A thin film material and its preparation method and application

Abstract

The present invention provides a thin film material, a preparation method and an application thereof. The thin film material of the present invention is formed by interweaving nanoscale fiber filaments, on which bead-like structures are distributed, and the raw materials for preparing the thin film material include polyvinylidene fluoride, modified sepiolite and a solvent. The thin film material is formed by interweaving nanoscale fiber filaments, on which bead-like structures are distributed, which, on the one hand, effectively improves the specific surface area and porosity of the thin film material, thereby improving the performance of the thin film material; on the other hand, the thin film material has excellent heat resistance stability and dimensional stability. Finally, the thin film material has excellent comprehensive performance. The present invention also provides a preparation method and an application of the thin film material.

Description

Technical Field

[0001] The invention belongs to the technical field of film material preparation, and in particular relates to a film material and a preparation method and application thereof. Background Art

[0002] The battery separator is an important component of lithium-ion batteries. Its main functions are: (1) to isolate the positive and negative electrodes of the battery so that electrons inside the battery cannot pass freely and prevent short circuits; (2) to allow lithium ions in the electrolyte to pass through the micropores of the separator and transfer freely between the positive and negative electrodes, ensuring that the electrochemical reaction of the battery proceeds in an orderly and reversible manner. The structure and performance of the battery separator directly affect the capacity, cycle performance and safety performance of the battery.

[0003] With the growing 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. Nanostructured battery separators have the advantages of high surface-to-volume ratio, high porosity and short ion diffusion distance, which can improve ion transmission efficiency, battery capacity and energy density. Currently, the more commonly used methods for preparing nanostructured battery separators are melt-blowing, wet method, vacuum filtration method and electrospinning method.

[0004] In the meltblowing method, high temperature and air flow velocity can cause fiber instability and dispersion of particles in the fiber web. The wet method requires that the polymer precursor first forms fibers in a liquid suspension, and then a binder is added to the matrix fiber, and the fibers are bonded by heat treatment and pressurization. However, the final fiber structure and performance are mainly limited by the type and composition of the polymer in the precursor suspension. The vacuum filtration method for preparing nanofiber membranes also requires the preparation of a suspension containing polymer fiber precursors, and with the help of vacuum filtration, the fiber web is formed on the filter paper. Since it is difficult to obtain uniform vacuum force on a larger surface, the size of the membrane produced by the vacuum filtration method is limited. The electrospinning method can prepare nanofibers quickly and efficiently, and can control the size of the fiber structure. It is also very simple to operate and easy to use. It is an excellent nanofiber preparation method that has emerged.

[0005] At present, the most commonly used commercial separators on the market are polyolefin separators. However, polyolefin separators have disadvantages such as low porosity, poor electrolyte wettability, and severe dimensional shrinkage at high temperatures, which makes it difficult to meet the needs of high-performance power lithium batteries. The non-woven fiber membranes prepared by electrospinning technology, which has emerged in recent years, have attracted widespread attention from researchers due to their high porosity, large specific surface area, and excellent electrochemical properties.

[0006] Polyvinylidene fluoride (PVDF) is a popular substrate commonly used to prepare diaphragm materials. Compared with polyolefins and other materials, PVDF has a relative dielectric constant of up to 8.3, which can weaken the interaction between ion pairs. It is more conducive to the dissociation of lithium. In addition, polyolefin diaphragm materials have high crystallinity and low polarity, while electrolytes are highly polar organic solvents. Therefore, the surface energy of polyolefin diaphragms is low, and their affinity with electrolytes is poor. They cannot be fully swollen by electrolytes. Most electrolytes exist in pores and are prone to leakage. In contrast, PVDF has high polarity and good affinity for electrolytes. It can fully absorb electrolytes to prevent leakage. In addition, PVDF as an electrolyte has some ideal properties: such as (1) both mechanical strength and toughness; (2) wide voltage window; (3) good thermal stability, non-combustibility, long-term working temperature up to 150°C, decomposition temperature up to 400°C; (4) high electrochemical stability, no adverse reactions with other materials; (5) good processing performance and other excellent characteristics.

[0007] However, the strength of the existing PVDF membrane prepared by electrospinning is not ideal, which affects the mechanical properties and service life of the membrane. Summary of the invention

[0008] The present invention aims to solve at least one of the above technical problems existing in the prior art. To this end, the present invention provides a thin film material having good strength and mechanical properties, and having better performance and service life when used in battery separators and the like.

[0009] The invention also provides a method for preparing the thin film material.

[0010] The invention also provides a battery separator.

[0011] A first aspect of the present invention provides a thin film material, which is formed by interweaving nano-scale fiber filaments, on which bead structures are distributed, and the raw materials for preparing the thin film material include polyvinylidene fluoride, modified sepiolite and a solvent.

[0012] One of the technical solutions of the present invention regarding the thin film material has at least the following beneficial effects:

[0013] The film material of the present invention is formed by interweaving nano-scale fiber filaments, and bead structures are distributed on the nano-scale fiber filaments. The nano-scale bead network structure, on the one hand, effectively increases the specific surface area and porosity of the film material, so that the performance of the film material is better; on the other hand, the film material has excellent heat resistance stability and dimensional stability. Finally, the film material has excellent comprehensive performance.

[0014] The thin film material of the present invention is prepared from raw materials including polyvinylidene fluoride, modified sepiolite and solvent. Polyvinylidene fluoride is the main material of the thin film material. Sepiolite is a non-metallic mineral material composed of two layers of tetrahedral SiO2 units, and its theoretical molecular formula is Mg8Si 12 O 30 (OH)4(H2O)4·8H2O. Sepiolite has a 2:1 layered chain structure, consisting of a central oxygen atom and a layer of discontinuous oxygen atom octahedrons. The Si-O-Si three-dimensional bond structure in sepiolite can combine the molecular chains together, making its crystal form elongated in one direction, so it presents a fibrous or rod-like structure under the microscopic view. Due to these unique crystal structures of sepiolite, it has excellent adsorption, high specific surface area, good thermal stability, chemical stability and mechanical stability. It has a wide range of applications in medicine, ceramics, casting, plastics, construction and other fields. The film material of the present invention is prepared from the modified sepiolite in the raw material. Compared with the ordinary sepiolite, the modified sepiolite uses an acidic solvent to dissolve and remove the excess metal impurities in the sepiolite, and can make the original sepiolite open the agglomeration in the microstructure, so that it can restore the original fiber or rod-like structure, so that it can better coat and entangle with the polyvinylidene fluoride nanofibers in the subsequent electrostatic spinning process, and finally optimize the performance of the diaphragm by improving the fiber structure. The addition of the modified sepiolite can further improve the thermal stability and ionic conductivity of the film material. The role of the solvent is to dissolve the polyvinylidene fluoride and provide a dispersed carrier for the polyvinylidene fluoride and the modified sepiolite.

[0015] According to some embodiments of the present invention, the mass ratio of the polyvinylidene fluoride to the modified sepiolite is 1:0.5-2.

[0016] According to some embodiments of the present invention, the mass volume ratio of the polyvinylidene fluoride and the solvent is 10 g to 15 g:100 mL.

[0017] According to some embodiments of the present invention, the average molecular weight of the polyvinylidene fluoride is 7 million to 9 million.

[0018] According to some embodiments of the present invention, the average molecular weight of the polyvinylidene fluoride is 8 million to 9 million.

[0019] According to some embodiments of the present invention, the average molecular weight of the polyvinylidene fluoride is 8 million.

[0020] The solubility of the solution prepared with different molecular weights will be very different. Taking polyvinylidene fluoride with an average molecular weight of 4 million or 6 million as an example, the prepared solution will be relatively thin and cannot reach the viscosity required for spinning. Therefore, if the molecular weight is too small, more solutes need to be added, which will cause the quantitative solution to be unable to fully dissolve. If the molecular weight is too large, the solution will be too viscous, which will easily clog the needle during the spinning process. Therefore, 8 million to 9 million is the appropriate molecular weight.

[0021] According to some embodiments of the present invention, the solvent is a mixed solvent of dimethylformamide and acetone.

[0022] Dimethylformamide (N,N-Dimethylformamide, referred to as DMF) has a high dipole constant and dipole moment and is a good solvent for PVDF, but its volatility is poor. In order to accelerate the volatilization of the electrospinning dispersant, a small amount of acetone needs to be added to DMF. However, the greater 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 the electrostatic force to overcome the surface tension of the droplets during the drawing process, resulting in uneven fiber drawing and a large number of fibers combining to form clusters. Therefore, the solvent needs to be a mixed solvent of dimethylformamide and acetone.

[0023] According to some embodiments of the invention, the volume ratio of dimethylformamide to acetone is 7:3.

[0024] Taking other volume ratios, such as 8:2 and 6:4, as examples, under the same conditions (voltage, propulsion speed, receiving distance, temperature and humidity), the fiber dispersion degree of 7:3 is optimal. The volume ratio of 8:2 is prone to many droplets that cannot evaporate into fibers in time due to insufficient evaporation. The volume ratio of 6:4 will increase the viscosity of the spinning solution due to the large amount of acetone added and the fast evaporation rate during electrospinning. This makes it difficult for the electrostatic force to overcome the surface tension of the droplets during the drawing process, resulting in uneven fiber drawing and a large number of fibers combining to form clusters.

[0025] PVDF is also soluble in a few solvents, such as NMP, TEP and DMAc.

[0026] Among them, NMP solvent has a high evaporation temperature, is sensitive to light, has certain pollution to the environment and is expensive.

[0027] TEP has certain toxicity, is stable and non-volatile at room temperature, and reacts with strong oxidants and strong bases.

[0028] DMSO is highly hygroscopic and reacts violently with chlorine.

[0029] According to some embodiments of the present invention, the preparation method of the modified sepiolite is: heating and stirring the sepiolite powder in an acid solution, and then washing and drying it.

[0030] According to some embodiments of the present invention, the preparation method of the modified sepiolite is:

[0031] (1) taking sepiolite powder and grinding it thoroughly in a grinding mortar, filtering the ground sepiolite powder through a sieve, and collecting it for later use;

[0032] (2) Then weigh an appropriate amount of sepiolite and put it into a container, add an appropriate amount of deionized water into the container, slowly stir to fully disperse it, let it stand until it is completely precipitated, and then filter out the precipitate and dry it;

[0033] (3) preparing an acidic solution, placing the dried sepiolite powder into the acidic solution, stirring in a heated water bath, and filtering to obtain acid-modified sepiolite;

[0034] (4) The obtained acid-modified sepiolite is heated, stirred and washed with deionized water for several times until it becomes neutral, dried, ground and set aside.

[0035] According to some embodiments of the present invention, in step (1) of the method for preparing modified sepiolite, the mesh size of the sieve is 200 meshes.

[0036] According to some embodiments of the present invention, in step (2) of the method for preparing modified sepiolite, stirring includes magnetic stirring, and stirring is performed until the material is fully dispersed, and the stirring time may be 12 hours.

[0037] According to some embodiments of the present invention, in step (2) of the method for preparing modified sepiolite, the drying temperature may be 60°C.

[0038] According to some embodiments of the present invention, in step (3) of the method for preparing modified sepiolite, the acidic solution comprises a hydrochloric acid solution.

[0039] According to some embodiments of the present invention, in step (3) of the method for preparing modified sepiolite, the hydrochloric acid solution comprises a hydrochloric acid solution with a mass fraction of 12%.

[0040] According to some embodiments of the present invention, in step (3) of the method for preparing modified sepiolite, the temperature of the heated water bath stirring may be 80°C.

[0041] According to some embodiments of the present invention, in step (3) of the method for preparing modified sepiolite, the stirring time in the heated water bath can be 8 h to 12 h.

[0042] According to some embodiments of the present invention, in step (4) of the method for preparing the modified sepiolite, after grinding, the particle size of the modified sepiolite is in the range of 2 nm to 200 nm.

[0043] The second aspect of the present invention provides a method for preparing the thin film material, comprising the following steps:

[0044] S1: dissolving the polyvinylidene fluoride in the solvent to obtain a sol-gel solution;

[0045] S2: adding the modified sepiolite to the sol-gel solution and dispersing the modified sepiolite uniformly to obtain a modified sol-gel solution;

[0046] S3: electrospinning the modified sol-gel solution to obtain the thin film material.

[0047] A technical solution in the method for preparing a thin film material of the present invention has at least the following beneficial effects:

[0048] The method for preparing the thin film material of the present invention comprises the following steps: first dissolving the polyvinylidene fluoride in the solvent to obtain a sol-gel solution, then adding the modified sepiolite to the sol-gel solution to obtain a modified sol-gel solution after uniform dispersion, and finally electrospinning the modified sol-gel solution to obtain the thin film material. The raw materials are readily available, the process is easily controlled, no expensive equipment is required, and industrial large-scale production is easy. The method for preparing the thin film material of the present invention solves the problem that the strength of the PVDF diaphragm prepared by the existing electrospinning method is not ideal, which affects the mechanical properties and service life of the diaphragm.

[0049] According to some embodiments of the present 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.

[0050] According to some embodiments of the present invention, in step S1, the temperature of the constant temperature heating may be about 60°C.

[0051] According to some embodiments of the present invention, in step S1, the constant temperature heating time may be about 12 hours.

[0052] According to some embodiments of the present invention, in step S1, the mass volume fraction of polyvinylidene fluoride in the mixture is 10%-15%.

[0053] According to some embodiments of the present invention, in step S2, the modified sepiolite is added to the sol-gel solution, and the mass ratio of polyvinylidene fluoride to modified sepiolite is 1:0.5-1.5.

[0054] According to some embodiments of the present invention, in step S2, uniform dispersion can be achieved by magnetic stirring and ultrasonic oscillation.

[0055] According to some embodiments of the present invention, in step S3, the electrospinning method is: loading the modified sol-gel solution into the syringe of the electrospinning equipment, and preparing the thin film material by electrospinning by adjusting parameters such as the solution flow rate, the loading voltage between the metal needle and the metal plate, and the distance between the metal needle and the metal plate.

[0056] According to some embodiments of the present invention, in the electrospinning, the flow rate of the sol-gel solution is 0.5 mL / h to 1 mL / h.

[0057] According to some embodiments of the present invention, in the electrospinning, the loading voltage between the metal needle and the metal plate is 10 kV to 20 kV.

[0058] According to some embodiments of the present invention, in the electrospinning, the distance from the metal needle to the metal plate is 10 cm to 20 cm.

[0059] 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 anhydrous ethanol and then drying it.

[0060] According to some embodiments of the present invention, the thin film material is immersed in anhydrous ethanol for 24 to 48 hours.

[0061] Both dimethylformamide and acetone are soluble in alcohol, but PVDF is insoluble in alcohol. The dimethylformamide and acetone remaining after spinning can be removed by soaking treatment, and alcohol is easy to volatilize and easy to handle.

[0062] According to some embodiments of the present invention, the thin film material is immersed in anhydrous ethanol and then dried. The drying temperature may be 50°C to 70°C.

[0063] According to some embodiments of the present invention, the film material is immersed in anhydrous ethanol and then dried. The drying time may be 24 hours.

[0064] A third aspect of the present invention provides a battery separator, which is prepared from the thin film material.

[0065] One of the technical solutions of the present invention regarding the battery separator has at least the following beneficial effects:

[0066] The battery separator of the present invention is prepared from the thin film material, and the thin film material is formed by interweaving nano-scale fiber filaments, and a bead structure is distributed on the nano-scale fiber filaments. The nano-scale bead network structure, on the one hand, effectively increases the specific surface area and porosity of the thin film material, so that the performance of the thin film material is better; on the other hand, the thin film material has excellent heat resistance stability and dimensional stability. Finally, the battery separator has excellent comprehensive performance.

[0067] The battery separator of the present 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 non-metallic mineral material composed of two layers of tetrahedral SiO2 units, and its theoretical molecular formula is Mg8Si 12 O 30 (OH)4(H2O)4·8H2O. Sepiolite has a 2:1 layered chain structure, consisting of a central oxygen atom and a layer of discontinuous oxygen atom octahedrons. The Si-O-Si three-dimensional bond structure in sepiolite can combine the molecular chains together, making its crystal form elongated in one direction, so it presents a fibrous or rod-like structure under the microscopic view. Due to these unique crystal structures of sepiolite, it has excellent adsorption, high specific surface area, good thermal stability, chemical stability and mechanical stability. It has a wide range of applications in medicine, ceramics, casting, plastics, construction and other fields. The film material of the present invention is used to prepare the modified sepiolite in the raw material. Compared with ordinary sepiolite, the modified sepiolite uses an acidic solvent to dissolve and remove excess metal impurities in the sepiolite, and can open the agglomeration of the original sepiolite in the microstructure, so that it can restore its original fiber or rod-like structure, so that it can better coat and entangle with the polyvinylidene fluoride nanofibers in the subsequent electrostatic spinning process, and finally optimize the performance of the diaphragm by improving the fiber structure. The addition of modified sepiolite can further improve the thermal stability and ionic conductivity of the film material. The role of the solvent is to dissolve polyvinylidene fluoride and provide a dispersed carrier for polyvinylidene fluoride and modified sepiolite. The battery diaphragm prepared by the electrostatic spinning method causes polyvinylidene fluoride and modified sepiolite to be coated or entangled in the fiber state, so that the prepared nanofibers have better mechanical properties and better thermal stability, thereby improving the safety performance of the battery diaphragm. And due to the unique properties of the modified sepiolite inorganic filler, the prepared battery separator has higher ion conductivity and lower impedance, so that the battery has good cycle performance and higher charge and discharge efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 This is a microscopic morphology of the thin film material prepared in Example 1.

[0069] Figure 2This is a microscopic morphology of the thin film material prepared in Example 2.

[0070] Figure 3 This is a microscopic morphology of the thin film material prepared in Example 3.

[0071] Figure 4 These are the X-ray diffraction test results of the film materials prepared in Examples 1 to 3, pure PVDF film materials, and sepiolite powders before and after modification.

[0072] Figure 5 FTIR graphs of the thin film materials and PVDF diaphragm materials prepared in Examples 1 to 3 are shown.

[0073] Figure 6 It is a thermal stability test chart of the film materials prepared in Examples 1 to 3 and the commercial Celgard film and PVDF diaphragm materials.

[0074] Figure 7 The thermogravimetric TG test graphs of the film materials prepared in Examples 1 to 3 and the commercial Celgard film and PVDF diaphragm materials are shown in FIG.

[0075] Figure 8 The ionic conductivity curves of the thin film materials prepared in Examples 1 to 3 and the commercial Celgard film and PVDF separator materials are shown in FIG.

[0076] Fig. 9 The LSV curves of the film materials prepared in Examples 1 to 3 and the commercial Celgard film and PVDF separator materials are shown in FIG.

[0077] Fig.10 This is the CV curve of the thin film material prepared in Example 1.

[0078] Fig.11 This is a test chart of the cycle performance of a button battery after the thin film material prepared in Example 1 is assembled into a button battery.

[0079] Fig.12 The long cycle and efficiency diagram of the thin film material prepared in Example 1 and the commercial Celgard film and PVDF film materials after being assembled into button batteries. DETAILED DESCRIPTION

[0080] The following are specific embodiments of the present invention, and the technical solutions of the present invention are further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0081] In some embodiments of the present invention, the present invention provides a thin film material, which is formed by interweaving nano-scale fiber filaments, on which bead structures are distributed, and the raw materials for preparing the thin film material include polyvinylidene fluoride, modified sepiolite and a solvent.

[0082] It can be understood that the film material of the present invention is formed by interweaving nano-scale fiber filaments, and bead structures are distributed on the nano-scale fiber filaments. The nano-scale bead network structure, on the one hand, effectively increases the specific surface area and porosity of the film material, so that the performance of the film material is better; on the other hand, the film material has excellent heat resistance stability and dimensional stability. Finally, the film material has excellent comprehensive performance.

[0083] It can also be understood that the thin film material of the present invention is prepared from raw materials including polyvinylidene fluoride, modified sepiolite and solvent. Polyvinylidene fluoride is the main material of the thin film material. Sepiolite is a non-metallic mineral material composed of two layers of tetrahedral SiO2 units, and its theoretical molecular formula is Mg8Si 12 O 30 (OH)4(H2O)4·8H2O. Sepiolite has a 2:1 layered chain structure, consisting of a central oxygen atom and a layer of discontinuous oxygen atom octahedrons. The Si-O-Si three-dimensional bond structure in sepiolite can combine the molecular chains together, making its crystal form elongated in one direction, so it presents a fibrous or rod-like structure under the microscopic view. Due to these unique crystal structures of sepiolite, it has excellent adsorption, high specific surface area, good thermal stability, chemical stability and mechanical stability. It has a wide range of applications in medicine, ceramics, casting, plastics, construction and other fields. The film material of the present invention is prepared from the modified sepiolite in the raw material. Compared with the ordinary sepiolite, the modified sepiolite uses an acidic solvent to dissolve and remove the excess metal impurities in the sepiolite, and can make the original sepiolite open the agglomeration in the microstructure, so that it can restore the original fiber or rod-like structure, so that it can better coat and entangle with the polyvinylidene fluoride nanofibers in the subsequent electrostatic spinning process, and finally optimize the performance of the diaphragm by improving the fiber structure. The addition of the modified sepiolite can further improve the thermal stability and ionic conductivity of the film material. The role of the solvent is to dissolve the polyvinylidene fluoride and provide a dispersed carrier for the polyvinylidene fluoride and the modified sepiolite.

[0084] In some embodiments of the present invention, the mass ratio of polyvinylidene fluoride to modified sepiolite is 1:0.5-2.

[0085] In some embodiments of the present invention, the mass volume ratio of polyvinylidene fluoride to solvent is 10 g to 15 g:100 mL.

[0086] In some embodiments of the present invention, the average molecular weight of polyvinylidene fluoride is 7 million to 9 million.

[0087] In some embodiments of the present invention, the average molecular weight of polyvinylidene fluoride is 8 million to 9 million.

[0088] In some embodiments of the present invention, the average molecular weight of polyvinylidene fluoride is 8 million.

[0089] It is understandable that the solubility of solutions prepared with different molecular weights will be very different. Taking polyvinylidene fluoride with an average molecular weight of 4 million or 6 million as an example, the prepared solution will be relatively thin and cannot reach the viscosity required for spinning. Therefore, if the molecular weight is too small, more solutes need to be added, which will cause the quantitative solution to be unable to fully dissolve. If the molecular weight is too large, the solution will be too viscous, which will easily clog the needle during the spinning process. Therefore, 8 million to 9 million is the appropriate molecular weight.

[0090] In some embodiments of the present invention, the solvent is a mixed solvent of dimethylformamide and acetone.

[0091] Specifically, dimethylformamide (N,N-Dimethylformamide, referred to as DMF) has a high dipole constant and dipole moment and is a good solvent for PVDF, but its volatility is poor. In order to accelerate the volatilization of the electrospinning dispersant, a small amount of acetone needs to be added to DMF. However, the greater 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 the electrostatic force to overcome the surface tension of the droplets during the drawing process, resulting in uneven fiber drawing and a large number of fibers combining to form clusters. Therefore, the solvent needs to be a mixed solvent of dimethylformamide and acetone.

[0092] In some embodiments of the present invention, the volume ratio of dimethylformamide to acetone is 7:3.

[0093] Taking other volume ratios, such as 8:2 and 6:4, as examples, under the same conditions (voltage, propulsion speed, receiving distance, temperature and humidity), the fiber dispersion degree of 7:3 is optimal. The volume ratio of 8:2 is prone to many droplets that cannot evaporate into fibers in time due to insufficient evaporation. The volume ratio of 6:4 will increase the viscosity of the spinning solution due to the large amount of acetone added and the fast evaporation rate during electrospinning. This makes it difficult for the electrostatic force to overcome the surface tension of the droplets during the drawing process, resulting in uneven fiber drawing and a large number of fibers combining to form clusters.

[0094] PVDF is also soluble in a few solvents, such as NMP, TEP and DMAc.

[0095] Among them, NMP solvent has a high evaporation temperature, is sensitive to light, has certain pollution to the environment and is expensive.

[0096] TEP has certain toxicity, is stable and non-volatile at room temperature, and reacts with strong oxidants and strong bases.

[0097] DMSO is highly hygroscopic and reacts violently with chlorine.

[0098] In some embodiments of the present invention, the preparation method of the modified sepiolite is: heating and stirring the sepiolite powder in an acid solution, and then washing and drying.

[0099] In some embodiments of the present invention, the preparation method of modified sepiolite is:

[0100] (1) taking sepiolite powder and grinding it thoroughly in a grinding mortar, filtering the ground sepiolite powder through a sieve, and collecting it for later use;

[0101] (2) Then weigh an appropriate amount of sepiolite and put it into a container, add an appropriate amount of deionized water into the container, slowly stir to fully disperse it, let it stand until it is completely precipitated, and then filter out the precipitate and dry it;

[0102] (3) preparing an acidic solution, placing the dried sepiolite powder into the acidic solution, stirring in a heated water bath, and filtering to obtain acid-modified sepiolite;

[0103] (4) The obtained acid-modified sepiolite is heated, stirred and washed with deionized water for several times until it becomes neutral, dried, ground and set aside.

[0104] In some embodiments of the present invention, in step (1) of the method for preparing modified sepiolite, the mesh size of the sieve is 200 meshes.

[0105] In some embodiments of the present invention, in step (2) of the method for preparing modified sepiolite, stirring includes magnetic stirring, and stirring is performed until the mixture is fully dispersed, and the stirring time may be 12 hours.

[0106] In some embodiments of the present invention, in step (2) of the method for preparing modified sepiolite, the drying temperature may be 60°C.

[0107] In some embodiments of the present invention, in step (3) of the method for preparing modified sepiolite, the acidic solution comprises a hydrochloric acid solution.

[0108] In some embodiments of the present invention, in step (3) of the method for preparing modified sepiolite, the hydrochloric acid solution comprises a hydrochloric acid solution with a mass fraction of 12%.

[0109] In some embodiments of the present invention, in step (3) of the method for preparing modified sepiolite, the temperature of the heated water bath stirring may be 80°C.

[0110] In some embodiments of the present invention, in step (3) of the method for preparing modified sepiolite, the stirring time in the heated water bath can be 8 h to 12 h.

[0111] In some embodiments of the present invention, in step (4) of the method for preparing modified sepiolite, after grinding, the particle size of the modified sepiolite is in the range of 2 nm to 200 nm.

[0112] In some other embodiments of the present invention, the present invention provides a method for preparing a thin film material, comprising the following steps:

[0113] S1: dissolving polyvinylidene fluoride in a solvent to obtain a sol-gel solution;

[0114] S2: adding modified sepiolite to the sol-gel solution and dispersing the modified sepiolite uniformly to obtain a modified sol-gel solution;

[0115] S3: electrospinning the modified sol-gel solution to obtain a thin film material.

[0116] It can be understood that the preparation method of the film material of the present invention is to first dissolve polyvinylidene fluoride in a solvent to obtain a sol-gel solution, then add modified sepiolite to the sol-gel solution, and obtain a modified sol-gel solution after uniform dispersion, and finally electrospin the modified sol-gel solution to obtain a film material. The raw materials are easy to obtain, the process is easy to control, no expensive equipment is required, and it is easy to industrialize and mass produce. The preparation method of the film material of the present invention solves the problem that the strength of the PVDF diaphragm prepared by the existing electrospinning method is not ideal, which affects the mechanical properties and service life of the diaphragm.

[0117] 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 the polyvinylidene fluoride is completely dissolved.

[0118] In some embodiments of the present invention, in step S1, the temperature of the constant temperature heating may be about 60°C.

[0119] In some embodiments of the present invention, in step S1, the constant temperature heating time may be about 12 hours.

[0120] In some embodiments of the present invention, in step S1, the mass volume fraction of polyvinylidene fluoride in the mixture is 10%-15%.

[0121] In some embodiments of the present invention, in step S2, modified sepiolite is added to the sol-gel solution, and the mass ratio of polyvinylidene fluoride to modified sepiolite is 1:0.5-1.5.

[0122] In some embodiments of the present invention, in step S2, uniform dispersion can be achieved by magnetic stirring and ultrasonic vibration.

[0123] In some embodiments of the present invention, in step S3, the electrospinning method is: loading the modified sol-gel solution into the syringe of the electrospinning equipment, and preparing the thin film material by electrospinning by adjusting parameters such as the solution flow rate, the loading voltage between the metal needle and the metal plate, and the distance between the metal needle and the metal plate.

[0124] In some embodiments of the present invention, during electrospinning, the flow rate of the sol-gel solution is 0.5 mL / h to 1 mL / h.

[0125] In some embodiments of the present invention, during electrospinning, the voltage applied between the metal needle and the metal plate is 10 kV to 20 kV.

[0126] In some embodiments of the present invention, in electrospinning, the distance from the metal needle to the metal plate is 10 cm to 20 cm.

[0127] In 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 anhydrous ethanol and then drying it.

[0128] In some embodiments of the present invention, the film material is immersed in anhydrous ethanol for 24 to 48 hours.

[0129] Both dimethylformamide and acetone are soluble in alcohol, but PVDF is insoluble in alcohol. The dimethylformamide and acetone remaining after spinning can be removed by soaking treatment, and alcohol is easy to volatilize and easy to handle.

[0130] In some embodiments of the present invention, the film material is immersed in anhydrous ethanol and then dried. The drying temperature may be 50° C. to 70° C.

[0131] In some embodiments of the present invention, the film material is immersed in anhydrous ethanol and then dried. The drying time may be 24 hours.

[0132] In some other embodiments of the present invention, the present invention provides a battery separator, which is prepared from a thin film material.

[0133] The battery separator of the present invention is prepared from a thin film material, and the thin film material is formed by interweaving nano-scale fiber filaments, and a bead structure is distributed on the nano-scale fiber filaments. The nano-scale bead network structure, on the one hand, effectively increases the specific surface area and porosity of the thin film material, so that the performance of the thin film material is better; on the other hand, the thin film material has excellent heat resistance stability and dimensional stability. Finally, the battery separator has excellent comprehensive performance.

[0134] Furthermore, the raw materials for preparing the battery separator of the present invention include polyvinylidene fluoride, modified sepiolite and solvent. Polyvinylidene fluoride is the main material of the film material. Sepiolite is a non-metallic mineral material composed of two layers of tetrahedral SiO2 units, and its theoretical molecular formula is Mg8Si 12 O 30(OH)4(H2O)4·8H2O. Sepiolite has a 2:1 layered chain structure, consisting of a central oxygen atom and a layer of discontinuous oxygen atom octahedrons. The Si-O-Si three-dimensional bond structure in sepiolite can combine the molecular chains together, making its crystal form elongated in one direction, so it presents a fibrous or rod-like structure under the microscopic view. Due to these unique crystal structures of sepiolite, it has excellent adsorption, high specific surface area, good thermal stability, chemical stability and mechanical stability. It has a wide range of applications in medicine, ceramics, casting, plastics, construction and other fields. The film material of the present invention is used to prepare the modified sepiolite in the raw material. Compared with ordinary sepiolite, the modified sepiolite uses an acidic solvent to dissolve and remove excess metal impurities in the sepiolite, and can open the agglomeration of the original sepiolite in the microstructure, so that it can restore its original fiber or rod-like structure, so that it can better coat and entangle with the polyvinylidene fluoride nanofibers in the subsequent electrostatic spinning process, and finally optimize the performance of the diaphragm by improving the fiber structure. The addition of modified sepiolite can further improve the thermal stability and ionic conductivity of the film material. The role of the solvent is to dissolve polyvinylidene fluoride and provide a dispersed carrier for polyvinylidene fluoride and modified sepiolite. The battery diaphragm prepared by the electrostatic spinning method causes polyvinylidene fluoride and modified sepiolite to be coated or entangled in the fiber state, so that the prepared nanofibers have better mechanical properties and better thermal stability, thereby improving the safety performance of the battery diaphragm. And due to the unique properties of the modified sepiolite inorganic filler, the prepared battery separator has higher ion conductivity and lower impedance, so that the battery has good cycle performance and higher charge and discharge efficiency.

[0135] The technical solution of the present invention will be better understood with reference to specific embodiments below.

[0136] Example 1

[0137] This embodiment prepares a thin film material, and the specific preparation process is as follows:

[0138] 1.0 g of PVDF powder with an average molecular weight of 8000000 was placed in 10 mL of a solvent of dimethylformamide and acetone in a volume ratio of 7:3, and heated at a constant temperature of 60° C. for 12 h in an oil bath stirring pot until the powder was completely dissolved in the mixed solvent to prepare a polyvinylidene fluoride sol solution with a mass volume ratio of 10%;

[0139] Adding different amounts of modified sepiolite to a 10% polyvinylidene fluoride sol solution in a mass volume ratio of (PVDF: sepiolite = 1:0.5), magnetically stirring for 24 hours, and then ultrasonically vibrating for 30 minutes to obtain a modified sol-gel solution;

[0140] The modified sol-gel solution was injected into a 5 mL medical syringe, the ambient temperature was 30°C, the humidity was RH = 40%, and electrospinning was performed in the equipment parameters of solution flow rate of 0.8 ml / h, the distance between the metal needle and the metal plate was 10 cm, and the voltage between the metal needle and the metal plate was 18.5 kV. The spinning time for each film was 4 h;

[0141] The film material prepared by electrospinning was completely immersed in anhydrous ethanol at room temperature for 48 hours;

[0142] The film material fully soaked in anhydrous ethanol is placed in a 60°C vacuum drying oven for 24 hours to obtain the film.

[0143] Example 2

[0144] This embodiment prepares a thin film material, and the specific preparation process is as follows:

[0145] 1.0 g of PVDF powder with an average molecular weight of 8000000 was placed in 10 mL of a solvent of dimethylformamide and acetone in a volume ratio of 7:3, and heated at a constant temperature of 60° C. for 12 h in an oil bath stirring pot until the powder was completely dissolved in the mixed solvent to prepare a polyvinylidene fluoride sol solution with a mass volume ratio of 10%;

[0146] Adding different amounts of modified sepiolite to a 10% polyvinylidene fluoride sol solution in a mass volume ratio of (PVDF: sepiolite = 1:1), magnetically stirring for 24 hours, and then ultrasonically vibrating for 30 minutes to obtain a modified sol-gel solution;

[0147] The modified sol-gel solution was injected into a 5 mL medical syringe, the ambient temperature was 30°C, the humidity was RH = 40%, and electrospinning was performed in the equipment parameters of solution flow rate of 0.8 ml / h, the distance between the metal needle and the metal plate was 10 cm, and the voltage between the metal needle and the metal plate was 18.5 kV. The spinning time for each film was 4 h;

[0148] The film material prepared by electrospinning was completely immersed in anhydrous ethanol at room temperature for 48 hours;

[0149] The film material fully soaked in anhydrous ethanol is placed in a 60°C vacuum drying oven for 24 hours to obtain the film.

[0150] Example 3

[0151] This embodiment prepares a thin film material, and the specific preparation process is as follows:

[0152] 1.0 g of PVDF powder with an average molecular weight of 8000000 was placed in 10 mL of a solvent of dimethylformamide and acetone in a volume ratio of 7:3, and heated at a constant temperature of 60° C. for 12 h in an oil bath stirring pot until the powder was completely dissolved in the mixed solvent to prepare a polyvinylidene fluoride sol solution with a mass volume ratio of 10%;

[0153] Adding different amounts of modified sepiolite to a 10% polyvinylidene fluoride sol solution in a mass volume ratio of (PVDF: sepiolite = 1:1.5), magnetically stirring for 24 hours, and then ultrasonically vibrating for 30 minutes to obtain a modified sol-gel solution;

[0154] The modified sol-gel solution was injected into a 5 mL medical syringe, the ambient temperature was 30°C, the humidity was RH = 40%, and electrospinning was performed in the equipment parameters of solution flow rate of 0.8 ml / h, the distance between the metal needle and the metal plate was 10 cm, and the voltage between the metal needle and the metal plate was 18.5 kV. The spinning time for each film was 4 h;

[0155] The film material prepared by electrospinning was completely immersed in anhydrous ethanol at room temperature for 48 hours;

[0156] The film material fully soaked in anhydrous ethanol is placed in a 60°C vacuum drying oven for 24 hours to obtain the film.

[0157] In Examples 1 to 3, the preparation method of the modified sepiolite is:

[0158] (1) taking sepiolite powder and grinding it thoroughly in a grinding mortar, filtering the ground sepiolite powder through a sieve, and collecting it for later use;

[0159] (2) Then weigh an appropriate amount of sepiolite and put it into a container, add an appropriate amount of deionized water into the container, slowly stir to fully disperse it, let it stand until it is completely precipitated, and then filter out the precipitate and dry it;

[0160] (3) preparing an acidic solution, placing the dried sepiolite powder into the acidic solution, stirring in a heated water bath, and filtering to obtain acid-modified sepiolite;

[0161] (4) The obtained acid-modified sepiolite is heated, stirred and washed with deionized water for several times until it becomes neutral, dried, ground and set aside.

[0162] Wherein, in step (1), the mesh size of the sieve includes 200 meshes.

[0163] In step (2), stirring includes magnetic stirring, stirring until fully dispersed, and the stirring time is 12 hours.

[0164] The drying temperature was 60°C.

[0165] In step (3), the acidic solution is a hydrochloric acid solution with a mass fraction of 12%.

[0166] In step (3), the temperature of the heated water bath with stirring is 80°C.

[0167] In step (3), the stirring time in the heated water bath is 10 h.

[0168] In step (4), after grinding, the particle size range of the modified sepiolite is about 100 nm.

[0169] Experimental Testing

[0170] The microscopic morphologies of the thin film materials prepared in Examples 1 to 3 were observed by scanning microscopy. Figures 1 to 3 As shown. It can be seen that the fibers of the film material are rough, and there are many bead-like structures on the fiber filaments, and the film will have a larger specific surface area. With the increase in the amount of modified sepiolite added, the bead-like structure becomes more obvious and the number is greater. On the one hand, the bead-like structure effectively increases the specific surface area and porosity of the film material, so that when the film material is used for battery separators, it can improve the ionic conductivity of the electrolyte, so that the battery has good cycle performance and high charge and discharge efficiency; on the other hand, the film material has excellent heat resistance and dimensional stability, so when the film material is used for battery separators, it improves the safety performance of the battery separator. Ultimately, the overall performance of the battery is improved.

[0171] The film materials prepared in Examples 1, 2, and 3, as well as the PVDF film materials and the sepiolite powders before and after modification were observed by X-ray powder diffraction. Figure 4 As shown. Figure 4 It can be seen that after the acid-washed sepiolite was modified, a large amount of impurity metals in the original sepiolite were dissolved and washed away. It can also be clearly seen from the diffraction peak that the acid-washed sepiolite achieved the expected purpose. In the subsequent composite process, with the increase in the amount of sepiolite added, the corresponding characteristic peaks are also constantly enhanced, indicating that the sepiolite and PVDF are successfully composited.

[0172] The thin film materials prepared in Examples 1, 2, and 3, as well as the PVDF material, were tested by FTIR infrared experiments. Figure 5 .from Figure 5 It can be seen that the functional groups corresponding to PVDF and sepiolite can be clearly found in the image, which further illustrates the successful compounding of sepiolite and PVDF.

[0173] Figure 6 The thermal stability test graphs of the film materials prepared in Examples 1 to 3 and the commercial Celgard film and PVDF diaphragm materials are shown. Figure 6It can be seen that as the temperature rises to 160°C, the commercial Celgard film shows obvious condensation changes, and its structure is also destroyed. The PVDF diaphragm material also has a slight curl, while the diaphragm material with the addition of sepiolite changes less, and the thermal stability will be better with the increase of the amount of sepiolite added. When the temperature reaches 200°C, the commercial Celgard film is almost completely melted, and the PVDF diaphragm also undergoes severe deformation, and this phenomenon is significantly improved with the addition of sepiolite. Therefore, it can be explained that the addition of sepiolite can greatly improve the thermal stability of the diaphragm material.

[0174] Figure 7 The following are the thermogravimetric TG test graphs of the film materials prepared in Examples 1, 2, and 3, as well as the commercial Celgard film and PVDF diaphragm materials. Figure 7 It can be seen that the thermal stability of PVDF diaphragm material is better than that of commercial Celgard film, and with the addition of sepiolite, the thermal stability is further improved, and the remaining mass can also correspond to the mass of the added sepiolite, which once again shows that sepiolite, because of its own properties, is conducive to improving the thermal stability of the diaphragm.

[0175] Figure 8 The ionic conductivity curves of the thin film materials prepared in Examples 1 to 3 and the commercial Celgard film and PVDF separator materials are shown. The thin film materials prepared in Examples 1 to 3 and the commercial Celgard film and PVDF separator materials are assembled into steel-on-steel button cells. The test results are shown in FIG. Figure 8 As shown, from Figure 8 It can be seen that compared with the commercial Celgard film, the PVDF and the composite membranes with added sepiolite have better performance. The specific parameters are shown in Table 1. The membrane with 0.5g of sepiolite has the best performance (reaching 3.52×10 -3 ·S·cm -1 Far exceeds the commercial Celgard film 0.43×10 -3 ·S·cm -1 And pure PVDF diaphragm material 2.1×10 -3 ·S·cm -1 ), although the performance decreases with the increase of the amount of sepiolite, it is still better than the pure PVDF membrane as a whole, indicating that the addition of sepiolite is beneficial to promote the ion shuttle in the electrolyte and thus has a higher ion conductivity, but the reason why the performance decreases with the increase of the amount of sepiolite added can be explained as excessive sepiolite will cause PVDF to be unable to completely cover and thus affect the nanofiber structure, which will have a certain hindering effect on the lithium ion shuttle and ultimately lead to a decrease in ion conductivity.

[0176] Table 1

[0177] Sample <![CDATA[R b ]]> h(cm) <![CDATA[σ(S·cm -1 )]]> Celgard Diaphragm 2.9 0.0025 <![CDATA[0.43×10 -3 ]]> PVDF membrane 1.55 0.00654 <![CDATA[2.1×10 -3 ]]> Film of Example 1 1.33 0.00942 <![CDATA[3.52×10 -3 ]]> Film of Example 2 1.50 0.00832 <![CDATA[2.76×10 -3 ]]> Film of Example 3 1.65 0.00642 <![CDATA[1.94×10 -3 ]]>

[0178] Fig. 9 The LSV curves of the film materials prepared in Examples 1 to 3 and the commercial Celgard film and PVDF separator materials are shown in FIG.

[0179] The thin film materials prepared in Examples 1 to 3, as well as commercial Celgard thin films and PVDF separator materials were used to assemble lithium-to-steel button cells. The test results are shown in FIG. Fig. 9 As shown, from Fig. 9 It can be seen that the test results of button batteries prepared using the film materials prepared in Examples 1 to 3 or commercial Celgard film and PVDF diaphragm materials are all greater than 4.2V, indicating that the prepared diaphragm materials have excellent electrochemical stability and meet the standards for use in lithium-ion batteries.

[0180] Fig.10 is the CV curve of the diaphragm of Example 1. Fig.10 It can be seen that the images of the first three circles are almost completely overlapped, indicating that the diaphragm material has excellent reversible cycle performance, which is conducive to the long cycle of the battery.

[0181] Fig.11 This is a test chart of the cycle performance of the thin film material prepared in Example 1 after being assembled into a button battery. Fig.11 It can be seen that after 130 cycles at 0.5C rate, the button battery assembled from the thin film material prepared in Example 1 has almost no capacity decay and has a very high coulombic efficiency, indicating that the thin film material prepared in Example 1 has very good long cycle performance, further indicating that high ionic conductivity and high electrochemical stability are conducive to long battery cycles and extended battery life.

[0182] Fig.12 The long cycle and coulomb efficiency diagram of the thin film material prepared in Example 1 and the commercial Celgard film and PVDF film material assembled into button cells. Fig.12 It can be seen that the PVDF diaphragm is superior to the commercial Celgard film in terms of capacity release, but the structure is not very stable. The performance deteriorates seriously after a certain period of circulation, and the long-cycle performance is poor. This problem can be significantly improved by adding sepiolite, such as Fig.12 The addition of sepiolite greatly improves the long cycle performance of the battery while maintaining high capacity release, and also has a high coulombic efficiency, which once again shows that the addition of sepiolite is conducive to further improving the various properties of the PVDF diaphragm, thereby improving battery performance and extending battery life.

[0183] It should be noted that in the above tests, the tested Celgard membrane, PVDF membrane and the films prepared in Examples 1 to 3 have the same thickness, which is about 80 μm.

[0184] The present invention has been described in detail above in conjunction with the embodiments, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A battery separator, It is characterized in that The battery separator is prepared from a thin film material, the thin film material is formed by interweaving nano-scale fiber filaments, and bead structures are distributed on the nano-scale fiber filaments. The raw materials for preparing the thin film material include polyvinylidene fluoride, modified sepiolite and a solvent, and the solvent is a mixed solvent of dimethylformamide and acetone. The preparation method of the modified sepiolite is: (1) grinding sepiolite powder in a grinding mortar, filtering the ground sepiolite powder through a sieve, and collecting the ground sepiolite powder for later use; (2) Weighing sepiolite into a container, adding deionized water into the container, stirring to disperse it, leaving it to stand until it precipitates, and then filtering the precipitate to remove it and dry it; (3) preparing an acidic solution, placing the dried sepiolite powder into the acidic solution, stirring in a heated water bath, and filtering to obtain acid-modified sepiolite; (4) The obtained acid-modified sepiolite is heated, stirred and washed with deionized water for several times until it becomes neutral, dried, ground and set aside.

2. The battery separator according to claim 1, It is characterized in that The mass ratio of the polyvinylidene fluoride to the modified sepiolite is 1:0.5-2.

3. The battery separator according to claim 1, It is characterized in that The mass volume ratio of the polyvinylidene fluoride to the solvent is 10g-15g:100mL.

4. The battery separator according to any one of claims 1 to 3, It is characterized in that The method for preparing the thin film material comprises the following steps: S1: dissolving the polyvinylidene fluoride in the solvent to obtain a sol-gel solution; S2: adding the modified sepiolite to the sol-gel solution and dispersing the modified sepiolite uniformly to obtain a modified sol-gel solution; S3: electrospinning the modified sol-gel solution to obtain the thin film material.

5. The battery separator according to claim 4, It is characterized in that In the electrospinning, the flow rate of the sol-gel solution is 0.5 mL / h to 1 mL / h.

6. The battery separator according to claim 4, It is characterized in that In the electrospinning, the voltage applied between the metal needle and the metal plate is 10 kV to 20 kV.

7. The battery separator according to claim 4, It is characterized in that In the electrospinning, the distance between the metal needle and the metal plate is 10 cm to 20 cm.

Images