CN103258978A - Preparation method of P(VDF-HFP) (Poly(Vinyl Fluoride-Hexafluoropropylene)) inorganic compound porous nano fiber lithium ion battery separator - Google Patents

Abstract

The invention relates to a preparation method of a P(VDF-HFP) inorganic composite porous nanofiber lithium-ion battery diaphragm. The specific steps of the method are: (1) adding P(VDF-HFP) and PEG to an organic solvent, heating and stirring to dissolve to form a transparent solution, cooling to room temperature, and dispersing the inorganic nanoparticles in the solution by stirring and ultrasonic treatment , to obtain a spinning solution; (2) electrospinning the obtained spinning solution to obtain a nascent P(VDF-HFP) inorganic composite nanofiber membrane. (3) Immerse the obtained nascent P(VDF-HFP) inorganic composite fiber membrane in distilled water to remove PEG, and dry it to obtain the P(VDF-HFP) inorganic composite porous nanofiber lithium-ion battery separator. The lithium ion battery diaphragm prepared by the invention has high liquid absorption rate, good electrochemical stability and good heat shrinkage resistance at room temperature.

Description

A preparation method of P(VDF-HFP) inorganic composite porous nanofiber lithium-ion battery diaphragm

technical field

The invention relates to a preparation method of a P(VDF-HFP) inorganic composite porous nanofiber lithium ion battery diaphragm, belonging to the field of nano functional materials and lithium ion batteries.

technical background

Lithium-ion batteries are mainly composed of positive and negative electrodes, a separator, and an electrolyte. The separator is between the positive and negative materials to isolate the positive and negative electrodes, prevent short circuit, prevent electrons from passing through, and allow ions to pass through. The performance of the separator determines the internal resistance and internal interface structure of the battery, which in turn affects the capacity, charge and discharge performance, cycle performance, and safety performance of the battery. Therefore, the performance of the separator has an important impact on the overall performance of the lithium-ion battery.

Gel polymer electrolyte refers to the polymer network system formed by the swelling of the polymer separator after absorbing the electrolyte. It has the diffusion ability of liquid and the cohesiveness of solid, and is widely used in lithium-ion batteries. At present, the gel polymer electrolyte materials for lithium-ion batteries that have been studied more include polymethyl methacrylate (PMMA), polyethylene oxide (PEO), polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) and their copolymer. Among them, polyvinylidene fluoride-hexafluoropropylene P (VDF-HFP) not only has good thermal stability, chemical corrosion resistance, oxidation resistance, and weather resistance of PVDF, but also has the characteristics of easy processing and strong flexibility. The amorphous HFP in the molecule can promote the absorption of the electrolyte, and the crystalline PVDF can provide strong support for the matrix. It is currently a gel polymer material with better performance for lithium-ion batteries. Polyethylene glycol (PEG) can be blended with P(VDF-HFP) and dissolved in organic solvents, and can also be dissolved in water.

Qi et al. dissolved polylactic acid in a dichloromethane/n-butanol mixed solvent to prepare a spinning solution, prepared porous nanofibers by electrospinning, and controlled the pore structure on the surface of the nanofibers by adjusting the composition ratio of dichloromethane and n-butanol (Qi et al. Z, Yu H, Chen Y, et al. Highly porous fibers prepared by electrospinning a ternary system of nonsolvent/solv-ent/po-ly(l-lactic acid). Materials Letters. 2009, 63(3-4): 415 -418.). Zhang et al. dissolved PAN and PEO in DMF to obtain a blend solution, and prepared nanofibers by electrospinning technology. After drying, they were immersed in deionized water to remove PEO to form PAN porous nanofibers (ZHANG L F, HSIEH Y L.Nanoporous ultrahigh specific surf-acepolyacrylonitrile fibers. Nanotechnology, 2006, 17(17): 4416-4423.). In patent CN102268745, PAN and PEO are respectively dissolved in DMF and chloroform (CHCl ₃ ), and then the two solutions are compounded to obtain a spinning solution, and porous nanofibers are prepared by electrospinning. The _CHCl3 used in this method has carcinogenic effect, and it is easy to decompose under light irradiation to generate highly toxic phosgene, which endangers personal safety. Patent CN102493009A adds a dispersing liquid immiscible with the solvent to the fiber-forming polymer solution, then adds a surfactant to prepare an emulsion, and conducts electrospinning, through the volatilization of the dispersing liquid, or during the spinning process and the subsequent washing process. The dispersion liquid is washed away to obtain porous nanofibers. The addition of surfactant in this method affects the properties of nanofibers to a certain extent. In addition, although these methods prepared porous nanofibers, they did not propose to use them as lithium-ion battery separators, nor did they test and analyze their electrochemical properties.

Patent CN102790195 mixes P(VDF-HFP) and inorganic particles and adopts a solution casting method to prepare a composite lithium-ion battery diaphragm. The separator prepared by the method has low porosity and ion conductivity, and as a lithium-ion battery separator, it will increase the internal resistance of the battery and affect the cycle performance of the battery. In patents CN102820446, US2010/0316903A1 and US6432586B1, a porous layer composed of inorganic oxide particles and polymer organic matter or binder is coated on a microporous membrane substrate to prepare a lithium-ion battery composite separator. The composite membrane prepared by this method has a relatively large thickness, low liquid absorption rate, relatively large internal resistance of the battery, and is easy to delaminate during processing and use, and the inorganic particles are easy to fall off, which further affects the performance of the battery.

In patents WO2012050682A2, TW201230453A and US2012082884A1, composite nanofibers of P(VDF-HFP) and inorganic ceramic particles are directly deposited on positive or negative electrode materials by electrospinning. The diaphragm prepared by this method is directly compounded on the electrode material, and the thickness and uniformity of the diaphragm are tested to a certain extent, which is not conducive to online debugging in the production process. In addition, the compounding of the diaphragm and electrode material increases the complexity of the process, which is not conducive to production management. , is also not conducive to the optimal configuration of the separator and electrode materials.

Patent CN102779964 combines high molecular organic matter and small molecular organic matter with an organic solvent, and then adds inorganic nanoparticles to prepare a mixed solution, and coats the mixed solution on the film substrate by electrospinning to form a composite film, then extracts the small molecular organic matter, and A porous nanofiber composite membrane is formed. The interaction between the composite film layers prepared by this method is not strong, and after absorbing the electrolyte, it is easy to separate and affect the performance of the battery. Patent CN102268783 adds single-walled carbon nanotubes and lithium salts to an organic solvent to form a mixed solution, dissolves them in PVDF, and then dissolves them in polyvinylpyrrolidone to prepare a spinning solution, which is formed by electrospinning, and the resulting fiber membrane is dipped in ethanol 1-2h to obtain a PVDF porous nanofiber lithium-ion battery separator with high ion transfer number. The PVDF used in this method has high crystallinity, which is not conducive to the absorption of electrolyte and the improvement of ion conductivity. The fiber membrane is to remove polyvinylpyrrolidone in ethanol to form porous nanofibers. The high cost is not conducive to large-scale production.

Contents of the invention

Aiming at the deficiencies of the prior art, the problem to be solved by the present invention is to provide a method for preparing a P(VDF-HFP) inorganic composite porous nanofiber lithium-ion battery. The preparation method has simple process, easy control, convenient operation and low cost, and the obtained product has excellent thermal stability, high liquid absorption rate and electrochemical stability window.

In order to solve the above-mentioned technical problems, the present invention provides a preparation method for preparing P(VDF-HPF) inorganic composite porous nanofiber lithium-ion battery diaphragm, which is characterized in that the diaphragm is composed of P(VDF-HFP)/inorganic particle composite porous nanofiber Fiber composition, the specific production steps are:

Step 1: Add P(VDF-HFP) and PEG to the organic solvent, heat and stir at 40-50°C to form a transparent solution, cool to room temperature, add inorganic nanoparticles, stir at room temperature, preliminarily disperse the nanoparticles, and ultrasonically Disperse for 15 to 30 minutes, and further disperse the nanoparticles to obtain a spinning solution;

The second step: electrospinning the obtained spinning solution to obtain a nascent P(VDF-HFP) inorganic composite nanofiber membrane.

The third step: soak the obtained primary P(VDF-HFP) inorganic composite fiber membrane in distilled water, remove the PEG component, take it out and place it in a drying oven for drying treatment, and remove the moisture in the fiber membrane to obtain the P(VDF-HFP ) Inorganic composite porous nanofiber lithium-ion battery separator.

Preferably, the organic solvent in the first step is N,N-dimethylformamide, N,N-dimethylacetamide, acetone, N-methylpyrrolidone, hexafluoroisopropanol, tetrahydrofuran A mixture of one or more than two.

Preferably, the inorganic nanoparticles in the first step are one or more of aluminum oxide, silicon dioxide, titanium dioxide, barium phthalate, magnesium oxide, zirconium dioxide, zinc oxide, and silicon carbide. mixture.

Preferably, the mass ratio of P(VDF-HFP), PEG and inorganic nanoparticles in the first step is: 0.7-0.9:0.05-0.25:0.01-0.08.

Preferably, the electrospinning conditions in the second step are as follows: the temperature is room temperature, the relative humidity is 20-65%, the spinning rate is 0.1-1.0 mL/h, and the distance between the spinneret and the receiver is 10 ～25cm, the spinning voltage is 10～25kV.

Preferably, the electrospinning receiving device in the second step is one or more of aluminum foil, iron plate, iron mesh, copper mesh, iron roller, aluminum roller and non-woven material.

Preferably, the temperature of the distilled water in the third step is 20-55° C., and the time is 2-4 hours.

Preferably, the drying temperature in the third step is 60-120° C., and the drying time is 1-4 hours.

Compared with the prior art, the present invention has the advantages of:

1. The P(VDF-HFP) inorganic composite porous nanofiber lithium-ion battery diaphragm prepared by the present invention not only has good liquid absorption performance of PVDF-HFP material, but also removes PEG components to form a porous structure on the fiber to further improve the porosity and Liquid absorption rate, nano-inorganic substances can absorb a small amount of water and HF generated by the decomposition of electrolyte solution during the battery cycle, improve battery charge and discharge efficiency, and prolong battery cycle life.

2. The method for preparing P(VDF-HFP) inorganic composite porous nanofiber lithium-ion battery diaphragm provided by the present invention does not use surfactants and other substances irrelevant to the product and carcinogenic, the pore-forming process is carried out in water, and the operation is convenient. The process flow is short and the cost is low.

3. The P(VDF-HFP) inorganic composite porous nanofiber lithium-ion battery diaphragm prepared by the present invention is composed of nanofibers containing inorganic particles, the thickness is small and easy to control, and no delamination and nanoparticle will occur during production and use. Shedding phenomenon.

4. The P(VDF-HFP) inorganic composite porous nanofiber lithium-ion battery diaphragm prepared by the present invention has lower thermal shrinkage, good electrochemical stability, higher porosity and liquid absorption rate, and mechanical strength can Meet the requirements of the battery assembly process.

5. The P(VDF-HFP) inorganic composite porous nanofiber lithium-ion battery diaphragm prepared by the present invention has solution corrosion resistance and good interface stability.

Detailed ways

Specific examples of the present invention are given below. These specific examples are only used to further describe the present invention, and do not limit the protection scope of the claims of the present application.

Example 1

At room temperature, weigh the dried P(VDF-HFP), PEG and nano Al ₂ O ₃ (mass ratio is 8:1.8:0.2), first add P(VDF-HFP) and PEG to a certain amount of DMF /acetone mixed solvent, under the condition of 45 ℃, carry out magnetic stirring and dissolve until a transparent mixed solution is formed. Cool the obtained mixed solution to room temperature, then add nano-Al ₂ O ₃ into the mixed solution, stir at room temperature for a certain period of time to initially disperse the nanoparticles, and then ultrasonically treat for 20 minutes to further uniformly disperse the nanoparticles in the solution to obtain a spinning liquid.

Under the conditions of room temperature 25°C and humidity 30%, the above-mentioned spinning solution was electrospun at a spinning rate of 0.1ml/h, and the applied voltage was 10kv; the spinning distance between the needle and the receiver was 10cm, Deposit the spun fibers on the receiver of the electrospinning equipment; after the spinning is completed, the prepared P(VDF-HFP) inorganic composite nanofiber membrane is removed from the receiver, soaked in distilled water at 20°C for 4h, and then taken out , placed in a drying oven and dried at a temperature of 60° C. for 4 hours to obtain a P(VDF-HFP) inorganic composite porous nanofiber membrane.

The P(VDF-HFP) inorganic composite porous nanofiber membrane was placed in a hot box at 150°C for 1.5h, and the shrinkage rate was 2.5%. The fiber membrane was immersed in ethylene carbonate/dimethyl carbonate/dicarbonate of 1mol lithium hexafluorophosphate In the electrolyte solution of ethyl ester (mass ratio 1:1:1), the liquid absorption rate obtained is 573.6%, the ion conductivity is 1.16mS/cm, and the electrochemical stability window is 5.2V.

Example 2

At room temperature, weigh the dried P(VDF-HFP), PEG and nano-ZrO ₂ (mass ratio is 9:0.5:0.5), first add P(VDF-HFP) and PEG to a certain amount of DMAc/acetone In the mixed solvent, magnetic stirring was performed at 50° C. to dissolve until a transparent mixed solution was formed. Cool the obtained mixed solution to room temperature, then add nano- _ZrO2 into the mixed solution, stir at room temperature for a certain period of time to initially disperse the nanoparticles, and then ultrasonically treat for 15 minutes to further uniformly disperse the nanoparticles in the solution to obtain a spinning solution.

At a room temperature of 25°C and a humidity of 40%, the above-mentioned spinning solution was electrospun at a spinning rate of 0.4ml/h, and the applied voltage was 15kv; the spinning distance between the needle and the receiver was 15cm, The spun fibers were deposited on the receiver of the electrospinning equipment; after the spinning was completed, the prepared P(VDF-HFP) inorganic composite nanofiber membrane was removed from the receiver, soaked in distilled water at 40°C for 3 hours, and then taken out , placed in a drying oven and dried at a temperature of 80° C. for 3.5 hours to obtain a P(VDF-HFP) inorganic composite porous nanofiber membrane.

The P(VDF-HFP) inorganic composite porous nanofiber membrane was placed in a hot box at 150°C for 1.5h, and the shrinkage rate was 1.7%. The fiber membrane was immersed in ethylene carbonate/dimethyl carbonate/dicarbonate of 1mol lithium hexafluorophosphate In the electrolyte solution of ethyl ester (mass ratio 1:1:1), the liquid absorption rate obtained is 484.3%, the ion conductivity is 1.58mS/cm, and the electrochemical stability window is 5.0V.

Example 3

At room temperature, weigh the dried P(VDF-HFP), PEG and nano TiO ₂ (mass ratio is 8.5:1:0.5), first add P(VDF-HFP) and PEG to a certain amount of DMF/acetone In the mixed solvent, magnetic stirring was performed at 50° C. to dissolve until a transparent mixed solution was formed. Cool the obtained mixed solution to room temperature, then add nano- _TiO2 into the mixed solution, stir at room temperature for a certain period of time to preliminarily disperse the nanoparticles, and then ultrasonically treat for 30 minutes to further uniformly disperse the nanoparticles in the solution to obtain a spinning solution.

At a room temperature of 25°C and a humidity of 30%, the above-mentioned spinning solution was electrospun at a spinning rate of 0.6ml/h, and the applied voltage was 20kv; the spinning distance between the needle and the receiver was 20cm, The spun fibers were deposited on the aluminum foil receiver of the electrospinning equipment; after the spinning was completed, the prepared P(VDF-HFP) inorganic composite nanofiber membrane was removed from the receiver and immersed in distilled water at 55°C for 2h Take it out, place it in a drying oven and dry it at a temperature of 90° C. for 3 hours to obtain a P(VDF-HFP) inorganic composite porous nanofiber membrane.

The P(VDF-HFP) inorganic composite porous nanofiber membrane was placed in a hot box at 150°C for 1.5h, and the shrinkage rate was 2.0%. The fiber membrane was immersed in ethylene carbonate/dimethyl carbonate/dicarbonate of 1mol lithium hexafluorophosphate In the electrolyte solution of ethyl ester (mass ratio 1:1:1), the liquid absorption rate obtained is 461.4%, the ion conductivity is 2.29mS/cm, and the electrochemical stability window is 5.1V.

Example 4

At room temperature, weigh the dried P(VDF-HFP), PEG and nano Al ₂ O ₃ (mass ratio is 7:2.5:0.5), first add P(VDF-HFP) and PEG to a certain amount of DMF /acetone mixed solvent, under the condition of 50 ℃, carry out magnetic stirring and dissolve until a transparent mixed solution is formed. Cool the obtained mixed solution to room temperature, then add nano-Al ₂ O ₃ into the mixed solution, stir at room temperature for a certain period of time to initially disperse the nanoparticles, and then ultrasonically treat for 20 minutes to further uniformly disperse the nanoparticles in the solution to obtain a spinning liquid.

Under the conditions of room temperature 25°C and humidity 42%, the above-mentioned spinning solution was electrospun at a spinning rate of 0.8ml/h, and the applied voltage was 25kv; the spinning distance between the needle and the receiver was 25cm, The spun fibers were deposited on the receiver of the electrospinning equipment; after the spinning was completed, the prepared P(VDF-HFP) inorganic composite nanofiber membrane was removed from the receiver, immersed in distilled water at 50°C for 2.4h Take it out, place it in a drying oven and dry it at a temperature of 100° C. for 2 hours to obtain a P(VDF-HFP) inorganic composite porous nanofiber membrane.

The P(VDF-HFP) inorganic composite porous nanofiber membrane was placed in a hot box at 150°C for 1.5h, and the shrinkage rate was 2.4%. The fiber membrane was immersed in ethylene carbonate/dimethyl carbonate/dicarbonate of 1mol lithium hexafluorophosphate In the electrolyte solution of ethyl ester (mass ratio 1:1:1), the liquid absorption rate obtained is 464.3%, the ion conductivity is 1.52mS/cm, and the electrochemical stability window is 5.3V.

Example 5

At room temperature, weigh the dried P(VDF-HFP), PEG and nano-ZnO (mass ratio is 7.4:2.5:0.5), first add P(VDF-HFP) and PEG to a certain amount of DMF solvent, Dissolve under magnetic stirring at 50°C until a transparent mixed solution is formed. Cool the obtained mixed solution to room temperature, then add nano-ZnO into the mixed solution, stir at room temperature for a certain period of time to preliminarily disperse the nanoparticles, and then ultrasonically treat for 20 minutes to further uniformly disperse the nanoparticles in the solution to obtain a spinning solution.

Under the conditions of room temperature 25°C and humidity 35%, the above spinning solution was electrospun at a spinning rate of 1.0ml/h, and the applied voltage was 15kv; the spinning distance between the needle and the receiver was 20cm, The spun fibers were deposited on the receiver of the electrospinning equipment; after the spinning was completed, the prepared P(VDF-HFP) inorganic composite nanofiber membrane was removed from the receiver, immersed in distilled water at 30°C for 3.5h Take it out, place it in a drying oven and dry it at a temperature of 110° C. for 1.5 hours to obtain a P(VDF-HFP) inorganic composite porous nanofiber membrane.

The P(VDF-HFP) inorganic composite porous nanofiber membrane was placed in a hot box at 150°C for 1.5h, and the shrinkage rate was 2.0%. The fiber membrane was immersed in ethylene carbonate/dimethyl carbonate/dicarbonate of 1mol lithium hexafluorophosphate In the electrolyte solution of ethyl ester (mass ratio 1:1:1), the liquid absorption rate obtained is 393.4%, the ion conductivity is 1.39mS/cm, and the electrochemical stability window is 5.0V.

Example 6

At room temperature, weigh the dried P(VDF-HFP), PEG and nano-ZnO (mass ratio is 7.7:1.5:0.8), first add P(VDF-HFP) and PEG to a certain amount of DMF solvent, Dissolve under magnetic stirring at 50°C until a transparent mixed solution is formed. Cool the obtained mixed solution to room temperature, then add nano-ZnO into the mixed solution, stir at room temperature for a certain period of time to preliminarily disperse the nanoparticles, and then ultrasonically treat for 30 minutes to further uniformly disperse the nanoparticles in the solution to obtain a spinning solution.

At a room temperature of 25°C and a humidity of 42%, the above-mentioned spinning solution was electrospun at a spinning rate of 0.6ml/h, and the applied voltage was 18kv; the spinning distance between the needle and the receiver was 15cm, The spun fibers were deposited on the receiver of the electrospinning equipment; after the spinning was completed, the prepared P(VDF-HFP) inorganic composite nanofiber membrane was removed from the receiver, soaked in distilled water at 45°C for 2.8h, and then taken out , placed in a drying oven and dried at a temperature of 120° C. for 1 h to obtain a P(VDF-HFP) inorganic composite porous nanofiber membrane.

The P(VDF-HFP) inorganic composite porous nanofiber membrane was placed in a hot box at 150°C for 1.5h, and the shrinkage rate was 2.1%. The fiber membrane was immersed in ethylene carbonate/dimethyl carbonate/dicarbonate of 1mol lithium hexafluorophosphate In the electrolyte solution of ethyl ester (mass ratio 1:1:1), the liquid absorption rate obtained is 413.6%, the ion conductivity is 1.42mS/cm, and the electrochemical stability window is 5.4V.

Claims (8)

1. The preparation method of polyvinylidene fluoride-hexafluoropropylene inorganic composite porous nanofiber lithium-ion battery diaphragm, is characterized in that, the specific steps are: The first step: Add polyvinylidene fluoride-hexafluoropropylene and PEG to the organic solvent, heat and stir at 40-50 ° C to dissolve, form a transparent solution, cool to room temperature, add inorganic nanoparticles, stir at room temperature, and initially disperse the nanoparticles. Ultrasonic dispersion for 15 to 30 minutes to further disperse the nanoparticles to obtain a spinning solution; The second step: electrospinning the obtained spinning solution to obtain primary polyvinylidene fluoride-hexafluoropropylene inorganic composite nanofiber membrane. The third step: soak the obtained nascent polyvinylidene fluoride-hexafluoropropylene inorganic composite fiber membrane in distilled water for 2 to 4 hours to remove the PEG component, then take it out and place it in a drying oven for drying treatment to remove the moisture in the fiber membrane to obtain Polyvinylidene fluoride-hexafluoropropylene inorganic composite porous nanofiber lithium-ion battery separator. 2. the preparation method of polyvinylidene fluoride-hexafluoropropylene inorganic composite porous nanofiber lithium-ion battery diaphragm as claimed in claim 1, is characterized in that, the organic solvent in the first step is N, N-dimethyl One or a mixture of two or more of methyl formamide, N,N-dimethylacetamide, acetone, N-methylpyrrolidone, hexafluoroisopropanol, and tetrahydrofuran. 3. the preparation method of polyvinylidene fluoride-hexafluoropropylene inorganic composite porous nanofiber lithium-ion battery diaphragm as claimed in claim 1, is characterized in that, the inorganic nanoparticle in the described first step is aluminum oxide, One or a mixture of two or more of silicon dioxide, titanium dioxide, barium phthalate, magnesium oxide, zirconium dioxide, zinc oxide, and silicon carbide. 4. the preparation method of polyvinylidene fluoride-hexafluoropropylene inorganic composite porous nanofiber lithium-ion battery diaphragm as claimed in claim 1, is characterized in that, polyvinylidene fluoride-hexafluoropropylene in the first step, The mass ratio of PEG and inorganic nanoparticles is: 0.7-0.9:0.05-0.25:0.01-0.08. 5. The preparation method of polyvinylidene fluoride-hexafluoropropylene inorganic composite porous nanofiber lithium-ion battery diaphragm as claimed in claim 1, is characterized in that, in the second step, the electrospinning condition is: temperature is room temperature, The relative humidity is 20-65%, the spinning rate is 0.1-1.0mL/h, the distance between the spinneret and the receiver is 10-25cm, and the spinning voltage is 10-25kV. 6. The preparation method of polyvinylidene fluoride-hexafluoropropylene inorganic composite porous nanofiber lithium-ion battery diaphragm as claimed in claim 1, is characterized in that, the electrospinning receiving device in the second step is aluminum foil, iron One or more of plates, iron nets, copper nets, iron rollers, aluminum rollers and non-woven materials. 7. The preparation method of polyvinylidene fluoride-hexafluoropropylene inorganic composite porous nanofiber lithium-ion battery diaphragm as claimed in claim 1, characterized in that, the temperature of distilled water in the third step is 20-55°C, and the time is For 2 ~ 4h. 8. The preparation method of polyvinylidene fluoride-hexafluoropropylene inorganic composite porous nanofiber lithium-ion battery diaphragm as claimed in claim 1, characterized in that, the temperature of the vacuum drying oven in the third step is 60-120°C , drying time is 1-4h.