CN106450101B - A method of preparing lithium battery diaphragm with coaxial electrostatic spinning - Google Patents

Abstract

The invention provides a method for preparing a lithium battery separator by coaxial electrospinning, belonging to the technical field of lithium battery separators. The lithium battery separator is a composite fiber membrane with a core/shell structure prepared by coaxial electrospinning technology. The core and shell layers of the composite fiber membrane are concentric, and the core layer is made of polyarylethersulfone ketone nanofibers with high melting point. Composition, the shell layer is composed of polyvinylidene fluoride nanofibers with low melting point, especially the coaxial composite film is hot-pressed at a certain temperature and pressure, and the shell layer fibers are micro-melted or melted to make the bonding between the fibers The tensile strength of the composite film in all directions is greatly improved. The lithium battery separator has a porosity of more than 75%, an electrolyte absorption rate of more than 550%, and can withstand high temperatures of 180°C. Therefore, the separator prepared by this method has both good electrochemical properties and thermal and mechanical properties. And electric vehicles and other fields have high application value.

Description

A method for preparing lithium battery separators by coaxial electrospinning

technical field

The invention relates to a lithium-ion battery diaphragm and a preparation method thereof. Specifically, the invention relates to a method for preparing a lithium-ion battery diaphragm by coaxial electrospinning, which belongs to the technical field of lithium-ion battery diaphragms.

Background technique

Due to the advantages of high energy density and high power density, lithium-ion batteries have been widely used in portable electronic products such as mobile phones and notebooks. With the shortage of oil resources and the increasingly serious environmental problems, they are gradually expanding to electric vehicles and hybrid vehicles. In the field of new energy vehicles, power lithium-ion batteries have great potential for development, and will also face more and more challenges.

The lithium-ion battery separator plays the role of conducting lithium ions in the liquid electrolyte, and at the same time isolates the positive and negative electrodes of the battery to prevent the two from contacting each other and causing a short circuit. At present, the commonly used lithium battery separators in the market are mainly polyethylene (PE) and polypropylene (PP) separators prepared by dry or wet methods. This type of separator has good electrochemical stability and suitable mechanical strength, and has a certain thermal shutdown performance. However, some disadvantages of traditional polyolefin separators make it difficult to meet the requirements of high energy density and high safety performance of power lithium-ion batteries, such as low porosity of polyolefin separators, poor electrolyte wettability and severe heat loss at high temperatures. Dimensional shrinkage. The porosity of commercial polyolefin separators is generally around 40%, and non-polar polyolefin materials have poor wettability with carbonate-based electrolytes, so that the electrolyte absorption rate of the separator is low, and good ions cannot be obtained. The electrical conductivity seriously affects the high-rate discharge performance and cycle stability of lithium-ion batteries; the severe dimensional shrinkage of polyolefin separators at high temperatures can cause internal short circuits in batteries, which may eventually lead to fire or explosion accidents. New energy electric vehicles use tens of thousands of battery cells connected in series as the driving force, and the thermal effect of the battery during operation is more significant. Therefore, in order to meet the higher requirements for the performance of the separator for electric vehicles and lithium batteries for energy storage, it is necessary to develop Li-ion battery separator with good electrochemical performance and high safety performance.

Electrospinning technology uses polymer solution to spin at room temperature. The source of spinnable materials is wide, the process is simple, and the morphology and structure of the obtained nanofibers can be adjusted. It can be used to prepare polymer nanofibers with small fiber diameter and large specific surface area. Fiber membrane. A polymer solution with a certain viscosity is polarized in a high-voltage electric field, and the charged polymer jet is stretched at a high speed, and the solvent is volatilized and finally solidified on the receiving plate to obtain a fiber film with a diameter of micro-nano scale. The fiber membrane prepared by electrospinning generally has a high porosity, usually up to 70%, so the electrospun separator has good air permeability, which can greatly reduce the internal resistance of the battery and improve the charge and discharge performance.

Electrospun polyvinylidene fluoride (PVDF) separator has outstanding advantages such as high porosity, good electrolyte wettability, and good compatibility with electrodes. It has great development potential in the field of lithium-ion batteries, but the melting point of PVDF is 175 It is about ℃, which is equivalent to the melting temperature of polypropylene (PP). It is easy to shrink in size at high temperature, and it is difficult to improve the high temperature stability of lithium battery separator. Polyaryl ether sulfone ketone (PPESK) resin containing phthalazine structure has high heat resistance, and its glass transition temperature is between 250-370°C. Its molecule contains a large number of polar groups such as ether bond (-O-), carbonyl group (C=O) and sulfone group (O=S=O), which is beneficial to improve the wettability of the diaphragm material to the carbonate electrolyte . The electrospun polyarylether sulfone ketone randomly oriented nanofiber separator not only has good air permeability and ionic conductivity, but also can maintain its normal shape at a high temperature of 220 ° C, which greatly improves the electrochemical performance and high temperature size of the lithium battery separator. Stability is a lithium battery separator product with great potential.

The characteristics of the forming process of the electrospinning technology itself determine that the fibers are simply piled up into a film with a certain thickness, and the nanofibers are only bonded together by lap joints, so the bonding performance is poor. The relative slip between them is easy to occur, and the mechanical strength is generally low, which limits its practical application. Therefore, it is necessary to solve the problem of poor mechanical properties of electrospun nanofibrous membranes in order to prepare comprehensive high-performance lithium-ion battery separators with excellent electrochemical properties and suitable mechanical strength.

The present invention adopts coaxial electrospinning technology, polyvinylidene fluoride (PVDF) polymer solution is used as spinning core layer, polyarylether sulfone ketone (PPESK) resin solution is used as spinning shell layer, at the same voltage and receiving distance Electrospinning is carried out under high-voltage electrostatic field conditions, and the two polymer solutions are simultaneously polarized under a high-voltage electrostatic field to generate jets. The polymer jets are fully stretched, solvent volatilization and solidification, and finally a concentric fiber non-woven fabric with randomly arranged fibers is produced. The cloth diaphragm gives full play to the excellent properties of the two materials. The prepared composite separator is subjected to hot-pressing post-treatment at a certain temperature, and the low-melting-point shell fibers are slightly melted or melted to enhance the bonding force between the fibers, and at the same time, the core layer fibers can still withstand high temperatures due to their good high-temperature resistance. Keeping the original shape, the tensile strength of the composite membrane in all directions is greatly improved.

Patent CN103474600A proposes a method for preparing a polyimide nanofiber membrane with a cross-linked structure. The cross-linked structure is achieved by etching the precursor polyamic acid nanofiber film in an ammonia solution of Ph=8-10, and the loosely overlapped nanofibers pass through the cross-linked points to form a network structure, and then the electric heating drum The polyimide nanofiber membrane with cross-linked structure was prepared by gradient temperature thermal imidization in an air drying oven. The pores of this kind of separator can reach about 80%, which greatly reduces the battery impedance and improves the high-rate discharge performance. At the same time, the mechanical strength of the separator is greatly improved, but the conditions of the cross-linking reaction are difficult to control, which is not conducive to obtaining high performance with uniform performance. diaphragm.

Patent CN101562243A proposes an electrospinning preparation method of a high-performance polyarylether resin lithium battery separator. The method is to place the high-performance polyarylether resin solution and the general-purpose engineering resin solution in different syringe pumps of the spinning machine, and conduct mixed electrospinning on the two types of resin solutions at the same time, and utilize the gap between various fibers during the spinning process. Intertwined, woven, and finally collected on the receiving device in the form of fiber non-woven fabrics to prepare a high-performance lithium battery separator. The composite separator has good ion permeability and excellent wettability to the electrolyte, but the mechanical properties of the interface bonding point between the two different fibers are poor, and the diameters of the two polymer fibers are quite different, which is easy to cause Electrochemical performance instability caused by non-uniform separator thickness.

Patent CN103469488A proposes a method for preparing a reinforced electrospun nanofiber lithium-ion battery separator. In this method, two polymer spinning liquid systems whose melting temperatures differ by more than 30°C are mixed and spun by electrospinning technology, and then hot-pressed at a temperature between the melting points of low-melting point polymers and high-melting point polymers. , so that the fiber membranes are bonded and the mechanical strength of the fiber membrane is improved, but the higher heat treatment temperature will melt the low-melting point polymer, which will have a greater negative impact on the porosity of the separator, which will not be conducive to obtaining a higher High ionic conductivity and electrochemical performance.

Contents of the invention

The present invention aims to solve the above deficiencies in the prior art of lithium-ion battery separators, and provides a method for preparing a high-performance lithium-ion battery separator with high porosity, good electrochemical performance and relatively high mechanical strength. In order to achieve the above object, the technical solution provided by the present invention is: a method for preparing a lithium battery diaphragm by coaxial electrospinning, characterized in that: the lithium battery diaphragm is a core prepared by coaxial electrospinning technology The composite fiber membrane with shell structure is characterized in that: the core-shell two layers of the composite fiber membrane are concentric, the core layer is made of polyarylether sulfone ketone nanofibers with high melting point, and the shell layer is made of polyvinylidene fluoride with low melting point In particular, the coaxial composite membrane is hot-pressed at a certain temperature and pressure, and the shell fibers are slightly melted or melted to enhance the bonding force between the fibers, and the tensile strength of the composite membrane in all directions is uniform. be greatly improved. The lithium battery separator has a porosity of more than 75%, an electrolyte absorption rate of more than 550%, and can withstand high temperatures of 180°C. Therefore, the separator prepared by this method has both good electrochemical properties and thermal and mechanical properties. And electric vehicles and other fields have high application value.

The lithium battery diaphragm of the present invention is a core/shell structure composite coaxial fiber membrane through hot pressing, wherein the core fiber is polyarylether sulfone ketone (PPESK) material, and the shell fiber is polyvinylidene fluoride ( PVDF) material. The core-shell fiber is prepared by a coaxial electrospinning device. During the coaxial electrospinning, the core layer and the shell layer polymer solution are respectively installed in two different syringes. The spinneret system consists of two coaxial but different inner diameters. Composed of capillary tubes, under the action of a high-voltage electric field, the outer layer liquid flows out and joins the core layer liquid. The two liquids will not mix together before solidification. The shell layer liquid is stretched by high frequency, and the interface between the inner layer and the inner layer solution will be formed when spraying at high speed. Under strong shear stress, the core layer solution moves coaxially along the shell layer under the action of shear stress, bends, whips, deforms and solidifies into ultrafine coaxial composite nanofibers. After the solvent is fully volatilized, the composite fiber membrane will be hot-pressed above the glass transition temperature of the low-melting polyvinylidene fluoride, and the polyvinylidene fluoride fibers in the shell will be slightly melted or partially melted, and the nanofibers will stick to each other. The knots increase the effective bonding points in the fiber membrane, so that the tensile strength of the core/shell composite fiber membrane is greatly improved in all directions, and it can resist the impact in the winding direction of the separator during the lithium battery assembly process. During the hot pressing process, the polyarylether sulfone ketone fiber in the shell can still maintain its original shape due to its high melting point and heat resistance, so the coaxial fiber membrane after hot pressing can still maintain a high Porosity and liquid absorption, which are the most significant advantages compared with ordinary heat-treated separators, thus have the potential to become an ideal lithium battery separator product.

Technical scheme of the present invention:

A method for preparing a lithium battery separator by coaxial electrospinning, the steps are as follows:

The first step: dissolving polyarylether sulfone ketone resin and polyvinylidene fluoride resin in an organic solvent respectively to form uniform and stable spinning solution A and spinning solution B, wherein the concentration of polyarylether sulfone ketone resin solution is 10-25wt%, the concentration of polyvinylidene fluoride resin solution is 8%-20wt%;

The organic solvent is one of N,N dimethylacetamide (DMAc), N,N dimethylformamide (DMF), N-methyl-pyrrolidone (NMP), tetrahydrofuran (THF), acetone Or a mixture of two or more.

The second step: the two syringes take spinning solution A and spinning solution B respectively, and fix them on the bracket of the electrospinning machine. The main channel of the coaxial electrospinning device is connected; a layer of aluminum foil is pasted on the receiving roller as the fiber receiving device, and the distance between the end of the main channel of the coaxial electrospinning device and the receiving roller is set to 10-25cm. The end of the channel is connected to the positive pole of the high-voltage power supply through wires, and the receiving roller is connected to the negative pole of the high-voltage power supply;

Step 3: Set the temperature and humidity of the electrospinning machine to the predetermined value, adjust the voltage to 8-25kV, inject the polyarylethersulfone ketone resin solution at a speed of 0.02mm/min-0.2mm/min, and inject the polyvinylidene fluoride resin solution The speed is 0.04-0.2mm/min, and the injection speed of the polyvinylidene fluoride resin solution is always higher than the injection speed of the polyarylether sulfone ketone resin solution, and the spinning is started; during the spinning process, the two spinning solutions are not mixed before solidification, A high-voltage electric field is applied to the inner and outer layers of liquid, and a composite Taylor cone is formed at the spinning nozzle. The composite Taylor cone is further drawn into a core/shell structure jet stream, and undergoes strong whipping and bending deformation during the stretching process. Due to the rapid volatilization of the solvent during the jet drafting process and the gradual refinement of the jet stream, the electrospun polyarylether sulfone ketone core-polyvinylidene fluoride shell composite nanofiber membrane with a coaxial structure is finally collected on the fiber receiving device;

The electrospun polyarylether sulfone ketone core-polyvinylidene fluoride shell composite nanofiber membrane is placed under vacuum conditions, and dried until the solvent is fully volatilized to obtain the dried electrospun polyarylether sulfone ketone core-polyvinylidene fluoride Shell composite nanofibrous membrane;

Step 4: Remove the dried electrospun polyarylether sulfone ketone core-polyvinylidene fluoride shell composite nanofiber membrane from the aluminum foil, cut it into the desired shape, and place it on the stainless steel mold of the hot press machine. Set the hot-pressing temperature at 150-250°C, keep warm for 0.5-2h, and press at 1-5MPa for hot-pressing. The hot-pressing process is carried out under vacuum conditions; the coaxial fiber composite film obtained by hot-pressing is dried under vacuum conditions , that is, to obtain a lithium battery separator, the lithium battery separator has a porosity of 70%-90%, an electrolyte absorption rate of more than 550%, can withstand a high temperature of 180° C., and a thickness of 30-80 μm.

The time for spinning in the third step is 1-8 hours; the temperature of the electrostatic spinning machine is 20-50° C., and the humidity is 20%-50%.

In the third step, the drying temperature is 40-120° C., and the drying time is 12-24 hours.

The polyaryl ether sulfone ketone resin refers to a class of soluble high-performance thermoplastic resin developed on the basis of polyaryl ether resin, which is a polyaryl ether sulfone ketone resin containing a phthalazine structure, referred to as PPESK, wherein S represents a sulfone group (O=S=O), K represents a carbonyl group (C=O), and the ratio of S/K is adjustable. The polyvinylidene fluoride resin refers to a homopolymer of vinylidene fluoride or a copolymer of vinylidene fluoride and other small amounts of fluorine-containing vinyl monomers. PVDF resin has good chemical corrosion resistance, high temperature resistance, and oxidation resistance. etc., its glass transition temperature is -39°C, its melting point is 170°C, its thermal decomposition temperature is about 350°C, and its long-term use temperature is -40～150°C.

The present invention has beneficial effects: (1) Polyaryl ether sulfone ketone resin containing phthalazinyl biphenyl structure has excellent high temperature resistance, and coaxial compounding with polyvinylidene fluoride can greatly improve the high temperature thermal stability of the diaphragm , the prepared electrospun polyarylether sulfone ketone/polyvinylidene fluoride coaxial composite fiber membrane basically does not shrink in size at a high temperature of 180 ° C, which is conducive to coping with the complex thermal conditions during the operation of electric vehicles and greatly improves the The safety performance of power lithium battery; (2) The prepared randomly oriented coaxial composite fiber membrane is hot-pressed above the glass transition temperature of polyvinylidene fluoride, and the polyvinylidene fluoride fiber is slightly melted or partially melted, thereby increasing the The effective bonding points in the composite fiber membrane hinder the deformation of the fiber network during the stretching process, greatly improving the tensile strength of the coaxial composite membrane in all directions. Tensile tests show that the high-performance static electricity prepared by the present invention The tensile strength of spun polyarylether sulfone ketone lithium battery separator is 4-15 times higher than that of randomly oriented polyarylether sulfone ketone nanofiber membrane, which can meet the mechanical properties required for lithium battery separator assembly, and due to the use of high melting point The polyarylether sulfone ketone fiber is used as the core layer, which can still maintain the original shape during the hot pressing process, and the porosity loss of the coaxial composite membrane is small, and maintains a high porosity while ensuring good mechanical properties. (3) Polyaryl ether sulfone ketone molecules contain a large number of polar groups such as ether bonds (-O-), carbonyl groups (C=O) and sulfone groups (O=S=O), and polyvinylidene fluoride molecules contain (C-F) polar groups, so the electrospun polyarylether sulfone ketone/polyvinylidene fluoride coaxial composite nanofiber membrane has good wettability to carbonate electrolytes, and the liquid absorption rate can be as high as 550%, effectively reducing the The internal resistance of the lithium battery greatly improves the ionic conductivity of the diaphragm electrolyte system, prolongs the cycle life of the lithium battery, and improves the ability to discharge at a high rate.

Description of drawings

Figure 1 is a scanning electron micrograph of an electrospun 20% PPESK/15% PVDF core-shell composite fiber membrane, where the solution injection speeds are 0.08mm/min and 0.12mm/min respectively.

Fig. 2 is the stress-strain curve of the electrospun 20%PPESK/12%PVDF core-shell composite fiber membrane treated by hot pressing.

Fig. 3 is a Nyquist curve of coaxial electrospun 15%PPESK/12%PVDF core-shell composite fiber lithium battery separator treated by hot pressing.

Fig. 4 is a schematic diagram of a device used in a method for preparing a lithium battery separator by coaxial electrospinning.

Detailed ways

The specific implementation manners of the present invention will be further described below in conjunction with the accompanying drawings and technical solutions.

Example 1

Take a certain amount of tetrahydrofuran and N-methylpyrrolidone mixed solvent with a volume ratio of 3:7, dissolve a certain amount of PPESK powder in a round bottom flask, and prepare a PPESK polymer solution with a mass fraction of 10%; take a certain volume ratio A 4:6 mixed solvent of N,N dimethylacetamide (DMAc) and acetone was used to dissolve a certain amount of PVDF powder in a round bottom flask to prepare a PVDF solution with a mass fraction of 8%, and the two solutions were respectively Place in a magnetic stirrer at a constant temperature of 60°C for 12 hours to obtain a spinning solution, which is then stored in a brown glass bottle for use. Use a disposable syringe with a capacity of 10ml to take 4ml of polyarylether sulfone ketone spinning solution and 10ml of polyvinylidene fluoride spinning solution respectively, choose a flat stainless steel needle with a diameter of 0.3mm as the core layer solution needle for coaxial spinning, and place the two The two syringes are respectively fixed on the spinning machine bracket, the position of the coaxial spinning needle is adjusted so that the needle is at the center of the receiving roller, and a layer of aluminum foil is wound on the receiving roller to receive the fiber. Set the temperature inside the electrospinning machine to 30°C, the humidity to 20%, adjust the distance between the flat stainless steel needle and the receiving roller to 15cm, adjust the voltage to 8kV, and inject the polyaryl ether sulfone ketone core layer solution at a speed of 0.02mm /min, the injection speed of the polyvinylidene fluoride shell solution is 0.04mm/min, the speed of the receiving roll is 100r/min, and the spinning time is 6h. After the spinning is completed, the diaphragm is removed from the receiving roll and placed in a vacuum oven Treat at 60°C for 12h. Cut the dried diaphragm into a regular rectangular shape, place it on the stainless steel mold used in the hot press, set the hot pressing temperature to 150°C, the holding time to 1h, and the pressure to 1MPa. The autoclaved diaphragm was dried in a vacuum oven at room temperature for 12 hours, and then used.

After testing, the PPESK/PVDF core/shell composite nanofiber membrane prepared under this condition has a thickness of 53 μm and a porosity of 85%. The liquid absorption rate in lithium iron phosphate electrolyte (EC:DEC=1:1 volume ratio) Reaching 750%, the ionic conductivity of the separator electrolyte system reaches 3.5mS cm ^-1 , and the tensile strength is 8.6MPa, which is 910% higher than the 0.95MPa of the randomly oriented PPESK separator.

Example 2

Take a certain amount of tetrahydrofuran and N,N dimethylacetamide (DMAc) mixed solvent with a volume ratio of 4:6, dissolve a certain amount of PPESK powder in a round bottom flask, and prepare a PPESK polymer solution with a mass fraction of 15%. ; Remove a certain amount of N,N dimethylacetamide (DMAc) and acetone mixed solvent with a volume ratio of 3:7, dissolve a certain amount of PVDF powder in a round bottom flask, and prepare a PVDF solution with a mass fraction of 12% , the two solutions were respectively placed in a magnetic stirrer at a constant temperature of 60°C for 12 hours to obtain a spinning solution, which was then stored in a brown glass bottle for use. Use a disposable syringe with a capacity of 10ml to take 4ml of polyarylether sulfone ketone spinning solution and 10ml of polyvinylidene fluoride spinning solution respectively, choose a flat stainless steel needle with a diameter of 0.3mm as the core layer solution needle for coaxial spinning, and place the two The two syringes are respectively fixed on the spinning machine bracket, the position of the coaxial spinning needle is adjusted so that the needle is at the center of the receiving roller, and a layer of aluminum foil is wound on the receiving roller to receive the fiber. Set the temperature inside the electrospinning machine to 35°C, the humidity to 20%, adjust the distance between the flat stainless steel needle and the receiving roller to 10cm, adjust the voltage to 15kV, and inject the polyarylethersulfoneketone core layer solution at a speed of 0.08mm /min, the injection speed of the polyvinylidene fluoride shell solution is 0.2mm/min, the speed of the receiving roll is 100r/min, and the spinning time is 2.5h. After the spinning is completed, the diaphragm is removed from the receiving roll and placed in a vacuum Treat in an oven at 80°C for 12h. Cut the dried diaphragm into a regular rectangular shape, place it on the stainless steel mold used in the hot press, set the hot pressing temperature to 200°C, the holding time to 2h, and the pressure to 3MPa. The autoclaved diaphragm was dried in a vacuum oven at room temperature for 12 hours, and then used.

After testing, the 15% PPESK/12% PVDF core/shell composite nanofiber membrane prepared under this condition has a thickness of 40 μm and a porosity of 81%. In lithium iron phosphate electrolyte (EC:DEC=1:1 volume ratio) The liquid absorption rate reaches 735%, the ionic conductivity of the diaphragm electrolyte system reaches 2.8mS cm ^-1 , and the tensile strength is 26MPa, which is 1444% higher than the 1.8MPa of the randomly oriented PPESK diaphragm.

Example 3

Take a certain amount of tetrahydrofuran and N,N dimethylformamide (DMF) mixed solvent with a volume ratio of 6:4, dissolve a certain amount of PPESK powder in a round bottom flask, and prepare a PPESK polymer solution with a mass fraction of 20%. ; Remove a certain amount of N,N dimethylacetamide (DMAc) and acetone mixed solvent with a volume ratio of 5:5, dissolve a certain amount of PVDF powder in a round bottom flask, and prepare a PVDF solution with a mass fraction of 16% , the two solutions were respectively placed in a magnetic stirrer at a constant temperature of 60°C for 12 hours to obtain a spinning solution, which was then stored in a brown glass bottle for use. Use a disposable syringe with a capacity of 10ml to take 6ml of polyarylether sulfone ketone spinning solution and 8ml of polyvinylidene fluoride spinning solution respectively, choose a flat stainless steel needle with a diameter of 0.3mm as the core layer solution needle for coaxial spinning, and put the two The two syringes are respectively fixed on the spinning machine bracket, the position of the coaxial spinning needle is adjusted so that the needle is at the center of the receiving roller, and a layer of aluminum foil is wound on the receiving roller to receive the fiber. Set the temperature inside the electrospinning machine to 30°C, the humidity to 20%, adjust the distance between the flat stainless steel needle and the receiving roller to 25cm, adjust the voltage to 25kV, and inject the polyarylethersulfoneketone core layer solution at a speed of 0.12mm /min, the injection speed of the polyvinylidene fluoride shell solution is 0.16mm/min, the speed of the receiving roll is 100r/min, and the spinning time is 1.5h. After the spinning is completed, the diaphragm is removed from the receiving roll and placed in a vacuum Treat in an oven at 120°C for 12h. Cut the dried diaphragm into a regular rectangular shape, place it on the stainless steel mold used in the hot press, set the hot pressing temperature to 250°C, the holding time to 1h, and the pressure to 5MPa. The autoclaved diaphragm was dried in a vacuum oven at room temperature for 12 hours, and then used.

The 20% PPESK/16% PVDF core/shell composite nanofiber membrane prepared under these conditions has a thickness of 35 μm and a porosity of 78%. The ratio reaches 720%, the ionic conductivity of the separator electrolyte system reaches 3.2mS cm ^-1 , and the tensile strength is 28MPa, which is 875% higher than the 3.2MPa of the randomly oriented 20% PPESK separator.

Example 4

Take a certain amount of N,N dimethylacetamide (DMAc) solvent, dissolve a certain amount of PPESK powder in a round bottom flask, and prepare a PPESK polymer solution with a mass fraction of 25%; the volume ratio of a certain amount is 7:3 N, N dimethylacetamide (DMAc) and acetone mixed solvent, dissolve a certain amount of PVDF powder in a round bottom flask, prepare a PVDF solution with a mass fraction of 20%, and place the two solutions on a magnetic stirrer Magnetic stirring at a constant temperature of 60°C for 12 hours in a container to obtain a spinning solution, which was then stored in a brown glass bottle for later use. Use a disposable syringe with a capacity of 10ml to take 5ml of polyarylether sulfone ketone spinning solution and 8ml of polyvinylidene fluoride spinning solution respectively, choose a flat stainless steel needle with a diameter of 0.3mm as the core layer solution needle for coaxial spinning, and place the two The two syringes are respectively fixed on the spinning machine bracket, the position of the coaxial spinning needle is adjusted so that the needle is at the center of the receiving roller, and a layer of aluminum foil is wound on the receiving roller to receive the fiber. Set the temperature inside the electrospinning machine to 25°C, the humidity to 25%, adjust the distance between the flat stainless steel needle and the receiving roller to 20cm, adjust the voltage to 20kV, and inject the polyarylethersulfoneketone core layer solution at a speed of 0.08mm /min, the injection speed of the polyvinylidene fluoride shell solution is 0.12mm/min, the speed of the receiving roll is 100r/min, and the spinning time is 2.5h. After the spinning is completed, the diaphragm is removed from the receiving roll and placed in a vacuum Treat in an oven at 100°C for 12h. Cut the dried diaphragm into a regular rectangular shape, place it on the stainless steel mold used in the hot press, set the hot pressing temperature to 300°C, the holding time to 0.5h, and the pressure to 2MPa. The autoclaved diaphragm was dried in a vacuum oven at room temperature for 12 hours, and then used.

The 25% PPESK/20% PVDF core/shell composite nanofiber membrane prepared under these conditions has a thickness of 42 μm and a porosity of 72%. The efficiency reaches 650%, the ionic conductivity of the separator electrolyte system reaches 2.5mS cm ^-1 , and the tensile strength is 18MPa, which is 514% higher than the 3.5MPa of the randomly oriented 25% PPESK separator.

Claims (5)

1. a kind of method preparing lithium battery diaphragm with coaxial electrostatic spinning, which is characterized in that steps are as follows：

The first step：Polyarylethersulfone ketone resin and polyvinylidene fluoride resin are dissolved separately in organic solvent, stable homogeneous is formed Spinning solution A and spinning solution B, wherein a concentration of 10-25wt% of polyarylethersulfone ketone resin solution, Kynoar tree A concentration of 8%-20wt% of lipoprotein solution；

Second step：Two syringes take spinning solution A and spinning solution B respectively, and are fixed on the holder of electrostatic spinning machine, injection Device is connected with coaxial electrostatic spinning equipment, and the syringe and coaxial electrostatic spinning equipment main channel phase of polyarylethersulfone ketone resin solution are housed Even；One layer of aluminium foil is pasted in receiving roll as fiber reception device, setting coaxial electrostatic spinning equipment main channel end and reception The distance between roller is 10-25cm, and coaxial electrostatic spinning equipment main channel end is connected by conducting wire with high-voltage power cathode, is received Roller is connected with high voltage power supply cathode；

Third walks：Setting electrostatic spinning machine temperature and humidity is predetermined value, and adjustment voltage is 8-25kV, and polyarylethersulfone ketone resin is molten Liquid injection speed is 0.02mm/min-0.2mm/min, and polyvinylidene fluoride resin solution injection speed is 0.04-0.2mm/min, It remains that polyvinylidene fluoride resin solution injection speed is more than polyarylethersulfone ketone resin solution injection speed, starts spinning；

Electrostatic spinning poly (aryl ether sulfone ketone) core-Kynoar shell composite nano-fiber membrane is placed under vacuum condition, it is dry to molten Agent is fully volatilized, electrostatic spinning poly (aryl ether sulfone ketone) core-Kynoar shell composite nano-fiber membrane after being dried；

4th step：By electrostatic spinning poly (aryl ether sulfone ketone) core-Kynoar shell composite nano-fiber membrane after drying from aluminium-foil paper On remove, be cut into required shape, be placed on the stainless steel mould of hot press, be arranged 150-250 DEG C of hot pressing temperature, heat preservation 0.5-2h, hot pressing pressure 1-5MPa, carry out hot pressing, and hot pressing carries out under vacuum；The coaxial fiber that hot pressing is obtained Composite membrane, which is placed under vacuum condition, to be dried to get to lithium battery diaphragm, and the lithium battery diaphragm porosity is 70%-90%, Electrolyte imbibition rate is up to 550% or more, is resistant to 180 DEG C of high temperature, and thickness is 30-80 μm.

2. preparation method according to claim 1, which is characterized in that the organic solvent be N, N dimethyl acetamide, N, the mixing of one or more of N-dimethylformamide, N- methyl-pyrrolidons, tetrahydrofuran, acetone.

3. preparation method according to claim 1 or 2, which is characterized in that the time of spinning is 1-8h in third step；It is described Electrostatic spinning machine temperature be 20-50 DEG C, humidity 20%-50%.

4. preparation method according to claim 1 or 2, which is characterized in that drying temperature is 40-120 DEG C in third step, is done The dry time is 12-24h.

5. preparation method according to claim 3, which is characterized in that drying temperature is 40-120 DEG C in third step, dry Time is 12-24h.