Preparation method of a three-layer co-extruded lithium-ion battery separator

Abstract

The present invention belongs to the technical field of lithium-ion battery diaphragms, and specifically relates to a preparation method for a three-layer co-extruded lithium-ion battery diaphragm. The annealing box used in this method includes a box body, a motor, and a sealing cover; a uniformly arranged heating plate is fixedly connected to the inner surface of the box body; a driving shaft is horizontally arranged in the front-rear direction inside the box body; a first driven shaft and a second driven shaft are respectively arranged on the left and right sides of the driving shaft inside the box body; an interlayer film is wound and connected inside the box body between the driving shaft and the first driven shaft, and the interlayer film is connected in a horizontal manner; a diaphragm is wound and connected inside the box body between the driving shaft and the second driven shaft, and the diaphragm is obliquely connected; through the present invention, the annealing temperature can be effectively controlled, the external environment is isolated, the influence of the external environment on the diaphragm is avoided, and the uniformity of the diaphragm being heated is ensured. Therefore, the quality of the produced diaphragm is stable, which is convenient for large-scale and rapid production requirements.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery separators, and specifically relates to a preparation method for a three-layer co-extruded lithium-ion battery separator. Background Art

[0002] The separator plays a role in separating the positive and negative electrodes in a lithium-ion battery, isolating electron conduction, and providing a channel for lithium-ion transmission. It is a key material that determines the internal interface structure, internal resistance, capacity, cycle performance, especially the safety performance of the lithium battery. Under overcharge / overdischarge or other extreme conditions, the internal temperature of the lithium battery will rise rapidly. When the internal temperature of the battery approaches the melting point of the pore-forming material of the separator, the pore-forming material will soften and undergo a pore-closing behavior, thereby blocking ion transmission and forming an open circuit, playing a role in safety protection. However, for a single-layer separator, since the pore-closing temperature and the melting temperature are the same, when the separator closes the pores, due to the rapid increase in temperature, the reaction is too late and it is extremely easy to cause membrane rupture, thereby causing the direct contact between the positive and negative electrodes of the battery, resulting in short circuit and explosion.

[0003] At the same time, in the prior art, the core of the roll-shaped separator is prone to uneven heating and cooling during annealing, which will further cause the quality of the separator to decline, and even unqualified products may appear. Moreover, the annealing process requires accurate temperature changes within a specified time range. Relying solely on room temperature cooling is difficult to meet the processing requirements. At the same time, when the separator processing factory is located in summer or winter, there will also be large temperature changes. Therefore, these external environmental changes will have a serious impact on the production of the separator and other problems.

[0004] In view of this, in order to overcome the above technical problems, the company has designed and developed a preparation method for a three-layer co-extruded lithium-ion battery separator, and adopted a special annealing box to solve the above technical problems. Summary of the Invention

[0005] In order to make up for the deficiencies of the prior art and solve the problems in the prior art that the core of the roll-shaped separator is prone to uneven heating and cooling during annealing, which will further cause the quality of the separator to decline, and even unqualified products may appear. Moreover, the annealing process requires accurate temperature changes within a specified time range. Relying solely on room temperature cooling is difficult to meet the processing requirements. At the same time, when the separator processing factory is located in summer or winter, there will also be large temperature changes. Therefore, these external environmental changes will have a serious impact on the production of the separator and other problems, the present invention provides a preparation method for a three-layer co-extruded lithium-ion battery separator.

[0006] The technical solution adopted by the present invention to solve its technical problems is: a preparation method for a three-layer co-extruded lithium-ion battery separator, and the preparation method includes the following steps:

[0007] S1: First, add two different polypropylene resins into the inlets of two different extruders respectively for melting and plasticizing. The temperature of the conveying section is 60 - 70 °C, the temperature of the compression section is 150 - 200 °C, the temperature of the metering section is 200 - 230 °C, and the rotational speed is 100 - 250 rpm;

[0008] S2: Synchronously co - extrude the two different polypropylene resins obtained after melting and plasticizing in S1 from the three - layer composite casting die head of a three - layer co - extrusion casting machine, and draw them into a film under a high draw ratio to obtain a casting film with an A / B / A three - layer co - extrusion structure;

[0009] S3: Place the above casting film with an A / B / A three - layer co - extrusion structure in an annealing box for annealing treatment. The annealing temperature is 130 - 150 °C, and the time is 1 - 24 h;

[0010] S4: Conduct longitudinal cold stretching and hot stretching on the above casting film after annealing treatment to form a porous film structure, prepare a separator with a microporous structure and an A / B / A three - layer co - extrusion structure, and finally cool the obtained porous film to room temperature after heat setting;

[0011] The annealing box used in S3 includes a box body, a motor, and a sealing cover; the box body is designed with a cuboid structure; a cavity is provided inside the box body; heating plates are fixedly connected to the inner surface of the box body and are evenly arranged; a driving shaft is horizontally arranged in the front-rear direction inside the box body; a first driven shaft is arranged at the left position of the driving shaft inside the box body; a second driven shaft is arranged at the right position of the driving shaft inside the box body; the driving shaft, the first driven shaft, and the second driven shaft are all rotatably connected to the box body through bearings, and the front end faces of the first driven shaft and the second driven shaft both pass through the box body and extend to the outside of the box; a power box cover is fixedly connected to the front end face of the box body; a motor is fixedly connected to the front end face of the power box cover; the output shaft of the motor passes through the power box cover and extends to the inside of the power box cover, and the output shaft of the motor is fixedly connected to the front end face of the driving shaft; a driving gear is fixedly connected to the outer arc surface of the output shaft of the motor near the flange surface of the motor; a driven gear is fixedly connected to the outer arc surface of the second driven shaft at the front position of the box body, and the driving gear and the driven gear are meshed; a driving turntable is fixedly connected to the outer arc surface of the output shaft of the motor near the front end face of the box body; a driven turntable is fixedly connected to the outer arc surface of the first driven shaft near the front end face of the first driven gear; a transmission belt is connected between the driving turntable and the driven turntable; an interlayer film is wound and connected between the driving shaft and the first driven shaft at the inside position of the box body, and the interlayer film is connected in a horizontal manner; a diaphragm is wound and connected between the driving shaft and the second driven shaft at the inside position of the box body, and the diaphragm is obliquely connected; an opening is provided at the upper right edge position of the box body; a sealing door is provided at the opening position of the box body; a control box is fixedly connected to the left side surface of the box body near the front end face of the box body;During operation, when annealing of the separator is required, for space saving, the separator often has a roll structure. However, the roll structure is likely to cause uneven heating and cooling of the separator, thereby degrading the quality of the separator and even resulting in unqualified products. Moreover, the annealing process requires accurate temperature changes within a specified time range, and it is difficult to meet the processing requirements simply by relying on room temperature cooling. At the same time, when the separator processing factory is located in summer or winter, there are also significant temperature variations. Therefore, all these external environmental changes will seriously affect the production of the separator. To reduce the impact of environmental changes on separator production and ensure the stability of separator quality, through the annealing chamber, first open the sealing door, wind the separator around the second driven shaft, then connect the end of the separator to the driving shaft, and achieve synchronous winding on the driving shaft in cooperation with the already wound interlayer film. Then close the sealing door and turn on the power supply. First, the power supply will heat the heating plate to heat the temperature inside the chamber. Then start the motor. The output shaft of the motor rotates. On the one hand, it will drive the driving shaft to rotate. On the other hand, it will drive the transmission belt to move through the driving turntable, thereby driving the rotation of the driven turntable and achieving the same-direction rotation of the first driven shaft. At the same time, the rotation of the output shaft of the motor will drive the rotation of the driving gear. The driving gear will then drive the rotation of the driven gear, and the driven gear will then drive the reverse rotation of the second driven shaft. Therefore, synchronous winding and separation of the separator and the interlayer film can be achieved. The interlayer film has better thermal conductivity than the separator, so it can ensure uniform heating of the separator. Moreover, through the forward and reverse rotation of the motor, winding between the driving shaft and the second driven shaft can be achieved, effectively ensuring rapid heating and uniform cooling of the separator. Through a preparation method of a three-layer coextruded lithium-ion battery separator and the annealing chamber used in this method, it solves the problems in the prior art that the core of the roll-structured separator is prone to uneven heating and cooling, thereby degrading the quality of the separator and even resulting in unqualified phenomena. Moreover, the annealing process requires accurate temperature changes within a specified time range, and it is difficult to meet the processing requirements simply by relying on room temperature cooling. At the same time, when the separator processing factory is located in summer or winter, there are also significant temperature variations. Therefore, all these external environmental changes will seriously affect the production of the separator, etc. It realizes controllable annealing temperature, isolates the external environment, avoids the influence of the external environment on the separator, ensures the uniformity of separator heating. Therefore, the produced separator has stable quality and is convenient for large-scale and rapid production requirements.;

[0012] Preferably, collar rings are rotatably connected to the outer arc surfaces of the first driven shaft and the second driven shaft; the diaphragm and the interlayer film are wound around the outer arc surfaces of the corresponding collar rings; stepped grooves are formed in the outer arc surfaces of the first driven shaft and the second driven shaft at the positions corresponding to the collar rings; adjusting grooves are formed at the bottom positions of the stepped grooves; adjusting plates are arranged inside the adjusting grooves; the opposite side surfaces of the adjusting plates and the corresponding collar rings are designed with rough surface structures; during operation, when the first driven shaft and the second driven shaft rotate, the interlayer film and the diaphragm will be wound at this time, or the interlayer film and the diaphragm wound on their surfaces will be transferred and wound onto the surface of the driving shaft, realizing the replacement winding of the diaphragm between the driving shaft and the second driven shaft. However, due to the annealing factor, the high temperature in the box will cause the diaphragm to soften or shrink to a certain extent, which will be subjected to subsequent processes such as longitudinal cold stretching and hot stretching in the later cast film. In order to reduce the influence on the natural size of the diaphragm during the annealing winding process, or the problem that the diaphragm shrinks due to heat and the tensile stress of the diaphragm between the driving shaft and the second driven shaft increases, collar rings and adjusting plates are provided; when the diaphragm is wound on the surface of the collar ring, the contraction of the diaphragm will generate a tangential pulling force on the collar ring. Since an adjusting plate is provided between the second driven shaft and the collar ring, and the opposite side surfaces of the adjusting plate and the corresponding collar ring are designed with rough surface structures; when the tangential pulling force generated by the diaphragm contraction is greater than the frictional force between the adjusting plate and the corresponding collar ring, the collar ring will rotate relative to the first driven shaft or the second driven shaft, realizing the release of the tangential tensile stress generated by the diaphragm contraction, and avoiding the influence of excessive contraction stress on the quality of the diaphragm.

[0013] Preferably, the adjusting plate and the corresponding adjusting groove are connected by a hinged manner; springs are connected between both side surfaces of the adjusting plate and the corresponding adjusting groove; a strip-shaped groove is formed at the position of the inner arc surface of the collar corresponding to the adjusting plate, and the adjusting plate is in contact connection with the strip-shaped groove; the minor diameter of the collar is larger than the outer diameter of the first driven shaft or the second driven shaft; guiding grooves are formed at both end face positions of the first driven shaft and the second driven shaft close to the corresponding collar; the collar is designed with a guiding convex surface structure at the position of the corresponding guiding groove; uniformly arranged rolling grooves are formed on the arc surface of the first driven shaft and the second driven shaft on one side relative to the corresponding guiding groove; ball bearings are rotatably connected inside the rolling grooves, and the ball bearings are rotatably connected with the groove bottom of the corresponding guiding groove; during operation, when the automatic release adjustment of the diaphragm contraction stress is achieved through the friction between the adjusting plate and the collar, on the one hand, after long-term use, the rough surfaces of the collar and the adjusting plate are severely worn, and thus the friction coefficient changes, making it easy for relative rotation to occur between the collar and the first driven shaft or the second driven shaft during the normal winding process of the diaphragm and the interlayer film, affecting the normal use of the annealing box. On the other hand, direct contact between the collar and the first driven shaft or the second driven shaft also generates a large friction force on the large contact surface, causing great interference to the normal adjustment of the adjusting plate. Therefore, by setting springs and ball bearings, through the hinge connection of the adjusting plate and the pulling force of the spring, under normal conditions, the adjusting plate will be located in one of the strip-shaped grooves. When the tangential pulling force of the diaphragm or the interlayer film on the collar is large, the adjusting plate will rotate, causing the spring to deform. When the rotation amount of the adjusting plate is large, it will move to the adjacent strip-shaped groove, realizing the relative rotation adjustment between the collar and the first driven shaft or the second driven shaft. Moreover, in order to effectively reduce the influence of the rotating contact surface on the adjustment, guiding grooves are formed, and the collar is rotatably connected in the guiding grooves. By arranging ball bearings between the collar and the groove bottom of the guiding groove, rolling connection between the collar and the first driven shaft and the second driven shaft is achieved, greatly reducing the friction force and improving the adjustment accuracy.

[0014] Preferably, the material of the interlayer film is designed as a thermally conductive graphite film material; during operation, by using the thermally conductive graphite film material for the interlayer film, its heat conduction and heat dissipation effects are relatively excellent. Compared with ordinary thermally conductive materials, it can quickly conduct the temperature inside the box into the core of the rolled diaphragm, achieving rapid and uniform heating of the diaphragm and ensuring the quality unity and stability of the same roll of diaphragm.

[0015] Preferably, heat conduction holes are formed in the active shaft, the first driven shaft, and the second driven shaft in the front-back direction; high-pressure hot steam is conducted inside the heat conduction holes; during operation, since any heat conduction material will have a certain amount of heat energy loss and time period during the conduction process, in order to further promote the heating of the core of the diaphragm, by forming heat conduction holes in the active shaft, the first driven shaft, and the second driven shaft, and by introducing high-pressure hot steam into the heat conduction holes, the inside of the diaphragm and the interlayer film can be quickly heated, ensuring the rapid heating of the core.

[0016] Preferably, two temperature control ports are formed in the upper surface of the box body; a condenser is connected above the left temperature control hole through a pipeline, and the condenser is fixedly connected to the left side surface of the box body; an exhaust duct is fixedly connected above the right temperature control hole; a wind blade is rotatably connected inside the exhaust duct; during operation, due to the annealing requirement, the temperature inside the box body needs to be slowly cooled. Therefore, since the inside of the box body is relatively sealed and not conducive to heat dissipation, by providing the exhaust duct and the wind blade, the temperature inside the box can be dissipated according to requirements by adjusting the rotation speed of the wind blade. At the same time, by providing the condenser, on the one hand, the condenser can play a role in quickly cooling, meeting the requirements of products that need to be quickly cooled, and at the same time ensuring that under the production conditions in summer, the temperature is relatively high, and the temperature can be reduced to the specified temperature range to ensure meeting the annealing requirements.

[0017] Preferably, a sealing cover is threadedly connected to the outer arc surface of the exhaust duct; during operation, during the heating process of the heating plate, since the temperature control port formed in the upper part of the box body is open, it is not conducive to the rapid heating and heat preservation inside the box body. Therefore, by threadedly connecting the sealing cover to the outer arc surface of the exhaust duct, the box body can be effectively sealed through the sealing cover.

[0018] Preferably, an annular sealing groove is formed in the upper surface of the exhaust duct; a sealing ring is fixedly connected inside the sealing groove; an insulating cavity is formed inside the sealing cover; an aerogel felt is provided inside the insulating cavity; during operation, in order to further ensure the sealing performance and heat insulation performance of the sealing cover, by forming an annular sealing groove in the upper surface of the exhaust duct, through the sealing ring in the annular sealing groove, the effective sealing performance of the sealing cover is ensured. By providing the aerogel felt in the insulating cavity of the sealing cover, the heat insulation performance at the position of the sealing cover is ensured, reducing the heat dissipation inside the box body.

[0019] The beneficial effects of the present invention are as follows:

[0020] 1. A preparation method of a three-layer co-extruded lithium-ion battery separator. The annealing box used in this method is provided with a box body, a motor, and a sealing cover. The inner surface of the box body is fixedly connected with uniformly arranged heating plates. The active shaft is horizontally arranged in the front-rear direction inside the box body. The first driven shaft is arranged on the left side of the active shaft inside the box body. The second driven shaft is arranged on the right side of the active shaft inside the box body. A sandwich film is wound and connected inside the box body between the active shaft and the first driven shaft, and the sandwich film is connected in a horizontal manner. A separator is wound and connected inside the box body between the active shaft and the second driven shaft, and the separator is obliquely connected. Through a preparation method of a three-layer co-extruded lithium-ion battery separator and the annealing box used in this method, it solves the problems in the prior art that the core of the rolled separator is prone to uneven heating and cooling, resulting in a decline in the quality of the separator and even unqualified phenomena. And the annealing process requires accurate temperature changes within a specified time range. It is difficult to meet the processing requirements simply relying on room temperature cooling. At the same time, when the separator processing factory is located in summer or winter, there will also be large temperature changes. Therefore, these external environmental changes will have a serious impact on the production of the separator. It realizes controllable annealing temperature, isolates the external environment, avoids the influence of the external environment on the separator, and ensures the uniformity of the separator's heat absorption. Therefore, the quality of the produced separator is stable, which is convenient for large-scale and rapid production requirements.

[0021] 2. A preparation method of a three-layer co-extruded lithium-ion battery separator. The annealing box used in this method is provided with an exhaust duct, a sealing cover, and a condenser. Two temperature control ports are opened on the upper surface of the box body. A condenser is connected by a pipe above the left temperature control hole, and the condenser is fixedly connected to the left side surface of the box body. An exhaust duct is fixedly connected above the right temperature control hole. A wind blade is rotatably connected inside the exhaust duct. A sealing cover is threadedly connected to the outer arc surface of the exhaust duct. Therefore, by setting the exhaust duct and the wind blade, the temperature inside the box can be dissipated according to requirements by adjusting the rotation speed of the wind blade. At the same time, by setting the condenser, on the one hand, the condenser can play a role in rapid cooling to meet the requirements of products that need rapid cooling. On the other hand, under the production conditions in summer, the temperature is relatively high, and it can ensure that the temperature is reduced to the specified temperature range to meet the requirements of annealing. At the same time, by threadedly connecting the sealing cover to the outer arc surface of the exhaust duct, the box body can be effectively sealed through the sealing cover, ensuring the rapid heating and heat preservation inside the box body. Brief Description of the Drawings

[0022] The present invention will be further described below with reference to the drawings.

[0023] Figure 1 is the flowchart of the method of the present invention

[0024] Figure 2 is the external view of the annealing box used in the present invention;

[0025] Figure 3 is a perspective view of the annealing box used in the present invention;

[0026] Figure 4 is a top view of the annealing box used in the present invention;

[0027] Figure 5 is Figure 3 a partial enlarged view of part A in

[0028] Figure 6 is a perspective view of the second driven shaft of the annealing box used in the present invention;

[0029] Figure 7 is Figure 6 a sectional view taken along line B-B in

[0030] In the figure: box body 1, heating plate 11, sealing door 12, control box 13, motor 2, driving shaft 21, first driven shaft 22, second driven shaft 23, power box cover 24, driving gear 25, driven gear 26, transmission belt 27, sandwich film 28, diaphragm 29, sealing cover 3, condenser 31, exhaust duct 32, fan blade 33, sealing ring 34, aerogel felt 35, collar 36, adjusting plate 37, spring 38, ball 39. Specific Embodiments

[0031] In order to make the technical means, creative features, achieved purposes and functions of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

[0032] As Figures 1 to 7 shown, a preparation method of a three-layer co-extruded lithium-ion battery separator according to the present invention includes the following steps:

[0033] S1: First, two different polypropylene resins are respectively added into the inlets of two different extruders for melting and plasticizing, wherein the temperature of the conveying section is 60 - 70 °C, the temperature of the compression section is 150 - 200 °C, the temperature of the metering section is 200 - 230 °C, and the rotation speed is 100 - 250 rpm;

[0034] S2: The two different polypropylene resins obtained after melting and plasticizing in S1 are co-extruded synchronously from the three-layer composite casting die head of a three-layer co-extrusion casting machine, and are drawn into a film under a high draw ratio to obtain a casting film with an A / B / A three-layer co-extruded structure;

[0035] S3: The casting film with the A / B / A three-layer co-extruded structure is placed in an annealing box for annealing treatment, the annealing temperature is 130 - 150 °C, and the time is 1 - 24 h;

[0036] S4: Perform longitudinal cold stretching and hot stretching on the cast film after the above annealing treatment to form a porous film structure, prepare a separator 29 with a microporous structure and an A / B / A three-layer coextrusion structure, and finally cool the obtained porous film to room temperature after heat setting;

[0037] Among them, the annealing box used in S3 includes a box body 1, a motor 2 and a sealing cover 3; the box body 1 is designed in a cuboid structure; a cavity is formed inside the box body 1; heating plates 11 are fixedly connected to the inner surface of the box body 1 and are evenly arranged; a driving shaft 21 is horizontally arranged in the front-back direction inside the box body 1; a first driven shaft 22 is arranged at the left side position of the driving shaft 21 inside the box body 1; a second driven shaft 23 is arranged at the right side position of the driving shaft 21 inside the box body 1; the driving shaft 21, the first driven shaft 22 and the second driven shaft 23 are all rotatably connected to the box body 1 through bearings, and the front end faces of the first driven shaft 22 and the second driven shaft 23 both pass through the box body 1 and extend to the outside of the box; a power box cover 24 is fixedly connected to the front end face of the box body 1; a motor 2 is fixedly connected to the front end face of the power box cover 24; the output shaft of the motor 2 passes through the power box cover 24 and extends into the power box cover 24, and the output shaft of the motor 2 is fixedly connected to the front end face of the driving shaft 21; a driving gear 25 is fixedly connected to the outer arc surface of the output shaft of the motor 2 near the flange surface of the motor 2; a driven gear 26 is fixedly connected to the outer arc surface of the second driven shaft 23 at the front position of the box body 1, and the driving gear 25 and the driven gear 26 are meshed; a driving turntable is fixedly connected to the outer arc surface of the output shaft of the motor 2 near the front end face of the box body 1; a driven turntable is fixedly connected to the outer arc surface of the first driven shaft 22 near the front end face of the first driven gear 26; a transmission belt 27 is connected between the driving turntable and the driven turntable; an interlayer film 28 is wound and connected between the driving shaft 21 and the first driven shaft 22 at the inner position of the box body 1, and the interlayer film 28 is connected in a horizontal manner; a diaphragm 29 is wound and connected between the driving shaft 21 and the second driven shaft 23 at the inner position of the box body 1, and the diaphragm 29 is obliquely connected; an opening is formed at the upper right edge position of the box body 1; a sealing door 12 is arranged at the opening position of the box body 1; a control box 13 is fixedly connected to the left side surface of the box body 1 near the front end face of the box body 1;During operation, when annealing of the diaphragm 29 is required, in order to save space, the diaphragm 29 is often in a rolled structure. However, the rolled structure is likely to cause uneven heating and cooling of the diaphragm 29, thereby resulting in a decline in the quality of the diaphragm 29 and even unqualified problems. Moreover, the annealing process requires accurate temperature changes within a specified time range, and it is difficult to meet the processing requirements simply by relying on room temperature cooling. At the same time, when the diaphragm 29 processing factory is located in summer or winter, there will also be significant temperature changes. Therefore, all these external environmental changes will have a serious impact on the production of the diaphragm 29. To reduce the impact of environmental changes on the production of the diaphragm 29 and ensure the stability of the quality of the diaphragm 29, through the annealing box, first open the sealing door 12, wind the diaphragm 29 around the second driven shaft 23, then connect the end of the diaphragm 29 to the driving shaft 21, and cooperate with the already wound sandwich film 28 to achieve synchronous winding on the driving shaft 21. Then close the sealing door 12 and turn on the power supply. First, the power supply will heat the heating plate 11 to heat the temperature inside the box body 1. Then start the motor 2. The output shaft of the motor 2 rotates. On the one hand, it will drive the driving shaft 21 to rotate. On the other hand, it will drive the transmission belt 27 to move through the driving turntable, thereby driving the rotation of the driven turntable and realizing the same-direction rotation of the first driven shaft 22. At the same time, the rotation of the output shaft of the motor 2 will drive the rotation of the driving gear 25. The driving gear 25 will then drive the driven gear 26 to rotate, and the driven gear 26 will then drive the reverse rotation of the second driven shaft 23. Therefore, the synchronous winding and separation of the diaphragm 29 and the sandwich film 28 can be achieved. The sandwich film 28 has better thermal conductivity than the diaphragm 29. Therefore, it can ensure that the diaphragm 29 is evenly heated. And through the forward and reverse rotation of the motor 2, the winding between the driving shaft 21 and the second driven shaft 23 can be realized, effectively ensuring the rapid heating and uniform cooling of the diaphragm 29. Through a preparation method of a three-layer co-extruded lithium-ion battery diaphragm and the annealing box used in this method, the problems in the prior art are solved, such as the core of the rolled diaphragm 29 in a rolled structure is prone to uneven heating and cooling, thereby resulting in a decline in the quality of the diaphragm 29 and even unqualified phenomena. Moreover, the annealing process requires accurate temperature changes within a specified time range, and it is difficult to meet the processing requirements simply by relying on room temperature cooling. At the same time, when the diaphragm 29 processing factory is located in summer or winter, there will also be significant temperature changes. Therefore, all these external environmental changes will have a serious impact on the production of the diaphragm 29, etc. The controllable annealing temperature is achieved, the external environment is isolated, the influence of the external environment on the diaphragm 29 is avoided, and the uniformity of the heating of the diaphragm 29 is ensured. Therefore, the produced diaphragm 29 has stable quality and is convenient for large-scale rapid production requirements.;

[0038] As an embodiment of the present invention, collar rings 36 are rotatably connected to the outer arc surfaces of the first driven shaft 22 and the second driven shaft 23; the diaphragm 29 and the interlayer film 28 are both wound around the outer arc surfaces of the corresponding collar rings 36; stepped grooves are formed in the outer arc surfaces of the first driven shaft 22 and the second driven shaft 23 at the positions of the corresponding collar rings 36; adjustment grooves are formed at the bottom of the stepped grooves; adjustment plates 37 are arranged inside the adjustment grooves; the opposite side surfaces of the adjustment plates 37 and the corresponding collar rings 36 are both designed with rough surface structures; during operation, when the first driven shaft 22 and the second driven shaft 23 rotate, the interlayer film 28 and the diaphragm 29 will be wound at this time, or the interlayer film 28 and the diaphragm 29 wound on their surfaces will be transferred and wound onto the surface of the driving shaft 21, realizing the replacement winding of the diaphragm 29 between the driving shaft 21 and the second driven shaft 23. However, due to the annealing factor, the high temperature in the box body 1 will cause the diaphragm 29 to soften or shrink to a certain extent, which will be subjected to subsequent processes such as longitudinal cold stretching and hot stretching in the later cast film. In order to reduce the influence on the natural size of the diaphragm 29 during the annealing winding process, or the problem that the diaphragm 29 shrinks due to heat and the tensile stress of the diaphragm 29 between the driving shaft 21 and the second driven shaft 23 increases, the collar rings 36 and the adjustment plates 37 are provided; when the diaphragm 29 is wound around the surface of the collar ring 36, the contraction of the diaphragm 29 will generate a tangential tension on the collar ring 36. Since an adjustment plate 37 is provided between the second driven shaft 23 and the collar ring 36, and the opposite side surfaces of the adjustment plate 37 and the corresponding collar ring 36 are both designed with rough surface structures; when the tangential tension generated by the contraction of the diaphragm 29 is greater than the frictional force between the adjustment plate 37 and the corresponding collar ring 36, the collar ring 36 will rotate relative to the first driven shaft 22 or the second driven shaft 23, realizing the release of the tangential tensile stress generated by the contraction of the diaphragm 29, and avoiding the influence of excessive contraction stress on the quality of the diaphragm 29.

[0039] As an embodiment of the present invention, the adjusting plate 37 and the corresponding adjusting groove are connected by a hinged manner; springs 38 are connected between the two side surfaces of the adjusting plate 37 and the corresponding adjusting groove; a strip-shaped groove is formed in the inner arc surface of the collar 36 at the position of the adjusting plate 37, and the adjusting plate 37 is in contact connection with the strip-shaped groove; the small diameter of the collar 36 is larger than the outer diameter of the first driven shaft 22 or the second driven shaft 23; guiding grooves are formed at both end faces of the first driven shaft 22 and the second driven shaft 23 close to the corresponding collar 36; the collar 36 is designed with a guiding convex surface structure at the position of the corresponding guiding groove; uniformly arranged rolling grooves are formed in the arc surface of the first driven shaft 22 and the second driven shaft 23 on one side relative to the corresponding guiding groove; ball bearings 39 are rollingly connected inside the rolling grooves, and the ball bearings 39 are rollingly connected with the bottom of the corresponding guiding groove; during operation, when the automatic release adjustment of the contraction stress of the diaphragm 29 is realized through the friction force between the adjusting plate 37 and the collar 36, on the one hand, after long-term use, the rough surfaces of the collar 36 and the adjusting plate 37 are severely worn, and thus the friction coefficient changes, making it easy for relative rotation to occur between the collar 36 and the first driven shaft 22 or the second driven shaft 23 during the normal winding process of the diaphragm 29 and the interlayer film 28, affecting the normal use of the annealing box. On the other hand, the direct contact between the collar 36 and the first driven shaft 22 or the second driven shaft 23 also generates a large friction force on the relatively large contact surface, which greatly interferes with the normal adjustment of the adjusting plate 37. Therefore, by providing the springs 38 and the ball bearings 39, through the hinge connection of the adjusting plate 37 and the pulling and tensioning force of the springs 38, under normal conditions, the adjusting plate 37 will be located in one of the strip-shaped grooves. When the tangential pulling force of the diaphragm 29 or the interlayer film 28 on the collar 36 is relatively large, the adjusting plate 37 will rotate and cause the spring 38 to deform. When the rotation amount of the adjusting plate 37 is relatively large, it will move to the adjacent strip-shaped groove to realize the relative rotation adjustment between the collar 36 and the first driven shaft 22 or the second driven shaft 23. And in order to effectively reduce the influence of the rotating contact surface on the adjustment, guiding grooves are formed, and the collar 36 is rotatably connected in the guiding grooves. By providing the ball bearings 39 between the collar 36 and the bottom of the guiding grooves, rolling connection between the collar 36 and the first driven shaft 22 and the second driven shaft 23 is realized, greatly reducing the friction force and improving the adjustment accuracy.

[0040] As an embodiment of the present invention, the material of the interlayer film 28 is designed as a thermally conductive graphite film material; during operation, by using the thermally conductive graphite film material for the interlayer film 28, its heat conduction and heat dissipation effects are relatively excellent. Compared with ordinary thermally conductive materials, it can quickly conduct the temperature inside the box body 1 into the core of the wound diaphragm 29, realizing the rapid and uniform heating of the diaphragm 29 and ensuring the quality unity and stability of the same roll of diaphragm 29.

[0041] As an implementation manner of the present invention, heat conduction holes are provided in the active shaft 21, the first driven shaft 22, and the second driven shaft 23 in the front-back direction; high-pressure hot steam is conducted inside the heat conduction holes; during operation, since any heat conduction material will have a certain amount of heat energy loss and time period during the conduction process, in order to further promote the heating of the core of the diaphragm 29, heat conduction holes are provided inside the active shaft 21, the first driven shaft 22, and the second driven shaft 23, and by introducing high-pressure hot steam into the heat conduction holes, the inside of the diaphragm 29 and the interlayer film 28 can be quickly heated, ensuring the rapid heating of the core.

[0042] As an implementation manner of the present invention, two temperature control ports are provided on the upper surface of the box body 1; a condenser 31 is connected above the temperature control hole on the left side through a pipeline, and the condenser 31 is fixedly connected to the left side surface of the box body 1; a discharge air pipe 32 is fixedly connected above the position of the temperature control hole on the right side; a wind blade 33 is rotatably connected inside the discharge air pipe 32; during operation, due to the annealing requirement, the temperature inside the box body 1 needs to be slowly cooled. Therefore, since the inside of the box body 1 is relatively sealed and not conducive to heat dissipation, by providing the discharge air pipe 32 and the wind blade 33, the temperature inside the box can be dissipated according to the requirements by adjusting the rotation speed of the wind blade 33. At the same time, by providing the condenser 31, on the one hand, the condenser 31 can play a role in quickly cooling, meeting the requirements of products that require rapid cooling, and at the same time ensuring that under the production conditions in summer, the temperature is relatively high, and the temperature can be reduced to the specified temperature range to ensure meeting the annealing requirements.

[0043] As an implementation manner of the present invention, a sealing cover 3 is threadedly connected to the outer arc surface of the discharge air pipe 32; during operation, during the heating process of the heating plate 11, since the temperature control port provided on the upper surface of the box body 1 is open, it is not conducive to the rapid heating and heat preservation inside the box body 1. Therefore, by threadedly connecting the sealing cover 3 to the outer arc surface of the discharge air pipe 32, the box body 1 can be effectively sealed by the sealing cover 3.

[0044] As an implementation manner of the present invention, an annular sealing groove is provided on the upper surface of the discharge air pipe 32; a sealing ring 34 is fixedly connected inside the sealing groove; an insulating cavity is provided inside the sealing cover 3; an aerogel felt 35 is provided inside the insulating cavity; during operation, in order to further ensure the sealing performance and heat insulation performance of the sealing cover 3, by providing an annular sealing groove on the upper surface of the discharge air pipe 32, and through the sealing ring 34 in the annular sealing groove, the effective sealing performance of the sealing cover 3 is ensured. By providing the aerogel felt 35 in the insulating cavity of the sealing cover 3, the heat insulation performance of the position of the sealing cover 3 is ensured, reducing the heat dissipation inside the box body 1.

[0045] The specific working process is as follows:

[0046] During operation, first open the sealing door 12, wind the diaphragm 29 around the second driven shaft 23, then connect the end of the diaphragm 29 to the driving shaft 21, and cooperate with the already wound sandwich film 28 to achieve synchronous winding on the driving shaft 21. Then close the sealing door 12 and turn on the power supply. First, the power supply will heat the heating plate 11 to heat the temperature inside the box body 1. Then start the motor 2. The output shaft of the motor 2 rotates. On the one hand, it will drive the driving shaft 21 to rotate. On the other hand, it will drive the transmission belt 27 to move through the driving turntable, and then drive the rotation of the driven turntable to achieve the same-direction rotation of the first driven shaft 22. At the same time, the rotation of the output shaft of the motor 2 will drive the rotation of the driving gear 25. The driving gear 25 will then drive the rotation of the driven gear 26, and the driven gear 26 will then drive the reverse rotation of the second driven shaft 23. Therefore, the synchronous winding and separation of the diaphragm 29 and the sandwich film 28 can be achieved. The sandwich film 28 has better thermal conductivity than the diaphragm 29, so it can ensure that the diaphragm 29 is evenly heated. And through the forward and reverse rotation of the motor 2, the winding between the driving shaft 21 and the second driven shaft 23 can be realized, effectively ensuring the rapid heating and uniform cooling of the diaphragm 29; By setting the collar 36 and the adjusting plate 37; when the diaphragm 29 is wound around the surface of the collar 36, the contraction of the diaphragm 29 will generate a tangential tension on the collar 36. Since there is an adjusting plate 37 between the second driven shaft 23 and the collar 36, and the opposite side surfaces of the adjusting plate 37 and the corresponding collar 36 are both designed with rough surface structures; when the tangential tension generated by the contraction of the diaphragm 29 is greater than the friction force between the adjusting plate 37 and the corresponding collar 36, the collar 36 will generate relative rotation with the first driven shaft 22 or the second driven shaft 23 to release the tangential tensile stress generated by the contraction of the diaphragm 29; By setting the spring 38 and the ball 39, through the hinge of the adjusting plate 37 and the tensile force of the spring 38, under normal conditions, the adjusting plate 37 will be located in one of the strip grooves. When the tangential tension of the diaphragm 29 or the sandwich film 28 on the collar 36 is relatively large, it will cause the adjusting plate 37 to rotate and deform the spring 38. When the rotation amount of the adjusting plate 37 is relatively large, it will move to the adjacent strip groove to achieve the relative rotation adjustment between the collar 36 and the first driven shaft 22 or the second driven shaft 23. And in order to effectively reduce the influence of the rotating contact surface on the adjustment, a guiding groove is opened, and the collar 36 is rotatably connected in the guiding groove. By setting the ball 39 between the collar 36 and the bottom of the guiding groove, the rolling connection between the collar 36 and the first driven shaft 22 and the second driven shaft 23 is realized, greatly reducing the friction force and improving the adjustment accuracy; By using a thermally conductive graphite film material for the sandwich film 28, its heat conduction and heat dissipation effects are relatively excellent. Compared with ordinary thermally conductive materials, it can quickly transfer the temperature inside the box body 1 to the core of the wound diaphragm 29, achieving the rapid and uniform heating of the diaphragm 29;By opening heat-conducting holes inside the main drive shaft 21, the first driven shaft 22, and the second driven shaft 23, and introducing high-pressure hot steam into the heat-conducting holes, the inside of the diaphragm 29 and the sandwich film 28 can be quickly heated, ensuring that the core is quickly heated. By setting the exhaust duct 32 and the fan blade 33, the temperature inside the box can be dissipated as required by adjusting the rotation speed of the fan blade 33. At the same time, by setting the condenser 31, on the one hand, the condenser 31 can play a role in quickly cooling down, meeting the requirements of products that require rapid cooling. At the same time, it is ensured that under the production conditions in summer, the temperature is relatively high, and the temperature can be reduced to the specified temperature range. By opening an annular sealing groove on the upper surface of the exhaust duct 32, and through the sealing ring 34 in the annular sealing groove, the effective sealing performance of the sealing cover 3 is ensured. By setting the aerogel felt 35 in the heat-insulating cavity of the sealing cover 3, the heat insulation performance of the position of the sealing cover 3 is ensured.

[0047] Example 1

[0048] Take two rolls of diaphragms and place them in the annealing box of the present invention, and then perform annealing treatment according to the requirements. The required annealing temperature is 145 °C and the time is 24 h. According to the requirements of this annealing condition, samples of the two rolls of diaphragms obtained are subjected to performance testing, and the average value is taken. It is required to use the GB standard method, and performance tests are carried out using instruments such as Sansi tensile machine, Gurley air permeability tester, and Rili S300 scanning electron microscope.

[0049] Example 2

[0050] Take another two rolls of diaphragms of the same batch as above and place them in a common annealing device, and then perform annealing treatment according to the requirements. The required annealing temperature is 145 °C and the time is 24 h. According to the requirements of this annealing condition, samples of the two rolls of diaphragms obtained are subjected to performance testing, and the average value is taken. It is required to use the GB standard method, and performance tests are carried out using instruments such as Sansi tensile machine, Gurley air permeability tester, and Rili S300 scanning electron microscope.

[0051] Example 3

[0052] Take another two rolls of diaphragms of the same batch as above without annealing treatment, and samples of the two rolls of diaphragms obtained are subjected to performance testing, and the average value is taken. It is required to use the GB standard method, and performance tests are carried out using instruments such as Sansi tensile machine, Gurley air permeability tester, and Rili S300 scanning electron microscope.

[0053] Table 1

[0054]

[0055] As can be seen from Table 1, the three-layer coextruded lithium-ion battery separator prepared by the present invention has excellent tensile properties. When annealed using the annealing box of the present invention, the performance of the obtained separator has been greatly improved compared with that of ordinary annealing devices. In particular, the tensile strength can reach more than 150 Mpa, which can meet the needs of a large number of users; the puncture strength reaches more than 500 gf, which can better avoid the puncture phenomenon during battery assembly; the thermal shrinkage rate is much lower than that of the separator products obtained by traditional annealing, so that the separator will not cause a short-circuit phenomenon due to large shrinkage during use; the air permeability and porosity are also within appropriate ranges, which can better meet the performance of lithium-ion batteries. Compared with the performance of the separator obtained without annealing treatment, the performance of this product is far worse than that after annealing treatment. Therefore, from the overall performance parameters, the annealing box provided by the present invention has good popularization and application value in the production of three-layer coextruded lithium-ion battery separators.

[0056] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of a three-layer co-extruded lithium-ion battery separator, characterized in that: The preparation method comprises the following steps: S1: First, two different polypropylene resins are respectively added into the inlets of two different extruders for melting and plasticizing, wherein the temperature of the conveying section is 60-70 °C, the temperature of the compression section is 150-200 °C, the temperature of the metering section is 200-230 °C, and the rotation speed is 100-250 rpm; S2: The two different polypropylene resins obtained after melting and plasticizing in S1 are co-extruded synchronously from the three-layer composite casting die head of a three-layer co-extrusion casting machine, and are drawn into a film under a high draw ratio to obtain a casting film with an A / B / A three-layer co-extrusion structure; S3: The casting film with the A / B / A three-layer co-extrusion structure is placed in an annealing box for annealing treatment, the annealing temperature is 130-150 °C, and the time is 1-24 h; S4: The casting film after the annealing treatment is subjected to longitudinal cold stretching and hot stretching to form a porous film structure, and a separator (29) with a microporous structure and an A / B / A three-layer co-extrusion structure is prepared. Finally, the obtained porous film is heat-set and then cooled to room temperature; The annealing box used in S3 includes a box body (1), a motor (2), and a sealing cover (3); the box body (1) is designed in a cuboid structure; a cavity is provided inside the box body (1); heating plates (11) are fixedly connected to the inner surface of the box body (1) and are evenly arranged; a driving shaft (21) is horizontally arranged in the front-back direction inside the box body (1); a first driven shaft (22) is provided at the left position of the driving shaft (21) inside the box body (1); a second driven shaft (23) is provided at the right position of the driving shaft (21) inside the box body (1); the driving shaft (21), the first driven shaft (22), and the second driven shaft (23) are all rotatably connected to the box body (1) through bearings, and the front end faces of the first driven shaft (22) and the second driven shaft (23) both pass through the box body (1) and extend to the outside of the box; a power box cover (24) is fixedly connected to the front end face of the box body (1); a motor (2) is fixedly connected to the front end face of the power box cover (24); the output shaft of the motor (2) passes through the power box cover (24) and extends into the power box cover (24), and the output shaft of the motor (2) is fixedly connected to the front end face of the driving shaft (21); a driving gear (25) is fixedly connected to the outer arc surface of the output shaft of the motor (2) near the flange surface of the motor (2); a driven gear (26) is fixedly connected to the outer arc surface of the second driven shaft (23) at the front position of the box body (1), and the driving gear (25) and the driven gear (26) are meshed; a driving turntable is fixedly connected to the outer arc surface of the output shaft of the motor (2) near the front end face of the box body (1); a driven turntable is fixedly connected to the outer arc surface of the first driven shaft (22) near the front end face of the first driven gear (26); a transmission belt (27) is connected between the driving turntable and the driven turntable; an interlayer film (28) is wound between the driving shaft (21) and the first driven shaft (22) inside the box body (1), and the interlayer film (28) is connected in a horizontal manner; a diaphragm (29) is wound between the driving shaft (21) and the second driven shaft (23) inside the box body (1), and the diaphragm (29) is obliquely connected; an opening is provided at the upper right edge position of the box body (1); a sealing door (12) is provided at the opening position of the box body (1); a control box (13) is fixedly connected to the left side surface of the box body (1) near the front end face of the box body (1).

2. The preparation method of a three-layer co-extruded lithium-ion battery separator according to claim 1, characterized in that: Collars (36) are rotatably connected to the outer arc surfaces of the first driven shaft (22) and the second driven shaft (23); the diaphragm (29) and the interlayer film (28) are both wound around the outer arc surfaces of the corresponding collars (36); stepped grooves are provided at the positions of the corresponding collars (36) on the outer arc surfaces of the first driven shaft (22) and the second driven shaft (23); adjustment grooves are provided at the bottom positions of the stepped grooves; adjustment plates (37) are provided inside the adjustment grooves; the opposite side surfaces of the adjustment plates (37) and the corresponding collars (36) are both designed with rough surface structures.

3. The preparation method of a three-layer coextruded lithium-ion battery separator according to claim 2, characterized in that: The adjusting plate (37) and the corresponding adjusting groove are connected by a hinged manner; springs (38) are connected between the two side surfaces of the adjusting plate (37) and the corresponding adjusting groove; a strip-shaped groove is formed in the inner arc surface of the collar (36) at the position of the adjusting plate (37), and the adjusting plate (37) is in contact connection with the strip-shaped groove; the minor diameter of the collar (36) is larger than the outer diameter of the first driven shaft (22) or the second driven shaft (23); guide grooves are formed at both end faces of the first driven shaft (22) and the second driven shaft (23) close to the corresponding collar (36); the collar (36) is designed with a guide convex surface structure at the position of the corresponding guide groove; uniformly arranged rolling grooves are formed in the arc surface of the first driven shaft (22) and the second driven shaft (23) on one side of the corresponding guide groove; ball bearings (39) are rotatably connected inside the rolling grooves, and the ball bearings (39) are rotatably connected with the bottom of the corresponding guide groove.

4. The preparation method of a three-layer co-extruded lithium-ion battery separator according to claim 1, characterized in that: The material of the interlayer film (28) is designed as a thermally conductive graphite film material.

5. The preparation method of a three-layer co-extruded lithium-ion battery separator according to claim 4, wherein: Heat conduction holes are formed in the front-rear direction inside the driving shaft (21), the first driven shaft (22), and the second driven shaft (23); high-pressure hot steam is conducted inside the heat conduction holes.

6. The preparation method of a three-layer coextruded lithium-ion battery separator according to claim 1, characterized in that: Two temperature control ports are formed in the upper surface of the box body (1); a condenser (31) is connected above the left temperature control hole through a pipeline, and the condenser (31) is fixedly connected to the left side surface of the box body (1); an exhaust duct (32) is fixedly connected above the right temperature control hole; a wind blade (33) is rotatably connected inside the exhaust duct (32).

7. The preparation method of a three-layer co-extruded lithium-ion battery separator according to claim 6, characterized in that: A sealing cover (3) is threadedly connected to the outer arc surface of the exhaust duct (32).

8. The preparation method of a three-layer co-extruded lithium-ion battery separator according to claim 7, characterized in that: An annular sealing groove is formed in the upper surface of the exhaust duct (32); a sealing ring (34) is fixedly connected inside the sealing groove; a heat insulation cavity is formed inside the sealing cover (3); an aerogel felt (35) is arranged inside the heat insulation cavity.

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