CN115838974A - Thin film material and preparation method and application thereof - Google Patents
Thin film material and preparation method and application thereof Download PDFInfo
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- CN115838974A CN115838974A CN202211360921.XA CN202211360921A CN115838974A CN 115838974 A CN115838974 A CN 115838974A CN 202211360921 A CN202211360921 A CN 202211360921A CN 115838974 A CN115838974 A CN 115838974A
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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
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Abstract
The invention provides a film material and a preparation method and application thereof. The film material is formed by interweaving nano-scale fiber filaments, bead-shaped structures are distributed on the nano-scale fiber filaments, and the raw materials for preparing the film material comprise polyvinylidene fluoride, modified sepiolite and a solvent. The film material is formed by interweaving the nano-scale fiber yarns, and the bead-shaped structures are distributed on the nano-scale fiber yarns, so that on one hand, the specific surface area and the porosity of the film material are effectively improved, and the film material has better performance; on the other hand, the film material has excellent heat resistance stability and dimensional stability. Finally, the film material has excellent comprehensive performance. The invention also provides a preparation method and application of the film material.
Description
Technical Field
The invention belongs to the technical field of thin film material preparation, and particularly relates to a thin film material and a preparation method and application thereof.
Background
The battery diaphragm is an important component of the lithium ion battery, and has the main functions of: (1) The positive electrode and the negative electrode of the battery are isolated, so that electrons in the battery cannot freely pass through the battery, and short circuit is prevented; (2) Lithium ions in the electrolyte are allowed to pass through the micro-channels of the diaphragm and are freely transmitted between the positive electrode and the negative electrode, so that the electrochemical reaction of the battery is ensured to be orderly and reversibly carried out. The structure and performance of the battery separator directly affect the capacity, cycle performance and safety performance of the battery.
With the ever-increasing demand for large-scale energy storage and high-performance electric vehicles, energy density and power density are considered to be important components of advanced lithium batteries. The battery diaphragm with the nano structure has the advantages of high surface-to-volume ratio, high porosity, short ion diffusion distance and the like, and can improve the ion transmission efficiency, the battery capacity and the energy density. The current preparation methods of the nano-structure battery diaphragm commonly used include a melt-blowing method, a wet method, a vacuum filtration method and an electrostatic spinning method.
In the melt-blowing process, high temperatures and air flow velocities can cause fiber instability, resulting in particle dispersion in the web. The wet method requires that a polymer precursor is first formed into fibers in a liquid suspension, then a binder is added to the base fibers, and the fibers are bonded by heat treatment and pressurization, but the structure and properties of the finally formed fibers are mainly limited by the type and composition of the polymer in the precursor suspension. The vacuum filtration process for making nanofiber membranes also requires the preparation of a suspension containing the precursor polymer fibers, with the aid of vacuum filtration, to form a web of fibers on the filter paper. The size of the membranes produced by vacuum filtration is limited due to the difficulty of obtaining uniform vacuum forces over large surfaces. The electrostatic spinning method can be used for preparing the nano-fiber rapidly and efficiently, can control the structural size of the fiber, is very simple to operate, is easy to operate, and is an excellent nano-fiber preparation method which is formed at present.
At present, a common commercial diaphragm in the market is a polyolefin diaphragm, but the polyolefin diaphragm has the defects of low porosity, poor electrolyte wettability, easy generation of severe size shrinkage at high temperature and the like, and is difficult to meet the requirement of a high-performance power lithium battery. Nonwoven fabric fiber membranes prepared by electrospinning technology which has emerged in recent years have attracted extensive attention of researchers due to their high porosity, large specific surface area and excellent electrochemical properties.
Polyvinylidene fluoride (PVDF) is a popular substrate commonly used to prepare membrane materials. PVDF has a relative dielectric constant as high as 8.3 compared to polyolefins and other materials, and can reduce the interaction between ion pairs. It is more favorable for the dissociation of lithium. In addition, the polyolefin diaphragm material has high crystallinity and small polarity, and the electrolyte belongs to an organic solvent with high polarity, so that the surface energy of the polyolefin diaphragm is lower, the affinity with the electrolyte is poorer, most of the electrolyte which cannot be fully swelled by the electrolyte exists in pores and is easy to leak. Besides, PVDF has some desirable properties as an electrolyte: for example, (1) mechanical strength and toughness; (2) a wide voltage window; (3) The thermal stability is good, the material is not combusted, the long-term working temperature can reach 150 ℃, and the decomposition temperature can reach 400 ℃; (4) The electrochemical stability is high, and adverse reactions with other materials are avoided; and (5) good processability and the like.
However, the PVDF membrane prepared by the existing electrostatic spinning method has not ideal strength, and the mechanical property and the service life of the membrane are influenced.
Disclosure of Invention
The present invention is directed to solving at least one of the above problems in the prior art. Therefore, the invention provides a film material which has good strength and mechanical properties, and has better performance and service life when being used for battery separators and the like.
The invention also provides a preparation method of the film material.
The invention also provides a battery diaphragm.
The invention provides a film material, which is formed by interweaving nano-scale fiber filaments, wherein bead-shaped structures are distributed on the nano-scale fiber filaments, and raw materials for preparing the film material comprise polyvinylidene fluoride, modified sepiolite and a solvent.
The invention relates to one technical scheme of the thin film material, which at least has the following beneficial effects:
the film material of the invention is formed by interweaving nano-scale fiber yarns, and bead-shaped structures are distributed on the nano-scale fiber yarns. On one hand, the nano wire bead-shaped network structure effectively improves the specific surface area and the porosity of the film material, so that the film material has better performance; on the other hand, the film material has excellent heat resistance stability and dimensional stability. Finally, the film material has excellent comprehensive performance.
The film material provided by the invention comprises polyvinylidene fluoride, modified sepiolite and a solvent. Polyvinylidene fluoride is the main material of the film material. Sepiolite is a SiO with two tetrahedra layers 2 Non-metallic mineral material of elementary composition having the theoretical formula Mg 8 Si 12 O 30 (OH) 4 (H 2 O) 4 ·8H 2 And O. The sepiolite belongs to a 2:1 type layer chain structure, is formed by connecting a central oxygen atom with a discontinuous oxygen atom octahedron, and can combine molecular chains together due to a Si-O-Si bonded three-dimensional steric bond structure in the sepiolite, so that the crystal form of the sepiolite extends along one direction, and a fibrous or rod-shaped structure is microscopically shown. Due to the unique crystal structures of the sepiolite, the sepiolite has the advantages of excellent adsorbability, high specific surface area, good thermal stability, chemical stability, mechanical stability and the like. The method has wide application in a plurality of fields such as medicine, ceramics, casting, plastics, building and the like. Compared with the common sepiolite, the modified sepiolite in the raw materials for preparing the film material has the effects of dissolving and removing redundant metal impurities in the sepiolite by using an acidic solvent, opening agglomeration of the original sepiolite on a microstructure, recovering the original fiber or rod-shaped structure, better coating and interlacing with polyvinylidene fluoride nano fibers in the subsequent electrostatic spinning process, and finally optimizing the performance of the diaphragm by improving the fiber structure. The addition of the modified sepiolite can further improve the thermal stability and the ionic conductivity of the film material. The solvent is used for dissolving the polyvinylidene fluoride and providing a dispersed carrier for the polyvinylidene fluoride and the modified sepiolite.
According to some embodiments of the invention, the mass ratio of the polyvinylidene fluoride to the modified sepiolite is 1.
According to some embodiments of the invention, the mass to volume ratio of the polyvinylidene fluoride to the solvent is 10g to 15g.
According to some embodiments of the invention, the polyvinylidene fluoride has an average molecular weight of 700 to 900 ten thousand.
According to some embodiments of the invention, the polyvinylidene fluoride has an average molecular weight of 800 to 900 ten thousand.
According to some embodiments of the invention, the polyvinylidene fluoride has an average molecular weight of 800 ten thousand.
Solutions prepared with different molecular weights will have very different solubilities. Taking polyvinylidene fluoride with average molecular weight of 400 ten thousand or 600 ten thousand as an example, the prepared solution is relatively thin and can not reach the viscosity required by spinning, so that when the molecular weight is too low, more solute needs to be added, and the quantitative solution can not be fully dissolved. And the solution is easily too viscous due to overlarge molecular weight, so that a needle tube is easily blocked in the spinning process, and 800-900 ten thousand of the solution has proper molecular weight.
According to some embodiments of the invention, the solvent is a mixed solvent of dimethylformamide and acetone.
Dimethylformamide (DMF) has high dipole constant and dipole moment, is a good solvent for PVDF, but has poor volatility. In order to accelerate the volatilization of the electrostatic spinning dispersant, a small amount of acetone needs to be added into DMF. However, the larger the amount of acetone added, the faster the volatilization rate during electrospinning, resulting in an increase in the viscosity of the spinning solution. This makes it difficult for electrostatic forces to overcome the surface tension of the droplets during drawing, resulting in uneven drawing of the fibers and the bonding of a large number of fibers to form clusters. Thus, the solvent needs to be a mixed solvent of dimethylformamide and acetone.
According to some embodiments of the invention, the volume ratio of dimethylformamide to acetone is 7:3.
In other volume ratios, such as 8:2 and 6: for example, under the same conditions (voltage, advancing speed, receiving distance, temperature and humidity), the degree of fiber dispersion 7:3 is the most preferable. 8:2 is susceptible to the appearance of many droplets that do not evaporate into fibers in time because they do not evaporate sufficiently quickly. 6: the volume ratio of 4 is higher in the adding amount of acetone, so that the volatilization speed is higher in electrostatic spinning, and the viscosity of the spinning solution is increased. This makes it difficult for electrostatic forces to overcome the surface tension of the droplets during drawing, resulting in uneven drawing of the fibers and the bonding of a large number of fibers to form clusters.
PVDF is also soluble in a few solvents such as NMP, TEP and DMAc.
Among them, the NMP solvent has high volatilization temperature, is sensitive to light, has a certain pollution to the environment and is expensive.
TEP has certain toxicity, is stable and not easy to volatilize at normal temperature, and reacts with strong oxidant and strong base.
DMSO is strongly hygroscopic and reacts violently with chlorine.
According to some embodiments of the invention, the modified sepiolite is prepared by a method comprising: heating and stirring the sepiolite powder in an acid solution, washing and drying.
According to some embodiments of the invention, the modified sepiolite is prepared by:
(1) Taking sepiolite powder, fully grinding the sepiolite powder in a grinding bowl, filtering the ground sepiolite powder by using a screen, and collecting the sepiolite powder for later use;
(2) Weighing a proper amount of sepiolite, putting the sepiolite into a container, adding a proper amount of deionized water into the container, slowly stirring to fully disperse the sepiolite, standing until the sepiolite is completely precipitated, and performing suction filtration to take out and dry the precipitate;
(3) Preparing an acid solution, adding the dried sepiolite powder into the acid solution, heating in a water bath, stirring, and performing suction filtration to obtain acid modified sepiolite;
(4) And heating, stirring and washing the obtained acid modified sepiolite with deionized water for several times until the sepiolite is neutral, drying and grinding for later use.
According to some embodiments of the invention, in the step (1) of the preparation method of the modified sepiolite, the mesh number of the screen comprises 200 meshes.
According to some embodiments of the present invention, in the step (2) of the preparation method of the modified sepiolite, the stirring includes magnetic stirring, and the stirring is performed until the sepiolite is sufficiently dispersed, and the stirring time may be 12 hours.
According to some embodiments of the present invention, in the step (2) of the method for preparing modified sepiolite, the drying temperature may be 60 ℃.
According to some embodiments of the invention, in the step (3) of the method for preparing modified sepiolite, the acidic solution comprises hydrochloric acid solution.
According to some embodiments of the invention, in the step (3) of the preparation method of the modified sepiolite, the hydrochloric acid solution comprises a 12% hydrochloric acid solution by mass fraction.
According to some embodiments of the present invention, in the step (3) of the preparation method of the modified sepiolite, the temperature of the heating water bath stirring may be 80 ℃.
According to some embodiments of the present invention, in the step (3) of the preparation method of the modified sepiolite, the time for stirring in the heating water bath may be 8 to 12 hours.
According to some embodiments of the present invention, in the step (4), after grinding, the particle size of the modified sepiolite is in the range of 2nm to 200nm.
In a second aspect, the present invention provides a method for preparing said film material, comprising the steps of:
s1: dissolving the polyvinylidene fluoride in the solvent to obtain a sol-gel solution;
s2: adding the modified sepiolite into the sol-gel solution, and uniformly dispersing to obtain a modified sol-gel solution;
s3: and (3) carrying out electrostatic spinning on the modified sol-gel solution to obtain the film material.
The invention relates to a technical scheme in a preparation method of a film material, which at least has the following beneficial effects:
the preparation method of the thin film material comprises the steps of dissolving polyvinylidene fluoride in a solvent to obtain a sol-gel solution, adding the modified sepiolite into the sol-gel solution, dispersing uniformly to obtain a modified sol-gel solution, and finally performing electrostatic spinning on the modified sol-gel solution to obtain the thin film material. The raw materials are easy to obtain, the process is easy to control, expensive equipment is not needed, and the industrial large-scale production is easy to realize. The preparation method of the film material solves the problems that the PVDF diaphragm prepared by the existing electrostatic spinning method has not ideal strength, and the mechanical property and the service life of the diaphragm are influenced.
According to some embodiments of the invention, in step S1, the polyvinylidene fluoride is dissolved in the solvent to obtain a mixture, and the mixture is heated at a constant temperature until the polyvinylidene fluoride is completely dissolved.
According to some embodiments of the present invention, the constant temperature heating temperature in step S1 may be about 60 ℃.
According to some embodiments of the present invention, in step S1, the constant temperature heating time may be about 12 hours.
According to some embodiments of the invention, in step S1, the mass volume fraction of the polyvinylidene fluoride in the mixture is 10% to 15%.
According to some embodiments of the invention, in step S2, the modified sepiolite is added to the sol-gel solution, and the mass ratio of the polyvinylidene fluoride to the modified sepiolite is 1:0.5 to 1.5.
According to some embodiments of the present invention, in step S2, the uniform dispersion may be achieved by magnetic stirring and ultrasonic vibration.
According to some embodiments of the invention, in step S3, the method of electrospinning is: and (3) loading the modified sol-gel solution into a needle cylinder of electrostatic spinning equipment, and preparing the film material by performing an electrostatic spinning method by regulating and controlling parameters such as solution flow rate, loading voltage between the metal needle and the metal plate, distance between the metal needle and the metal plate and the like.
According to some embodiments of the invention, the flow rate of the sol-gel solution in the electrospinning is 0.5mL/h to 1mL/h.
According to some embodiments of the invention, the voltage applied between the metal needle and the metal plate in the electrostatic spinning is 10kV to 20kV.
According to some embodiments of the invention, the distance from the metal needle to the metal plate in said electrospinning is from 10cm to 20cm.
According to some embodiments of the present invention, the method for preparing a thin film material further comprises, after step S3, soaking the thin film material in absolute ethanol, and then drying.
According to some embodiments of the invention, the membrane material is soaked in absolute ethyl alcohol for 24 to 48 hours.
Dimethylformamide and acetone can be dissolved in alcohol, PVDF is insoluble in alcohol, residual dimethylformamide and acetone after spinning can be removed through soaking treatment, and alcohol is easy to volatilize and treat.
According to some embodiments of the present invention, the thin film material is soaked in absolute ethanol and then dried, which may be at a temperature of 50 ℃ to 70 ℃.
According to some embodiments of the present invention, the thin film material is soaked in absolute ethanol and then dried, and the drying time can be 24 hours.
The third aspect of the invention provides a battery diaphragm which is prepared from the thin film material.
The invention relates to one of the technical schemes of the battery diaphragm, which at least has the following beneficial effects:
the battery diaphragm is prepared from the thin film material, the thin film material is formed by interweaving nano-scale fiber yarns, and beaded structures are distributed on the nano-scale fiber yarns. On one hand, the nano wire bead-shaped network structure effectively improves the specific surface area and the porosity of the film material, so that the film material has better performance; on the other hand, the film material has excellent heat resistance stability and dimensional stability. Finally, the battery separator has excellent overall properties.
The battery diaphragm provided by the invention is prepared from raw materials including polyvinylidene fluoride, modified sepiolite and a solvent. Polyvinylidene fluoride is the main material of the film material. Sepiolite is a SiO with two tetrahedra layers 2 Non-metallic mineral material of elementary composition having the theoretical formula Mg 8 Si 12 O 30 (OH) 4 (H 2 O) 4 ·8H 2 And (O). The sepiolite belongs to a 2:1 type layer chain structure, is formed by connecting a central oxygen atom with a discontinuous oxygen atom octahedron, and can combine molecular chains together due to a Si-O-Si bonded three-dimensional steric bond structure in the sepiolite, so that the crystal form of the sepiolite extends along one direction, and a fibrous or rod-shaped structure is microscopically shown. Due to the unique crystal structures of the sepiolite, the sepiolite has excellent adsorbability, high specific surface area, good thermal stability, chemical stability and mechanical stabilityAnd the like. The method has wide application in a plurality of fields such as medicine, ceramics, casting, plastics, building and the like. Compared with the common sepiolite, the modified sepiolite in the raw materials for preparing the film material has the effects of dissolving and removing redundant metal impurities in the sepiolite by using an acidic solvent, opening agglomeration of the original sepiolite on a microstructure, recovering the original fiber or rod-shaped structure, better coating and interlacing with polyvinylidene fluoride nano fibers in the subsequent electrostatic spinning process, and finally optimizing the performance of the diaphragm by improving the fiber structure. The addition of the modified sepiolite can further improve the thermal stability and the ionic conductivity of the film material. The solvent is used for dissolving the polyvinylidene fluoride and providing a dispersed carrier for the polyvinylidene fluoride and the modified sepiolite. The battery diaphragm prepared by the electrostatic spinning method ensures that the polyvinylidene fluoride and the modified sepiolite are coated or entangled in a fiber state, so that the prepared nanofiber has better mechanical property and thermal stability, and the use safety performance of the battery diaphragm is improved. And due to the special performance of the modified sepiolite inorganic filler, the prepared battery diaphragm has higher ionic conductivity and lower impedance, so that the battery has good cycle performance and higher charge-discharge efficiency.
Drawings
FIG. 1 is a micro-topography of the thin film material prepared in example 1.
FIG. 2 is a micro-topography of the thin film material prepared in example 2.
FIG. 3 is a micro-topography of the thin film material prepared in example 3.
FIG. 4 is the X-ray diffraction test results of the membrane materials prepared in examples 1 to 3 and pure PVDF membrane material, sepiolite powder before and after modification.
Fig. 5 is an FTIR plot of the thin film materials prepared in examples 1 to 3 and the PVDF separator material.
Fig. 6 is a graph of thermal stability tests of the membrane materials prepared in examples 1 to 3 and commercial Celgard membrane and PVDF separator materials.
FIG. 7 is a thermogravimetric TG test plot of the membrane materials prepared in examples 1 to 3 and commercial Celgard membranes and PVDF membrane materials
Fig. 8 is an ion conductivity curve of the membrane materials prepared in examples 1 to 3 and commercial Celgard membrane and PVDF separator materials.
Fig. 9 is an LSV curve of the membrane materials prepared in examples 1 to 3 and commercial Celgard membrane and PVDF separator materials.
FIG. 10 is a CV curve of the film material prepared in example 1.
FIG. 11 is a graph showing the cycle performance of the film material prepared in example 1 after being assembled into a button cell.
Fig. 12 is a graph of long cycle and efficiency after assembly of the membrane material prepared in example 1 and commercial Celgard and PVDF membrane materials into a button cell.
Detailed Description
The following are specific examples of the present invention, and the technical solutions of the present invention are further described with reference to the examples, but the present invention is not limited to the examples.
In some embodiments of the present invention, the present invention provides a membrane material, the membrane material is formed by interweaving nano-scale fiber filaments, bead-shaped structures are distributed on the nano-scale fiber filaments, and the membrane material is prepared from raw materials including polyvinylidene fluoride, modified sepiolite and a solvent.
It is understood that the thin film material of the present invention is formed by interweaving nano-scale fiber filaments, and bead-shaped structures are distributed on the nano-scale fiber filaments. On one hand, the nano wire bead-shaped network structure effectively improves the specific surface area and the porosity of the film material, so that the film material has better performance; on the other hand, the film material has excellent heat resistance stability and dimensional stability. Finally, the film material has excellent comprehensive performance.
It can also be understood that the film material of the invention is prepared from raw materials including polyvinylidene fluoride, modified sepiolite and solvent. Polyvinylidene fluoride is the main material of the film material. Sepiolite is a SiO with two tetrahedra layers 2 Non-metallic mineral material of elementary composition having the theoretical formula Mg 8 Si 12 O 30 (OH) 4 (H 2 O) 4 ·8H 2 And O. The sepiolite belongs to a 2:1 type layer chain structure, is formed by connecting a central oxygen atom with a discontinuous oxygen atom octahedron, and can combine molecular chains together due to a Si-O-Si bonded three-dimensional steric bond structure in the sepiolite, so that the crystal form of the sepiolite extends along one direction, and a fibrous or rod-shaped structure is microscopically shown. Due to the unique crystal structures of the sepiolite, the sepiolite has the advantages of excellent adsorbability, high specific surface area, good thermal stability, chemical stability, mechanical stability and the like. The method has wide application in a plurality of fields such as medicine, ceramics, casting, plastics, building and the like. Compared with the common sepiolite, the modified sepiolite in the raw materials for preparing the film material has the effects of dissolving and removing redundant metal impurities in the sepiolite by using an acidic solvent, opening agglomeration of the original sepiolite on a microstructure, recovering the original fiber or rod-shaped structure, better coating and interlacing with polyvinylidene fluoride nano fibers in the subsequent electrostatic spinning process, and finally optimizing the performance of the diaphragm by improving the fiber structure. The addition of the modified sepiolite can further improve the thermal stability and the ionic conductivity of the film material. The solvent is used for dissolving the polyvinylidene fluoride and providing a dispersed carrier for the polyvinylidene fluoride and the modified sepiolite.
In some embodiments of the invention, the mass ratio of the polyvinylidene fluoride to the modified sepiolite is 1.
In some embodiments of the invention, the mass to volume ratio of the polyvinylidene fluoride to the solvent is 10g to 15g.
In some embodiments of the invention, the polyvinylidene fluoride has an average molecular weight of 700 to 900 ten thousand.
In some embodiments of the invention, the polyvinylidene fluoride has an average molecular weight of 800 to 900 ten thousand.
In some embodiments of the invention, the polyvinylidene fluoride has an average molecular weight of 800 ten thousand.
It will be appreciated that solutions formulated with different molecular weights will vary greatly in solubility. Taking polyvinylidene fluoride with average molecular weight of 400 ten thousand or 600 ten thousand as an example, the prepared solution is relatively thin and can not reach the viscosity required by spinning, so that when the molecular weight is too low, more solute needs to be added, and the quantitative solution can not be fully dissolved. And the solution is easily too viscous due to too large molecular weight, so that the needle tube is easily blocked in the spinning process, and 800-900 ten thousand of the solution has proper molecular weight.
In some embodiments of the present invention, the solvent is a mixed solvent of dimethylformamide and acetone.
In particular, dimethylformamide (DMF) has a high dipole constant and moment, and is a good solvent for PVDF, but its volatility is poor. To accelerate the volatilization of the electrospinning dispersion, a small amount of acetone was added to DMF. However, the larger the amount of acetone added, the faster the volatilization speed in electrospinning, resulting in an increase in the viscosity of the spinning solution. This makes it difficult for electrostatic forces to overcome the surface tension of the droplets during drawing, resulting in uneven drawing of the fibers and the bonding of a large number of fibers to form clusters. Thus, the solvent needs to be a mixed solvent of dimethylformamide and acetone.
In some embodiments of the invention, the volume ratio of dimethylformamide to acetone is 7:3.
In other volume ratios, such as 8:2 and 6: for example, under the same conditions (voltage, advancing speed, receiving distance, temperature and humidity), the degree of fiber dispersion 7:3 is the most preferable. 8:2 is susceptible to the appearance of many droplets that do not evaporate into fibers in time because they do not evaporate sufficiently quickly. 6: the volume ratio of 4 is higher because of the larger addition of acetone, and the volatilization speed is higher during electrostatic spinning, so that the viscosity of the spinning solution is increased. This makes it difficult for electrostatic forces to overcome the surface tension of the droplets during drawing, resulting in uneven drawing of the fibers and the bonding of a large number of fibers to form clusters.
PVDF is also soluble in a few solvents such as NMP, TEP and DMAc.
Among them, the NMP solvent has high volatilization temperature, is sensitive to light, has a certain pollution to the environment and is expensive.
TEP has certain toxicity, is stable and not easy to volatilize at normal temperature, and reacts with strong oxidant and strong base.
DMSO is strongly hygroscopic and reacts violently with chlorine.
In some embodiments of the invention, the modified sepiolite is prepared by: heating and stirring sepiolite powder in acid solution, washing and drying.
In some embodiments of the invention, the modified sepiolite is prepared by:
(1) Taking sepiolite powder, fully grinding the sepiolite powder in a grinding bowl, filtering the ground sepiolite powder by using a screen, and collecting the sepiolite powder for later use;
(2) Weighing a proper amount of sepiolite, putting the sepiolite into a container, adding a proper amount of deionized water into the container, slowly stirring to fully disperse the sepiolite, standing until the sepiolite is completely precipitated, and performing suction filtration to take out and dry the precipitate;
(3) Preparing an acid solution, adding the dried sepiolite powder into the acid solution, heating in a water bath, stirring, and performing suction filtration to obtain acid modified sepiolite;
(4) And heating, stirring and washing the obtained acid modified sepiolite with deionized water for several times until the sepiolite is neutral, drying and grinding for later use.
In some embodiments of the invention, in step (1) of the process for preparing modified sepiolite, the mesh number of the screen comprises 200 mesh.
In some embodiments of the present invention, in the step (2) of the preparation method of the modified sepiolite, the stirring includes magnetic stirring, and the stirring is performed until the sepiolite is sufficiently dispersed, and the stirring time may be 12 hours.
In some embodiments of the present invention, in the step (2) of the preparation method of the modified sepiolite, the temperature of drying may be 60 ℃.
In some embodiments of the invention, in step (3) of the process for preparing modified sepiolite, the acidic solution comprises a hydrochloric acid solution.
In some embodiments of the present invention, in the step (3) of the preparation method of the modified sepiolite, the hydrochloric acid solution comprises a 12% by mass hydrochloric acid solution.
In some embodiments of the present invention, in the step (3) of the preparation method of the modified sepiolite, the temperature of the heating water bath stirring may be 80 ℃.
In some embodiments of the present invention, in the step (3) of the preparation method of the modified sepiolite, the stirring time of the heating water bath may be 8 to 12 hours.
In some embodiments of the invention, in the step (4) of the method for preparing the modified sepiolite, after grinding, the particle size of the modified sepiolite is in the range of 2nm to 200nm.
In still other embodiments of the present invention, the present invention provides a method of making a thin film material comprising the steps of:
s1: dissolving polyvinylidene fluoride in a solvent to obtain a sol-gel solution;
s2: adding modified sepiolite into the sol-gel solution, and uniformly dispersing to obtain a modified sol-gel solution;
s3: and (3) carrying out electrostatic spinning on the modified sol-gel solution to obtain the film material.
The preparation method of the thin film material comprises the steps of dissolving polyvinylidene fluoride in a solvent to obtain a sol-gel solution, adding modified sepiolite into the sol-gel solution, dispersing uniformly to obtain a modified sol-gel solution, and finally performing electrostatic spinning on the modified sol-gel solution to obtain the thin film material. The raw materials are easy to obtain, the process is easy to control, expensive equipment is not needed, and the industrial large-scale production is easy to realize. The preparation method of the film material solves the problems that the PVDF diaphragm prepared by the existing electrostatic spinning method has not ideal strength, and the mechanical property and the service life of the diaphragm are influenced.
In some embodiments of the present invention, in step S1, polyvinylidene fluoride is dissolved in a solvent to obtain a mixture, and the mixture is heated at a constant temperature until polyvinylidene fluoride is completely dissolved.
In some embodiments of the present invention, the constant temperature heating temperature in step S1 may be about 60 ℃.
In some embodiments of the present invention, in step S1, the constant temperature heating time may be about 12 hours.
In some embodiments of the present invention, in step S1, the mass volume fraction of the polyvinylidene fluoride in the mixture is 10% to 15%.
In some embodiments of the present invention, in step S2, the modified sepiolite is added to the sol-gel solution, and the mass ratio of the polyvinylidene fluoride to the modified sepiolite is 1:0.5 to 1.5.
In some embodiments of the present invention, in step S2, the uniform dispersion may be achieved by magnetic stirring and ultrasonic vibration.
In some embodiments of the present invention, in step S3, the method of electrospinning is: and (3) loading the modified sol-gel solution into a needle cylinder of electrostatic spinning equipment, and preparing the film material by performing an electrostatic spinning method by regulating and controlling parameters such as solution flow rate, loading voltage between the metal needle and the metal plate, distance between the metal needle and the metal plate and the like.
In some embodiments of the invention, the flow rate of the sol-gel solution during electrospinning is from 0.5mL/h to 1mL/h.
In some embodiments of the present invention, the voltage applied between the metal needle and the metal plate in the electrospinning is 10kV to 20kV.
In some embodiments of the invention, the distance from the metal needle to the metal plate is 10cm to 20cm in electrospinning.
In some embodiments of the present invention, the method for preparing a thin film material further comprises soaking the thin film material in absolute ethanol after step S3, and then drying.
In some embodiments of the present invention, the film material is soaked in absolute ethyl alcohol for 24-48 h.
Dimethylformamide and acetone are both soluble in alcohol, and PVDF is insoluble in alcohol, so that residual dimethylformamide and acetone after spinning can be removed through soaking treatment, and the alcohol is easy to volatilize and treat.
In some embodiments of the present invention, the thin film material is soaked in absolute ethanol and then dried, which may be at a temperature of 50 ℃ to 70 ℃.
In some embodiments of the present invention, the thin film material is soaked in absolute ethanol and then dried, and the drying time can be 24 hours.
In still other embodiments of the present invention, a battery separator is provided, the battery separator being made from a thin film material.
The battery diaphragm is prepared from a thin film material, the thin film material is formed by interweaving nano-scale fiber yarns, and beaded structures are distributed on the nano-scale fiber yarns. On one hand, the nano wire bead-shaped network structure effectively improves the specific surface area and the porosity of the film material, so that the film material has better performance; on the other hand, the film material has excellent heat resistance stability and dimensional stability. Finally, the battery separator has excellent overall properties.
Furthermore, the battery diaphragm provided by the invention comprises polyvinylidene fluoride, modified sepiolite and a solvent. Polyvinylidene fluoride is the main material of the film material. Sepiolite is a SiO with two tetrahedra layers 2 Non-metallic mineral material of elementary composition having the theoretical formula Mg 8 Si 12 O 30 (OH) 4 (H 2 O) 4 ·8H 2 And O. The sepiolite belongs to a 2:1 type layer chain structure, is formed by connecting a central oxygen atom with a discontinuous oxygen atom octahedron, and can combine molecular chains together due to a Si-O-Si bonded three-dimensional steric bond structure in the sepiolite, so that the crystal form of the sepiolite extends along one direction, and a fibrous or rod-shaped structure is microscopically shown. Due to the unique crystal structures of the sepiolite, the sepiolite has the advantages of excellent adsorbability, high specific surface area, good thermal stability, chemical stability, mechanical stability and the like. The method has wide application in a plurality of fields such as medicine, ceramics, casting, plastics, building and the like. Compared with the common sepiolite, the modified sepiolite in the raw material preparation of the thin film material has the effects of dissolving and removing redundant metal impurities in the sepiolite by using an acidic solvent, opening the agglomeration of the original sepiolite on the microstructure, recovering the original fiber or rod-shaped structure, and enabling the original sepiolite to be better in phase with polyvinylidene fluoride nano fibers in the subsequent electrostatic spinning processAnd (4) coating and interlacing, and finally optimizing the performance of the diaphragm by improving the fiber structure. The addition of the modified sepiolite can further improve the thermal stability and the ionic conductivity of the film material. The solvent is used for dissolving the polyvinylidene fluoride and providing a dispersed carrier for the polyvinylidene fluoride and the modified sepiolite. The battery diaphragm prepared by the electrostatic spinning method enables polyvinylidene fluoride and modified sepiolite to be coated or entangled in a fiber state, so that the prepared nanofiber has better mechanical property and thermal stability, and the use safety performance of the battery diaphragm is improved. And due to the special performance of the modified sepiolite inorganic filler, the prepared battery diaphragm has higher ionic conductivity and lower impedance, so that the battery has good cycle performance and higher charge-discharge efficiency.
The technical solution of the present invention will be better understood by referring to the following specific examples.
Example 1
The embodiment prepares a film material, and the specific preparation process comprises the following steps:
taking 1.0g of PVDF powder with the average molecular weight of 8000000, placing the PVDF powder in 10mL of a solvent with the volume ratio of dimethylformamide to acetone being 7:3, heating the PVDF powder in an oil bath stirring pot at a constant temperature of 60 ℃ for 12 hours until the PVDF powder is completely dissolved in the mixed solvent, and preparing a polyvinylidene fluoride sol solution with the mass volume ratio of 10%;
adding modified sepiolite with different contents into a polyvinylidene fluoride sol solution with the mass volume ratio of 10% (PVDF: sepiolite =1: 0.5), magnetically stirring for 24h, and then ultrasonically vibrating for 30min to obtain a modified sol-gel solution;
injecting the modified sol-gel solution into a 5mL medical syringe, wherein the ambient temperature is 30 ℃, the humidity is RH =40%, performing electrostatic spinning in the condition that the equipment parameters are that the solution flow rate is 0.8mL/h, the distance between the metal needle and the metal plate is 10cm, and the voltage between the metal needle and the metal plate is 18.5kV, wherein the spinning time of each film is 4h;
completely immersing the film material prepared by the electrostatic spinning method in absolute ethyl alcohol for 48 hours at room temperature;
and (3) putting the film material fully soaked in the absolute ethyl alcohol into a vacuum drying oven at 60 ℃ for 24h for drying treatment, thus obtaining the film material.
Example 2
The embodiment prepares a film material, and the specific preparation process comprises the following steps:
taking 1.0g of PVDF powder with the average molecular weight of 8000000, placing the PVDF powder in 10mL of a solvent with the volume ratio of dimethylformamide to acetone of 7:3, heating the PVDF powder in an oil bath stirring pot at a constant temperature of 60 ℃ for 12 hours until the PVDF powder is completely dissolved in the mixed solvent, and preparing a polyvinylidene fluoride sol solution with the mass volume ratio of 10%;
adding modified sepiolite with different contents into a polyvinylidene fluoride sol solution with the mass volume ratio of 10 percent, wherein the mass ratio is (PVDF: sepiolite = 1:1), magnetically stirring for 24h, and then ultrasonically vibrating for 30min to obtain a modified sol-gel solution;
injecting the modified sol-gel solution into a 5mL medical syringe, wherein the ambient temperature is 30 ℃, the humidity is RH =40%, performing electrostatic spinning in the condition that the equipment parameters are that the solution flow rate is 0.8mL/h, the distance between the metal needle and the metal plate is 10cm, and the voltage between the metal needle and the metal plate is 18.5kV, wherein the spinning time of each film is 4h;
completely immersing the film material prepared by the electrostatic spinning method in absolute ethyl alcohol for 48 hours at room temperature;
and (3) putting the film material fully soaked in the absolute ethyl alcohol into a vacuum drying oven at 60 ℃ for 24h for drying treatment, thus obtaining the film material.
Example 3
The embodiment prepares a film material, and the specific preparation process comprises the following steps:
taking 1.0g of PVDF powder with the average molecular weight of 8000000, placing the PVDF powder in 10mL of a solvent with the volume ratio of dimethylformamide to acetone of 7:3, heating the PVDF powder in an oil bath stirring pot at a constant temperature of 60 ℃ for 12 hours until the PVDF powder is completely dissolved in the mixed solvent, and preparing a polyvinylidene fluoride sol solution with the mass volume ratio of 10%;
adding modified sepiolite with different contents into a polyvinylidene fluoride sol solution with the mass volume ratio of 10% (PVDF: sepiolite = 1.5), magnetically stirring for 24h, and then ultrasonically vibrating for 30min to obtain a modified sol-gel solution;
injecting the modified sol-gel solution into a 5mL medical syringe, wherein the ambient temperature is 30 ℃, the humidity is RH =40%, performing electrostatic spinning in the condition that the equipment parameters are that the solution flow rate is 0.8mL/h, the distance between the metal needle and the metal plate is 10cm, and the voltage between the metal needle and the metal plate is 18.5kV, wherein the spinning time of each film is 4h;
completely immersing the film material prepared by the electrostatic spinning method in absolute ethyl alcohol for 48 hours at room temperature;
and (3) putting the film material fully soaked in the absolute ethyl alcohol into a vacuum drying oven at 60 ℃ for 24h for drying treatment, thus obtaining the film material.
In examples 1 to 3, the preparation method of the modified sepiolite comprises the following steps:
(1) Taking sepiolite powder, fully grinding the sepiolite powder in a grinding bowl, filtering the ground sepiolite powder by using a screen, and collecting the sepiolite powder for later use;
(2) Weighing a proper amount of sepiolite, putting the sepiolite into a container, adding a proper amount of deionized water into the container, slowly stirring to fully disperse the sepiolite, standing until the sepiolite is completely precipitated, and performing suction filtration to take out and dry the precipitate;
(3) Preparing an acid solution, adding the dried sepiolite powder into the acid solution, heating in a water bath, stirring, and performing suction filtration to obtain acid modified sepiolite;
(4) And heating, stirring and washing the obtained acid modified sepiolite with deionized water for several times until the sepiolite is neutral, drying and grinding for later use.
Wherein, in the step (1), the mesh number of the screen mesh comprises 200 meshes.
In the step (2), the stirring comprises magnetic stirring, and the stirring is carried out until the mixture is fully dispersed, wherein the stirring time is 12 hours.
The drying temperature was 60 ℃.
In the step (3), the acidic solution is a hydrochloric acid solution with a mass fraction of 12%.
In the step (3), the temperature of the heating water bath is 80 ℃.
In the step (3), the heating water bath is stirred for 10 hours.
In the step (4), after grinding, the particle size range of the modified sepiolite is about 100 nm.
Test of
The microscopic morphologies of the thin film materials prepared in examples 1 to 3 were observed by a scanning microscope, as shown in fig. 1 to 3, respectively. It can be seen that the fibers of the film material are coarse, the filaments of the fibers have a plurality of bead-like structures, and the film has a larger specific surface area. As the addition amount of the modified sepiolite is increased, the bead-shaped structure is more obvious and the quantity is more. On one hand, the bead-shaped structure effectively improves the specific surface area and the porosity of the film material, so that when the film material is used for a battery diaphragm, the ionic conductivity of the electrolyte can be improved, and the battery has good cycle performance and higher charge-discharge efficiency; on the other hand, the thin film material has excellent heat resistance stability and dimensional stability, so that when the thin film material is used for a battery separator, the use safety of the battery separator is improved. Finally, the overall performance of the battery is improved.
The film materials prepared in examples 1, 2 and 3, as well as the PVDF film material and sepiolite powder before and after modification were observed by X-ray powder diffraction. The results are shown in FIG. 4. It can be seen from fig. 4 that, after the acid-washed sepiolite modifies the sepiolite, a large amount of impurity metals in the original sepiolite are dissolved and washed away, and it can be also clearly seen from the diffraction peak that the acid-washed sepiolite achieves the expected purpose, and in the subsequent compounding process, the corresponding characteristic peak is continuously enhanced with the increase of the addition amount of the sepiolite, which indicates that the sepiolite is successfully compounded with PVDF.
The thin film materials prepared in examples 1, 2, 3, as well as the PVDF material, were tested by FTIR infrared experiments. The results are shown in FIG. 5. As can be seen from fig. 5, the functional groups corresponding to PVDF and sepiolite can be found clearly in the image, further illustrating the successful combination of sepiolite and PVDF.
Fig. 6 is a graph showing thermal stability tests of the thin film materials prepared in examples 1 to 3 and commercial Celgard thin films and PVDF separator materials. It can be seen from fig. 6 that the commercial Celgard film has obvious polycondensation change and damaged structure as the temperature rises to 160 ℃, the PVDF separator material has slight curl, the separator material added with sepiolite has less change, and the thermal stability is better as the adding amount of sepiolite increases, when the temperature reaches 200 ℃, the commercial Celgard film is almost completely melted, the PVDF separator has serious deformation, and the phenomenon is obviously improved as the sepiolite is added, so that the adding of sepiolite can greatly improve the thermal stability of the separator material.
Fig. 7 is a thermogravimetric TG test plot of the membrane materials prepared in examples 1, 2, 3, as well as commercial Celgard membrane and PVDF separator materials. It can be seen from fig. 7 that the thermal stability of the PVDF separator material is better than that of the commercial Celgard film, and with the addition of sepiolite, the thermal stability is further improved, and the final remaining mass can also correspond to the mass of the added sepiolite, which again indicates that the sepiolite is beneficial to improving the thermal stability of the separator because of its own properties.
Fig. 8 shows the ion conductivity curves of the membrane materials prepared in examples 1 to 3 and the commercial Celgard membrane and PVDF separator materials. The thin film materials prepared in examples 1 to 3 and the commercial Celgard thin film and PVDF separator material are assembled into a steel-steel button cell, the test results are shown in fig. 8, it can be seen from fig. 8 that compared with the commercial Celgard thin film, both PVDF and the composite separator with sepiolite have better performance, the specific parameters are shown in table 1, and the separator performance with 0.5g sepiolite is optimal (reaching 3.52 × 10) -3 ·S·cm -1 Far exceeding commercial Celgard film 0.43X 10 -3 ·S·cm -1 And pure PVDF membrane material 2.1 x 10 -3 ·S·cm -1 ) Although the performance is reduced with the increase of the amount of sepiolite, the sepiolite composite membrane is better than a pure PVDF membrane as a whole, which shows that the addition of sepiolite is beneficial to promoting the ion shuttling in the electrolyte so as to have higher ion conductivity, but the reason that the performance is reduced with the increase of the addition amount of sepiolite can be explained as that the PVDF cannot be completely coated by the excessive sepiolite composite membrane so as to influence the structure of the nanofiber, and the sepiolite composite membrane plays a certain role in hindering the lithium ion shuttling and finally causes the reduction of the ion conductivity.
TABLE 1
| Test specimen | R b | h(cm) | σ(S·cm -1 ) |
| Celgard diaphragm | 2.9 | 0.0025 | 0.43×10 -3 |
| PVDF film | 1.55 | 0.00654 | 2.1×10 -3 |
| Film of example 1 | 1.33 | 0.00942 | 3.52×10 -3 |
| Film of example 2 | 1.50 | 0.00832 | 2.76×10 -3 |
| Film of example 3 | 1.65 | 0.00642 | 1.94×10 -3 |
Fig. 9 is an LSV curve of the membrane materials prepared in examples 1 to 3 and commercial Celgard membrane and PVDF separator materials.
The film materials prepared in examples 1 to 3, the commercial Celgard film and the PVDF separator material are assembled into a lithium-steel button cell, and the test results are shown in fig. 9, and it can be seen from fig. 9 that the test results of the button cell prepared by using the film materials prepared in examples 1 to 3, the commercial Celgard film and the PVDF separator material are all greater than 4.2V, which indicates that the prepared separator material has excellent electrochemical stability and meets the use standard of the lithium ion battery.
Fig. 10 is a CV curve of the separator of example 1, and as can be seen from fig. 10, the images of the first three circles are substantially completely overlapped, which shows that the separator material has excellent reversible cycling performance and is beneficial to long cycling of the battery.
FIG. 11 is a graph showing the cycle performance of the film material prepared in example 1 after being assembled into a button cell. As can be seen in fig. 11. After 130 cycles at 0.5C rate, the capacity of the button cell assembled by the film material prepared in example 1 is almost not attenuated, and the button cell has high coulombic efficiency, which shows that the film material prepared in example 1 has excellent long cycle performance, and further shows that the high ionic conductivity and the high electrochemical stability are beneficial to long cycle of the cell, and the service life of the cell is prolonged.
Fig. 12 is a graph of long cycle and coulombic efficiency after assembly of the film material prepared in example 1 and commercial Celgard film and PVDF film materials into button cells. As can be seen from fig. 12, the PVDF separator is due to the commercial Celgard film in terms of capacity release, but the structure is not very stable, the performance is seriously reduced after a certain period of cycle, and the long cycle performance is poor, and the problem can be obviously improved by adding sepiolite, as shown in fig. 12, the long cycle performance of the battery is greatly improved on the premise of maintaining high capacity release, and the sepiolite also has very high coulombic efficiency, and it is again explained that the addition of sepiolite is beneficial to further improving various performances of the PVDF separator, so that the battery performance is improved, and the battery life is prolonged.
In the above test, the thicknesses of the Celgard separator, the PVDF membrane, and the films prepared in examples 1 to 3 were the same, and were all about 80 μm.
The present invention has been described in detail with reference to the embodiments, but the present invention is not limited to the embodiments described above, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present invention.
Claims (10)
1. The thin film material is characterized by being formed by interweaving nano-scale fiber filaments, bead structures are distributed on the nano-scale fiber filaments, and raw materials for preparing the thin film material comprise polyvinylidene fluoride, modified sepiolite and a solvent.
2. The film material according to claim 1, wherein the mass ratio of the polyvinylidene fluoride to the modified sepiolite is 1.
3. The film material according to claim 1, wherein the mass-to-volume ratio of the polyvinylidene fluoride to the solvent is 10g to 15g.
4. A film material according to any one of claims 1 to 3, wherein said solvent is a mixed solvent of dimethylformamide and acetone.
5. A membrane material according to any one of claims 1 to 3, wherein the modified sepiolite is prepared by: heating and stirring sepiolite powder in acid solution, washing and drying.
6. A method of preparing a film material according to any one of claims 1 to 5, comprising the steps of:
s1: dissolving the polyvinylidene fluoride in the solvent to obtain a sol-gel solution;
s2: adding the modified sepiolite into the sol-gel solution, and uniformly dispersing to obtain a modified sol-gel solution;
s3: and (3) carrying out electrostatic spinning on the modified sol-gel solution to obtain the film material.
7. The method according to claim 6, wherein the flow rate of the sol-gel solution in the electrospinning is 0.5 to 1mL/h.
8. The method of claim 6, wherein the electrostatic spinning is carried out at a voltage of 10kV to 20kV from the metal needle to the metal plate.
9. The method of claim 6, wherein the distance from the metal needle to the metal plate in said electrospinning is 10cm to 20cm.
10. A battery separator prepared from the thin film material of any one of claims 1 to 5.
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