WO2019140780A1 - Method and system for manufacturing separator membrane of secondary lithium-ion battery - Google Patents

Abstract

The present invention relates to a method for manufacturing a separator membrane of a secondary lithium-ion battery, the method comprising: A1: blending and melting polyethylene with a pore former in an extruder to obtain a melted body; A2: cooling the melted body obtained in step A1 on a cooling roller, and forming an oil-containing substrate; A3: delivering the oil-containing substrate of step A2 into a pre-stretching device by means of a transmission roller for pre-stretching, and forming a pre-stretched substrate; A4: placing the pre-stretched substrate of step A3 into an extraction device having an ultrasonic wave generator to perform ultrasonic extraction, and obtaining an oil-removed substrate after the extraction; A5: delivering the oil-removed substrate of step A4 into a stretching device by means of a transmission roller to perform synchronous stretching, and forming a thin membrane; and A6: transporting the thin membrane of step A5 to a thermal processing device to perform thermal processing, and forming a microporous separator membrane. The present invention further relates to a system. The present invention realizes low-speed extraction, and achieves high-speed membrane manufacturing by means of controlling a stretching ratio in a longitudinal direction.

Description

Method and system for producing lithium ion secondary battery separator Technical field

The invention relates to the technical field of battery separator production, and in particular to a method and a system for producing a lithium ion secondary battery separator.

Background technique

Lithium-ion secondary batteries are increasingly used in consumer electronics, electric vehicles, and energy storage because of their high energy density and long cycle life.

The separator is one of the important components of a lithium ion secondary battery, and has a great influence on the characteristics of the battery, particularly the safety of the battery. The separator can be classified into a dry diaphragm and a wet diaphragm according to the manufacturing method thereof. Due to its excellent characteristics and thin thickness, the wet diaphragm is suitable for high energy density ternary battery systems. Compared with the dry film forming process, the manufacturing process is complicated and the production cost is high. The wet method is widely used in the battery field of electric vehicles. The diaphragm has certain challenges. Therefore, there is an urgent need for a high-performance, low-cost film forming method. Increasing the product yield of the separator and increasing the production speed of the separator can effectively reduce the production cost of the wet diaphragm.

The traditional wet film forming process is first stretched and then extracted. As the production line speed increases, the extraction speed also becomes faster. High-speed extraction brings a series of problems: 1 When extracting at high speed, the length of the extraction tank must be increased, and the production line is extended. The investment cost of the production line increases; 2 When the high-speed extraction, the extraction film of the extraction tank has a large amount of liquid, the extractant cannot be completely volatilized, resulting in poor film surface; 3 high-speed extraction improves the precision of the equipment, and the stability of the production line is not easy to control. In summary, the conventional process of first stretching and then extracting cannot achieve high-speed production, and the production efficiency is low. At present, the traditional film making process has a film forming speed of 30-50 m/min.

Therefore, designing a lithium ion secondary battery separator capable of avoiding the above problems and being fast, efficient, and high quality is one of the problems to be solved in the field.

Summary of the invention

In view of the problems in the prior art, an object of the present invention is to provide a method and system for producing a lithium ion secondary battery separator which has the advantages of fastness, high efficiency, high quality and the like.

The object of the invention is achieved by the following technical solutions:

A method for producing a lithium ion secondary battery separator, comprising the following steps:

A1: mixing and melting polyethylene and a pore former in an extruder to obtain a melt;

A2: cooling the melt obtained in the step A1 on a cooling roll to form an oil-containing substrate;

A3: the oil-containing substrate in step A2 is pre-stretched through a driving roller into a pre-stretching device to form a pre-stretched substrate;

A4: the pre-stretched substrate in step A3 is sent to an extraction device having an ultrasonic generator through a driving roller for ultrasonic extraction, the extraction device contains an extracting agent, and after the extraction, a degreased substrate is obtained;

A5: the oil-removed substrate in step A4 is passed through a driving roller into a stretching device for stretching to form a film;

A6: The film in the step A5 is transferred to a heat treatment device through a driving roller for heat treatment to form a microporous separator having a stable pore structure.

The polyethylene has a viscosity average molecular weight of 300,000 to 2.5 million in the step A1, a mass percentage of the polyethylene of 15% to 50%, and a mass percentage of the pore former of 50% to 85%. The porogen is a mineral oil or a synthetic oil.

The transverse or longitudinal magnification of the pre-stretching in step A3 is 0.1-5 times, the temperature is 85-130 ° C, and the pre-stretching mode is unidirectional pre-stretching or biaxial pre-stretching; stretching in step A5 The transverse magnification or the longitudinal magnification is 1.1-10 times, and the stretching mode in the step A5 is uniaxial stretching or biaxial stretching.

The power density of the ultrasonic wave in step A4 is 1.0-2.95 w/cm ² and the frequency is 10-200 kHz; the extracting agent is miscible with the pore forming agent, and the extracting agent is chloroform, dichloromethane or decane. One type, the extraction time is 3-5 min.

The temperature in the cooling roll in step A2 is 15-40 ° C, and the heat treatment temperature in step A6 is 100-140 ° C.

The film forming speed in the step A6 is 100 m/min or more.

The invention also provides a production system of a lithium ion secondary battery separator, comprising an extruder, a cooling roller, a pre-stretching device, an extracting device, a stretching device and a heat treatment device, wherein the extruder is provided below the outlet a cooling roller, the end of the cooling roller is provided with a pre-stretching device, and the pre-stretching device, the extracting device, the stretching device and the heat treatment device are provided with a driving roller between two adjacent devices.

The extraction device is filled with an extractant, and the extraction device includes an extraction tank and a plurality of ultrasonic generators located below the extraction tank.

A plurality of driving rollers are disposed in the extraction tank, and the plurality of driving rollers are located between the liquid surface of the extracting agent in the extraction tank and the bottom of the extraction tank, and the plurality of driving rollers constitute a W-shaped or V-shaped structure.

The extruder is a twin-screw extruder, the pre-stretching device is a stretching machine, the stretching device is a stretching machine, and the heat treatment device is a heat setting device.

Formula and common sense

The following physical and chemical properties of the obtained microporous membrane were measured:

Thickness (micron): GB/T 6672-2001 ISO 4593:1993. The thickness test was performed using a Ono thickness gauge.

Tensile strength (Kgf/cm2): GB 6672-2001. The spline having a width of 15 mm was stretched at a speed of 200 mm/min using a Shimadzu universal tensile tester.

Needle strength (gf): The force required to pierce the diaphragm at a certain speed with a needle of φ1 mm.

Air permeability (seconds / 100 ml): The time required to pass 100 mL of air through a φ 1 inch circular section with Gurley.

Porosity (%): The formula is as follows

"(raw material density * sample area * thickness) - weight" / (raw material density * sample area * thickness).

The invention has the beneficial effects:

The invention pre-stretches the oil-containing substrate to a certain extent, reduces the interfacial tension between the polyethylene and the pore former in the substrate, makes the extracting agent easier to replace the pore former; and then applies the pre-stretched substrate. Ultrasonic extraction accelerates the diffusion of the extractant in the substrate, shortens the extraction time, improves the extraction efficiency, and lays a foundation for high-speed production; therefore, the film forming method of the present invention realizes low-speed extraction by controlling the longitudinal stretching ratio, thereby Achieve high-speed film formation.

DRAWINGS

1 is an SEM image of a lithium ion secondary battery separator produced in Example 1 of the present invention;

2 is a schematic structural view of a production system of a lithium ion secondary battery separator of the present invention;

3 is a flow chart showing a production process of a lithium ion secondary battery separator of the present invention;

4 is a flow chart showing the production process of a conventional lithium ion secondary battery separator.

Among them, 1-pretensioning device, 2-oil-containing substrate, 3-drive roller, 4-extraction tank, 40-drive roller, 5-stretching device, 6-heat treatment device, 7-ultrasonic generator, 8-cooling Roll, 9-extruder, 10-die.

Detailed ways

The present invention provides a method and a system for producing a lithium ion secondary battery separator. The specific embodiments are described below by way of specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention this invention.

Example 1

Referring to the process flow diagram described in Figure 3, a mass percentage of 30% polyethylene (molecular weight of 800,000) is mixed with 70% by mass of mineral oil (40 ° C, kinematic viscosity of 45-55 mm ² /s) , adding a twin-screw extruder, fully melting at 195 ° C, the melt passed through the extruder die, forming a 1 mm thick oil-containing substrate on a 25 ° C cooling roll, the speed of the oil-based substrate was pulled on the cooling roll After 6 m/min, the oil-containing substrate was pre-stretched in a stretching machine at 120 ° C to form a pre-stretched substrate, the transverse stretching ratio was 2 times, the longitudinal stretching ratio was 2 times, and then transported through a driving roller. The extraction tank equipped with the ultrasonic generator was extracted at 17 kHz for 3 min to form a degreased substrate, and then the degreased substrate was driven into the stretching machine under the driving roller, and stretched at 120 ° C, transversely, The longitudinal stretching ratio was 3.5 times, and a film was obtained. The film was heat-treated at 130 ° C to form a microporous separator having a stable pore structure, and the microporous film characteristics were measured. The microstructure thereof is shown in FIG. The above parameters are detailed in Table 1.

Example 2

Referring to the process flow diagram described in Figure 3, a mass percentage of 30% polyethylene (molecular weight of 800,000) is mixed with 70% by mass of mineral oil (40 ° C, kinematic viscosity of 45-55 mm ² /s) , adding a twin-screw extruder, fully melting at 195 ° C, the melt passed through the extruder die, forming a 1 mm thick oil-containing substrate on a 25 ° C cooling roll, the speed of the oil-based substrate was pulled on the cooling roll After 10 m/min, the oil-containing substrate was pre-stretched in a stretching machine at 120 ° C to form a pre-stretched substrate, and the transverse stretching ratio was 4 times (no longitudinal stretching), and then transported through a driving roller to be loaded. The extraction tank of the ultrasonic generator is extracted at 17 kHz for 3 min to form a degreased substrate, and then the degreased substrate is driven into a stretching machine by a driving roller, and stretched at 120 ° C, and the transverse stretching ratio is performed. The film was 1.75 times and the longitudinal stretching ratio was 7 times, and a film was obtained. The film was heat-treated at 130 ° C to form a microporous separator having a stable pore structure, and the properties of the microporous film were measured.

Example 3

Referring to the process flow diagram described in Figure 3, a mass percentage of 30% polyethylene (molecular weight of 800,000) is mixed with 70% by mass of mineral oil (40 ° C, kinematic viscosity of 45-55 mm ² /s) , adding a twin-screw extruder, fully melting at 195 ° C, the melt passed through the extruder die, forming a 1 mm thick oil-containing substrate on a 25 ° C cooling roll, the speed of the oil-based substrate was pulled on the cooling roll After 15 m/min, the oil-containing substrate was pre-stretched in a stretching machine at 120 ° C to form a pre-stretched substrate, the transverse stretching ratio was 2 times, the longitudinal stretching ratio was 2 times, and then transported through a driving roller. The extraction tank equipped with the ultrasonic generator was extracted at 17 kHz for 3 min to form a degreased substrate, and then the degreased substrate was driven into the stretching machine under the driving roller, and stretched at 120 ° C, transversely, The longitudinal stretching ratio was 3.5 times, and a film was obtained. The film was heat-treated at 130 ° C to form a microporous separator having a stable pore structure, and the properties of the microporous film were measured.

Example 4

Referring to the process flow diagram described in Figure 3, a mass percentage of 30% polyethylene (molecular weight of 800,000) is mixed with 70% by mass of mineral oil (40 ° C, kinematic viscosity of 45-55 mm ² /s) , adding a twin-screw extruder, fully melting at 195 ° C, the melt passed through the extruder die, forming a 1.6 mm thick oil-containing substrate on a 25 ° C cooling roll, the cooling roll was pulled on the oil-containing substrate The speed was 20 m/min, and then the oil-containing substrate was pre-stretched in a stretching machine at 120 ° C to form a pre-stretched substrate, the transverse stretching ratio was 4 times, the longitudinal stretching ratio was 1.6 times, and then conveyed by a driving roller. After entering the extraction tank equipped with the ultrasonic generator, extracting at 17 kHz for 3 min to form a degreased substrate, and then removing the oil substrate into the stretching machine under the driving roller, and stretching at 120 ° C, transversely The stretching ratio was 2 times and the longitudinal stretching ratio was 5 times, and a film was obtained. The film was heat-treated at 130 ° C to form a microporous separator having a stable pore structure, and the properties of the microporous film were measured.

Example 5

Referring to the process flow diagram described in FIG. 3, 50% by mass of polyethylene (molecular weight: 800,000) and 50% by mass of paraffin oil (having a kinematic viscosity of 45-55 mm ² /s at 40 ° C) are mixed. , adding a twin-screw extruder, fully melting at 195 ° C, the melt passed through the extruder die, forming a 1.3 mm thick oil-containing substrate on a 25 ° C cooling roll, the cooling roll was pulled on the oil-containing substrate The speed was 20 m/min, and then the oil-containing substrate was pre-stretched in a stretching machine at 120 ° C to form a pre-stretched substrate, the transverse stretching ratio was 4 times, the longitudinal stretching ratio was 1.6 times, and then conveyed by a driving roller. After entering the extraction tank equipped with the ultrasonic generator, extracting at 17 kHz for 3 min to form a degreased substrate, and then removing the oil substrate into the stretching machine under the driving roller, and stretching at 120 ° C, transversely The stretching ratio was 2.5 times and the longitudinal stretching ratio was 7 times, and a film was obtained. The film was heat-treated at 130 ° C to form a microporous separator having a stable pore structure, and the properties of the microporous film were measured.

Comparative example 1:

Referring to the process flow diagram described in FIG. 4, 30% by mass of polyethylene (molecular weight: 800,000) is mixed with 70% by mass of mineral oil (having a kinematic viscosity of 45-55 mm 2 /s at 40 ° C). It was added to a twin-screw extruder and fully melted at 195 ° C. The melt was passed through an extruder die to form a 1 mm thick oil-containing substrate on a 25 ° C cooling roll, and the speed of drawing the oil-containing substrate on the cooling roll was 6m/min, then the oil-containing substrate was biaxially stretched at 120 ° C to form a stretched film, the transverse stretching ratio was 7 times, the longitudinal stretching ratio was 7 times, and the stretched film was transported through the driving roller into the extraction tank for extraction to form a film. The film was heat-treated at 130 ° C to form a microporous separator having a stable pore structure, and the properties of the microporous membrane were measured.

Table 1 shows the relationship between different process parameters and film forming speed.

In the embodiment of the invention, the extraction speed is the product of the traction speed of the oil-bearing substrate and the pre-stretching longitudinal magnification, and the film forming speed is the product of the oil-based substrate traction speed and the total longitudinal stretching ratio. In the conventional process, the extraction speed is the oil-based substrate traction speed. The product is multiplied by the tensile longitudinal magnification, and the film forming speed is the extraction speed. The transverse stretch or the longitudinal magnification of the pre-stretching in the present invention is 0.1 to 5 times, and the transverse or longitudinal magnification of the stretching is 1.1 to 10 times, and the above embodiment is exemplified by one of them.

By comparing Example 1 with Comparative Example 1, the extraction can be carried out at a lower speed at the same film forming speed, and the problem that the extraction speed restricts the film forming speed is solved.

Comparing Examples 2, 3, 4, and 5 with Comparative Example 1, the film forming speed was effectively improved by different stretching ratios (pre-stretching longitudinal magnification × stretching longitudinal magnification) without increasing the extraction speed. .

Comparing the above table, the low-speed extraction is realized by the process of the present invention, and the high-speed film formation is realized by controlling the longitudinal stretching ratio.

Table 2 shows the characteristics of the separator of the present invention and comparison with the conventional process

Implementation

Implementation

Implementation

Implementation

Implementation

Comparison

	example 1	Example 2	Example 3	Example 4	Example 5	example 1
Diaphragm thickness μm	12	12	12	12	12	12
Porosity %	43	41	41	42	43	40
Breathability value Sec/100ml	176	172	184	164	158	201
Acupuncture gf	461	432	456	421	485	424
Longitudinal tensile strength kgf/cm2	1653	1682	1693	1756	1843	1663
Transverse tensile strength kgf/cm2	1631	1594	1571	1635	1713	1632
Longitudinal elongation %	56	52	48	43	41	57
Horizontal elongation %	63	59	52	51	47	61

It can be seen from Table 2 that the separator produced by the present invention has the same characteristics as the separator produced by the conventional process.

In summary, the film forming method of the present invention realizes low-speed extraction, achieves high-speed film formation by controlling the longitudinal stretching ratio, and adopts ultrasonic extraction, and the film forming method of the present invention does not change the separator. The characteristics of the diaphragm are the same as those produced by the conventional process.

Referring to FIG. 2, the present invention also relates to a system for a lithium ion secondary battery separator, comprising an extruder 9, a cooling roller 8, a pretensioning device 1, an extraction device, a stretching device 5, and a heat treatment device 6, A cooling roller 8 is disposed below the outlet of the extruder 9, and the end of the cooling roller 8 is provided with a pre-tensioning device 1, which is adjacent to the pre-stretching device 1, the extraction device, the stretching device 5, and the heat treatment device 6. A drive roller 3 is provided between the two devices.

The pre-stretching device 1, the extracting device, the stretching device 5, and the heat-treating device 6 are sequentially coupled to the driving roller 3.

The extraction device is filled with an extracting agent, and the extraction device includes an extraction tank 4 and a plurality of ultrasonic generators 7 disposed at the bottom of the extraction tank 4; a plurality of driving rollers 40 are disposed in the extraction tank 4 A plurality of driving rollers 40 are disposed between the liquid level of the extractant in the extraction tank 4 and the bottom of the extraction tank 4, and the plurality of driving rollers 40 constitute a W-shaped or V-shaped structure.

The extruder 9 is a twin-screw extruder, the pre-stretching device 1 is a stretching machine, the stretching device 5 is a stretching machine, and the heat treatment device 6 is a heat-setting device.

When the system is in use, a porogen and polyethylene are first introduced into the extruder 9, and heating and mixing are carried out in the extruder 9 to form a mixed melt through which the mixed melt passes. The die 10 of the machine 9 is extruded, and the melt is directly cooled on the cooling roll 8 (the temperature in the cooling roll is 15-40 ° C) to form a cooled oil-containing substrate 2, which enters the oil-containing substrate 2 Pre-stretching device 1 (temperature is 85-130 ° C), pre-stretching in the pre-stretching device 1 (may be unidirectional transverse or longitudinal pre-stretching, or bidirectional lateral and longitudinal pre-tensioning Stretching, wherein the longitudinal direction is the direction in which the oil-containing substrate is pulled), after passing through the pre-stretching device 1, a pre-stretching substrate is formed, and the pre-stretching substrate is driven into the extraction device by the driving roller 3, The extracting agent in the extraction device extracts the pore former in the stretching substrate, the ultrasonic generator 7 in the extraction device is turned on, and the ultrasonic wave generated by the ultrasonic generator 7 makes the extracting agent easier to pre-stretch Diffusion in the substrate, so that it is differentiated and dissolved in the extractant, effectively improving the extraction efficiency, Shortening the extraction time, wherein the ultrasonic power density is 1.0-2.95w/cm ² , the frequency is 10-200kHz, and the extraction time can be 3-5min, wherein the extracting agent is one of chloroform, dichloromethane or decane. . The pre-stretched substrate is passed through an extraction device to form a degreased substrate, and the degreased substrate continues to be driven by the driving roller 40 into the stretching device 5, and the stretching device 5 pairs the degreased substrate Stretching (may be unidirectional transverse or longitudinal stretching, or bidirectional transverse and longitudinal stretching, wherein the longitudinal direction is the direction in which the oil-removing substrate is pulled) to form a film, after which the film is on the drive roller 3 The heat treatment device 6 (heat treatment temperature is 100-140 ° C) is driven, and after treatment by the heat treatment device 6, a microporous membrane having a stable pore structure is formed.

The pore former in the present invention is a mineral oil or a synthetic oil. The polyethylene in the present invention has a viscosity average molecular weight of 300,000 to 2.5 million, wherein the mass percentage of the polyethylene is 15% to 50%, and the quality of the pore former is The percentage is 50% to 85%. The above embodiment in the present invention is exemplified by a polyethylene having a viscosity average molecular weight of 800,000, a polyethylene mass percentage of 30%, and a pore former mass percentage of 70%. The pre-stretching in the present invention may be uniaxial stretching or biaxial stretching, and the stretching may be uniaxial stretching or biaxial stretching.

The system of the lithium ion secondary battery separator of the invention has the advantages of simple structure, convenient operation, shortened production cycle, high-speed diaphragm production, and reduced production cost of the enterprise.

It should be noted that the above-mentioned embodiments are only used to explain the technical solutions of the present invention, and are not limited thereto; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand The technical solutions described in the foregoing embodiments may be modified, or some or all of the technical features may be equivalently replaced; and the modifications or substitutions do not deviate from the technical solutions of the embodiments of the present invention. The scope.

Claims (10)

1. A method for producing a separator for a lithium ion secondary battery, comprising the steps of:

   A1: mixing and melting polyethylene and a pore former in an extruder to obtain a melt;

   A2: cooling the melt obtained in the step A1 on a cooling roll to form an oil-containing substrate;

   A3: the oil-containing substrate in step A2 is pre-stretched through a driving roller into a pre-stretching device to form a pre-stretched substrate;

   A4: the pre-stretched substrate in step A3 is sent to an extraction device having an ultrasonic generator through a driving roller for ultrasonic extraction, the extraction device contains an extracting agent, and after the extraction, a degreased substrate is obtained;

   A5: the oil-removed substrate in step A4 is passed through a driving roller into a stretching device for stretching to form a film;

   A6: The film in the step A5 is transferred to a heat treatment device through a driving roller for heat treatment to form a microporous separator having a stable pore structure.
2. The method for producing a lithium ion secondary battery separator according to claim 1, wherein the polyethylene has a viscosity average molecular weight of 300,000 to 2.5 million in the step A1 and a mass percentage of the polyethylene of 15%. -50%, the pore former is 50%-85% by mass, and the pore former is mineral oil or synthetic oil.
3. The method for producing a lithium ion secondary battery separator according to claim 1, wherein the lateral magnification or the longitudinal magnification of the pre-stretching in the step A3 is 0.1 to 5 times, the temperature is 85 to 130 ° C, and the pre-tensioning is performed. The stretching mode is unidirectional pre-stretching or biaxial pre-stretching; the transverse magnification or the longitudinal magnification in the step A5 is 1.1-10 times, and the stretching mode in the step A5 is uniaxial stretching or biaxial stretching. .
4. The method for producing a lithium ion secondary battery separator according to claim 1, wherein the power density of the ultrasonic waves in step A4 is 1.0 to 2.95 w/cm 2 and the frequency is 10 to 200 kHz; and the extracting agent and the pores are formed. The agents are mutually soluble, and the extracting agent is one of chloroform, dichloromethane or decane, and the extraction time is 3-5 min.
5. The method of producing a lithium ion secondary battery separator according to claim 1, wherein the temperature in the cooling roll in step A2 is 15 to 40 ° C, and the temperature in the step A6 is 100 to 140 ° C.
6. The method of producing a lithium ion secondary battery separator according to claim 1, wherein the film forming speed in the step A6 is 100 m/min or more.
7. A system for using a lithium ion secondary battery separator according to any one of claims 1 to 6, comprising an extruder, a cooling roll, a pretensioning device, an extracting device, a stretching device, and a heat treatment device a cooling roller is disposed under the outlet of the extruder, and a pre-stretching device is disposed at an end of the cooling roller, and the pre-stretching device, the extracting device, the stretching device, and the heat treatment device are adjacent between the two devices. A drive roller is provided.
8. A system for a lithium ion secondary battery separator according to claim 7, wherein said extraction means is filled with an extracting agent, and said extracting means comprises an extraction tank and a plurality of ultrasonic waves occurring under said extraction tank Device.
9. The system of the lithium ion secondary battery separator according to claim 8, wherein the extraction tank is provided with a plurality of driving rollers, and the plurality of driving rollers are located below the liquid level of the extracting agent in the extraction tank. Between the bottoms of the extraction tanks, the plurality of drive rollers form a W-shaped or V-shaped structure.
10. The system of a lithium ion secondary battery separator according to claim 7, wherein the extruder is a twin-screw extruder, the pre-stretching device is a stretching machine, and the stretching device is a stretching machine. The heat treatment device is a heat setting device.

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