A para-aramid separator and a method of making the same

Abstract

The application relates to the technical field of battery materials, in particular to a para-aramid membrane and a preparation method thereof. The preparation method of the para-aramid membrane comprises the following steps: placing a substrate coated with aramid nanofiber dispersion liquid in a proton donor to obtain aramid nanofiber gel with the dispersion of the proton donor; immersing the aramid nanofiber gel with the dispersion of the proton donor into a proton solution, replacing the solute in the proton solution with the proton donor, and then heating and drying to obtain the para-aramid membrane; wherein the solute comprises low-decomposition-temperature / low-boiling-point salts and / or organic substances. The preparation method of the para-aramid membrane provided by the application can prepare the para-aramid membrane with high porosity, tensile strength and thermal stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, in particular to a para-aramid separator and a preparation method thereof. BACKGROUND

[0002] Lithium batteries have been widely used in new energy vehicles, smart phones, wearable devices, power station energy storage and other fields, but safety accidents such as fire and explosion related to lithium batteries occur frequently, causing social concerns about the safety of lithium batteries.

[0003] The separator is a core component that ensures the safety of lithium batteries, which plays a role in isolating the positive and negative electrodes and preventing short circuits. However, the existing commercial polyolefin separator has low mechanical strength, is not resistant to high temperature, is easily pierced by lithium dendrites, and is easily shrunk at high temperature, causing internal short circuit of the lithium battery, and even fire and explosion. The commercial polyolefin separator cannot guarantee the safety of the lithium battery.

[0004] Para-aramid has excellent mechanical properties, excellent thermal stability and good flame retardancy, and is an ideal separator material. The para-aramid separator prepared using para-aramid is expected to significantly improve the safety of lithium batteries. However, the strong hydrogen bond network and high crystallinity make para-aramid difficult to dissolve (only soluble in concentrated sulfuric acid), have a high melting point (> 400 °C), and are difficult to form, making it difficult to prepare a separator with high porosity. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of a para-aramid separator, which solves the problem that it is difficult to prepare a separator with high porosity due to the difficulty of dissolving para-aramid and its high melting point in the prior art.

[0006] The present application also provides a para-aramid separator to solve the problem that the separator in the prior art cannot guarantee the safety of the lithium battery.

[0007] In order to solve the above problems, the present application provides a preparation method of a para-aramid separator, and the technical scheme adopted is:

[0008] A preparation method of a para-aramid separator, comprising the following steps: placing a substrate coated with aramid nanofiber dispersion liquid in a proton donor to obtain aramid nanofiber gel dispersed with a proton donor; immersing the aramid nanofiber gel dispersed with the proton donor in a proton solution, and after the solute in the proton solution is replaced with the proton donor, heating and drying to obtain a para-aramid separator; wherein the solute includes a low-decomposition-temperature / low-boiling-point salt and / or an organic matter.

[0009] The present application has the following advantages:

[0010] 1) The present application obtains high-porosity para-aramid separator by immersing aramid nanofiber gel dispersed with proton donor into proton solution, replacing solute in proton solution with proton donor, and fixing the structure of the separator through heating and drying to reduce the shrinkage of the separator and the collapse of the pore structure.

[0011] 2) The present application can adjust the pore size and porosity of the para-aramid separator by adjusting the type and concentration of the proton donor and the type and concentration of the proton solution, thereby obtaining a para-aramid separator with adjustable pore structure and further adjusting the mechanical strength and rate performance of the para-aramid separator.

[0012] 3) Compared with aramid microfibers, the aramid nanofibers used in the present application have higher mechanical strength and specific surface area, and after forming, they have smaller and more uniform pore structure, which can improve the safety and electrochemical performance of lithium batteries.

[0013] 4) The preparation method of the present application is compatible with existing industrial processing equipment, has the potential for large-scale application, can realize large-scale and efficient preparation, and promotes its practical application to improve the safety of lithium batteries.

[0014] In order to obtain aramid nanofiber gel dispersed with proton donor with high porosity, preferably, the proton donor is a proton solvent or steam of a proton solvent, and the proton solvent includes at least one of water, ethanol, methanol, ethylene glycol, glycerol, propanol, isopropanol, and butanol.

[0015] In order to enable effective replacement of solute in the proton solution with the proton donor, preferably, the low-decomposition-temperature / low-boiling-point salt includes at least one of carbonate, bicarbonate, ammonium salt, and nitrate; the organic matter includes oxalic acid; and the mass concentration of the solute in the proton solution is 0.5-20%.

[0016] Further preferably, the ammonium salt is ammonium carbonate.

[0017] In order to enable sufficient replacement of solute in the proton solution with the proton donor, preferably, the replacement time is 2-72 h.

[0018] Preferably, the heating and drying includes first-step heating and second-step heating, the temperature of the first-step heating is 30-120 °C, and the time is 0.5-12 h; the temperature of the second-step heating is 100-200 °C, and the time is 0.5-12 h. The present application uses two-step heating to heat and dry the para-aramid separator, the first-step heating removes the solvents in the proton donor and the proton solution, fixes the structure of the separator, reduces the shrinkage of the separator and the collapse of the pore structure during the second-step heating, and the second-step heating removes the solute in the proton solution to improve the porosity of the para-aramid separator.

[0019] In order to make the aramid nanofiber gel with a smaller and uniform pore structure after forming, preferably, the mass concentration of the aramid nanofiber dispersion liquid is 0.5-2%.

[0020] In order to obtain the aramid nanofiber dispersion liquid, preferably, the preparation method of the aramid nanofiber dispersion liquid comprises the following steps: stirring aramid micrometer fibers in an alkaline solvent system to obtain an aramid nanofiber dispersion liquid. The alkaline solvent system is used in the present application, which weakens the hydrogen bond interaction between aramid molecules at normal temperature and pressure, and makes the aramid fibers nanometerized, and the conditions are mild and the efficiency is high.

[0021] In order to improve the nanometerization efficiency of aramid fibers, preferably, the alkaline solvent system comprises an alkaline solvent system solute and an alkaline solvent system solvent, the alkaline solvent system solute comprises at least one of potassium tert-butoxide, potassium hydroxide, sodium tert-butoxide and sodium hydroxide; and the alkaline solvent system solvent comprises at least one of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, tetrahydrofuran, acetone, toluene, xylene, benzene and dichloromethane.

[0022] In order to further improve the nanometerization efficiency of aramid fibers, preferably, the mass ratio of the aramid micrometer fibers, the alkaline solvent system solute and the alkaline solvent system solvent is 1: (0.5-1.5): (50-200).

[0023] The present application also provides a para-aramid separator.

[0024] The para-aramid separator is prepared by the preparation method of the para-aramid separator.

[0025] The para-aramid separator of the present application is a para-aramid separator with controllable pore structure, which has high porosity, mechanical strength, thermal stability and rate performance, and can improve the safety and electrochemical performance of lithium batteries. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 SEM image of the para-aramid separator prepared for Example 1 of the preparation method of the para-aramid separator of the present application.

[0027] Figure 2 SEM image of the para-aramid separator prepared for Example 2 of the preparation method of the para-aramid separator of the present application.

[0028] Figure 3 SEM image of the para-aramid separator prepared for Example 3 of the preparation method of the para-aramid separator of the present application.

[0029] Figure 4SEM image of the para-aramid separator prepared for Example 3 of the preparation method of the para-aramid separator of the present application. DETAILED DESCRIPTION

[0030] In the prior art, it is difficult to prepare a separator with high porosity due to the difficulty of dissolving and high melting point of para-aramid. The present application provides a preparation method of a para-aramid separator, comprising the following steps: placing a substrate coated with aramid nanofiber dispersion liquid in a proton donor to obtain aramid nanofiber gel dispersed with a proton donor; immersing the aramid nanofiber gel dispersed with the proton donor in a proton solution, replacing the solute in the proton solution with the proton donor, and then heating and drying to obtain a para-aramid separator; wherein the solute comprises a salt with low decomposition temperature / low boiling point and / or an organic matter.

[0031] The technical concept of the present application is that aramid nanofiber has higher mechanical strength and specific surface area, and has smaller and uniform pore structure after forming, which can improve the safety and electrochemical performance of lithium batteries. The substrate coated with aramid nanofiber dispersion liquid is placed in a proton donor to obtain aramid nanofiber gel dispersed with a proton donor, at this time the proton donor forms a dispersed pore structure in the aramid nanofiber gel; the aramid nanofiber gel dispersed with the proton donor is immersed in a proton solution, and the replacement of the solute in the proton solution with the proton donor is carried out, that is, the solute is used to replace the proton donor in the aramid nanofiber gel, to obtain aramid nanofiber gel dispersed with a pore structure, at this time the solute is in the pore structure; the aramid nanofiber gel dispersed with the pore structure is dried and heated to remove the proton donor and the proton solution, to realize the fixation of the separator structure and the stability of the pore structure, and further to obtain a para-aramid separator with adjustable pore structure, which has high porosity, mechanical strength, thermal stability and rate performance, and can improve the safety and electrochemical performance of lithium batteries.

[0032] Specifically, the preparation method of the para-aramid separator comprises the following steps:

[0033] Firstly, para-aramid, alkaline solvent system solute and alkaline solvent system solvent are added into the alkaline solvent system solvent, stirred at a rotation speed of 600-1500 rpm for 3-48 h to obtain aramid nanofiber dispersion liquid with a mass concentration of 0.5-2%; wherein the mass ratio of para-aramid, alkaline solvent system solute, alkaline solvent system solvent is 1: (0.5-1.5): (50-200).

[0034] Secondly, the aramid nanofiber dispersion liquid is coated on a substrate, and then placed in a proton donor for 0.5-72 h to obtain aramid nanofiber gel dispersed with a proton donor; wherein the proton donor is a proton solvent or steam of a proton solvent, and the proton solvent comprises at least one of water, ethanol, methanol, ethylene glycol, glycerol, propanol, isopropanol and butanol.

[0035] Then, the aramid nanofiber gel dispersed with the proton donor is immersed in a proton solution for 2-72 h, so that the solute in the proton solution sufficiently replaces the proton donor in the aramid nanofiber gel, to obtain a replaced aramid nanofiber gel; wherein the mass concentration of the solute in the proton solution is 0.5-20%; the solvent in the proton solution includes at least one of water, ethanol, methanol, ethylene glycol, glycerol, propanol, isopropanol, and butanol;

[0036] Finally, the replaced aramid nanofiber gel is heated to 30-120 °C and kept for 0.5-12 h to remove the proton donor and the solvent in the proton solution, and then heated to 100-200 °C and kept for 0.5-12 h to remove the solute in the proton solution, to finally obtain the para-aramid separator.

[0037] The implementation process of the present application will be described in detail below in conjunction with specific examples. However, those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. In addition, it should be noted that only parts related to the application are shown in the examples for ease of description.

[0038] It should be noted that the examples in the present application and the features in the examples can be combined with each other without conflict. The present application will be described in detail below with reference to examples.

[0039] It should be noted that the endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The ranges and values should be interpreted as being approximate. Values between the endpoints of any range or values and individual points within ranges should be considered as being included in the present application. For values which are expressed as ranges, any intervening value or values between the stated values are also intended to be encompassed.

[0040] In the following examples, the para-aramid used is aramid chopped fiber, and the length of the chopped fiber is 5 mm. The raw materials used are all ordinary commercially available products that can be directly purchased or prepared according to conventional techniques in the art.

[0041] I. Specific examples of the preparation method of the para-aramid separator of the present application

[0042] Example 1

[0043] The preparation method of the para-aramid separator provided in this example includes the following steps:

[0044] First, 2 g of p-aramid, 1.5 g of potassium tert-butoxide is added to 100 g of dimethyl sulfoxide, and stirred at a speed of 1500 rpm for 3 h to obtain an aramid nanofiber dispersion liquid with a mass concentration of 2%;

[0045] Secondly, the aramid nanofiber dispersion liquid is coated on the substrate, and then placed in ethanol for 0.5 h to obtain an aramid nanofiber gel dispersed with ethanol;

[0046] Then, the aramid nanofiber gel dispersed with ethanol is immersed in a proton solution for 2 h, wherein the solute in the proton solution is oxalic acid with a mass concentration of 4%, and the solvent is ethanol, so that the ethanol in the aramid nanofiber gel is fully replaced by oxalic acid to obtain a replaced aramid nanofiber gel;

[0047] Finally, the replaced aramid nanofiber gel is heated to 120 °C and kept for 0.5 h to remove ethanol, and then heated to 200 °C and kept for 6 h to remove oxalic acid, and finally a p-aramid separator is obtained.

[0048] Example 2

[0049] The preparation method of the p-aramid separator provided in this embodiment comprises the following steps:

[0050] First, 2 g of p-aramid, 1.5 g of potassium tert-butoxide is added to 100 g of dimethyl sulfoxide, and stirred at a speed of 1500 rpm for 3 h to obtain an aramid nanofiber dispersion liquid with a mass concentration of 2%;

[0051] Secondly, the aramid nanofiber dispersion liquid is coated on the substrate, and then placed in ethanol for 0.5 h to obtain an aramid nanofiber gel dispersed with ethanol;

[0052] Then, the aramid nanofiber gel dispersed with ethanol is immersed in a proton solution for 2 h, wherein the solute in the proton solution is oxalic acid with a mass concentration of 4%, and the solvent is ethanol, so that the ethanol in the aramid nanofiber gel is fully replaced by oxalic acid to obtain a replaced aramid nanofiber gel;

[0053] Finally, the replaced aramid nanofiber gel is heated to 120 °C and kept for 0.5 h to remove ethanol, and then heated to 200 °C and kept for 6 h to remove oxalic acid, and finally a p-aramid separator is obtained.

[0054] Example 3

[0055] The preparation method of the p-aramid separator provided in this embodiment comprises the following steps:

[0056] First, 2 g of para-aramid, 3 g of sodium tert-butoxide are added to 200 g of dimethyl sulfoxide, and stirred at a speed of 1000 rpm for 6 h to obtain an aramid nanofiber dispersion liquid with a mass concentration of 1%;

[0057] Secondly, the aramid nanofiber dispersion liquid is coated on a substrate, and then placed in methanol vapor for 12 h to obtain aramid nanofiber gel dispersed with methanol;

[0058] Then, the aramid nanofiber gel dispersed with methanol is immersed in a proton solution for 24 h, wherein the solute in the proton solution is oxalic acid with a mass concentration of 4%, and the solvent is methanol, so that the oxalic acid fully replaces the methanol in the aramid nanofiber gel to obtain a replaced aramid nanofiber gel;

[0059] Finally, the replaced aramid nanofiber gel is first heated to 30 °C and kept for 12 h to remove the methanol, and then heated to 100 °C and kept for 12 h to remove the oxalic acid, and finally a para-aramid separator is obtained.

[0060] Example 4

[0061] The preparation method of the para-aramid separator provided in this embodiment comprises the following steps:

[0062] First, 2 g of para-aramid, 3 g of sodium tert-butoxide are added to 200 g of dimethyl sulfoxide, and stirred at a speed of 1000 rpm for 6 h to obtain an aramid nanofiber dispersion liquid with a mass concentration of 1%;

[0063] Secondly, the aramid nanofiber dispersion liquid is coated on a substrate, and then placed in methanol vapor for 12 h to obtain aramid nanofiber gel dispersed with methanol;

[0064] Then, the aramid nanofiber gel dispersed with methanol is immersed in a proton solution for 24 h, wherein the solute in the proton solution is oxalic acid with a mass concentration of 4%, and the solvent is methanol, so that the oxalic acid fully replaces the methanol in the aramid nanofiber gel to obtain a replaced aramid nanofiber gel;

[0065] Finally, the replaced aramid nanofiber gel is first heated to 30 °C and kept for 12 h to remove the methanol, and then heated to 100 °C and kept for 12 h to remove the oxalic acid, and finally a para-aramid separator is obtained.

[0066] In this application, when the proton solvent includes at least one of ethylene glycol, glycerol, propanol, isopropanol, and butanol, the technical effects obtained are the same as those of the above-mentioned embodiments.

[0067] In the present application, the technical effects obtained in the case where the low-decomposition temperature / low-boiling point salt includes at least one of a carbonate, a bicarbonate, and a nitrate are the same as the technical effects of the above-mentioned embodiments.

[0068] In the present application, the technical effects obtained in the case where the mass concentration of the solute in the protic solution is 0.5% and 20% are the same as the technical effects of the above-mentioned embodiments.

[0069] In the present application, the technical effects obtained in the case where the basic solvent system solvent includes at least one of dimethylformamide, dimethylacetamide, tetrahydrofuran, acetone, toluene, xylene, benzene, and dichloromethane are the same as the technical effects of the above-mentioned embodiments.

[0070] II. Experimental Examples

[0071] Experimental Example 1

[0072] The para-aramid separator membranes prepared in the above-mentioned embodiments 1-4 were subjected to surface morphology detection. Specifically, the micro-morphology of the samples was characterized using a scanning electron microscope at an acceleration voltage of 10 kV, and the detection results are shown in FIGS. 1-4. Figure 1 Figure 2 Figure 3 Figure 4

[0073] It can be seen that in the SEM images of the para-aramid separator membranes prepared in embodiments 1-4, there are small and uniformly distributed pore structures, indicating that the para-aramid separator membranes prepared by the para-aramid separator membrane preparation method of the present application have high porosity; and under different process conditions, para-aramid separator membranes with different pore structures can be obtained.

[0074] Experimental Example 2

[0075] The para-aramid separator membranes prepared in the above-mentioned embodiments 1-4 were subjected to tensile strength, heat shrinkage, and rate performance detection. Specifically, the tensile strength was tested using an electronic universal testing machine at a tensile speed of 1 mm / min and an initial distance of 10 cm. The heat shrinkage temperature was measured by heating the sample at 100, 120, 140, 160, 180, 200, 220, and 240 °C for 1 h, and the lowest temperature at which the sample shrunk by more than 10% was defined as the heat shrinkage temperature of the sample. The rate performance was tested by assembling a battery using the sample with lithium iron phosphate as the positive electrode and lithium sheet as the negative electrode, and testing the discharge capacity of the sample at 1C and 3C using a battery test system. The specific results are shown in Table 1.

[0076] Table 1 Comparison of the properties of the para-aramid separator membranes prepared in embodiments 1-4 and commercial polyolefin separator membranes

[0077] ​​​​

[0078] As can be seen from Table 1, the tensile strength of the para-aramid separator prepared in Examples 1-4 is above 101 MPa, and the highest is 135 MPa, which is much higher than the tensile strength 15 MPa of the commercial polyolefin separator; the heat shrinkage temperature of the para-aramid separator prepared in Examples 1-4 is 240 °C, which is much higher than the heat shrinkage temperature 120 °C of the commercial polyolefin separator; the discharge capacity of the battery corresponding to the para-aramid separator prepared in Examples 1-4 at 1C and 3C is 122 mAh g -1 and 80 mAh g -1 , respectively, which is higher than the discharge capacity 122 mAh g -1 and 77 mAh g -1 of the battery corresponding to the commercial polyolefin separator at 1C and 3C, respectively. -1 -1 .

[0079] Therefore, it is illustrated that the para-aramid separator prepared by the preparation method of the para-aramid separator provided in the application has high porosity, and the tensile strength and thermal stability thereof are much better than those of the commercial polyolefin separator, thereby effectively guaranteeing the safety of the lithium battery. Meanwhile, the discharge capacity of the para-aramid separator at 1C and 3C is obviously higher than that of the commercial polyolefin separator, and the electrochemical performance of the lithium battery can be improved.

[0080] The above merely describes preferred embodiments of the application but is not intended to limit the application. The application can be variously changed and modified by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.​

Claims

1. A method for preparing a para-aramid diaphragm, characterized in that: The method comprises the following steps: placing a substrate coated with an aramid nanofiber dispersion in a proton donor to obtain an aramid nanofiber gel dispersed with the proton donor; immersing the aramid nanofiber gel dispersed with the proton donor in a proton solution, replacing the solute in the proton solution with the proton donor, and heating and drying to obtain a para-aramid diaphragm; wherein the solute comprises a salt with a low decomposition temperature / low boiling point, and / or an organic matter; The heating drying includes a first step of heating and a second step of heating, wherein the first step of heating is performed at a temperature of 30-120°C for a time of 0.5-12 h; the second step of heating is performed at a temperature of 100-200°C for a time of 0.5-12 h; The proton donor is a proton solvent or the steam of a proton solvent, and the proton solvent includes at least one of water, ethanol, methanol, ethylene glycol, glycerol, propanol, isopropanol, and butanol; The low decomposition temperature / low boiling point salt includes at least one of carbonate, bicarbonate, ammonium salt, and nitrate; the organic matter includes oxalic acid; and the mass concentration of the solute in the proton solution is 0.5-20%.

2. The method for preparing a para-aramid diaphragm according to claim 1, wherein: The replacement time is 2 to 72 hours.

3. The method for preparing a para-aramid diaphragm according to claim 1, wherein: The mass concentration of the aramid nanofiber dispersion is 0.5-2%.

4. The method for preparing a para-aramid diaphragm according to claim 3, wherein: The preparation method of the aramid nanofiber dispersion comprises the following steps: placing aramid micron fibers in an alkaline solvent system and stirring the mixture to obtain the aramid nanofiber dispersion.

5. The method for preparing a para-aramid diaphragm according to claim 4, characterized in that: The alkaline solvent system includes an alkaline solvent system solute and an alkaline solvent system solvent, wherein the alkaline solvent system solute includes at least one of potassium tert-butoxide, potassium hydroxide, sodium tert-butoxide, and sodium hydroxide; and the alkaline solvent system solvent includes at least one of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, tetrahydrofuran, acetone, toluene, xylene, benzene, and dichloromethane.

6. The method for preparing a para-aramid diaphragm according to claim 5, characterized in that: The mass ratio of the aramid micron fiber, the alkaline solvent system solute, and the alkaline solvent system solvent is 1: (0.5-1.5): (50-200).

7. A para-aramid diaphragm, characterized in that: The para-aramid diaphragm is prepared by the preparation method of any one of claims 1 to 6.

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