Preparation method of high-strength nanofiber for cellulose-based diaphragm of lithium battery

Abstract

The invention discloses a preparation method of high-strength nanofibers for a lithium battery cellulose-based diaphragm, and belongs to the technical field of lithium battery diaphragms.The preparation method comprises the following steps that amino-terminated silane and an ethanol solution are mixed and stirred to be uniform, and hydrolysate is obtained; adding magnetic cellulose nanofibrils into the hydrolysate, carrying out stirring reaction at 60-80 DEG C for 8-10 hours, carrying out magnetic separation, and drying a separated product at 100 DEG C for 2 hours to obtain aminated magnetic cellulose nanofibrils; the preparation method comprises the following steps: adding aminated magnetic cellulose nanofibrils, an MOFs material containing amino functional groups and multi-aldehyde boric acid ester into dimethylformamide, stirring for 15-30 minutes, heating to 80 DEG C, stirring and reacting for 12 hours, carrying out suction filtration, washing a filter cake, and drying to obtain the high-strength nanofiber for the cellulose-based diaphragm of the lithium battery, and using the high-strength nanofiber for preparing the lithium battery diaphragm. And the obtained diaphragm has the advantages of high liquid absorption rate, good mechanical property and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium battery separator, and particularly relates to a preparation method of high-strength nanofiber for a lithium battery cellulose-based separator. BACKGROUND

[0002] Lithium ion batteries (LIBS) are widely used in the fields of automobiles, mobile phones, computers and portable electronic products due to their high energy density, long service life and high charging and discharging efficiency. As one of the important components of LIBS, the physical and chemical properties of the separator have a great influence on the performance of the battery. However, the commercialized separator with polyolefin as the main component has the disadvantages of low porosity, poor electrolyte wettability, low thermal stability and poor mechanical strength, which limits the further development and application of LIBS.

[0003] As a widely used natural polymer, cellulose has good thermal stability and electrolyte affinity, and is considered as a potential battery separator matrix material. The LIBS separator prepared by using cellulose nanofibril (CNF) has high mechanical strength and has a nanoscale pore size, which can effectively prevent battery short circuit. Then, the hydrogen bonding and van der Waals force between the CNFs make the microstructure of the existing CNF separator compact, resulting in low porosity and low liquid absorption rate of the separator, which seriously affects the ionic conductivity of the separator and further affects the performance of the battery. Therefore, it is a technical problem to be solved at present to provide a cellulose nanofibril (CNF) with high dispersing performance. SUMMARY

[0004] The application aims to provide a preparation method of high-strength nanofiber for a lithium battery cellulose-based separator, which solves the problem of poor dispersing performance of cellulose nanofibril for a lithium battery cellulose-based separator.

[0005] The object of the application can be achieved by the following technical solutions.

[0006] A preparation method of high-strength nanofiber for a lithium battery cellulose-based separator, comprising the following steps:

[0007] S1, mixing amino-terminated silane and ethanol solution, stirring uniformly to obtain a hydrolysis solution; adding magnetic cellulose nanofibril into the hydrolysis solution, stirring at 60-80 DEG C for 8-10 h, magnetic separation, drying the separated product at 100 DEG C for 2 h to obtain amino-functionalized magnetic cellulose nanofibril;

[0008] S2, adding the amino-functionalized magnetic cellulose nanofibril, MOFs material containing amino functional group and polyaldehyde borate into dimethylformamide, stirring for 15-30 min, heating to 80 DEG C and stirring for 12 h, suction filtration, drying the filter cake after washing to obtain high-strength nanofiber for a lithium battery cellulose-based separator.

[0009] Further, the amount of end-amino silane in S1 is 5-10% of the mass of the magnetic cellulose nanofibril, and the mass fraction of the ethanol solution is 40-90%.

[0010] Further, the end-amino silane is at least one of γ-aminopropyl triethoxysilane, γ-aminopropyl trimethoxysilane, and N-aminoethyl-3-aminopropyl triethoxysilane.

[0011] Further, the amount of the amino-functionalized magnetic cellulose nanofibril, the MOF containing amino functional groups, the polyaldehyde borate, and the dimethyl formamide in S2 is 10 g: 0.5-1 g: 0.3-0.5 g: 100-150 mL.

[0012] Further, the magnetic cellulose nanofibril is prepared by the following steps:

[0013] The cellulose nanofibril and ferrous chloride are added to deionized water, stirred uniformly, and then ammonia water is added dropwise. After the dropwise addition is completed, stirring is performed at 80°C and a rotation speed of 300-500 r / min for 30 min. The product is then washed with deionized water and subjected to magnetic separation. The separated product is dried at 100°C for 2 h to obtain the magnetic cellulose nanofibril.

[0014] Further, the amount of the cellulose nanofibril, ferrous chloride, deionized water, and ammonia water is 2.25-3 g: 0.25 g: 20 mL: 10 mL, and the mass fraction of the ammonia water is 2.5-3.0%. The cellulose nanofibril and ferrous chloride are used as main raw materials to prepare cellulose nanofibril carrying ferroferric oxide on the surface, i.e., the magnetic cellulose nanofibril.

[0015] Further, the polyaldehyde borate is prepared by a thiol-ene click reaction of 2-mercaptoacetaldehyde and 2,4,6-trivinylcyclohexene boroxine.

[0016] Further, the preparation process of the polyaldehyde borate includes the following steps:

[0017] 2-mercaptoacetaldehyde, 2,4,6-trivinylcyclohexene boroxine, benzoin dimethyl ether, and tetrahydrofuran are mixed, and the mixture is irradiated with ultraviolet light for 0.5-1 h. After the reaction is completed, tetrahydrofuran is removed by rotary evaporation to obtain the polyaldehyde borate.

[0018] The molar ratio of 2-mercaptoacetaldehyde to 2,4,6-trivinylcyclohexene boroxine is 3:1, and the amount of benzoin dimethyl ether is 1-2% of the mass of 2,4,6-trivinylcyclohexene boroxine. The wavelength of the ultraviolet light is 100-400 nm.

[0019] Further, the MOFs material containing amino functional groups is any one of UiO-66-NH2, UiO-67-NH2, MIL-125-NH2, MIL-101-NH2 or a mixture of one or more thereof.

[0020] Advantages of the present application:

[0021] The present application provides a preparation method of high-strength nanofiber for lithium battery cellulose-based separator, which comprises the following steps: treating magnetic cellulose nanofilament with amino-terminated silane to obtain aminated magnetic cellulose nanofilament; and using polyaldehyde borate as a crosslinking agent to make the aminated magnetic cellulose nanofilament and the MOFs material containing amino functional groups combined through chemical bonds by condensation reaction between aldehyde groups and amino groups, so as to obtain a cellulose nanofilament composite material with magnetism. Compared with the cellulose nanofilament, the cellulose nanofilament composite material has good magnetic response performance, can be arranged in a directional manner under the action of an external magnetic field, and can bear more load compared with the cellulose nanofilament arranged in a chaotic manner, so that the mechanical properties of the lithium battery can be significantly improved when the cellulose nanofilament composite material is applied to the lithium battery separator.

[0022] The present application introduces the MOFs material containing amino functional groups on the surface of the aminated magnetic cellulose nanofilament, which can increase the roughness of the surface of the aminated magnetic cellulose nanofilament and improve the dispersibility of the aminated magnetic cellulose nanofilament, and can also improve the low porosity and poor liquid absorption performance of the cellulose-based separator by utilizing the porous properties of the MOFs material.

[0023] The present application uses polyaldehyde borate as a crosslinking agent, which not only makes the aminated magnetic cellulose nanofilament and the MOFs material containing amino functional groups combined through chemical bonds, but also carries borate groups. The combination of the electron-deficient boron-containing groups and anions weakens the conduction of the anions, and the combination with the solvent affects the desolvation of the lithium ion battery in the electrolyte, which is helpful to improve the lithium ion migration number and the battery rate performance.

[0024] In addition, the high-strength nanofiber for lithium battery cellulose-based separator in the present application contains iron oxide, polyaldehyde borate and the MOFs material containing amino functional groups. The flame-retardant properties of these materials can also improve the flame-retardant performance of the cellulose-based separator, which is conducive to enhancing the safety of the lithium ion battery. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with 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 those skilled in the art without creative labor fall within the scope of protection of the present application.

[0026] Example 1

[0027] A preparation method of high-strength nanofiber for lithium battery cellulose-based separator, comprising the following steps:

[0028] S1, 0.5g γ-aminopropyl triethoxysilane and 100L 40wt% ethanol solution are mixed, stirred uniformly to obtain a hydrolysis solution; 10g magnetic cellulose nanofilament is added to the hydrolysis solution, stirred at 60℃ for 10h, magnetically separated, the separated product is dried at 100℃ for 2h to obtain aminated magnetic cellulose nanofilament;

[0029] S2, 10g aminated magnetic cellulose nanofilament, 0.5g UiO-66-NH2 and 0.3g polyaldehyde borate are added to 100mL dimethylformamide, stirred for 15min, heated to 80℃ and stirred for 12h, suction filtered, the filter cake is washed with anhydrous ethanol for 3 times and then placed in a vacuum drying oven at 110℃ for 4h to obtain high-strength nanofiber for lithium battery cellulose-based separator.

[0030] The magnetic cellulose nanofilament is prepared by the following steps:

[0031] 2.25g cellulose nanofilament and 0.25g ferrous chloride are added to 20mL deionized water, stirred uniformly, 10mL 2.5% ammonia water is added dropwise, after the dropwise addition is completed, stirring is carried out at 80℃ for 30min at a speed of 300r / min, then the product is washed with deionized water and magnetically separated, and the separated product is dried at 100℃ for 2h to obtain the magnetic cellulose nanofilament.

[0032] The preparation process of the polyaldehyde borate comprises the following steps:

[0033] 0.3mol 2-mercaptoacetaldehyde, 0.1mol 2,4,6-trivinylcycloboroxane, 0.16g benzoin dimethyl ether and 500mL tetrahydrofuran are mixed, and the mixture is irradiated with 100-400nm ultraviolet light for 0.5h, after the reaction is completed, the tetrahydrofuran is removed by rotary evaporation to obtain the polyaldehyde borate.

[0034] Example 2

[0035] A preparation method of high-strength nanofiber for lithium battery cellulose-based separator, comprising the following steps:

[0036] S1, 0.8g γ-aminopropyl trimethoxysilane and 100L 60wt% ethanol solution are mixed, stirred uniformly to obtain a hydrolysis solution; 10g magnetic cellulose nanofilament is added to the hydrolysis solution, stirred at 70℃ for 9h, magnetically separated, the separated product is dried at 100℃ for 2h to obtain aminated magnetic cellulose nanofilament;

[0037] S2, 10 g of aminated magnetic cellulose nanofibrils, 0.8 g of MIL-125-NH2 and 0.4 g of polyaldehyde borate ester were added into 120 mL of dimethylformamide, stirred for 20 min, and then the temperature was raised to 80°C for stirring reaction for 12 h. After filtration, the filter cake was washed with anhydrous ethanol for 4 times and then placed in a vacuum drying oven at 110°C for drying for 4 h to obtain high-strength nanofibers for lithium battery cellulose-based separators.

[0038] The magnetic cellulose nanofibrils were prepared by the following steps:

[0039] 2.5 g of cellulose nanofibrils and 0.25 g of ferrous chloride were added into 20 mL of deionized water, stirred uniformly, and then 10 mL of 2.5% ammonia water was added dropwise. After the dropwise addition was completed, stirring was carried out at 80°C for 30 min at a rotation speed of 400 r / min. Then, the product was separated by magnetic separation after washing with deionized water and dried at 100°C for 2 h to obtain the magnetic cellulose nanofibrils.

[0040] The preparation process of the polyaldehyde borate ester includes the following steps:

[0041] 0.3 mol of 2-mercaptoacetaldehyde, 0.1 mol of 2,4,6-trivinylcycloboroxane, 0.2 g of benzoin dimethyl ether and 500 mL of tetrahydrofuran were mixed, and then the mixture was irradiated under 100-400 nm ultraviolet light for 0.8 h. After the reaction was completed, tetrahydrofuran was removed by rotary evaporation to obtain the polyaldehyde borate ester.

[0042] Example 3

[0043] A preparation method of high-strength nanofibers for lithium battery cellulose-based separators includes the following steps:

[0044] S1, 1 g of N-aminoethyl-3-aminopropyl triethoxysilane was mixed with 100 L of 90 wt% ethanol solution to obtain a hydrolysis solution. 10 g of magnetic cellulose nanofibrils was added into the hydrolysis solution, and then stirring reaction was carried out at 80°C for 10 h. The product was separated by magnetic separation and dried at 100°C for 2 h to obtain aminated magnetic cellulose nanofibrils.

[0045] S2, 10 g of aminated magnetic cellulose nanofibrils, 1 g of MIL-101-NH2 and 0.5 g of polyaldehyde borate ester were added into 150 mL of dimethylformamide, stirred for 30 min, and then the temperature was raised to 80°C for stirring reaction for 12 h. After filtration, the filter cake was washed with anhydrous ethanol for 5 times and then placed in a vacuum drying oven at 110°C for drying for 4 h to obtain high-strength nanofibers for lithium battery cellulose-based separators.

[0046] The magnetic cellulose nanofibrils were prepared by the following steps:

[0047] 3 g of cellulose nanofibrils and 0.25 g of ferrous chloride were added to 20 mL of deionized water, stirred uniformly, 10 mL of 3.0% ammonia water was added dropwise, after the dropwise addition was completed, stirring at 500 r / min, 80℃ for 30 min, then washed with deionized water and then subjected to magnetic separation, the separated product was dried at 100℃ for 2 h, and magnetic cellulose nanofibrils were prepared.

[0048] The preparation process of the polyaldehyde borate ester includes the following steps:

[0049] 0.3 mol of 2-mercaptoacetaldehyde, 0.1 mol of 2,4,6-trivinylcycloboroxane, 0.32 g of benzoin dimethyl ether, and 500 mL of tetrahydrofuran were mixed, and irradiated with 100-400 nm ultraviolet light for 1 h. After the reaction was completed, the tetrahydrofuran was removed by rotary evaporation, and a polyaldehyde borate ester was prepared.

[0050] Comparative Example 1

[0051] A method for preparing high-strength nanofibers for a lithium battery cellulose-based separator, compared with Example 1, the only difference is that the magnetic cellulose nanofibrils are replaced with an equal amount of cellulose nanofibrils.

[0052] Comparative Example 2

[0053] A method for preparing high-strength nanofibers for a lithium battery cellulose-based separator, compared with Example 1, the only difference is that the polyaldehyde borate ester is replaced with an equal amount of glutaraldehyde.

[0054] Comparative Example 3

[0055] This comparative example is magnetic cellulose nanofibrils, and the preparation process is the same as Example 1.

[0056] Comparative Example 4

[0057] This comparative example is cellulose nanofibrils.

[0058] The materials in Examples 1-3 and Comparative Examples 1-4 were applied to the preparation of lithium battery separators, and the relevant properties of the obtained lithium battery separators were tested, and the specific test process was as follows:

[0059] Lithium battery separator preparation: 1.8 g of polyvinylidene fluoride was dissolved in 18 g of N,N-dimethylacetamide at room temperature and normal pressure, stirred for 2 h, then 0.2 g of fiber material (the fiber material was high-strength nanofiber prepared in Examples 1-3 and Comparative Examples 1-2, and magnetic cellulose nanofibril in Comparative Example 3, and cellulose nanofibril in Comparative Example 4) was added, and stirring was continued for 2 h. After ultrasonic treatment, the solution was left to stand, and bubbles were removed to obtain a casting solution. The casting solution was uniformly coated on a smooth PE flat plate by a film coater, and the coating thickness was 75 um. The prepared film was dried at 70°C for 12 h in an external magnetic field with a magnetic field strength of 5T. The film was then removed from the PE flat plate and immersed in deionized water for 12 h. Residual solvent was removed by ultrasonic treatment for 30 min. Finally, the film was dried in an oven at 70°C for 6 h to obtain a lithium battery separator.

[0060] Liquid absorption rate: The mass of the film before and after treatment was measured, and the calculation was performed by the formula. The solution used in the liquid absorption rate test was electrolyte, and the calculation method was: liquid absorption rate (%) = (Wb-Wa) / Wa x 100 (Wa-sample mass before liquid absorption, Wb-sample mass after liquid absorption);

[0061] Tensile strength: Referring to the standard GB / T 1040.3-2006, a universal tensile testing machine was used for testing;

[0062] Thermal stability: The various separators were placed in an environment of 160°C for 30 min, and the degree of deformation was observed;

[0063] Flame retardant performance: limiting oxygen index, tested according to GB / T 10707-2008, sample size was 100x6.5x3mm 3 ;

[0064] Rate performance: the various separators were assembled into button-type half-batteries for testing. First, 0.4 g of LiFePO4 powder, 0.05 g of acetylene black, and 0.05 g of polyvinylidene fluoride were mixed in 1 mL of 1-methyl-2-pyrrolidone, and then uniformly coated on an aluminum foil according to the actual solid content of 2 mg·cm -2 . The coated aluminum foil was placed in a vacuum oven and dried at 120°C for 12 h. After cooling to room temperature, the aluminum foil was removed and pressed using a roller press. Then, the aluminum foil was cut into a circular positive electrode sheet with a diameter of 8 mm using a punching machine.

[0065] The separators were assembled into button-type half-batteries with electrolyte, lithium sheet, and positive electrode sheet in an argon atmosphere glove box. The batteries were tested using a blue battery test system (model CT2001A, Wuhan Blue Battery Tester). The test voltage was 2.5-4.2V, and the discharge rate was increased in the order of 0.2-2.0C. The discharge specific capacity at 2C rate and the specific capacity retention rate at 2C rate were calculated. The higher the specific capacity, the better the rate performance of the battery.

[0066] The test results are shown in Table 1:

[0067] Table 1

[0068]

[0069] From the data recorded in Table 1, it can be seen that, compared with Comparative Examples 1-4, the lithium battery separator prepared from the nanofibers of Examples 1-3 not only has good liquid absorption rate and mechanical properties, but also has better rate performance of the battery formed therefrom.

[0070] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting; it is not intended to exclude myriad other embodiments of the present application that other present or future devices possess. That is, although the specification can contain many embodiments of the present application, these should not be construed as limiting the scope of the application, but rather as merely the best modes and preferred embodiments of the inventors to teach and convey the underlying application of the present application to others skilled in the art. It is therefore intended that the scope of the application be defined by the claims appended hereto rather than by the detailed description and exemplary embodiments described above. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the light of a dictionary, by those of ordinary skill in the art, by keeping in mind the ordinary meaning of such term and typical usage thereof in normal speech between those skilled in the art, and by applying "broad to mean and narrow to mean" where appropriate unless expressly dictated otherwise herein. No term is used herein that is not meant to be as commonly and popularly interpreted as being understood by those skilled in the art, and no term is defined through reference to a single dictionary if the term is more consistently defined in multiple references, common and popular usage between those skilled in the art, or through reference to multiple dictionaries.

[0071] While embodiments of the application have been shown and described, it is to be understood that various further modifications and changes can be made thereto without departing from the spirit and scope of the present application, which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing high-strength nanofibers for lithium battery cellulose-based separators, characterized in that: The following steps are involved: S1. Mixing the amino-terminated silane and ethanol solution and stirring to obtain a hydrolyzate; adding magnetic cellulose nanofibrils to the hydrolyzate, stirring and reacting at 60-80° C. for 8-10 hours, magnetically separating, and drying the separated product at 100° C. for 2 hours to obtain amino-modified magnetic cellulose nanofibrils; S2. Add the amino-modified magnetic cellulose nanofibrils, MOFs materials containing amino functional groups and polyaldehyde borate into dimethylformamide, stir for 15-30 minutes, heat to 80°C and stir to react for 12 hours, filter, wash the filter cake and dry it to obtain high-strength nanofibers for lithium battery cellulose-based separators.

2. The method for preparing high-strength nanofibers for lithium battery cellulose-based separators according to claim 1, characterized in that: The amount of terminal aminosilane in S1 is 5-10% of the mass of the magnetic cellulose nanofibrils.

3. The method for preparing high-strength nanofibers for lithium battery cellulose-based separators according to claim 1, characterized in that: The amino-terminated silane is at least one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane and N-aminoethyl-3-aminopropyltriethoxysilane.

4. The method for preparing high-strength nanofibers for lithium battery cellulose-based separators according to claim 1, characterized in that: The usage ratio of the amino-modified magnetic cellulose nanofibrils, the MOFs containing amino functional groups, the polyaldehyde borate and the dimethylformamide in S2 is 10 g: 0.5-1 g: 0.3-0.5 g: 100-150 mL.

5. The method for preparing high-strength nanofibers for lithium battery cellulose-based separators according to claim 1, characterized in that: Magnetic cellulose nanofibrils are prepared by the following steps: Cellulose nanofibrils and ferrous chloride were added to deionized water, stirred evenly, and ammonia water was added dropwise. After the addition was completed, the mixture was stirred and reacted at 80°C for 30 minutes. After that, the mixture was washed with deionized water and magnetically separated. The separated product was dried at 100°C for 2 hours to obtain magnetic cellulose nanofibrils.

6. The method for preparing high-strength nanofibers for lithium battery cellulose-based separators according to claim 5, characterized in that: The dosage ratio of the cellulose nanofibrils, ferrous chloride, deionized water and ammonia water is 2.25-3 g: 0.25 g: 20 mL: 10 mL, and the mass fraction of the ammonia water is 2.5-3.0%.

7. The method for preparing high-strength nanofibers for lithium battery cellulose-based separators according to claim 1, characterized in that: The preparation process of polyaldehyde borate comprises the following steps: 2-Mercaptoacetaldehyde, 2,4,6-trivinylboroxine, benzoin dimethyl ether and tetrahydrofuran are mixed and reacted under ultraviolet light for 0.5-1h. After the reaction is completed, tetrahydrofuran is removed by rotary evaporation to obtain polyaldehyde borate.

8. The method for preparing high-strength nanofibers for lithium battery cellulose-based separators according to claim 7, characterized in that: The molar ratio of mercaptoacetaldehyde to 2,4,6-trivinyl boroxine is 3:1, and the amount of benzoin dimethyl ether is 1-2% of the mass of 2,4,6-trivinyl boroxine.

9. The method for preparing high-strength nanofibers for lithium battery cellulose-based separators according to claim 1, characterized in that: The MOFs material containing amino functional groups is any one of U i O-66-NH2, U i O-67-NH2, MIL-125-NH2, MIL-101-NH2, or a mixture of more than one.

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