CN110581249A - Polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane and preparation method and application thereof - Google Patents
Polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane and preparation method and application thereof Download PDFInfo
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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
- 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
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/411—Organic material
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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
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/431—Inorganic material
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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
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/44—Fibrous material
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention provides a polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane and a preparation method and application thereof, belonging to the technical field of lithium battery diaphragms. The composite film provided by the invention comprises polyvinylidene fluoride-hexafluoropropylene, cellulose, carboxyl modified titanium dioxide nano-fiber and dibutyl phthalate. The polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane provided by the invention still does not have the phenomenon of thermal shrinkage at 160 ℃, can be normally used at 120 ℃, has higher porosity, has 50-70% of porosity and good affinity with electrolyte, and can be used as a lithium battery diaphragm.
Description
Technical Field
the invention relates to the technical field of lithium battery diaphragms, in particular to a polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane and a preparation method and application thereof.
Background
Lithium ion batteries have been widely used in portable electronic devices, electric vehicles, tools, and the like because of their advantages of high energy density, low self-discharge, long cycle life, and environmental friendliness. In the construction of lithium batteries, the separator is one of the key internal layer components. The diaphragm is used for isolating the positive and negative electrode materials and transmitting lithium ions, and the safety performance and the service life of the lithium ion battery are directly influenced by the performance of the diaphragm.
With the development of the field of lithium ion batteries, the market has higher and higher requirements on the performance of the lithium ion batteries, and simultaneously, the requirements on the diaphragm are also increased sharply. An ideal separator should have good ionic conductivity, chemical stability, and good wettability and storability to the electrolyte. The existing commercial lithium battery diaphragm mainly adopts a polyethylene and polypropylene microporous membrane, but the diaphragm has the defects of poor heat resistance, low porosity and poor electrolyte affinity.
disclosure of Invention
The invention aims to provide a polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane, a preparation method and application thereof.
In order to achieve the above object, the present invention provides the following technical solutions:
The invention provides a polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane which comprises the components of polyvinylidene fluoride-hexafluoropropylene, cellulose, carboxyl modified titanium dioxide nano fiber and dibutyl phthalate.
Preferably, the mass ratio of the polyvinylidene fluoride-hexafluoropropylene, the cellulose, the carboxyl modified titanium dioxide nano-fiber and the dibutyl phthalate is 1: 0.1-0.6: 0.05-0.15: 0.05-0.1.
Preferably, the preparation method of the carboxyl modified titanium dioxide nanofiber comprises the following steps:
Mixing and grinding titanium dioxide nano-fibers and citric acid, dispersing in water, and centrifuging to obtain the carboxyl modified titanium dioxide nano-fibers.
Preferably, the mass ratio of the titanium dioxide nanofiber to the citric acid is 1: 0.5-1.5.
Preferably, the diameter of the titanium dioxide nanofiber is 100-300 nm, and the length of the titanium dioxide nanofiber is 1-100 microns.
Preferably, the porosity of the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane is 50-70%, and the pore diameter is 1-10 microns.
The invention also provides a preparation method of the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane in the technical scheme, which is characterized by comprising the following steps:
mixing polyvinylidene fluoride-hexafluoropropylene, cellulose, carboxyl modified titanium dioxide nano-fiber, dibutyl phthalate and a solvent to obtain mixed slurry;
Coating the mixed slurry to obtain a composite membrane wet membrane;
And soaking the composite membrane wet membrane in a coagulating bath for phase transfer, and then drying to obtain the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane.
preferably, the solvent is N-methylpyrrolidone.
preferably, the temperature of the phase transfer is 20-40 ℃, and the time is 12-24 h.
The invention also provides an application of the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane or the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane obtained by the preparation method in the technical scheme as a lithium battery diaphragm.
The invention provides a polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane which comprises the components of polyvinylidene fluoride-hexafluoropropylene, cellulose, carboxyl modified titanium dioxide nano fiber and dibutyl phthalate. According to the preparation method, polyvinylidene fluoride-hexafluoropropylene is used as a substrate, cellulose is used as a framework for supporting the substrate, carboxyl modified titanium dioxide nano-fiber is used as a doping material, dibutyl phthalate is used as a plasticizer, and in the process of preparing the composite membrane, the carboxyl modified titanium dioxide nano-fiber can reduce the crystallinity of the polyvinylidene fluoride-hexafluoropropylene, so that the porosity of the composite membrane is improved, the affinity of the composite membrane and electrolyte is enhanced, and meanwhile, the high temperature resistance of the composite membrane is effectively improved by doping the carboxyl modified titanium dioxide nano-fiber; the cellulose has excellent high temperature resistance, when the cellulose is used as a framework of a supporting substrate, the heat resistance can be further improved, and the addition of the cellulose can reduce the crystallinity of polyvinylidene fluoride-hexafluoropropylene, namely, an amorphous area for lithium ion transmission is increased, so that the ionic conductivity of the composite membrane is improved. Experimental results show that the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane provided by the invention still does not have the phenomenon of thermal shrinkage at 160 ℃, can be normally used at 120 ℃, has high porosity, has the porosity of 50-70%, has good affinity with electrolyte, and can be used as a lithium battery diaphragm.
The invention also provides a preparation method of the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane in the technical scheme, which comprises the following steps: mixing polyvinylidene fluoride-hexafluoropropylene, cellulose, carboxyl modified titanium dioxide nano-fiber, dibutyl phthalate and a solvent to obtain mixed slurry; coating the mixed slurry to obtain a composite membrane wet membrane; and soaking the composite membrane wet membrane in a coagulating bath for phase transfer, and then drying to obtain the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane. The method has the advantages of simple process, short period, energy conservation and environmental protection.
Drawings
FIG. 1 is an SEM photograph of the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite film obtained in example 1 before and after heat treatment at 150 ℃;
FIG. 2 is a macroscopic view of the composite film obtained in example 1, the commercial PP film of comparative example 1, and the composite films obtained in comparative examples 2 to 3;
FIG. 3 is a macroscopic view of the composite film obtained in example 1, the commercial PP film obtained in comparative example 1, and the composite films obtained in comparative examples 2 to 3 after heat treatment at 160 ℃ for 0.5 h;
FIG. 4 shows the cell cycle performance at 120 ℃ of the membranes obtained in example 1, comparative example 1 and comparative example 3;
FIG. 5 is a graph showing the impedance spectra of the films obtained in example 1 and comparative examples 1 to 3 at room temperature.
Detailed Description
The invention provides a polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane, which comprises the components of polyvinylidene fluoride-hexafluoropropylene (which can be abbreviated as PVDF-HFP), cellulose, carboxyl modified titanium dioxide nano fiber and dibutyl phthalate (which can be abbreviated as DBP).
According to the preparation method, polyvinylidene fluoride-hexafluoropropylene is used as a substrate, cellulose is used as a framework for supporting the substrate, carboxyl modified titanium dioxide nano-fiber is used as a doping material, dibutyl phthalate is used as a plasticizer, and in the process of preparing the composite membrane, the carboxyl modified titanium dioxide nano-fiber can reduce the crystallinity of the polyvinylidene fluoride-hexafluoropropylene, so that the porosity of the composite membrane is improved, the affinity of the composite membrane and electrolyte is enhanced, and meanwhile, the high temperature resistance of the composite membrane is effectively improved by doping the carboxyl modified titanium dioxide nano-fiber; and the cellulose is used as a framework for supporting the substrate, so that the heat resistance and the ionic conductivity can be further improved.
In the present invention, the mass ratio of the polyvinylidene fluoride-hexafluoropropylene to the cellulose is preferably 1:0.1 to 0.6, more preferably 1:0.2 to 0.5, and most preferably 1:0.3 to 0.4. In the invention, the cellulose is used as a framework of a supporting substrate, the supporting function is realized on the polyvinylidene fluoride-hexafluoropropylene substrate, the crystallinity of the polyvinylidene fluoride-hexafluoropropylene can be reduced, and an amorphous area for lithium ion transmission is increased, so that the ionic conductivity of the composite membrane is improved; in addition, cellulose has excellent thermal stability, the thermal decomposition temperature of the cellulose is 270 ℃, and cellulose particles can be bonded and coated together by taking polyvinylidene fluoride-hexafluoropropylene as a substrate, so that a high-temperature resistant composite film is obtained.
In the present invention, the specification of the cellulose is not particularly limited, and commercially available cellulose may be used, and in the embodiment of the present invention, the average particle size of the cellulose is preferably 60 to 70 μm, and more preferably 65 μm.
in the invention, the mass ratio of the polyvinylidene fluoride-hexafluoropropylene to the carboxyl modified titanium dioxide nanofiber is preferably 1: 0.05-0.15, and more preferably 1: 0.08-0.12. According to the invention, the polyvinylidene fluoride-hexafluoropropylene is used as a substrate of the composite membrane, the carboxyl modified titanium dioxide nano fiber is used as a doping material to be dispersed in the substrate, the porosity of the composite membrane is effectively improved by adding the doping material, the affinity of the composite membrane and an electrolyte is further improved, and meanwhile, the titanium dioxide nano fiber has excellent heat resistance and can effectively improve the high temperature resistance of the composite membrane; in addition, the titanium dioxide nano-fibers are distributed in the substrate in a disordered way, and the growth of lithium dendrites can be inhibited to a certain extent, so that the mechanical strength of the composite membrane is improved.
In the present invention, the preparation method of the carboxyl-modified titanium dioxide nanofiber preferably comprises the following steps:
Mixing and grinding titanium dioxide nano-fibers and citric acid, dispersing in water, and centrifuging to obtain the carboxyl modified titanium dioxide nano-fibers.
According to the invention, titanium dioxide nano-fibers and citric acid are mixed and ground to obtain a mixture of the titanium dioxide nano-fibers and the citric acid. In the invention, the mixing and grinding can make the mixing of the titanium dioxide nano-fiber and the citric acid more uniform.
In the invention, the diameter of the titanium dioxide nanofiber is preferably 100-300 nm; the length is preferably 1 to 100 μm. In the invention, the titanium dioxide nano-fiber with the specification is beneficial to being uniformly dispersed in polyvinylidene fluoride-hexafluoropropylene.
In the invention, the mass ratio of the titanium dioxide nanofibers to the citric acid is preferably 1: 0.5-1.5, and more preferably 1: 0.8-1.2.
In the present invention, the source of the titanium dioxide nanofiber is not particularly limited, and may be a commercially available product or may be prepared by a method known to those skilled in the art, and in the embodiment of the present invention, after a titanium dioxide nanofiber precursor is prepared by an electrospinning method, it is preferably calcined at 550 ℃ to obtain the titanium dioxide nanofiber.
After the mixture of the titanium dioxide nano fiber and the citric acid is obtained, the mixture of the titanium dioxide nano fiber and the citric acid is dispersed in water, and then the mixture is sequentially centrifuged and dried to obtain the carboxyl modified titanium dioxide nano fiber.
In the invention, the time for dispersing the mixture of the titanium dioxide nano-fibers and the citric acid in water is preferably 1-2 h; the dispersion is preferably carried out by stirring. In the invention, the mixture of the titanium dioxide nano-fiber and the citric acid is dispersed in water, the citric acid which is free in the water is coated on the surface of the titanium dioxide fiber to form the titanium dioxide nano-fiber with carboxyl, and carboxyl groups on the titanium dioxide nano-fiber with carboxyl are mutually exclusive, so that the titanium dioxide nano-fiber modified by carboxyl is uniformly dispersed.
in the invention, the rotation speed of the centrifugation is preferably 8000-12000 rpm, more preferably 10000rpm, and the time of the centrifugation is preferably 3-7 min, more preferably 5 min.
in the present invention, the mass ratio of polyvinylidene fluoride-hexafluoropropylene to dibutyl phthalate (abbreviated as DBP) is preferably 1:0.05 to 0.1, and more preferably 1:0.07 to 0.08. In the invention, the DBP is used as a plasticizer and dispersed in the substrate, so that the mechanical property of the composite film can be improved.
In the invention, the porosity of the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane is preferably 50-70%, and more preferably 55-65%; the pore diameter is preferably 1-10 μm, and more preferably 1-3 μm; the thickness is preferably 36 to 45 μm, and more preferably 38 to 42 μm; the holes in the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane are communicated, the interior of the composite membrane is of a three-dimensional structure, and the liquid absorption rate of the electrolyte can be improved, so that the electrochemical performance is improved.
The invention also provides a preparation method of the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane in the technical scheme, which comprises the following steps:
Mixing polyvinylidene fluoride-hexafluoropropylene, cellulose, carboxyl modified titanium dioxide nano-fiber, dibutyl phthalate and a solvent to obtain mixed slurry;
Coating the mixed slurry to obtain a composite membrane wet membrane;
and soaking the composite membrane wet membrane in a coagulating bath for phase transfer, and then drying to obtain the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane.
The preparation method comprises the steps of mixing polyvinylidene fluoride-hexafluoropropylene, cellulose, carboxyl modified titanium dioxide nano-fibers, dibutyl phthalate and a solvent to obtain mixed slurry.
In the present invention, the solvent is preferably N-methylpyrrolidone; the N-methyl pyrrolidone is mutually soluble with water and is easy to remove.
in the invention, the preferable mixing is that polyvinylidene fluoride-hexafluoropropylene, cellulose and carboxyl modified titanium dioxide nano-fiber are respectively mixed with a solvent, then the dispersion liquid of the polyvinylidene fluoride-hexafluoropropylene, the cellulose and the carboxyl modified titanium dioxide nano-fiber are mixed, and dibutyl phthalate is added; the concentration of the mixed polyvinylidene fluoride-hexafluoropropylene and solvent is preferably 0.1 g/mL; the concentration of the cellulose dispersed in the solvent is preferably 0.05-1 g/mL, and more preferably 0.1 g/mL; the concentration of the carboxyl modified titanium dioxide nanotube dispersed in the solvent is preferably 0.02-0.1 g/mL; in the embodiment of the present invention, the polyvinylidene fluoride-hexafluoropropylene and the carboxyl-modified titanium dioxide nanofibers are respectively dispersed in the solvent preferably by stirring, and the stirring time is preferably 12 hours; the cellulose is dispersed in the solvent in a sealed stirring mode, the sealed stirring time is preferably 2 hours, and the sealed stirring can reduce the hydrolysis of the cellulose; after adding dibutyl phthalate, stirring is preferably continued for 2h to obtain a mixed slurry. The concentration of a dispersion liquid obtained by respectively dispersing the polyvinylidene fluoride-hexafluoropropylene, the cellulose and the carboxyl modified titanium dioxide nano fiber in a solvent is not particularly limited, and the concentration of a mixed slurry prepared finally is proper.
After the mixed slurry is obtained, defoaming the mixed slurry preferably; the specific defoaming mode is not particularly limited, and the conventional defoaming mode can be adopted, such as standing defoaming and vacuum defoaming. In the invention, defoaming can remove gas in the mixed slurry to facilitate uniform coating on a glass plate.
After defoaming is finished, the mixed slurry after defoaming is coated to obtain a composite membrane wet membrane.
The specific mode of the coating film is not particularly limited, and the required composite film can be obtained. In the embodiment of the present invention, the coating film is preferably a wet composite film formed by coating the defoamed mixed slurry on a glass plate.
After the composite membrane wet film is obtained, the composite membrane wet film is soaked in a coagulating bath for phase transfer, and then is dried, so that the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane is obtained.
In the present invention, the coagulation bath is preferably water or a mixture of water and N-methylpyrrolidone, and when the coagulation bath is water; the temperature of the phase transfer is preferably 20-40 ℃, and the time is preferably 12-24 h. In the invention, in the phase transfer process, the N-methyl pyrrolidone and water carry out mass transfer exchange, the water is filled in the wet film of the composite film, and then the three-dimensional pore structure is obtained after drying and water evaporation.
In the invention, the drying is preferably air-blast drying, the drying temperature is preferably 55-65 ℃, and the drying time is preferably 10-14 h.
The invention also provides the application of the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane in the technical scheme or the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane obtained by the preparation method in the technical scheme as a lithium battery diaphragm.
The polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane provided by the present invention, the preparation method and the application thereof are described in detail with reference to the following examples, but they should not be construed as limiting the scope of the present invention.
Example 1
(1) Mixing ethanol, acetic acid and tetrabutyl titanate according to the mass ratio of 10:4:3, magnetically stirring for 2 hours at normal temperature, adding polyvinylpyrrolidone with the concentration of 0.045g/mL, stirring until the polyvinylpyrrolidone is completely dissolved to obtain a titanium dioxide precursor solution, then obtaining a titanium dioxide nanofiber precursor by an electrostatic spinning method, calcining the titanium dioxide nanofiber precursor for 2 hours at 550 ℃ to obtain titanium dioxide nanofibers, wherein the diameter of the titanium dioxide nanofibers is 100-300 nm, and the length of the titanium dioxide nanofibers is 1-100 micrometers;
(2) Mixing and grinding titanium dioxide nano-fibers and citric acid according to the mass ratio of 1:1, dispersing in water, stirring for 2h, and centrifuging at 10000rpm for 5min to obtain carboxyl modified titanium dioxide nano-fibers;
(3) Adding the carboxyl modified titanium dioxide nano-fiber into an N-methyl pyrrolidone solvent, and stirring for 12h to obtain a carboxyl modified titanium dioxide nano-fiber dispersion liquid with the concentration of 0.025 g/mL;
(4) Adding polyvinylidene fluoride-hexafluoropropylene into N-methyl pyrrolidone, and stirring for 12 hours to obtain a polyvinylidene fluoride-hexafluoropropylene solution with the concentration of 0.1 g/mL;
(5) Adding cellulose with the average particle size of 65 mu m into N-methyl pyrrolidone, and stirring for 2 hours in a sealing way to obtain cellulose dispersion liquid with the concentration of 0.1 g/mL;
(6) Sequentially adding the carboxyl modified titanium dioxide nanofiber dispersion liquid obtained in the step (3) and the cellulose dispersion liquid obtained in the step (5) into the polyvinylidene fluoride-hexafluoropropylene solution obtained in the step (4), uniformly stirring, adding dibutyl phthalate, and continuously stirring for 2 hours to obtain mixed slurry; wherein the mass ratio of polyvinylidene fluoride-hexafluoropropylene to cellulose to carboxyl modified titanium dioxide nano-fiber to dibutyl phthalate is 1:0.6:0.05: 0.12;
(7) Coating the mixed slurry on a glass plate, immersing the glass plate in water at 30 ℃, drying the glass plate for 12 hours at 60 ℃ after soaking for 12 hours to obtain a polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane (marked as PVDF-HFP/Cellukose/TiO) with the thickness of 40-45 mu m2)。
The porosity of the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane obtained in the embodiment is 63.65% through testing, and the testing pore diameter range is 1-3 mu m.
Comparative example 1
Commercial PP films available from heyowa civic electronics ltd as Celgard 2400 model.
The commercial PP membrane of this comparative example was tested to have a porosity of 4.76% and a pore size in the range of 100-500 nm.
Comparative example 2
According to the method of example 1, a polyvinylidene fluoride-hexafluoropropylene film (marked as PVDF-HFP) was prepared without adding carboxyl-modified titanium dioxide nanofibers and cellulose, and the thickness of the obtained PVDF was 30-40 μm.
The porosity of the polyvinylidene fluoride-hexafluoropropylene film obtained by the comparative example is 49.77% through testing, and the range of the tested pore diameter is 1-3 mu m.
Comparative example 3
According to the method of the embodiment 1, the polyvinylidene fluoride-hexafluoropropylene/cellulose composite membrane (marked as PVDF-HFP/Cellukose) is prepared without adding the carboxyl modified titanium dioxide nano fiber, and the thickness of the obtained composite membrane is 40-45 μm.
The porosity of the polyvinylidene fluoride-hexafluoropropylene/cellulose composite membrane obtained by the comparative example is tested to be 50.6%, and the test pore diameter is 2-5 mu m.
Comparative example 4
a polyvinylidene fluoride-hexafluoropropylene/titanium dioxide composite film (designated as PVDF-HFP/TiO) was prepared according to the preparation method of example 1 without adding cellulose2)。
The porosity of the polyvinylidene fluoride-hexafluoropropylene/titanium dioxide composite membrane obtained by the comparative example is 55% through testing, and the testing pore diameter range is 2-5 mu m.
The morphology of the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane obtained in example 1 is characterized, and as shown in fig. 1 (a), it can be seen from fig. 1 (a) that the composite membrane obtained in this example has a porous structure, and the pore structures in the composite membrane are mutually communicated. After the composite film obtained in this example is heat-treated at 150 ℃ for 0.5h, the morphology of the composite film is tested again, and as shown in fig. 1 (b), it can be seen from fig. 1 (b) that after the composite film is heat-treated at 150 ℃ at high temperature, a part of the pore structure still exists in the composite film.
the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite film obtained in example 1, the commercial PP film (polypropylene film) obtained in comparative example 1, the polyvinylidene fluoride-hexafluoropropylene/cellulose composite film obtained in comparative example 3 and the polyvinylidene fluoride-hexafluoropropylene/titanium dioxide composite film obtained in comparative example 4 were all cut into circles of the same size, heat-treated at different temperatures for 0.5 hour per heat treatment, and then the shrinkage of each film was counted, with the results shown in table 1.
TABLE 1 statistical shrinkage tables for example 1, comparative example 1, and comparative examples 3-4
| temperature of | 130℃ | 140℃ | 150℃ | 160℃ |
| Example 1 | 0 | 0 | 0 | 0 |
| Comparative example 1 | 5％ | 16.7％ | 36.1％ | 77.8％ |
| comparative example 3 | 0 | 0 | 0 | 5％ |
| Comparative example 4 | 0 | 0 | 2.5％ | 5％ |
The polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite film obtained in example 1, the commercial PP film obtained in comparative example 1, the polyvinylidene fluoride-hexafluoropropylene film obtained in comparative example 2, and the polyvinylidene fluoride-hexafluoropropylene/cellulose composite film obtained in comparative example 3 were all cut into circles of the same size as shown in fig. 2 (wherein the macro-graphs of a-d are sequentially assigned to comparative example 1, comparative example 2, comparative example 3, and example 1), after heat treatment at 160 ℃ for 0.5h, a macroscopic view (i.e., a photograph) of each film was taken, and as a result, as shown in FIG. 3, wherein the macro-graphs of a-d are sequentially assigned to comparative example 1, comparative example 2, comparative example 3 and example 1, as can be seen by comparing fig. 2 and 3, the commercial PP separator had changed from white to transparent and shrunk into an oblong shape with a shrinkage rate as high as 77%; the pure polyvinylidene fluoride-hexafluoropropylene is changed from white to transparent, but the shrinkage rate is only 5 percent, and the original shape of the diaphragm can still be kept; the polyvinylidene fluoride-hexafluoropropylene/cellulose composite membrane is semitransparent, the PVDF-HFP material in the composite membrane is mainly melted at 160 ℃, and the composite membrane has only 5% shrinkage; the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane can still keep the original form without thermal shrinkage at the high temperature.
the electrolyte absorptivity of the composite membrane obtained in example 1 and the membranes obtained in comparative examples 1-3 are tested by adopting a weighing method, and the electrolyte is LiPF with the concentration of 1M6the results of the electrolytic solution are shown in Table 2. As can be seen from table 2, the composite membrane obtained in example 1 has the highest absorption rate for the electrolyte, indicating that it has better affinity for the electrolyte.
TABLE 2 electrolyte absorption rates of the composite membrane obtained in example 1 and the membranes obtained in comparative examples 1 to 3
the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane obtained in example 1, the commercial PP membrane obtained in comparative example 1 and the polyvinylidene fluoride-hexafluoropropylene/cellulose membrane obtained in comparative example 3 are tested for the battery cycle performance at 120 ℃, specifically, the charge-discharge interval is 2.5-4V, and the charge-discharge multiplying power is 0.5C. As shown in fig. 4, it can be seen from fig. 4 that the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite film can perform normal charge and discharge cycles at a high temperature of 120 ℃ and maintain a high specific charge and discharge capacity.
The impedance spectrograms of the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite film obtained in example 1, the commercial PP film obtained in comparative example 1, the polyvinylidene fluoride-hexafluoropropylene film obtained in comparative example 2 and the polyvinylidene fluoride-hexafluoropropylene/cellulose composite film obtained in comparative example 3 at normal temperature were tested, and the results are shown in fig. 5, and it can be seen from fig. 5 that the battery provided with the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite film has the optimal ionic conductivity, and the ionic conductivity can reach 1.68mS/cm through calculation.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane is characterized by comprising the components of polyvinylidene fluoride-hexafluoropropylene, cellulose, carboxyl modified titanium dioxide nano fiber and dibutyl phthalate.
2. The polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite film according to claim 1, wherein the mass ratio of the polyvinylidene fluoride-hexafluoropropylene, the cellulose, the carboxyl-modified titanium dioxide nanofiber and the dibutyl phthalate is 1: 0.1-0.6: 0.05-0.15: 0.05-0.1.
3. The polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane according to claim 1, wherein the preparation method of the carboxyl-modified titanium dioxide nanofiber comprises the following steps:
Mixing and grinding titanium dioxide nano-fibers and citric acid, dispersing in water, and centrifuging to obtain the carboxyl modified titanium dioxide nano-fibers.
4. The polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane according to claim 3, wherein a mass ratio of the titanium dioxide nanofibers and the citric acid is 1: 0.5-1.5.
5. The polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane according to claim 3 or 4, wherein the titanium dioxide nanofibers have a diameter of 100 to 300nm and a length of 1 to 100 μm.
6. The polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane according to any one of claims 1 to 4, wherein the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane has a porosity of 50 to 70% and a pore diameter of 1 to 10 μm.
7. a method for preparing the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane according to any one of claims 1 to 6, comprising the steps of:
Mixing polyvinylidene fluoride-hexafluoropropylene, cellulose, carboxyl modified titanium dioxide nano-fiber, dibutyl phthalate and a solvent to obtain mixed slurry;
coating the mixed slurry to obtain a composite membrane wet membrane;
And soaking the composite membrane wet membrane in a coagulating bath for phase transfer, and then drying to obtain the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite membrane.
8. The method according to claim 7, wherein the solvent is N-methylpyrrolidone.
9. The method according to claim 7, wherein the phase transition temperature is 20 to 40 ℃ and the time is 12 to 24 hours.
10. Use of the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite film according to any one of claims 1 to 6 or the polyvinylidene fluoride-hexafluoropropylene/cellulose/titanium dioxide composite film obtained by the preparation method according to any one of claims 7 to 9 as a lithium battery separator.
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Application publication date: 20191217 |