阅读说明：本技术 改性芳纶聚合体、芳纶铸膜液、锂电池隔膜及制备方法和锂电池 (Modified aramid polymer, aramid film casting liquid, lithium battery diaphragm, preparation method and lithium battery ) 是由 陈继朝 公言飞 刘鹏 梁云静 胡一波 于 2019-09-20 设计创作，主要内容包括：本申请提供一种改性芳纶聚合体、芳纶铸膜液、锂电池隔膜及制备方法和锂电池。改性芳纶聚合体：惰性气体环境,将第一反应单体和第一溶剂混合,冷却；加入第二反应单体和第三反应单体,反应后调节pH值至中性；第一反应单体为间苯二胺,第二反应单体为间苯二甲酰氯,第三反应单体包括对苯二胺和/或对苯二甲酰氯。芳纶铸膜液：将改性芳纶聚合体与陶瓷颗粒、成孔剂、第二溶剂混合,加热得芳纶铸膜液。锂电池隔膜包括基材和涂覆在基材表面的涂覆层,涂覆层由芳纶铸膜液制得。锂电池隔膜的制备方法包括将芳纶铸膜液涂覆在基材上,涂覆厚度1～10μm,进行凝固处理和干燥处理。锂电池包括锂电池隔膜。本申请提供的锂电池隔膜制的锂电池安全性能好。(The application provides a modified aramid polymer, an aramid film casting liquid, a lithium battery diaphragm, a preparation method and a lithium battery. Modified aramid polymer: mixing a first reaction monomer and a first solvent in an inert gas environment, and cooling; adding a second reaction monomer and a third reaction monomer, and adjusting the pH value to be neutral after reaction; the first reaction monomer is m-phenylenediamine, the second reaction monomer is isophthaloyl chloride, and the third reaction monomer comprises p-phenylenediamine and/or terephthaloyl chloride. Aramid fiber membrane casting liquid: and mixing the modified aramid polymer with ceramic particles, a pore-forming agent and a second solvent, and heating to obtain an aramid film casting solution. The lithium battery diaphragm comprises a base material and a coating layer coated on the surface of the base material, wherein the coating layer is prepared from aramid fiber membrane casting liquid. The preparation method of the lithium battery diaphragm comprises the steps of coating the aramid fiber membrane casting solution on a base material, coating the aramid fiber membrane casting solution to a thickness of 1-10 mu m, and performing solidification treatment and drying treatment. The lithium battery includes a lithium battery separator. The lithium battery made of the lithium battery diaphragm provided by the application has good safety performance.)

1. A modified aramid polymer is characterized in that the preparation method comprises the following steps:

mixing a first reaction monomer and a first solvent in an inert gas environment, and cooling;

then adding a second reaction monomer and a third reaction monomer, and adjusting the pH value to be neutral after the reaction is finished;

the first reaction monomer is m-phenylenediamine, the second reaction monomer is isophthaloyl chloride, and the third reaction monomer comprises p-phenylenediamine and/or terephthaloyl chloride;

and the cooling end point is that the system temperature is cooled to-15-0 ℃.

2. The modified aramid polymer according to claim 1, wherein the concentration of the first reactive monomer is 0.8 to 1.2mol/L, the concentration of the second reactive monomer is 0.8 to 1.5mol/L, and the concentration of the third reactive monomer is 0.01 to 0.2mol/L in the reaction system;

preferably, the reaction temperature is-15-5 ℃, and the reaction time is 3-30 minutes.

3. The modified aramid polymer of claim 1, further comprising adding a cosolvent when the temperature of the first solvent is raised to 60-100 ℃, and then cooling, wherein the cosolvent comprises calcium chloride and/or lithium chloride, and the end point temperature of the cooling is 20-35 ℃;

preferably, the addition amount of the cosolvent is 1-15% of the mass of the first solvent.

4. The aramid fiber membrane casting solution is characterized in that the preparation method comprises the following steps: mixing the modified aramid polymer of any one of claims 1 to 3 with ceramic particles, a pore-forming agent, a second solvent, and heating to obtain the aramid film casting solution;

preferably, the pore-forming agent comprises one or more of lithium chloride, sodium chloride, magnesium chloride, calcium carbonate, calcium chloride, methanol, ethanol, propanol, glycerol, polyethylene glycol, acetone, acetic acid, tetrahydrofuran and polyvinylpyrrolidone;

preferably, the ceramic particles comprise one or more of silicon dioxide, aluminum oxide, calcium oxide, titanium dioxide, magnesium oxide, zinc oxide, tin dioxide and zirconium dioxide, and the particle size of the ceramic particles is in the range of 0.01-10 μm.

5. The aramid film casting solution according to claim 4, wherein the heating temperature is 80-100 ℃; in a reaction system, the concentration of the modified aramid polymer is 2-6 wt%, the concentration of the pore-forming agent is 5-7 wt%, the concentration of the ceramic particles is 3-5 wt%, and the concentration of the second solvent is 82-90 wt%.

6. A lithium battery separator, which comprises a base material and a coating layer coated on the surface of the base material, wherein the coating layer is prepared from the aramid film casting solution of any one of claims 4 or 5.

7. A preparation method of the lithium battery diaphragm as claimed in claim 6, characterized by comprising the steps of coating the aramid fiber membrane casting solution on the base material, wherein the coating thickness is 1-10 μm, and then performing solidification treatment and drying treatment;

preferably, the aramid fiber membrane casting solution is subjected to defoaming treatment before coating, wherein the temperature of the defoaming treatment is 30-50 ℃, and the time is 5-60 minutes.

8. The preparation method according to claim 7, wherein the coagulation treatment is performed in a coagulation bath, the coagulation bath is a mixed solution of an organic solvent and water, preferably, the organic solvent comprises one or more of N-methylpyrrolidone, dimethylacetamide, N-dimethylformamide, dimethyl phthalate or ethanol, and the proportion of the organic solvent is 10-90%; the time of the solidification treatment is 1-10 minutes.

9. The method according to claim 7, wherein the drying treatment is carried out at a temperature of 40 to 80 ℃ for 10 to 120 minutes;

preferably, before the drying treatment, the method further comprises the step of soaking the product after the solidification treatment in water for 10-240 minutes.

10. A lithium battery comprising the lithium battery separator as claimed in claim 6.

Technical Field

The invention relates to the field of lithium batteries, in particular to a modified aramid polymer, an aramid film casting solution, a lithium battery diaphragm, a preparation method of the lithium battery diaphragm and a lithium battery.

Background

Lithium ion batteries are used in a large number of mobile electronic devices and power plants because of their high energy density and long cycle life. However, a great deal of attention has been paid to a frequently occurring safety accident in which a separator, which is one of important components of a lithium ion battery, provides a lithium ion transport channel and prevents a short circuit from occurring between positive and negative electrode contacts, having a very important influence on the safety of the lithium ion battery.

The polyolefin diaphragm is the most widely used lithium ion battery diaphragm at present, but the polyolefin diaphragm has the problems of too high thermal shrinkage and insufficient electrolyte wettability. The PE and PP diaphragms which are most widely applied at present are softened and deformed at the temperature of over 100 ℃. In order to improve the thermal stability and wettability of polyolefin separators, the current main solution is to apply a coating on one or both sides of the polyolefin separator.

The aramid fiber has excellent performances of ultrahigh strength, high modulus, high temperature resistance, chemical corrosion resistance and the like, the thermal decomposition temperature of the aramid fiber can reach 400-430 ℃, and the heat resistance and the safety performance of the lithium ion battery can be greatly improved. At present, the commonly used para-aramid polymer is used as a coating material, and the problems of easy gelation, short preservation time, decomposition of aramid fiber, molecular weight degradation, loss and the like caused by the dissolving process of the aramid fiber exist. Meanwhile, the meta-aramid fiber used has the problems of no high temperature resistance, easy puncture, low film breaking temperature, high thermal shrinkage rate, poor electrolyte wettability and the like.

In view of the above, the present invention is particularly proposed.

Disclosure of Invention

The invention aims to provide a modified aramid polymer, which solves the problems of easy gelation, short storage time, decomposition of aramid fibers, molecular weight degradation and loss and the like caused by the dissolving process of the aramid fibers when the para-aramid polymer is used as a coating material. Meanwhile, the problems of no high temperature resistance, easy puncture, low film breaking temperature, high thermal shrinkage rate, poor electrolyte wettability and the like in the case of using meta-aramid fiber are solved.

The second purpose of the invention is to provide an aramid fiber membrane casting solution, and a lithium battery diaphragm prepared from the aramid fiber membrane casting solution has good puncture strength, thermal shrinkage performance and electrolyte wettability.

The third purpose of the invention is to provide a lithium battery diaphragm which has good puncture strength, thermal shrinkage performance and electrolyte wettability.

The fourth purpose of the invention is to provide a preparation method of the lithium battery diaphragm, which has the advantages of simple process, controllable conditions and easy expanded production, and the prepared lithium battery diaphragm has good performance.

A fifth object of the present invention is to provide a lithium battery having better safety performance.

In order to achieve the above purpose of the present invention, the following technical solutions are adopted:

a modified aramid polymer, the preparation method comprising:

mixing a first reaction monomer and a first solvent in an inert gas environment, and cooling;

then adding a second reaction monomer and a third reaction monomer, and adjusting the pH value to be neutral after the reaction is finished;

the first reaction monomer is m-phenylenediamine, the second reaction monomer is isophthaloyl chloride, and the third reaction monomer comprises p-phenylenediamine and/or terephthaloyl chloride;

and the cooling end point is that the system temperature is cooled to-15-0 ℃.

The para-aramid has excellent heat resistance, but para-aramid molecules have a linear straight chain structure, and the molecular structure is regular and easy to crystallize and separate out to form a gel structure. The zigzag chain segment is added in the meta-aramid structure, so that the linearity degree of the polymer is smaller than that of para-aramid, a crystalline structure is not easy to form, and the heat resistance of the meta-aramid is slightly poor. The product formed by the reaction of the first reaction monomer and the second reaction monomer is meta-aramid, the third reaction monomer is introduced to increase the rigidity group of the para-position rod-shaped structure, the linear degree of a macromolecular chain and the filling density among molecules are improved by introducing the rigidity group of the para-position rod-shaped structure into the molecular chain of the meta-aramid, the interaction force among the molecules is enhanced, the advantage of long preservation time of meta-aramid polymer gel is kept, the improvement effect on the heat resistance of the meta-aramid polymer is very obvious, and the meta-aramid polymer gel has good solubility.

Preferably, the first solvent comprises one or more of N-methylpyrrolidone, dimethylacetamide, N-dimethylformamide, and dimethyl phthalate.

Preferably, in the reaction system, the concentration of the first reaction monomer is 0.8-1.2 mol/L, the concentration of the second reaction monomer is 0.8-1.5 mol/L, and the concentration of the third reaction monomer is 0.01-0.2 mol/L;

preferably, the reaction temperature is-15-5 ℃, and the reaction time is 3-30 minutes.

The reaction monomer concentration, the reaction temperature and the reaction time are optimized, and the reaction can be further optimized to obtain the modified aramid polymer with better performance. Different from para-aramid, the modified meta-aramid polymer generated by the reaction improves the solubility of the polymer, so that higher concentration can be used, and the polymer with higher concentration is synthesized.

Preferably, the method further comprises the steps of heating the first solvent to 60-100 ℃, adding a cosolvent, and then cooling, wherein the cosolvent comprises calcium chloride and/or lithium chloride, and the final temperature of cooling is 20-35 ℃;

preferably, the addition amount of the cosolvent is 1-15% of the mass of the first solvent.

The addition of the cosolvent is beneficial to better dissolving the reaction monomer in the solvent, and the reaction efficiency is improved.

The preparation method of the aramid fiber membrane casting solution comprises the following steps: mixing the modified aramid polymer with ceramic particles, a pore-forming agent and a second solvent, and heating to obtain the aramid film casting solution;

preferably, the second solvent comprises one or more of N-methylpyrrolidone, dimethylacetamide, N-dimethylformamide, and dimethyl phthalate;

preferably, the pore-forming agent comprises one or more of lithium chloride, sodium chloride, magnesium chloride, calcium carbonate, calcium chloride, methanol, ethanol, propanol, glycerol, polyethylene glycol, acetone, acetic acid, tetrahydrofuran and polyvinylpyrrolidone;

preferably, the ceramic particles comprise one or more of silicon dioxide, aluminum oxide, calcium oxide, titanium dioxide, magnesium oxide, zinc oxide, tin dioxide and zirconium dioxide, and the particle size of the ceramic particles is in the range of 0.01-10 μm.

The aramid fiber membrane casting solution prepared from the modified aramid fiber polymer, the ceramic particles, the pore-forming agent and the solvent has the advantages of small interfacial stress with a base membrane, good contact, low high-temperature thermal shrinkage and good heat resistance, is not easy to fall off, effectively solves the problem of poor wettability of the base membrane to electrolyte, and improves the puncture strength of the base membrane.

Preferably, the heating temperature is 80-100 ℃; in a reaction system, the concentration of the modified aramid polymer is 2-6 wt%, the concentration of the pore-forming agent is 5-7 wt%, the concentration of the ceramic particles is 3-5 wt%, and the concentration of the second solvent is 82-90 wt%.

The aramid fiber membrane casting solution with better performance can be obtained by optimizing the heating temperature and the concentrations of the modified aramid fiber polymer, the ceramic particles and the pore-forming agent.

A lithium battery diaphragm comprises a base material and a coating layer coated on the surface of the base material, wherein the coating layer is prepared from the aramid fiber membrane casting solution.

The lithium battery diaphragm prepared by the aramid fiber membrane casting solution has greatly improved heat resistance and high-temperature thermal shrinkage performance, the diaphragm breaking temperature can reach more than 300 ℃, and the use safety performance is greatly improved.

The preparation method of the lithium battery diaphragm comprises the steps of coating the aramid fiber membrane casting solution on the base material, wherein the coating thickness is 1-10 mu m, and then carrying out solidification treatment and drying treatment;

the thickness of the coating may be any value between 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm and 1-10 μm.

Preferably, the aramid fiber membrane casting solution is subjected to defoaming treatment before coating, wherein the temperature of the defoaming treatment is 30-50 ℃, and the time is 5-60 minutes.

The lithium battery diaphragm prepared by the aramid fiber membrane casting solution has the advantages of simple preparation process, controllable conditions and easiness in expanded production, and the puncture strength, the heat shrinkage performance and the electrolyte wettability of the diaphragm are effectively improved.

The coagulation treatment is carried out in a coagulation bath which is a mixed solution of an organic solvent and water, preferably, the organic solvent comprises one or more of N-methylpyrrolidone, dimethylacetamide, N-dimethylformamide, dimethyl phthalate or ethanol, and the proportion of the organic solvent is 10-90%; the time of the solidification treatment is 1-10 minutes.

The optimization of the type of coagulation bath and the coagulation treatment time can further optimize the performance of the lithium battery separator prepared.

Preferably, the drying treatment temperature is 40-80 ℃, and the drying treatment time is 10-120 minutes;

preferably, before the drying treatment, the method further comprises the step of soaking the product after the solidification treatment in water for 10-240 minutes.

The optimization of the temperature and time of the drying treatment and the soaking operation before the drying treatment enable the solvent and the water to be completely volatilized, and the performance of the lithium battery diaphragm is further optimized.

A lithium battery comprises the lithium battery diaphragm.

The safety performance of the lithium battery prepared by using the lithium battery diaphragm is obviously improved.

Compared with the prior art, the invention has the beneficial effects that:

(1) the modified aramid polymer is used, and the para-position rod-shaped rigid group is introduced into the molecular chain of the polymer, so that the linear degree of the macromolecular chain and the intermolecular filling density are improved, the intermolecular interaction force is enhanced, the advantage of long preservation time of the meta-aramid polymer gel is retained, and meanwhile, the improvement effect on the heat resistance of the meta-aramid polymer is very obvious;

(2) the aramid fiber membrane casting solution prepared from the modified aramid fiber polymer, the ceramic particles, the pore-forming agent and the solvent has the advantages of small interfacial stress with a base membrane, good contact, low high-temperature thermal shrinkage and good heat resistance, is not easy to fall off, effectively solves the problem of poor wettability of the base membrane to electrolyte, and improves the puncture strength of the base membrane;

(3) the heat resistance and high-temperature thermal shrinkage performance of the lithium battery diaphragm prepared from the aramid fiber membrane casting solution are greatly improved, the diaphragm breaking temperature can reach more than 300 ℃, and the use safety performance of the lithium battery diaphragm is greatly improved;

(4) the lithium battery diaphragm prepared by the aramid fiber membrane casting solution has the advantages of simple preparation process, controllable conditions and easiness in expanded production, and the puncture strength, the heat shrinkage performance and the electrolyte wettability of the diaphragm are effectively improved.

(5) The safety performance of the lithium battery prepared by using the lithium battery diaphragm is obviously improved.

Drawings

To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are required to be used in the embodiments will be briefly described below, and it should be understood that the following drawings only illustrate some embodiments of the present invention, and therefore should not be considered as limiting the scope of the present invention.

FIG. 1 is an infrared spectrum of a modified aramid polymer obtained in example 1;

FIG. 2 is an electron micrograph of a lithium battery separator obtained in example 1;

fig. 3 is a graph showing the measurement result of the optical contact angle of the lithium battery separator obtained in example 2.

Detailed Description

The terms as used herein:

"prepared from … …" is synonymous with "comprising". The terms "comprises," "comprising," "includes," "including," "has," "having," "contains," "containing," or any other variation thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

The conjunction "consisting of … …" excludes any unspecified elements, steps or components. If used in a claim, the phrase is intended to claim as closed, meaning that it does not contain materials other than those described, except for the conventional impurities associated therewith. When the phrase "consisting of … …" appears in a clause of the subject matter of the claims rather than immediately after the subject matter, it defines only the elements described in the clause; other elements are not excluded from the claims as a whole.

When an amount, concentration, or other value or parameter is expressed as a range, preferred range, or as a range of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. For example, when the range "1 ~ 5" is disclosed, the ranges described should be construed to include the ranges "1 ~ 4", "1 ~ 3", "1 ~ 2 and 4 ~ 5", "1 ~ 3 and 5", and the like. When a range of values is described herein, unless otherwise stated, the range is intended to include the endpoints thereof and all integers and fractions within the range.

In these examples, the parts and percentages are by mass unless otherwise indicated.

"part by mass" means a basic unit of measure indicating a mass ratio of a plurality of components, and 1 part may represent any unit mass, for example, 1g or 2.689 g. If we say that the part by mass of the component A is a part by mass and the part by mass of the component B is B part by mass, the ratio of the part by mass of the component A to the part by mass of the component B is a: b. alternatively, the mass of the A component is aK and the mass of the B component is bK (K is an arbitrary number, and represents a multiple factor). It is unmistakable that, unlike the parts by mass, the sum of the parts by mass of all the components is not limited to 100 parts.

"and/or" is used to indicate that one or both of the illustrated conditions may occur, e.g., a and/or B includes (a and B) and (a or B).

Embodiments of the present invention will be described in detail below with reference to specific examples, but those skilled in the art will appreciate that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

Example 1

A preparation method of the modified aramid polymer comprises the following steps:

heating a first solvent N-methyl pyrrolidone to 60 ℃ in an inert gas environment, adding a cosolvent calcium chloride, stirring, dissolving, and cooling to 20 ℃ at the end point; the addition amount of the cosolvent is 1 percent of the mass of the first solvent;

adding a first reaction monomer m-phenylenediamine powder, dissolving, cooling to-15 ℃, then adding a second reaction monomer m-phthaloyl chloride powder and a third reaction monomer p-phthaloyl chloride powder, stirring, reacting at-15 ℃ for 30 minutes, and after the reaction is finished, adjusting the pH value to be neutral to prepare a modified aramid polymer; the concentration of the first reaction monomer is 0.8mol/L, the concentration of the second reaction monomer is 0.8mol/L, and the concentration of the third reaction monomer is 0.2 mol/L;

the embodiment also provides an aramid fiber membrane casting solution, and the preparation method comprises the following steps:

mixing the modified aramid polymer with ceramic particle silicon dioxide, a pore-forming agent sodium chloride and a second solvent N-methyl pyrrolidone; in a reaction system, the concentration of the modified aramid polymer is 6 wt%, the concentration of the pore-forming agent is 7 wt%, the concentration of the ceramic particles is 5 wt%, and the concentration of the second solvent is 82 wt%; the particle size of the ceramic particles is 0.01 μm;

heating the mixed solution to 100 ℃, and stirring to uniformly mix the modified aramid polymer, the ceramic particles and the pore-forming agent to prepare an aramid film casting solution;

the embodiment also provides a lithium battery diaphragm, and the preparation method comprises the following steps:

defoaming treatment: defoaming the aramid fiber membrane casting solution until no bubbles exist; the temperature of the defoaming treatment is 50 ℃, and the time is 5 minutes;

coating: coating the aramid fiber membrane casting solution subjected to defoaming treatment on a polyolefin substrate, wherein the coating thickness is 3.3 mu m, and staying for 100 seconds;

and (3) solidification treatment: soaking the product obtained in the step in a coagulating bath for coagulating treatment, wherein the coagulating bath is a mixed solution of ethanol and water, the proportion of the ethanol is 90%, and the time of the coagulating treatment is 10 minutes; forming microporous structures of the surface layer and the inner film of the gel film by exchanging a solvent and a non-solvent in a coagulating bath;

after 30 minutes, removing the porous base membrane obtained in the step, soaking the porous base membrane in water for 10 minutes, and taking out the porous base membrane for later use;

and (3) drying treatment: and drying in an oven at the temperature of 80 ℃ for 10 minutes to completely volatilize the solvent and the water to obtain the high-temperature-resistant lithium battery diaphragm.

The infrared spectrum scanning of the prepared modified aramid polymer was performed using a tens 2 type infrared spectrometer, and the results are shown in fig. 1, and the infrared spectrum peak values and the attribution analysis are shown in table 1 below.

TABLE 1

Wave number (cm)-1)	Attribution
		3271	N-H stretching vibration
1650	C ═ O stretching vibration
		1507	Benzene ring stretching vibration
1500～1300	C-H in-plane bending vibration
		1300～1000	C-C skeleton vibration

From infrared test data of the synthesized modified aramid polymer, typical benzene ring stretching vibration, amino stretching vibration and carbonyl stretching vibration of aramid exist, and the synthesized polymer is the aramid polymer.

The microscopic electron microscope photo of the obtained lithium battery diaphragm is shown in fig. 2, and as can be seen from fig. 2, the lithium battery diaphragm has a uniform spongy microstructure, the formed microstructure has a small increase on the permeability value, and meanwhile, the lithium battery diaphragm has good electrolyte wettability and high temperature resistance.

Example 2

A preparation method of the modified aramid polymer comprises the following steps:

heating a first solvent, namely dimethylacetamide, to 100 ℃ in an inert gas environment, adding a cosolvent, namely calcium chloride, stirring, dissolving, and cooling, wherein the end point temperature of cooling is 35 ℃; the addition amount of the cosolvent is 15 percent of the mass of the first solvent;

adding a first reaction monomer m-phenylenediamine powder, dissolving, cooling to 0 ℃, then adding a second reaction monomer m-phthaloyl chloride powder and a third reaction monomer p-phthaloyl chloride powder, stirring, reacting at the temperature of 5 ℃ for 3 minutes, and adjusting the pH value to be neutral after the reaction is finished to obtain a modified aramid polymer; the concentration of the first reaction monomer is 1.2mol/L, the concentration of the second reaction monomer is 1.5mol/L, and the concentration of the third reaction monomer is 0.01 mol/L;

the embodiment also provides an aramid fiber membrane casting solution, and the preparation method comprises the following steps:

mixing the modified aramid polymer with ceramic particle calcium oxide, pore-forming agent acetone and second solvent N, N-dimethylformamide; in a reaction system, the concentration of the modified aramid polymer is 2 wt%, the concentration of the pore-forming agent is 5 wt%, the concentration of the ceramic particles is 3 wt%, and the concentration of the second solvent is 90 wt%; the particle size of the ceramic particles is 10 μm;

heating the mixed solution to 80 ℃, and stirring to uniformly mix the modified aramid polymer, the ceramic particles and the pore-forming agent to prepare an aramid film casting solution;

the embodiment also provides a lithium battery diaphragm, and the preparation method comprises the following steps:

defoaming treatment: defoaming the aramid fiber membrane casting solution until no bubbles exist; the temperature of the defoaming treatment is 30 ℃, and the time is 60 minutes;

coating: coating the aramid fiber membrane casting solution subjected to defoaming treatment on a polyolefin substrate, wherein the coating thickness is 3.2 microns, and staying for 5 seconds;

and (3) solidification treatment: soaking the product obtained in the step in a coagulating bath for coagulating treatment, wherein the coagulating bath is a mixed solution of dimethyl phthalate and water, the proportion of the dimethyl phthalate is 10%, and the time of the coagulating treatment is 1 minute; forming microporous structures of the surface layer and the inner film of the gel film by exchanging a solvent and a non-solvent in a coagulating bath;

after 2 minutes, removing the porous base membrane obtained in the step, soaking the porous base membrane in water for 240 minutes, and taking out the porous base membrane for later use;

and (3) drying treatment: and drying in an oven at 40 ℃ for 120 minutes to completely volatilize the solvent and the water to obtain the high-temperature-resistant lithium battery diaphragm.

The obtained measurement result of the optical contact angle of the lithium battery diaphragm is shown in fig. 3, and as can be seen from fig. 3, when the optical contact angle measurement instrument is used for carrying out the electrolyte contact angle test on the aramid fiber coated diaphragm, the contact angle between the diaphragm and the electrolyte is 23.4 degrees and is far smaller than the contact angle between the base film and the electrolyte, which indicates that the coated diaphragm has good wettability.

Example 3

A preparation method of the modified aramid polymer comprises the following steps:

heating a first solvent N, N-dimethylformamide to 80 ℃ in an inert gas environment, adding a cosolvent lithium chloride, stirring, dissolving, cooling, and controlling the temperature of the final point of cooling to be 30 ℃; the addition amount of the cosolvent is 10 percent of the mass of the first solvent;

adding a first reaction monomer m-phenylenediamine powder, dissolving, cooling to-5 ℃, then adding a second reaction monomer m-phthaloyl chloride powder and a third reaction monomer p-phenylenediamine powder, stirring, reacting at-5 ℃ for 15 minutes, and after the reaction is finished, adjusting the pH value to be neutral to prepare a modified aramid polymer; the concentration of the first reaction monomer is 1.0mol/L, the concentration of the second reaction monomer is 1.0mol/L, and the concentration of the third reaction monomer is 0.1 mol/L;

the embodiment also provides an aramid fiber membrane casting solution, and the preparation method comprises the following steps:

mixing the modified aramid polymer with ceramic particle aluminum oxide, pore-forming agent ethanol and second solvent dimethylacetamide; in a reaction system, the concentration of the modified aramid polymer is 4 wt%, the concentration of the pore-forming agent is 6 wt%, the concentration of the ceramic particles is 4 wt%, and the concentration of the second solvent is 86 wt%; the particle size of the ceramic particles is 5 μm;

heating the mixed solution to 90 ℃, and stirring to uniformly mix the modified aramid polymer, the ceramic particles and the pore-forming agent to prepare an aramid film casting solution;

the embodiment also provides a lithium battery diaphragm, and the preparation method comprises the following steps:

defoaming treatment: defoaming the aramid fiber membrane casting solution until no bubbles exist; the temperature of the defoaming treatment is 40 ℃, and the time is 30 minutes;

coating: coating the aramid fiber membrane casting solution subjected to defoaming treatment on a polyolefin substrate, wherein the coating thickness is 3.5 micrometers, and the aramid fiber membrane casting solution stays for 55 seconds;

and (3) solidification treatment: soaking the product obtained in the step in a coagulating bath for coagulating treatment, wherein the coagulating bath is a mixed solution of dimethylacetamide and water, the proportion of dimethylacetamide is 50%, and the time of coagulating treatment is 5 minutes; forming microporous structures of the surface layer and the inner film of the gel film by exchanging a solvent and a non-solvent in a coagulating bath;

after 15 minutes, removing the porous base membrane obtained in the step, soaking the porous base membrane in water for 150 minutes, and taking out the porous base membrane for later use;

and (3) drying treatment: and drying in an oven at the temperature of 60 ℃ for 60 minutes to completely volatilize the solvent and the water to obtain the high-temperature-resistant lithium battery diaphragm.

Example 4

A preparation method of the modified aramid polymer comprises the following steps:

heating a first solvent dimethyl phthalate to 80 ℃ in an inert gas environment, adding a cosolvent lithium chloride, stirring, dissolving, and cooling, wherein the final temperature of cooling is 30 ℃; the addition amount of the cosolvent is 15 percent of the mass of the first solvent;

adding a first reaction monomer m-phenylenediamine powder, dissolving, cooling to 0 ℃, then adding a second reaction monomer m-phthaloyl chloride powder and a third reaction monomer p-phenylenediamine powder, stirring, reacting at the temperature of 0 ℃ for 30 minutes, and adjusting the pH value to be neutral after the reaction is finished to obtain a modified aramid polymer; the concentration of the first reaction monomer is 1.2mol/L, the concentration of the second reaction monomer is 1.2mol/L, and the concentration of the third reaction monomer is 0.1 mol/L;

the embodiment also provides an aramid fiber membrane casting solution, and the preparation method comprises the following steps:

mixing the modified aramid polymer with ceramic particle tin dioxide, pore-forming agent tetrahydrofuran and second solvent dimethyl phthalate; in a reaction system, the concentration of the modified aramid polymer is 6 wt%, the concentration of the pore-forming agent is 5 wt%, the concentration of the ceramic particles is 5 wt%, and the concentration of the second solvent is 84 wt%; the particle size of the ceramic particles is 5 μm;

heating the mixed solution to 100 ℃, and stirring to uniformly mix the modified aramid polymer, the ceramic particles and the pore-forming agent to prepare an aramid film casting solution;

the embodiment also provides a lithium battery diaphragm, and the preparation method comprises the following steps:

defoaming treatment: defoaming the aramid fiber membrane casting solution until no bubbles exist; the temperature of the defoaming treatment is 50 ℃, and the time is 30 minutes;

coating: coating the aramid fiber membrane casting solution subjected to defoaming treatment on a polyolefin substrate, wherein the coating thickness is 3.3 micrometers, and the aramid fiber membrane casting solution stays for 55 seconds;

and (3) solidification treatment: soaking the product obtained in the step in a coagulating bath for coagulating treatment, wherein the coagulating bath is a mixed solution of N, N-dimethylformamide and water, the proportion of the N, N-dimethylformamide is 90%, and the time of the coagulating treatment is 10 minutes; forming microporous structures of the surface layer and the inner film of the gel film by exchanging a solvent and a non-solvent in a coagulating bath;

after 30 minutes, removing the porous base membrane obtained in the step, soaking the porous base membrane in water for 150 minutes, and taking out the porous base membrane for later use;

and (3) drying treatment: and drying in an oven at the temperature of 80 ℃ for 30 minutes to completely volatilize the solvent and the water to obtain the high-temperature-resistant lithium battery diaphragm.

Comparative example 1

Compared with example 1, the difference is that an aramid film casting solution is prepared using a para-aramid polymer, and a lithium battery separator is prepared using the prepared aramid film casting solution.

Comparative example 2

Compared with example 2, the difference is that a meta-aramid polymer is used to prepare an aramid film casting solution, and the prepared aramid film casting solution is used to prepare a lithium battery diaphragm.

The lithium battery separators obtained in examples 1 to 4 and comparative examples 1 to 2 were tested for their performance, and the results are shown in table 2 below:

TABLE 2

As can be seen from the comparison between example 1 and comparative example 1, the aramid polymer provided by the present application has better solubility, and compared with the para-aramid polymer, the polymer of the present invention has longer gel time and longer storage life. Meanwhile, the coating diaphragm has higher puncture strength and better electrolyte wettability.

It can be seen from comparison among examples 2, 3 and 4 and comparative example 2 that the lithium battery separator provided by the present application has higher film breaking temperature and puncture strength than the lithium battery separator provided by comparative example 2, is more excellent in high-temperature thermal shrinkage at 150 ℃, and the coated separator of the present invention has better electrolyte wettability.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Furthermore, those skilled in the art will appreciate that while some embodiments herein include some features included in other embodiments, rather than other features, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.