CN111234224A - Modified aramid polymer with polyimide structure, aramid film casting liquid, lithium battery diaphragm, preparation method of lithium battery diaphragm and lithium battery - Google Patents
Modified aramid polymer with polyimide structure, aramid film casting liquid, lithium battery diaphragm, preparation method of lithium battery diaphragm and lithium battery Download PDFInfo
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- CN111234224A CN111234224A CN202010046465.6A CN202010046465A CN111234224A CN 111234224 A CN111234224 A CN 111234224A CN 202010046465 A CN202010046465 A CN 202010046465A CN 111234224 A CN111234224 A CN 111234224A
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- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G73/00—Macromolecular compounds obtained by reactions forming a linkage containing nitrogen with or without oxygen or carbon in the main chain of the macromolecule, not provided for in groups C08G12/00 - C08G71/00
- C08G73/06—Polycondensates having nitrogen-containing heterocyclic rings in the main chain of the macromolecule
- C08G73/10—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
- C08G73/14—Polyamide-imides
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/403—Manufacturing processes of separators, membranes or diaphragms
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
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- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
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Abstract
The invention provides a modified aramid polymer with a polyimide structure, an aramid film casting solution, a lithium battery diaphragm, a preparation method and a lithium battery. The preparation method of the modified aramid polymer with the polyimide structure comprises the following steps: dissolving aromatic diamine in an organic solvent, adding aromatic diacid chloride and aromatic dianhydride in an inert gas environment, and carrying out a first reaction; adding a dehydrating agent to carry out a second reaction. The aramid fiber membrane casting solution comprises raw materials of modified aramid fiber polymer with a polyimide structure and inorganic particles. The lithium battery diaphragm comprises a base material and a coating layer coated on the surface of the base material, wherein the coating layer comprises an aramid fiber membrane casting solution. The preparation method of the lithium battery diaphragm comprises the steps of coating substances including the aramid fiber membrane casting solution on a base material, then carrying out solidification treatment, then placing the base material in water for soaking, and finally carrying out 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.
Description
Technical Field
The invention relates to the field of lithium batteries, in particular to a modified aramid polymer with a polyimide structure, an aramid film casting solution, a lithium battery diaphragm, a preparation method and a lithium battery.
Background
Lithium batteries are widely applied to mobile electronic devices and power devices, wherein a diaphragm is taken as an important component of the lithium batteries, the lithium batteries have very important influence on the safety of the lithium batteries, in order to improve the thermal stability and the wettability of the lithium battery diaphragm, the most widely used method is to coat a coating on a polyolefin diaphragm, and ceramics is a common coating material, but the problems of poor high temperature resistance, easy falling of the coating and the like exist. Aramid fiber has excellent properties such as high strength, high modulus, chemical corrosion resistance and the like, so the aramid fiber is developed and applied to a coating of a polyolefin diaphragm, and can improve the thermal stability and oxidation resistance of the diaphragm at high temperature. However, the high-energy density ternary battery needs to develop a diaphragm with more excellent thermal stability to improve the safety of the battery, the decomposition temperature of the aramid fiber is 420 ℃, the aramid fiber is used as a coating of a polyolefin diaphragm and applied to the field of lithium batteries, and the heat resistance, the thermal stability and the mechanical property of the aramid fiber are required to be further improved.
In view of the above, the present invention is particularly proposed.
Disclosure of Invention
The first purpose of the invention is to provide a modified aramid polymer with a polyimide structure, wherein the polyimide structure is introduced into aramid to improve the heat resistance of the aramid, so that the safety performance of a lithium battery is improved.
The second purpose of the invention is to provide an aramid fiber membrane casting solution, and the lithium battery diaphragm prepared by using the aramid fiber membrane casting solution has good thermal stability.
A third object of the present invention is to provide a lithium battery separator having good thermal stability and a high film rupture temperature.
The fourth purpose of the invention is to provide a preparation method of the lithium battery diaphragm, which has 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 purposes, the following technical scheme is adopted:
a modified aramid polymer having a polyimide structure, which is prepared by a method comprising:
dissolving aromatic diamine in an organic solvent, adding aromatic diacid chloride and aromatic dianhydride in an inert gas environment, and carrying out a first reaction; and then adding a dehydrating agent for a second reaction to obtain the modified aramid polymer with the polyimide structure.
The aromatic dianhydride compound with a certain proportion is added in the synthetic process of the aramid fiber, and a polyimide structure containing a nitrogen five-membered ring and an aromatic ring is introduced into a molecular chain of the polyamide, so that the rigidity of the molecular chain is increased, the interaction force among molecules is enhanced, and the heat resistance, the thermal stability and the mechanical property of the polymer are further improved while the superiority of the aramid fiber is not influenced.
Preferably, a cosolvent is further added into the organic solvent, and the cosolvent comprises calcium chloride and/or lithium chloride;
more preferably, the addition amount of the cosolvent is 1-15% of the mass of the organic solvent;
further preferably, the cosolvent is added, heated to 60-100 ℃, stirred and dissolved, and then cooled to 10-35 ℃;
preferably, the organic solvent comprises one or more of N-methylpyrrolidone, dimethylacetamide, N-dimethylformamide, and dimethyl phthalate.
The addition of the cosolvent contributes to better dissolution of the reaction monomers and improves the reaction efficiency, and the optimization of the organic solvent and the cosolvent, the optimization of the addition amount of the cosolvent and the optimization of the dissolution conditions can further improve the reaction efficiency.
Optionally, the aromatic diamine comprises one or more of p-phenylenediamine, m-phenylenediamine, and biphenyldiamine, the aromatic diacid chloride comprises terephthaloyl chloride and/or isophthaloyl chloride, and the aromatic dianhydride comprises pyromellitic dianhydride and/or biphenyltetracarboxylic dianhydride;
preferably, the aromatic diacid chloride and the aromatic dianhydride can be added in steps and times;
preferably, the molar ratio of the aromatic diamine to the aromatic diacid chloride to the aromatic dianhydride is 100 (90-99.9): (0.1 to 10);
further preferably, the molar ratio of the aromatic diamine, the aromatic diacid chloride and the aromatic dianhydride may be 100: 90: 10, 100: 91: 9,100: 91.5: 8.5, 100: 92: 8,100: 92.5: 7.5, 100: 93: 7,100: 93.5: 6.5, 100: 94: 6,100: 94.5: 5.5, 100: 95: 5,100: 95.5: 4.5, 100: 96: 4,100: 96.5: 3.5, 100: 97: 3,100: 97.5: 2.5, 100: 98: 2,100: 98.5: 1.5, 100: 99: 1,100: 99.5: 0.5 and 100: 99.9: 0.1 and 100 (90-99.9): (0.1-10).
More preferably, the method further comprises cooling the reaction system after the aromatic diamine is dissolved in the organic solvent, wherein the target cooling temperature is-15 to 10 ℃;
further preferably, the reaction temperature of the first reaction is-15 to 5 ℃, and the reaction time is 1 to 3 hours.
Preferably, the dehydrating agent comprises one or more of acetic anhydride, propionic anhydride and maleic anhydride;
preferably, a catalyst is also added during the second reaction, and the catalyst comprises one or more of triethylamine, pyridine and isoquinoline;
preferably, the temperature of the second reaction is 0-35 ℃, and the stirring reaction time is 1-5 hours;
the reaction is further optimized according to the types of reactants in the reaction system, the proportion of the reactants and the optimization of the temperature and the time of the reaction system, so that the reaction efficiency is improved, and a reaction product with excellent performance is obtained.
An aramid fiber membrane casting solution comprises the following raw materials: the modified aramid fiber polymer with the polyimide structure and the inorganic particles.
The aramid fiber membrane casting solution comprises a modified aramid fiber polymer with a polyimide structure and inorganic particles, and has the advantages of small interfacial stress with a base membrane, good contact and low possibility of falling off.
Preferably, the mass of the inorganic particles is 5-20% of that of the aramid fiber membrane casting solution;
optionally, the mass of the inorganic particles can be any one of 5%, 10%, 15%, 20% and 5-20% of the mass of the aramid film casting liquid;
preferably, the inorganic particles comprise one or more of alumina, boehmite, zirconia, magnesia, zinc oxide and silica;
preferably, the preparation method of the aramid film casting solution comprises the following steps: mixing the modified aramid polymer with the polyimide structure with the inorganic particles;
preferably, the mixing temperature is 15-30 ℃, and the stirring is carried out for 1-2 hours;
preferably, defoaming the aramid fiber membrane casting solution after mixing;
preferably, the temperature of the defoaming treatment is 30-50 ℃, and the time is 5-60 minutes.
The aramid fiber membrane casting solution with better performance is obtained by optimizing the raw materials of the aramid fiber membrane casting solution and the preparation method of the aramid fiber membrane casting solution.
A lithium battery diaphragm comprises a base material and a coating layer coated on the surface of the base material, wherein the coating layer comprises the aramid fiber membrane casting solution;
preferably, the thickness of the coating layer is 1-10 μm.
The heat resistance of the lithium battery diaphragm prepared by the aramid fiber membrane casting solution is greatly improved.
A preparation method of the lithium battery diaphragm comprises the steps of coating substances including the aramid fiber membrane casting solution on the base material, then carrying out solidification treatment, then placing the base material in water for soaking, and finally carrying out drying treatment;
preferably, the coating is kept for 5-60 seconds and then the solidification treatment is carried out;
preferably, the soaking time is 10-60 minutes;
preferably, the coagulation treatment is carried out in a coagulation bath selected from one of a coagulation bath containing a solvent and water or a steam coagulation bath;
preferably, the coagulating bath comprises a mixed solution of one or more solvents of N-methyl pyrrolidone, dimethylacetamide, N-dimethylformamide, dimethyl phthalate or ethanol and water, wherein the proportion of the solvents is 10-90%; the time of the solidification treatment is 1-10 minutes;
preferably, the drying treatment temperature is 40-80 ℃ and the drying treatment time is 10-60 minutes.
The lithium battery diaphragm prepared by the aramid fiber membrane casting solution has the advantages of simple preparation process, controllable conditions, easiness in expanded production and capability of effectively improving the heat resistance of the diaphragm, wherein the performances of reaction products are optimized for the optimization of coating thickness, soaking time, solidification treatment and drying treatment.
A lithium battery comprises the lithium battery diaphragm.
The heat resistance and the safety performance of the lithium battery prepared by using the lithium battery diaphragm are obviously improved.
Compared with the prior art, the invention has the beneficial effects that:
(1) aromatic polyimide is adopted to modify aramid fiber, an aromatic dianhydride compound with a certain proportion is added in the synthetic process of the aramid fiber, and a polyimide structure containing a nitrogen five-membered ring and an aromatic ring is introduced into a molecular chain of the polyamide, so that the rigidity of the molecular chain is increased, the interaction force among molecules is enhanced, the heat resistance, the thermal stability and the mechanical property of the polymer are further improved while the superiority of the aramid fiber is not influenced, and the safety performance of a lithium battery is further improved;
(2) the aramid fiber casting solution containing the modified aramid fiber polymer with the polyimide structure and the inorganic particles has the advantages of aramid fiber and polyimide, and has better thermal stability when being used as a coating material of a polyolefin diaphragm;
(3) the lithium battery diaphragm prepared by the aramid fiber membrane casting liquid has higher diaphragm breaking temperature, and the use safety performance of the lithium battery is greatly improved;
(4) the lithium battery diaphragm is prepared by using the aramid fiber membrane casting solution, the preparation process is simple, the conditions are controllable, the expanded production is easy, and the heat resistance and the safety performance 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 having a polyimide structure obtained in example 1.
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 modified aramid polymer with a polyimide structure is prepared by the following steps:
synthesis of Polymer: under the inert gas environment, adding 20kg of dimethylacetamide into a reaction kettle, adding 3kg of calcium chloride under stirring, heating to 100 ℃, stirring for dissolving for 1 hour, and cooling to 35 ℃;
adding 173g of p-phenylenediamine powder into the system, dissolving, and cooling to 10 ℃;
147.35g of terephthaloyl chloride powder is added into the system and stirred, the reaction temperature is 0 ℃, and the time is 0.5 hour;
then adding 35g of pyromellitic dianhydride powder for reaction at the reaction temperature of 0 ℃ for 1.5 hours;
finally, 147.35g of terephthaloyl chloride powder was added, and the reaction was carried out at 0 ℃ for 0.17 hour.
Imidization of the polymer: and after the synthesis reaction is finished, adding 60ml of acetic anhydride and 100ml of triethylamine into the system, stirring for 2 hours at the temperature of 0 ℃, and finishing the reaction to obtain the modified aramid polymer with the polyimide structure.
The embodiment also provides an aramid fiber membrane casting solution, and the preparation method comprises the following steps:
mixing the modified aramid polymer with the polyimide structure with inorganic particle alumina, wherein the mass of the alumina is 15% of that of the aramid casting solution, the temperature of a mixing system is 20 ℃, stirring for 1.5 hours to prepare a preliminary aramid casting solution, and then defoaming the preliminary aramid casting solution to ensure that the performance of the preliminary aramid casting solution is better, the temperature of the defoaming treatment is 30 ℃, and the defoaming time is 60 minutes.
The embodiment also provides a lithium battery diaphragm, and the preparation method comprises the following steps:
coating substances including the aramid fiber membrane casting solution subjected to defoaming treatment on a polyolefin substrate, wherein the coating thickness is 1 micrometer, and the aramid fiber membrane casting solution stays for 5 seconds;
soaking the product obtained in the step into a mixed solution of dimethylacetamide and water for coagulation treatment, wherein the proportion of dimethylacetamide is 80%, and the coagulation treatment time 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;
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 then drying in an oven at 70 ℃ for 30 minutes to completely volatilize the solvent and the water to obtain the high-temperature-resistant lithium battery diaphragm.
The lithium battery diaphragm can be processed and manufactured to obtain the lithium battery.
The prepared modified aramid polymer having a polyimide structure was subjected to infrared spectrum scanning 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 Infrared Spectrum Peak and Attribution
| Wave number (cm)-1) | Attribution |
| 3271 | Aramid fiber N-H telescopic vibration |
| 1780 | Asymmetric vibration of imine ring carbonyl |
| 1650 | C ═ O stretching vibration |
| 1380 | Imine ring C-N stretching vibration |
| 1507 | Stretching vibration of |
| 1500～1300 | C-H in-plane bending vibration |
| 1300～1000 | C-C skeleton vibration |
As can be seen from the infrared data, at 1780cm-1The characteristic absorption peak of imide ring is shown, which indicates that the polyimide structure is successfully introduced into the molecular structure of para-aramid.
Example 2
A modified aramid polymer with a polyimide structure is prepared by the following steps:
synthesis of Polymer: under the inert gas environment, adding 20kg of N, N-dimethylformamide into a reaction kettle, adding 2kg of calcium chloride under stirring, heating to 90 ℃, stirring for dissolving for 1 hour, and cooling to 25 ℃;
173g of m-phenylenediamine powder is added into the system, dissolved and cooled to 0 ℃;
adding 154.29g of terephthaloyl chloride powder into the system, and stirring, wherein the reaction temperature is-15 ℃ and the reaction time is 1 hour;
then 17.45g of pyromellitic dianhydride powder is added for reaction at the temperature of-15 ℃ for 1.5 hours;
finally 154.29g of terephthaloyl chloride powder was added, the reaction temperature was-15 ℃ and the reaction time was 0.5 hour.
Imidization of the polymer: after the synthesis reaction is finished, adding 45ml of propionic anhydride and 100ml of pyridine into the system for a second reaction, stirring for 5 hours at 20 ℃, and obtaining the modified aramid polymer with the polyimide structure after the reaction is finished.
The embodiment also provides an aramid fiber membrane casting solution, and the preparation method comprises the following steps:
mixing the modified aramid polymer with the polyimide structure and inorganic particle magnesium oxide, wherein the mass of the magnesium oxide is 5% of that of the aramid fiber membrane casting solution, the temperature of a mixing system is 15 ℃, stirring for 1 hour to prepare a preliminary aramid fiber membrane casting solution, and then defoaming the preliminary aramid fiber membrane casting solution to ensure that the performance of the preliminary aramid fiber membrane casting solution is better, the temperature of the defoaming treatment is 40 ℃, and the defoaming time is 30 minutes.
The embodiment also provides a lithium battery diaphragm, and the preparation method comprises the following steps:
coating the substances including the aramid fiber membrane casting solution subjected to defoaming treatment on a polyolefin substrate, wherein the coating thickness is 10 microns, and the substances stay for 60 seconds;
soaking the product obtained in the step in a mixed solution of ethanol and water for solidification treatment, wherein the proportion of the ethanol is 90%, and the time of the solidification 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;
removing the porous base membrane obtained in the step, soaking the porous base membrane in water for 30 minutes, and taking out the porous base membrane for later use;
and then 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 lithium battery diaphragm can be processed and manufactured to obtain the lithium battery.
Example 3
A modified aramid polymer with a polyimide structure is prepared by the following steps:
synthesis of Polymer: under the inert gas environment, adding 20kg of dimethyl phthalate into a reaction kettle, adding 0.2kg of lithium chloride under stirring, heating to 60 ℃, stirring for dissolving for 1 hour, and cooling to 10 ℃;
adding 173g of p-phenylenediamine powder into the system, dissolving, and cooling to-15 ℃;
adding 160.79g of terephthaloyl chloride powder into the system, stirring, and starting to react at the reaction temperature of 5 ℃ for 0.5 hour;
then adding 3.49g of pyromellitic dianhydride powder, reacting at 5 ℃ for 0.45 hour;
finally, 160.79g of isophthaloyl dichloride powder were added, and the reaction temperature was 5 ℃ for 0.05 hour.
Imidization of the polymer: after the synthesis reaction is finished, adding 45ml of maleic anhydride and 100ml of isoquinoline into the system, stirring for 1 hour at 35 ℃, and finishing the reaction to obtain the modified aramid polymer with the polyimide structure.
The embodiment also provides an aramid fiber membrane casting solution, and the preparation method comprises the following steps:
mixing the modified aramid polymer with the polyimide structure and inorganic particle zinc oxide, wherein the mass of the zinc oxide is 20% of that of the aramid fiber membrane casting solution, the temperature of a mixing system is 30 ℃, stirring for 2 hours to prepare a preliminary aramid fiber membrane casting solution, and then defoaming the preliminary aramid fiber membrane casting solution to ensure that the performance of the preliminary aramid fiber membrane casting solution is better, the temperature of the defoaming treatment is 50 ℃, and the defoaming time is 5 minutes.
The embodiment also provides a lithium battery diaphragm, and the preparation method comprises the following steps:
coating substances including the aramid fiber membrane casting solution subjected to defoaming treatment on a polyolefin substrate, wherein the coating thickness is 5 microns, and the aramid fiber membrane casting solution stays for 30 seconds;
soaking the product obtained in the step into a mixed solution of N, N-dimethylformamide and water for solidification, wherein the proportion of N, N-dimethylformamide is 10%, and the time for solidification 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;
removing the porous base membrane obtained in the step, soaking the porous base membrane in water for 60 minutes, and taking out the porous base membrane for later use; and then drying in an oven at 40 ℃ for 60 minutes to completely volatilize the solvent and the water to obtain the high-temperature-resistant lithium battery diaphragm.
The lithium battery diaphragm can be processed and manufactured to obtain the lithium battery.
Example 4
A modified aramid polymer with a polyimide structure is prepared by the following steps:
synthesis of Polymer: under the inert gas environment, adding 20kg of N-methyl pyrrolidone into a reaction kettle, adding 3kg of calcium chloride under stirring, heating to 100 ℃, stirring for dissolving for 1 hour, and cooling to 25 ℃;
adding 294.78g of biphenyldiamine powder into the system, dissolving, and cooling to 0 ℃;
adding 147.35g of isophthaloyl dichloride powder into the system, stirring, and starting to react at the reaction temperature of 0 ℃ for 0.5 hour;
then adding 47g of biphenyl tetracarboxylic dianhydride powder, and reacting at 0 ℃ for 1.5 hours;
finally, 147.35g of terephthaloyl chloride powder was added, and the reaction temperature was 0 ℃ and the reaction time was 0.17 hour.
Imidization of the polymer: and after the synthesis reaction is finished, adding 60ml of acetic anhydride and 100ml of triethylamine into the system, stirring for 2 hours at the temperature of 0 ℃, and finishing the reaction to obtain the modified aramid polymer with the polyimide structure.
The embodiment also provides an aramid fiber membrane casting solution, and the preparation method comprises the following steps:
mixing the modified aramid polymer with the polyimide structure and inorganic particle silicon oxide, wherein the mass of the silicon oxide is 20% of that of the aramid fiber membrane casting solution, the temperature of a mixing system is 30 ℃, stirring for 1 hour to prepare a preliminary aramid fiber membrane casting solution, and then defoaming the preliminary aramid fiber membrane casting solution to ensure that the performance of the preliminary aramid fiber membrane casting solution is better, the temperature of the defoaming treatment is 45 ℃, and the defoaming time is 30 minutes.
The embodiment also provides a lithium battery diaphragm, and the preparation method comprises the following steps:
coating substances including the aramid fiber membrane casting solution subjected to defoaming treatment on a polyolefin substrate, wherein the coating thickness is 1 micrometer, and the aramid fiber membrane casting solution stays for 5 seconds;
soaking the product obtained in the step in a mixed solution of dimethyl phthalate and water for solidification treatment, wherein the proportion of the dimethyl phthalate is 90%, and the time of the solidification 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;
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 then 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 lithium battery diaphragm can be processed and manufactured to obtain the lithium battery.
Comparative example 1
Compared with example 1, the difference is that the aramid film casting solution is prepared directly from the para-aramid polymer, and the lithium battery diaphragm is prepared from the prepared aramid film casting solution.
Comparative example 2
The difference compared to example 1 is that polyimide was used to make an integral film.
Comparative example 3
The difference compared to example 1 is that a coating film was prepared using soluble polyimide.
The lithium battery separators obtained in examples 1 to 4 and comparative examples 1 to 3 were tested for their performance, and the results are shown in table 2 below:
table 2 performance test data
It can be known through the comparison of embodiment 1 and comparative example 1 that the lithium battery diaphragm that this application provided is higher than the rupture of membranes temperature of the lithium battery diaphragm that comparative example 1 provided, and thermal stability is better, shows that through introducing the polyimide structure to modify aramid fiber, the heat resistance who obtains the modified aramid fiber that has the polyimide structure has obtained effective promotion.
As can be seen from comparison between example 1 and comparative example 2, the lithium battery separator provided in the present application has better mechanical strength, puncture strength, and air permeability than the lithium battery separator provided in comparative example 2, which indicates that the separator provided in the present application has better mechanical properties and ion permeability than the polyimide monolithic membrane.
As can be seen from comparison between example 1 and comparative example 3, the lithium battery separator provided by the present application has a higher rupture temperature and better thermal stability than the lithium battery separator provided by comparative example 3, which indicates that the lithium battery separator prepared using the modified aramid fiber having a polyimide structure has better heat resistance than soluble polyimide.
The reason for the above phenomenon is analyzed because the thermal decomposition temperature of polyimide itself is as high as 600 ℃, but the unique structural performance of polyimide determines that the polyimide needs high-temperature imidization ring formation in the synthesis process, the prepared polyimide has the disadvantages of low mechanical strength, large air permeability and the like, and if the soluble polyimide is prepared as a coating material, the flexible chain is introduced into the molecular structure to improve the solubility of the polyimide, the conjugation of the whole structure of the polyimide is damaged, and the thermal stability of the soluble polyimide coating film is poor.
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.
Claims (10)
1. A modified aramid polymer with a polyimide structure is characterized in that the preparation method comprises the following steps:
dissolving aromatic diamine in an organic solvent, adding aromatic diacid chloride and aromatic dianhydride in an inert gas environment, and carrying out a first reaction; and then adding a dehydrating agent for a second reaction to obtain the modified aramid polymer with the polyimide structure.
2. The modified aramid polymer having a polyimide structure according to claim 1, wherein a co-solvent is further added to the organic solvent, and the co-solvent includes calcium chloride and/or lithium chloride;
preferably, the addition amount of the cosolvent is 1-15% of the mass of the organic solvent;
preferably, the cosolvent is added, then the mixture is heated to 60-100 ℃, stirred and dissolved, and then the temperature is reduced to 10-35 ℃;
preferably, the organic solvent comprises one or more of N-methylpyrrolidone, dimethylacetamide, N-dimethylformamide, and dimethyl phthalate.
3. The modified aramid polymer having a polyimide structure according to claim 1, wherein the aromatic diamine includes one or more of p-phenylenediamine, m-phenylenediamine and biphenyldiamine, the aromatic diacid chloride includes terephthaloyl chloride and/or isophthaloyl chloride, and the aromatic dianhydride includes pyromellitic dianhydride and/or biphenyltetracarboxylic dianhydride;
preferably, the aromatic diacid chloride and the aromatic dianhydride can be added in steps and times;
preferably, the molar ratio of the aromatic diamine to the aromatic diacid chloride to the aromatic dianhydride is 100 (90-99.9): (0.1-10).
4. The modified aramid polymer having a polyimide structure according to claim 1, further comprising cooling a reaction system after the aromatic diamine is dissolved in the organic solvent, wherein a target temperature of the cooling is-15 to 10 ℃;
preferably, the reaction temperature of the first reaction is-15 to 5 ℃, and the reaction time is 1 to 3 hours.
5. The modified aramid polymer having a polyimide structure according to claim 1, wherein the dehydrating agent comprises one or more of acetic anhydride, propionic anhydride and maleic anhydride;
preferably, a catalyst is also added during the second reaction, and the catalyst comprises one or more of triethylamine, pyridine and isoquinoline;
preferably, the temperature of the second reaction is 0-35 ℃, and the stirring reaction time is 1-5 hours.
6. The aramid fiber membrane casting solution is characterized by comprising the following raw materials: the modified aramid polymer having a polyimide structure and inorganic particles as claimed in any one of claims 1 to 6.
7. The aramid film casting solution according to claim 6, wherein the mass of the inorganic particles is 5-20% of the mass of the aramid film casting solution;
preferably, the inorganic particles comprise one or more of alumina, boehmite, zirconia, magnesia, zinc oxide and silica;
preferably, the preparation method of the aramid film casting solution comprises the following steps: mixing the modified aramid polymer with the polyimide structure with the inorganic particles;
preferably, the mixing temperature is 15-30 ℃, and the stirring is carried out for 1-2 hours;
preferably, defoaming the aramid fiber membrane casting solution after mixing;
preferably, the temperature of the defoaming treatment is 30-50 ℃, and the time is 5-60 minutes.
8. A lithium battery diaphragm is characterized by comprising a base material and a coating layer coated on the surface of the base material, wherein the coating layer comprises the aramid film casting solution of claim 6;
preferably, the thickness of the coating layer is 1-10 μm.
9. A method of preparing a lithium battery separator according to claim 8, comprising: coating substances including the aramid fiber membrane casting solution on the base material, then carrying out solidification treatment, then placing the base material in water for soaking, and finally carrying out drying treatment;
preferably, the coating is kept for 5-60 seconds and then the solidification treatment is carried out;
preferably, the soaking time is 10-60 minutes;
preferably, the coagulation treatment is carried out in a coagulation bath selected from one of a coagulation bath containing a solvent and water or a steam coagulation bath;
preferably, the coagulating bath comprises a mixed solution of one or more solvents of N-methyl pyrrolidone, dimethylacetamide, N-dimethylformamide, dimethyl phthalate or ethanol and water, wherein the proportion of the solvents is 10-90%; the time of the solidification treatment is 1-10 minutes;
preferably, the drying treatment temperature is 40-80 ℃ and the drying treatment time is 10-60 minutes.
10. A lithium battery comprising the lithium battery separator as claimed in claim 8.
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