of polyolefin diaphragm for lithium ion batteries, wherein the diameter of a testing needle is 1mm, and the testing speed is 0.2cm/s.

(3) Thickness of (L)

The test was performed using a Millimar C1216 film thickness detector pair.

(4) Scanning electron microscope

Testing was performed using Hitachi SU 1510; the multiple is 2 ten thousand times.

(5) Adhesive property

The negative plate with the thickness of 85mm multiplied by 140mm and the battery diaphragm are hot pressed for 60 seconds at the temperature of 90 ℃ by adopting the pressure of 3.5MPa, cut into the sample strip with the thickness of 30mm multiplied by 140mm, and then tested on a universal tensile testing machine at the tensile rate of 300mm/min under the condition of room temperature, wherein the obtained data is the bonding force between the diaphragm and the negative plate.

Preparation example 5

Weighing 0.75g KOH and pouring the same into 1g water to obtain an aqueous solution with the KOH dissolved therein; then, it was slowly dropped into a mixed solution of 24g of DMAc and 1g of DMSO to obtain a solution containing KOH+DMSO+DMAc, with magnetic stirring during the dropping. 0.5g of Technora short fiber is added into the solution, and the solution is magnetically stirred for 1h at normal temperature to obtain a dark red solution. Coating by using a small experimental coater, and uniformly coating the slurry on a PE base film; then, the solution was passed through a coagulation bath of the first stage, which was 100% DMAc, and the extraction time was 20s. Then the mixture was placed in a second water tank, and the extraction time was 20s. And slightly wiping off residual moisture on the surface, and drying in an oven at 50 ℃ to form the para-aramid porous film layer on the surface.

SEM pictures of the para-aramid porous film layer were obtained as shown in fig. 7, in which PVDF agglomerates were not present.

Preparation example 6

Weighing 0.25g KOH and pouring the same into 1g water to obtain an aqueous solution with the KOH dissolved therein; then, it was slowly dropped into a mixed solution of 24g of DMAc and 1g of DMSO to obtain a solution containing KOH+DMSO+DMAc, with magnetic stirring during the dropping. To the above solution, 0.5g of Technora short fiber was added, and the solution was magnetically stirred at room temperature for 1 hour, so that the solution was not completely dissolved.

Preparation example 7

1.5g of KOH was weighed and poured into 1g of water to obtain an aqueous solution in which KOH was dissolved; then, it was slowly dropped into a mixed solution of 24g of DMAc and 1g of DMSO to obtain a solution containing KOH+DMSO+DMAc, with magnetic stirring during the dropping. 0.5g of Technora short fiber is added into the solution, and the solution is magnetically stirred for 1h at normal temperature to obtain a dark red solution. Coating by using a small experimental coater, and uniformly coating the slurry on a PE base film; then, the solution was passed through a coagulation bath of the first stage, which was 100% DMAc, and the extraction time was 20s. Then the mixture was placed in a second water tank, and the extraction time was 20s. And slightly wiping off residual moisture on the surface, and drying in an oven at 50 ℃ to form the para-aramid porous film layer on the surface.

Preparation example 8

0.75g of KOH was weighed out and poured into 1g of water to obtain an aqueous solution in which KOH was dissolved. Then, it was slowly dropped into a mixed solution of 24g of DMAc and 1g of DMSO to obtain a solution containing KOH+DMSO+DMAc, with magnetic stirring during the dropping. 0.5g of Technora short fiber is added into the solution, and the solution is magnetically stirred for 1h at normal temperature to obtain a dark red solution. The slurry was uniformly coated on a PE base film using a small-sized experimental coater. Then passing through the coagulation bath of the first stage, which is 90% dmac+10% ethanol, for 20s. Then the mixture was placed in a second water tank, and the extraction time was 20s. And slightly wiping off residual moisture on the surface, and drying in an oven at 50 ℃ to obtain the para-aramid porous film layer on the surface.

SEM pictures of the para-aramid porous film layer were obtained as shown in fig. 8, in which PVDF agglomerates were not present.

Preparation example 9

0.75g of KOH was weighed out and poured into 1g of water to obtain an aqueous solution in which KOH was dissolved. Then, it was slowly dropped into a mixed solution of 24g of DMAc and 1g of DMSO to obtain a solution containing KOH+DMSO+DMAc, with magnetic stirring during the dropping. 0.5g of Technora short fiber is added into the solution, and the solution is magnetically stirred for 1h at normal temperature to obtain a dark red solution. The slurry was uniformly coated on a PE base film using a small-sized experimental coater. Then, the solution was passed through a coagulation bath of the first stage, which was a solution of 0.1% PVDF in DMAc, for an extraction time of 20s. Then the mixture was placed in a second water tank, and the extraction time was 20s. And slightly wiping off residual moisture on the surface, and drying in an oven at 50 ℃ to form the para-aramid porous film layer on the surface.

SEM pictures of the para-aramid porous film layer were obtained as shown in fig. 9, in which a small amount of white island-like distribution of PVDF agglomerates was present.

Preparation example 10

0.75g of KOH was weighed out and poured into 1g of water to obtain an aqueous solution in which KOH was dissolved. Then, it was slowly dropped into a mixed solution of 24g of DMAc and 1g of DMSO to obtain a solution containing KOH+DMSO+DMAc, with magnetic stirring during the dropping. 0.5g of Technora short fiber is added into the solution, and the solution is magnetically stirred for 1h at normal temperature to obtain a dark red solution. The slurry was uniformly coated on a PE base film using a small-sized experimental coater. Then, the solution was passed through a coagulation bath of the first stage, which was a 2% DMAc solution of PVDF, for an extraction time of 20s. Then the mixture was placed in a second water tank, and the extraction time was 20s. And slightly wiping off residual moisture on the surface, and drying in an oven at 50 ℃ to form the para-aramid porous film layer on the surface.

SEM pictures of the para-aramid porous film layer were obtained as shown in FIG. 10, in which PVDF agglomerates were directly connected and no longer exhibited island-like distribution.

PREPARATION EXAMPLE 11

0.75g of KOH was weighed out and poured into 1g of water to obtain an aqueous solution in which KOH was dissolved. Then, it was slowly dropped into a mixed solution of 24g of DMAc and 1g of DMSO to obtain a solution containing KOH+DMSO+DMAc, with magnetic stirring during the dropping. 0.5g of Technora short fiber is added into the solution, and the solution is magnetically stirred for 1h at normal temperature to obtain a dark red solution. The slurry was uniformly coated on a PE base film using a small-sized experimental coater. Then through the coagulation bath of the first stage, which is a DMAc solution of 0.5% PVDF, for 20s. Then the mixture was placed in a second water tank, and the extraction time was 20s. And slightly wiping off residual moisture on the surface, and drying in an oven at 50 ℃ to form the para-aramid porous film layer on the surface.

SEM pictures of the para-aramid porous film layer obtained are shown in fig. 11, in which a certain amount of white island-like distribution of PVDF agglomerates was present.

Preparation example 12

0.75g of KOH was weighed out and poured into 1g of water to obtain an aqueous solution in which KOH was dissolved. Then, it was slowly dropped into a mixed solution of 24g of DMAc and 1g of DMSO to obtain a solution containing KOH+DMSO+DMAc, with magnetic stirring during the dropping. 0.5g of Technora short fiber is added into the solution, and the solution is magnetically stirred for 1h at normal temperature to obtain a dark red solution. The slurry was uniformly coated on a PE base film using a small-sized experimental coater. Then through the coagulation bath of the first stage, which is a 1.5% solution of PVDF in DMAc, for an extraction time of 20s. Then the mixture was placed in a second water tank, and the extraction time was 20s. And slightly wiping off residual moisture on the surface, and drying in an oven at 50 ℃ to form the para-aramid porous film layer on the surface.

And in the para-aramid porous membrane layer, PVDF agglomerates continue to present island-shaped distribution structures.

Preparation example 13

0.75g of KOH was weighed out and poured into 1g of water to obtain an aqueous solution in which KOH was dissolved. Then, it was slowly dropped into a mixed solution of 24g of DMAc and 1g of DMSO to obtain a solution containing KOH+DMSO+DMAc, with magnetic stirring during the dropping. 0.5g of Technora short fiber is added into the solution, and the solution is magnetically stirred for 1h at normal temperature to obtain a dark red solution. The slurry was uniformly coated on a PE base film using a small-sized experimental coater. Then, the aqueous solution of DMAc was passed through the coagulation bath of the first stage, which was an aqueous solution of 3% by mass, and the extraction time was 20s. Then the mixture was placed in a second water tank, and the extraction time was 20s. And slightly wiping off residual moisture on the surface, and drying in an oven at 50 ℃ to form the para-aramid porous film layer on the surface.

Then, a DMAc solution containing 8% PVDF was coated on the resulting aramid coated separator and immersed in 3% DMAc aqueous solution for 20s, followed by water for 20s, to obtain a PVDF porous coating on the aramid coating.

In the preparation examples 5 to 13 provided above, the steps of forming the para-aramid porous film layer by applying the slurry on the base film were all carried out by single-sided coating, and the thickness of the base film was 9. Mu.m.

The performance parameters of the aramid separator prepared in preparation examples 5 to 13 were characterized, and the results are shown in table 3.

TABLE 3 Performance parameters of aramid diaphragms

Project	Thickness of aramid fiber diaphragm	Breathable	Adhesive property
				Unit (B)	(μm)	s/100ml	N/m
Preparation example 5	9.5	153.5	0
				Preparation example 6	/	/	/
Preparation example 7	9.5	154.2	0
				Preparation example 8	9.5	156.1	0
Preparation example 9	9.5	158.2	2.5
				Preparation example 10	9.5	225.7	12.1
PREPARATION EXAMPLE 11	9.5	161.3	7.5
				Preparation example 12	9.6	175.3	9.6
Preparation example 13	9.6	235.0	10.5

As can be seen from fig. 6 to 11 and table 3:

in preparation examples 5, 7 and 8, PVDF was not introduced when forming the para-aramid porous film layer, and the separator did not have adhesive properties. In preparation examples 5 and 7, the mass ratio of the strong base to the para-aramid is 150:100 and 300:100 respectively, and the para-aramid can be better prepared by magnetic stirring for 1h at normal temperature, and the membrane formed after the slurry is coated has better air permeability; in preparation example 6, the mass ratio of the strong base to the para-aramid is 50:100, and the para-aramid cannot be completely dissolved by magnetic stirring for 1h at normal temperature, so that the para-aramid needs to be further dissolved and then coated with slurry.

In preparation examples 9 to 12, PVDF was introduced in different amounts when the para-aramid porous film layer was formed, and the adhesive properties of the separator were improved to different degrees. In preparation examples 11 and 12, PVDF has more proper dosage, and the bonding performance is improved more; at the same time, the agglomerates of PVDF are distributed in an island shape, and the air permeability can be close to that of preparation examples 5, 7 and 8 which do not contain PVDF. In preparation example 9, the PVDF was used in a lower amount, and the improvement of the adhesive properties was more remarkable in preparation example 11 and preparation example 12 than in preparation example 11 and preparation example 12. In preparation 10, PVDF was used in a higher amount, and the PVDF agglomerates were directly connected without showing island distribution, and the air permeability of preparation 11 and preparation 12 was better than those of preparation 11 and preparation 12.

In preparation examples 9 to 12, PVDF was introduced in the formation of the para-aramid porous film layer; in preparation example 13, a para-aramid porous film layer containing no PVDF was formed, and then PVDF was coated on the surface of the para-aramid porous film layer. The separators of preparation examples 9 to 12 had better air permeability than preparation example 13.

The embodiments described above are some, but not all embodiments of the application. The detailed description of the embodiments of the application is not intended to limit the scope of the application, as claimed, but is merely representative of selected embodiments of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.

Claims

1. A para-aramid dissolution system, comprising:

proton donors;

a solvent comprising an aprotic strongly polar solvent; and

a co-solvent comprising a strong base.

2. The para-aramid dissolution system according to claim 1, wherein the proton donor is water or an organic proton acid.

3. The dissolution system of para-aramid according to claim 1 or 2, wherein the mass ratio of the proton donor to the solvent is (0.01-10): 100.

4. the para-aramid dissolution system of claim 1, wherein the non-protic strongly polar solvent comprises one or more of DMAc, DMF, NMP and DMSO.

5. The dissolution system of para-aramid according to claim 1 or 4, wherein the solvent satisfies at least one of the following conditions (a) to (d);

(a) The solvent consists of one aprotic strongly polar solvent;

(b) The solvent consists of two aprotic strongly polar solvents;

(c) The solvent comprises the aprotic highly polar solvent and an aprotic polar solvent, wherein the aprotic polar solvent comprises one or more of methanol, ethanol and acetone; in the solvent, the mass ratio of the non-proton type strong polar solvent is 80% -99.9%;

(d) The solvent comprises the non-proton type strong polar solvent and water; in the solvent, the mass ratio of the non-proton type strong polar solvent is 90% -99.99%.

6. The para-aramid dissolution system according to claim 5, wherein the solvent satisfies the condition (a), wherein the solvent consists of one of DMAc, DMF, and NMP.

7. The dissolving system of para-aramid according to claim 5, wherein the solvent satisfies the condition (b), wherein the solvent is composed of DMSO and one of DMAc, DMF, and NMP, and wherein the mass ratio of DMSO in the solvent, wt1, satisfies 0.1% +.ltoreq.wt 1 < 50%.

8. The dissolving system of para-aramid according to claim 7, wherein the solvent consists of DMAc and DMSO, and wherein the mass ratio wt1 of DMSO in the solvent satisfies wt 1.ltoreq.5%.

9. The para-aramid dissolution system of claim 1 wherein the strong base comprises NaH, KH, t-BuOK, KOH, naOH, C ₂ H ₅ One or more of ONa.

10. The para-aramid dissolution system according to claim 1 or 9, wherein the co-solvent further comprises a basic salt comprising LiCl, naCl, KCl and CaCl ₂ One or more of the following.

11. The system according to claim 10, wherein the molar ratio of the basic salt in the cosolvent, wn1, is 1% or less and 50% or less.

12. Use of a dissolution system of para-aramid according to any one of claims 1 to 11 for dissolving para-aramid, comprising: and dissolving the para-aramid in a dissolving system of the para-aramid.

13. The use according to claim 12, wherein the dissolution treatment is carried out at room temperature for a period of time of 12h or less.

14. The use according to claim 12 or 13, wherein the para-aramid is selected from one of Kevlar para-aramid of dupont, twaron para-aramid of dupont, tepran para-aramid of shantai and tai pran of shan and da, technora heterocycle aramid of dupont, homo-polyamide containing p-phenylene terephthalamide structure and copolyamide containing p-phenylene terephthalamide structure.

15. The use of claim 14, wherein the para-aramid morphology comprises one or more of pulp, long fibers, and short fibers.

16. The preparation method of the aramid fiber diaphragm is characterized by comprising the following steps:

coating the dissolved para-aramid slurry formed by the application of any one of claims 12 to 15 on at least one side surface of a porous base film.

17. The method of producing an aramid separator according to claim 16, wherein the material of the porous base film comprises one or more of polyethylene terephthalate, polybutylene terephthalate, polyether, polyacetal, polyamide, polycarbonate, polyimide, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ultra-high molecular weight polypropylene, and nonwoven fabric.

18. An aramid separator made by the method of making an aramid separator as claimed in claim 16 or 17.

19. The preparation method of the aramid fiber ceramic composite diaphragm is characterized by comprising the following steps of:

mixing the ceramic slurry with the dissolved para-aramid slurry formed by the application of any one of claims 12 to 15 to obtain an aramid ceramic composite slurry;

and coating the aramid ceramic composite slurry on at least one side surface of the base film.

20. The method for producing an aramid ceramic composite separator according to claim 19, wherein the ceramic slurry satisfies at least one of the following conditions (e) to (g);

(e) The solvent of the ceramic slurry is an organic solvent or a mixed solution of the organic solvent and water, wherein the mass ratio of the organic solvent in the mixed solution of the organic solvent and water is more than or equal to 50 percent, and the organic solvent comprises one or more of DMAc, NMP, DMSO and acetone;

(f) The ceramic material in the ceramic slurry comprises one or more of alumina, boehmite, barium sulfate, zirconia and silicon dioxide;

(g) The mass ratio of the ceramic to the solvent in the ceramic slurry is (0.02-5): 1.

21. The method for preparing an aramid ceramic composite separator according to claim 19 or 20, wherein the volume ratio of the para-aramid slurry to the ceramic slurry is (2-4): (1-3).

22. The method of claim 19, wherein the material of the base film comprises one or more of polyolefin and non-woven fabric.

23. An aramid ceramic composite diaphragm, characterized in that it is made by the method for preparing an aramid ceramic composite diaphragm according to any one of claims 19 to 22.

24. The preparation method of the aramid fiber diaphragm is characterized by comprising the following steps:

dissolving para-aramid in a para-aramid dissolving system to form dissolved para-aramid slurry; wherein the dissolving system of the para-aramid fiber comprises strong alkali;

Coating the para-aramid pulp on at least one side surface of a base film, and forming a para-aramid porous film layer by the para-aramid pulp under a PVDF-containing system; wherein the PVDF is distributed in the para-aramid porous membrane layer.

25. The method for preparing an aramid separator according to claim 24, wherein,

the process of forming the para-aramid slurry into the para-aramid porous membrane layer under the PVDF-containing system is carried out by adopting a non-solvent induced phase separation method.

26. The method for preparing an aramid separator according to claim 25, wherein,

the process for forming the para-aramid slurry into a para-aramid porous membrane layer in a PVDF-containing system comprises the following steps: performing first-stage solidification in the first-stage solidification liquid, and then performing second-stage solidification in the second-stage solidification liquid; the first-stage coagulating liquid comprises a strong polar solvent and PVDF, and the second-stage coagulating liquid is water.

27. The method for preparing an aramid fiber membrane according to claim 26, wherein the mass ratio of the PVDF in the first-stage coagulation liquid is 0.5 to 1.5%, so that the PVDF is distributed in an island shape in the porous membrane layer.

28. The method for preparing an aramid fiber diaphragm according to claim 26, wherein the mass ratio of the strong polar solvent in the first-stage solidification liquid is more than or equal to 50%.

29. The method of producing an aramid separator according to claim 26, wherein the first period of solidification is 1s to 60s and/or the second period of solidification is 1s to 60s.

30. The method for preparing an aramid separator according to claim 24, wherein,

the process of dissolving the para-aramid in the dissolution system of the para-aramid adopts the dissolution system of the para-aramid as defined in any one of claims 1 to 11.

31. The method for preparing an aramid separator according to claim 30, wherein,

and the mass ratio of the cosolvent to the para-aramid is (50-300): 100 in the process of dissolving the para-aramid in a dissolution system of the para-aramid.

32. The method for producing an aramid separator according to any one of claims 24 to 31, further comprising, before the process of coating the para-aramid slurry on at least one side surface of the base film: and mixing ceramic slurry with the para-aramid slurry.

33. An aramid separator, characterized in that it is made by the method for preparing an aramid separator according to any one of claims 24 to 32;

the aramid fiber membrane comprises a base membrane and the para-aramid fiber porous membrane layer positioned on at least one side surface of the base membrane, wherein PVDF is distributed in the para-aramid fiber porous membrane layer.

34. The aramid separator of claim 33, wherein the PVDF is in an island-like distribution in the porous membrane layer.