Aramid boehmite composite nanofiber and synthesis method and application thereof

Abstract

The application relates to the technical field of nanomaterials, and particularly relates to aramid-boehmite composite nanofibers, a synthesis method and application thereof, which comprise the following steps: step one, preparing an Al(OH)3 dispersion solution; step two, preparing an Al(OH)3 precursor; step three, performing solvent exchange; step four, transferring aramid nanofiber gel subjected to solvent exchange into a Teflon container, heating in a closed environment, and obtaining a crude product; and step five, washing the crude product with deionized water and sufficiently drying to obtain aramid-boehmite composite nanofibers. The aramid-boehmite composite nanofibers with aramid nanofibers as cores and boehmite as sheath layers are synthesized by using a hydrothermal method, the aramid-boehmite composite nanofibers are used for coating modification of lithium ion battery separators, the heat resistance and porosity of the lithium ion battery separators are improved, and the Gurley number of the separators is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanomaterials, and particularly relates to aramid-boehmite composite nanofibers and a synthesis method and application thereof. BACKGROUND

[0002] A lithium ion battery is a rechargeable battery developed on the basis of a lithium secondary battery, has advantages of small volume, light weight, high energy density, and is widely used in the fields of traffic power, electric power storage, mobile communication, new energy storage, aerospace and military industry. The lithium ion battery mainly comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the separator is a microporous material with good chemical stability, ion conductivity, electronic insulation and certain mechanical strength, and its main function is to prevent the active materials of the positive electrode and the negative electrode in the lithium ion battery from directly contacting each other, thereby avoiding short circuit and active material falling in the lithium ion battery. The performance of the separator determines the interface structure and internal resistance of the lithium ion battery, and directly affects the capacity, cycle and safety performance of the battery, and is one of the most critical inner components of the lithium ion battery.

[0003] At present, the commercial lithium ion battery separator mainly uses a polyolefin microporous membrane with polypropylene (PP) and polyethylene (PE) as the matrix. The porosity of the polyolefin microporous membrane is low, and the polyolefin has poor heat resistance due to low melting point and softening temperature, so it is difficult to ensure high temperature integrity. The polyolefin microporous membrane is prone to thermal shrinkage or even melting damage at a high temperature of 150 DEG C or above, which not only causes the porosity of the separator to decrease and the ion conductivity to decrease, but also causes the positive electrode and the negative electrode of the battery to contact, resulting in short circuit of the battery, and there is a safety hazard.

[0004] The prior art generally improves the heat resistance of the polyolefin microporous membrane by coating modification. By coating inorganic nanoparticles such as alumina ceramic and boehmite on the polyolefin microporous membrane, the heat resistance of the polyolefin microporous membrane can be improved to about 130 DEG C, and the thermal shrinkage rate can be controlled within 5%. This method can only improve the heat resistance of the separator to a certain extent, but cannot maintain the integrity of the separator structure at a high temperature of 150 DEG C or above, and it is difficult to improve the porosity of the separator. SUMMARY

[0005] In view of the technical problems of poor heat resistance and low porosity of the polyolefin microporous membrane coated with inorganic nanoparticles, the present application provides a synthesis method and application of aramid-boehmite composite nanofibers. The aramid-boehmite composite nanofibers with aramid nanofibers as the core and boehmite as the sheath layer are synthesized by a hydrothermal method. The aramid-boehmite composite nanofibers are used for coating modification of the lithium ion battery separator, thereby improving the heat resistance and porosity of the lithium ion battery separator and reducing the Gurley number of the separator.

[0006] In a first aspect, the present application provides a method for synthesizing aramid-boehmite composite nanofibers, comprising the following steps:

[0007] Step one: preparing an Al(OH)3 dispersion;

[0008] Step two: adjusting the pH value of the Al(OH)3 dispersion to prepare an Al(OH)3 gel; 3+ The concentration of the Al(OH)3 precursor is 0.01-1 mol / L;

[0009] Step three: immersing the aramid nanofiber gel into the Al(OH)3 precursor for solvent exchange;

[0010] Step four: transferring the aramid nanofiber gel after solvent exchange into a Teflon container, heating to 120-200℃ in a closed environment, and heating for 2-48 h to obtain a crude product;

[0011] Step five: washing the crude product with deionized water and drying at 80℃ to obtain aramid-boehmite composite nanofibers.

[0012] Further, in step one, the Al(OH)3 dispersion is prepared by dispersing Al(OH)3 gel or Al(OH)3 amorphous powder into deionized water. The particle size of the Al(OH)3 amorphous powder is 30-50 nm.

[0013] Further, the Al(OH)3 gel is obtained by reacting an aqueous solution of 0.25 mol / L aluminum salt with an aqueous solution of 1 mol / L sodium hydroxide. The aluminum salt is preferably Al(NO3)3·9H2O, and the aqueous sodium hydroxide solution is used to adjust the pH value of the aqueous aluminum salt solution.

[0014] Further, in step two, the pH value of the Al(OH)3 dispersion is adjusted to 6.

[0015] Further, the method for preparing the aramid nanofiber gel comprises the following steps:

[0016] S1: adding a nanofiber dispersion containing para-aramid and a poor solvent into a Teflon container in sequence, stirring uniformly to obtain a mixed solution;

[0017] S2: placing the mixed solution until the mixed solution solidifies and loses fluidity to obtain a mixed gel;

[0018] S3: immersing the mixed gel into deionized water for solvent exchange to obtain an aramid nanofiber gel.

[0019] Further, the nanofiber dispersion liquid of para-aramid fiber includes the following components: 1 part by mass of para-aramid fiber, 0.25-1.5 parts by mass of KOH, 0-1.5 parts by mass of deionized water, and ≥19 parts by mass of DMSO. The para-aramid fiber is preferably any one of aramid fiber, aramid short fiber, and aramid pulp.

[0020] Further, the parts by mass of the poor solvent is 1 part.

[0021] Further, the poor solvent is one or more of dimethylacetamide DMAc, N,N-dimethylformamide DMF, dimethyl carbonate DMC, diethyl carbonate DC, and ethyl acetate.

[0022] In a second aspect, the present application provides an aramid-boehmite composite nanofiber synthesized by the above-mentioned synthesis method.

[0023] In a third aspect, the present application provides an application of the aramid-boehmite composite nanofiber synthesized by the above-mentioned synthesis method in the preparation of a lithium ion battery composite separator.

[0024] The present application has the following beneficial effects:

[0025] The present application first immerses aramid nanofiber gel into Al(OH)3 precursor for solvent exchange, so that the Al(OH)3 precursor fully enters the pores of the aramid nanofiber gel; then in-situ synthesizes nanometer boehmite on the surface of the aramid nanofiber by a hydrothermal method, to obtain aramid-boehmite composite nanofiber with aramid nanofiber as the core and boehmite as the sheath. The present application modifies the surface of aramid nanofiber by using nanometer boehmite, and uses the modified aramid-boehmite composite nanofiber to coat the lithium ion battery separator, which significantly improves the heat resistance and porosity of the lithium ion battery separator, and increases the Gurley number of the lithium ion battery separator. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0027] Figure 1 is a structural schematic diagram of aramid-boehmite composite nanofiber.

[0028] In the figure, 1-boehmite sheath, 2-aramid nanofiber core. DETAILED DESCRIPTION

[0029] In order to make the person skilled in the art better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the person skilled in the art without creative labor should belong to the protection scope of the present application.

[0030] Embodiment 1

[0031] A synthesis method of aramid boehmite composite nanofiber, comprising the following steps:

[0032] Step one: preparing a nanofiber dispersion solution of p-aramid short-cut fiber: 1 part by mass of p-aramid short-cut fiber, 0.25 parts by mass of KOH, 1 part by mass of water, are added into 19 parts by mass of DMSO, and stirred for 1 hour to obtain a uniformly dispersed nanofiber dispersion solution of p-aramid short-cut fiber.

[0033] Step two: preparing aramid nanofiber gel, the steps are as follows:

[0034] S1: the nanofiber dispersion solution of p-aramid short-cut fiber prepared in step one and 1 part by mass of DMC are sequentially added into a Teflon container and stirred uniformly to obtain a mixed solution;

[0035] S2: the mixed solution is left to stand until the mixed solution solidifies and loses fluidity to obtain a mixed gel;

[0036] S3: the mixed gel is immersed in deionized water for solvent exchange, repeated three times to obtain aramid nanofiber gel.

[0037] Step three: firstly, Al(NO3)3·9H2O is dissolved in deionized water to form a uniform solution with a concentration of 0.25 M at room temperature; then, 1 M NaOH (≥98%) aqueous solution is added to the above solution to adjust the pH value to 10.0; subsequently, the solution is continuously stirred for 1 hour, and the solution is centrifuged to collect the gel-like precipitate; the obtained gel-like precipitate is washed three times with deionized water to remove all soluble salts to obtain Al(OH)3 gel.

[0038] Step four: the Al(OH)3 gel is dispersed into deionized water to obtain Al(OH)3 hydrogel, nitric acid is added to the Al(OH)3 hydrogel, the pH value of the Al(OH)3 hydrogel is adjusted to 6, and an Al(OH)3 precursor with a concentration of 0.01 mol / L is prepared. 3+

[0039] ​Step five: immerse the aramid nanofiber gel into the Al(OH)3 precursor, and stand for 24 h to fully perform solvent exchange.

[0040] Step six: transfer the aramid nanofiber gel after solvent exchange into a Teflon container, then seal the Teflon container in a steel reactor, and heat in an electric furnace at 120℃ for 2 h to obtain a crude product.

[0041] Step seven: wash the crude product with deionized water for three times, and fully dry at 80℃ to obtain aramid boehmite composite nanofiber, as shown in Figure 1 The boehmite sheath layer of the aramid boehmite composite nanofiber is discontinuous on the surface of the aramid nanofiber core.

[0042] Example 2

[0043] A method for synthesizing aramid boehmite composite nanofiber, comprising the following steps:

[0044] Step one: prepare a nanofiber dispersion solution of para-aramid pulp: add 1 part by mass of para-aramid pulp, 1.5 parts by mass of KOH, and 1.5 parts by mass of water into 25 parts by mass of DMSO, and stir for 3 hours to obtain a uniformly dispersed nanofiber dispersion solution of para-aramid pulp.

[0045] Step two: prepare an aramid nanofiber gel, and the steps are as follows:

[0046] S1: add the nanofiber dispersion solution of para-aramid pulp prepared in step one and 0.1 parts by mass of ethyl acetate into a Teflon container in sequence, and stir uniformly to obtain a mixed solution;

[0047] S2: stand the mixed solution until the mixed solution solidifies and loses fluidity to obtain a mixed gel;

[0048] S3: immerse the mixed gel into deionized water for solvent exchange, and repeat three times to obtain an aramid nanofiber gel.

[0049] Step three: first dissolve Al(NO3)3·9H2O in deionized water to form a uniform solution with a concentration of 0.25 M at room temperature; then add a 1 M NaOH (≥98%) aqueous solution to the above solution to adjust the pH value to 10.0; subsequently continuously stir for 1 hour, and centrifuge the solution to collect a gel-like precipitate; wash the obtained gel-like precipitate with deionized water for three times to remove all soluble salts, and obtain an Al(OH)3 gel.

[0050] Step four: disperse the Al(OH)3 gel into deionized water to obtain an Al(OH)3 hydrogel, add nitric acid to the Al(OH)3 hydrogel, adjust the pH value of the Al(OH)3 hydrogel to 6, and prepare an Al3+ Al(OH)3 precursor with a concentration of 1 mol / L.

[0051] Step five: immerse the aramid nanofiber gel into the Al(OH)3 precursor, and stand for 24 h to fully perform solvent exchange.

[0052] Step six: transfer the aramid nanofiber gel after solvent exchange into a Teflon container, then seal the Teflon container in a steel reactor, and heat in an electric furnace at 200℃ for 48 h to obtain a crude product.

[0053] Step seven: wash the crude product with deionized water for three times, and fully dry at 80℃ to obtain aramid boehmite composite nanofiber.

[0054] Example 3

[0055] Add 1 part by mass of aramid boehmite composite nanofiber obtained in Example 1, 0.25 parts by mass of KOH, 1 part by mass of water into 19 parts by mass of DMSO, stir for 1 h to obtain aramid boehmite composite nanofiber coating slurry. Coating the above slurry on the surface of PE base film, and coagulate through coagulation bath, fully wash with deionized water, dry to obtain aramid boehmite composite nanofiber lithium ion battery composite diaphragm.

[0056] Example 4

[0057] Add 1 part by mass of aramid boehmite composite nanofiber obtained in Example 2, 1.5 parts by mass of KOH, 1.5 parts by mass of water into 25 parts by mass of DMSO, stir for 3 h to obtain aramid boehmite composite nanofiber coating slurry. Coating the above slurry on the surface of PE base film, and coagulate through coagulation bath, fully wash with deionized water, dry to obtain aramid boehmite composite nanofiber lithium ion battery composite diaphragm.

[0058] Heat treat the aramid boehmite composite nanofiber lithium ion battery composite diaphragm obtained in Example 3, Example 4 at 150℃ for 1 h, measure the bidirectional thermal shrinkage of the aramid boehmite composite nanofiber lithium ion battery composite diaphragm, and use the Gurley 4320 program digital timer to calculate the increase value of Gurley number compared with the base film.

[0059] The bidirectional thermal shrinkage of Example 3, Example 4 is 2%, 2.3% respectively, and the Gurley number increases by 45 s / 100cc, 48 s / 100cc respectively compared with the base film.

[0060] Although the present application has been described in detail with reference to the preferred embodiments, it should be understood that the application is not limited to those preferred embodiments. Various modifications and equivalents can be made by those skilled in the art without departing from the spirit and scope of the application. Any and all modifications and equivalents are intended to be included within the scope of the present application.

Claims

1. A method of synthesizing aramid-boehmite composite nanofibers, characterized by, The method comprises the following steps: Step one: preparing an Al(OH)3 dispersion solution; In step one, the Al(OH)3 dispersion solution is prepared by dispersing Al(OH)3 gel or Al(OH)3 amorphous powder into deionized water; The Al(OH)3 gel is obtained by reacting an aqueous solution of 0.25 mol / L aluminum salt with an aqueous solution of 1 mol / L sodium hydroxide; Step two: adjust the pH value of the Al(OH)3 dispersion liquid to prepare Al 3+ Al(OH)3 precursor with a concentration of 0.01-1 mol / L; In step two, the pH value of the Al(OH)3 dispersion solution is adjusted to 6; Step three: immersing the aramid nanofiber gel into the Al(OH)3 precursor for solvent exchange; The method for preparing the aramid nanofiber gel comprises the following steps: S1: adding a nanofiber dispersion solution of para-aramid and a poor solvent into a Teflon container in sequence and stirring uniformly to obtain a mixed solution; S2: placing the mixed solution until the mixed solution solidifies and loses fluidity to obtain a mixed gel; S3: immersing the mixed gel into deionized water for solvent exchange to obtain an aramid nanofiber gel; Step four: transferring the aramid nanofiber gel after solvent exchange into a Teflon container, heating to 120-200°C in a closed environment, and heating for 2-48 h to obtain a crude product; Step five: washing the crude product with deionized water and drying at 80°C to obtain aramid boehmite composite nanofibers; The nanofiber dispersion solution of para-aramid comprises the following components: 1 part of para-aramid, 0.25-1.5 parts of KOH, 0-1.5 parts of deionized water, and ≥19 parts of DMSO; The para-aramid is any one of aramid fibrid, aramid chopped fiber, and aramid pulp; The poor solvent is dimethyl carbonate or ethyl acetate.

2. The method for synthesizing aramid boehmite composite nanofibers as described in claim 1, characterized in that, The poor solvent is 1 part by mass.

3. Aramid boehmite composite nanofibers synthesized by the method according to any one of claims 1-2.

4. Use of the aramid boehmite composite nanofibers according to claim 3 in preparing a composite separator for lithium ion batteries.

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