CN112216927A - Lithium ion battery diaphragm and production process thereof - Google Patents
Lithium ion battery diaphragm and production process thereof Download PDFInfo
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- CN112216927A CN112216927A CN202011044739.4A CN202011044739A CN112216927A CN 112216927 A CN112216927 A CN 112216927A CN 202011044739 A CN202011044739 A CN 202011044739A CN 112216927 A CN112216927 A CN 112216927A
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- chilling roller
- lithium ion
- ion battery
- temperature melt
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
- B29C48/001—Combinations of extrusion moulding with other shaping operations
- B29C48/0018—Combinations of extrusion moulding with other shaping operations combined with shaping by orienting, stretching or shrinking, e.g. film blowing
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
- B29C48/001—Combinations of extrusion moulding with other shaping operations
- B29C48/0021—Combinations of extrusion moulding with other shaping operations combined with joining, lining or laminating
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
- B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
- B29C48/07—Flat, e.g. panels
- B29C48/08—Flat, e.g. panels flexible, e.g. films
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
- B29C48/25—Component parts, details or accessories; Auxiliary operations
- B29C48/88—Thermal treatment of the stream of extruded material, e.g. cooling
- B29C48/885—External treatment, e.g. by using air rings for cooling tubular films
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
- B29C48/25—Component parts, details or accessories; Auxiliary operations
- B29C48/88—Thermal treatment of the stream of extruded material, e.g. cooling
- B29C48/911—Cooling
- B29C48/9135—Cooling of flat articles, e.g. using specially adapted supporting means
- B29C48/914—Cooling of flat articles, e.g. using specially adapted supporting means cooling drums
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention discloses a lithium ion battery diaphragm and a production process thereof, wherein the production process comprises the following steps: mixing an olefin polymer with an organic solvent to prepare a mixture; extruding the mixture through an extruder and a die head to form high-temperature melt, and flowing out; the front and back surfaces of the cast piece are synchronously cooled by a main chilling roller and an auxiliary chilling roller respectively and then are cooled by a cooling tank to obtain a cast piece; and stretching, extracting and heat setting the casting sheet to obtain the microporous diaphragm. Through the mode, the main chilling roller and the auxiliary chilling roller are matched for synchronous cooling, and then the film is cooled through the main chilling roller and the cooling tank, so that the physical property consistency of the film can be greatly improved.
Description
Technical Field
The invention relates to the technical field of lithium ion battery diaphragms, in particular to a lithium ion battery diaphragm and a production process thereof.
Background
The lithium ion battery diaphragm is divided into a dry method and a wet method according to different preparation processes, and the wet method is also called a phase separation method or a thermal separation method. The wet process is to mix polypropylene (PP) or Polyethylene (PE) with white oil, to form uniform melt mixture after heating and melting by an extruder, then to cool and phase separate by a casting process to prepare a microporous membrane, to heat the membrane to a temperature close to the melting point, to perform biaxial tension to align molecular chains, to preserve heat for a certain time, to elute residual solvent by volatile substances, to prepare the mutually communicated microporous membrane material.
Currently, the following two common methods for thermally induced phase separation in the sheet casting process are used: 1. the method comprises the following steps of (1) setting the temperature of a chilling roller by using the chilling roller, attaching melt flowing out of a die head to the chilling roller, enabling the melt to be rapidly cooled, and enabling white oil to be rapidly separated from PE/PP to form micropores; 2. the method comprises the following steps of using a chilling roller and a water tank, wherein water with a certain temperature is filled in the water tank, cooling the melt by using the water and the chilling roller simultaneously when the melt is attached, and reducing the difference of the thermal phase separation speed of the front side (namely the film surface contacting the chilling roller) and the back side (namely the film surface not contacting the chilling roller) of the diaphragm. In the former method using the chill roll, when the melt is attached with the sheet, because the temperature of the air is inconsistent with that of the chill roll, the phase separation rate of the front surface and the back surface is inconsistent, and the crystallization rate is inconsistent, the consistency of the physical properties of the film is influenced; in the latter method using a chill roll and a water tank, since the boiling point of water is 100 ℃, and the melt enters the water tank after being cast, the film surface temperature is not necessarily lower than 100 ℃, and when the film surface temperature is higher than or equal to 100 ℃, the water in contact with the film surface boils, which adversely affects the appearance of the film.
Disclosure of Invention
The present invention is directed to solving at least one of the problems of the prior art. Therefore, the invention provides a lithium ion battery diaphragm and a production process thereof.
The technical scheme adopted by the invention is as follows:
the invention provides a production process of a lithium ion battery diaphragm, which comprises the following steps:
s1, mixing the olefin polymer with an organic solvent to prepare a mixture;
s2, enabling the mixture to pass through an extruder and a die head to form high-temperature melt to flow out, synchronously cooling the front and back surfaces of the high-temperature melt through a main chilling roller and an auxiliary chilling roller respectively, and cooling the high-temperature melt through a cooling tank to obtain a cast sheet;
and S3, stretching, extracting and heat setting the casting sheet to obtain the microporous diaphragm.
According to some embodiments of the present invention, step S2 specifically includes: the mixture passes through an extruder and a die head to form high-temperature melt to flow out, the high-temperature melt is attached to a main chilling roller, an auxiliary chilling roller is synchronously operated to be attached to the other side of the high-temperature melt on the main chilling roller, the temperature and the rotating speed of the auxiliary chilling roller are controlled to be the same as those of the main chilling roller, the rotating directions of the auxiliary chilling roller and the main chilling roller are opposite, and therefore the synchronous cooling of the front side and the back side of the high-temperature melt attached to the main chilling roller through the main chilling roller and the auxiliary chilling roller is achieved; the film sheet then travels a distance with the main chill roll and is immersed in a cooling bath so that it is cooled by the cooling bath.
The side of the melt, which is attached to the main chilling roller, is the front side, and the side of the melt, which is attached to the auxiliary chilling roller, is the reverse side.
In order to improve the uniformity of the formed cast sheet, the main chill roll and the auxiliary chill roll can be designed to be symmetrical with respect to the die angle. In order to facilitate accurate control, the auxiliary chill roll can be connected with a position control device, and the position control device can be controlled by a cylinder and a linear motor together. In addition, the auxiliary chilling roller can be connected with a temperature control device, the temperature control device can be used for controlling the process chilled water, and specifically, a water inlet pipe and a water outlet pipe are arranged on the auxiliary chilling roller, and the flow of the process chilled water entering and exiting the auxiliary chilling roller is controlled through the water inlet pipe and the water outlet pipe so as to control the temperature. The primary chill roll may also be fitted with similar temperature control devices. The primary chill roller and the secondary chill roller may be controlled in unison by the same control system.
In addition, the main chilling roller and/or the auxiliary chilling roller can be provided with an oil removing device, and the oil removing device can be an oil removing roller or an oil scraping knife. The diameter of the main chilling roller can be designed to be 0.8-1 m; the diameter of the auxiliary chill roll can be designed to be 0.1-0.3 m. The primary and secondary chill rollers may be made of 321 stainless steel or other materials.
According to some embodiments of the invention, the die head has a temperature of 140 to 280 ℃ and the primary chill roll and the secondary chill roll have a temperature of 20 to 55 ℃.
According to some embodiments of the present invention, step S1 specifically includes: mixing an olefin polymer A with an organic solvent A to prepare a mixture A, and mixing an olefin polymer B with an organic solvent B to prepare a mixture B;
in step S2, the die head includes a first discharging channel and a second discharging channel arranged in a stacked manner; step S2 specifically includes: the mixture A forms a first high-temperature melt flow through a first extruder and a first discharge channel of the die head; the mixture B forms a second high-temperature melt through a second extruder and a second discharge channel of the die head, the second high-temperature melt flows out, the first high-temperature melt and the second high-temperature melt are stacked and attached to the main chill roll, the front and back surfaces of the mixture B are synchronously cooled through the main chill roll and the auxiliary chill roll respectively, and then the mixture B is cooled through a cooling tank to obtain a cast sheet;
alternatively, step S2 specifically includes: forming a first high-temperature melt flow out of the mixture A through a first extruder and a first die head; the mixture B forms a second high-temperature melt through a second extruder and a second die head and flows out; the first high-temperature melt and the second high-temperature melt are stacked and attached to the main chilling roller, and the front and the back of the first high-temperature melt are synchronously cooled by the main chilling roller and the auxiliary chilling roller respectively and then cooled by the cooling tank to obtain the cast sheet.
According to the structural requirements of the actual lithium ion battery diaphragm, the target lithium ion battery diaphragm can be designed to have a multilayer structure, such as two layers, three layers, six layers and the like. Specifically, the membrane may have two different layers, for example, an asymmetric multilayer structure such as A/B or A/B/C, A/B/C/A, or a symmetric multilayer structure such as A/B/A, A/B/C/B/A. The two different layers can be made of olefin polymers with different molecular weights, for example, one layer is a polyethylene layer, and the other layer is an alpha-olefin polymer layer, such as polypropylene, ethylene-propylene copolymer, polyisobutylene, etc. According to the layer structure of the prepared diaphragm, the die head can be correspondingly designed to be provided with a plurality of discharge channels, so that the material of the corresponding layer body can be injected into the corresponding discharge channels, and the diaphragm with the corresponding multilayer structure can be formed through subsequent operation; or a plurality of die heads can be adopted, and cast sheets extruded by different die heads are laminated and compounded to form the diaphragm with the multilayer structure.
According to some embodiments of the present invention, in the step S1, the content of the olefin polymer in the mixture is 15 to 30 wt%, and the content of the organic solvent is 70 to 85 wt%.
According to some embodiments of the invention, the olefin polymer comprises polyethylene; preferably, the olefin polymer comprises ultra high molecular weight polyethylene and/or high density polyethylene. The ultra-high molecular weight polyethylene can be ultra-high molecular weight polyethylene with the molecular weight of 100-150 ten thousand, and the high density polyethylene can be polyethylene with the density of 0.940-0.976 g/cm3And a high density polyethylene having a molecular weight of less than 100 million. The organic solvent can be organic liquid with low melting point, low volatility and high flash point and safety; preferably, the organic solvent comprises white oil.
According to some embodiments of the invention, the olefin polymer comprises a weight ratio of 1: (1-4) are ultra-high molecular weight polyethylene and high density polyethylene.
According to some embodiments of the invention, in the step S3, the stretch has a longitudinal stretch ratio of 4 to 8 times and a transverse stretch ratio of 5 to 10 times.
According to some embodiments of the invention, the stretching comprises longitudinal stretching and transverse stretching; the temperature of the longitudinal drawing is 60-95 ℃; the temperature of the transverse drawing is 110-125 ℃.
In step S3, the extractant used for the extraction is generally a low-boiling, volatile organic solvent, such as Dichloromethane (DCM).
In a second aspect of the present invention, a lithium ion battery separator is provided, which is prepared by any one of the production processes of the lithium ion battery separator provided in the first aspect of the present invention, wherein the friction coefficient of the lithium ion battery separator is 0.4 to 0.7, and the deviation of the friction coefficient of the front and back surfaces of the lithium ion battery separator is 0.03 to 0.06.
The embodiment of the invention has the beneficial effects that:
the embodiment of the invention provides a production process of a lithium ion battery diaphragm, wherein an auxiliary chill roll is used for being matched with a high-temperature melt attached to a main chill roll to be synchronously cooled to form a cast sheet, the back surface of the cast sheet is contacted with the auxiliary chill roll when contacting the main chill roll to carry out thermotropic phase separation, and the thermotropic phase separation is fully carried out at the same time, and the thermotropic phase separation can be fully carried out on the front surface and the back surface of the cast sheet at the same speed by controlling the temperature consistency of the two chill rolls, so that the physical property consistency of a film is greatly improved; after being synchronously cooled by the main chilling roller and the auxiliary chilling roller, the cooling roller is cooled by the cooling tank, so that the problem that the appearance of the film surface is influenced by boiling of cooling liquid caused by overhigh temperature when the cooling liquid enters the cooling tank can be avoided. The diaphragm prepared by the production process of the lithium ion battery diaphragm has high physical property consistency, the friction coefficient of the diaphragm is within the range of 0.4-0.6, the deviation range of the friction coefficient of the front surface and the back surface of the diaphragm is 0.01-0.05, and the diaphragm has physical property consistency.
Drawings
FIG. 1 is a process flow diagram of a portion of the production of a lithium ion battery separator in accordance with the present invention;
FIG. 2 is a scanning electron microscope image of the front surface of the lithium ion battery separator prepared in example 1 of the present invention;
FIG. 3 is a scanning electron microscope image of the reverse side of the lithium ion battery separator prepared in example 1 of the present invention.
Detailed Description
The concept and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments to fully understand the objects, features and effects of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and those skilled in the art can obtain other embodiments without inventive effort based on the embodiments of the present invention, and all embodiments are within the protection scope of the present invention.
Example 1
A production process of a lithium ion battery diaphragm comprises the following steps:
uniformly mixing ultrahigh molecular weight polyethylene powder, High Density Polyethylene (HDPE) powder and white oil in a mass ratio of 1:2:7 to obtain a mixture; extruding the mixture by an extruder to obtain a high-temperature melt, and conveying the high-temperature melt to a die head at 200 ℃;
referring to fig. 1, the high-temperature melt flows out of the discharge port of the die head 10 and is attached to the main chill roll 20, the auxiliary chill roll 30 is synchronously operated to be attached to the other side of the high-temperature melt on the main chill roll 10, the temperatures of the main chill roll 10 and the auxiliary chill roll 30 are both controlled to be 30 ℃, and the rotation directions of the auxiliary chill roll 30 and the main chill roll 20 are opposite, so that the front side and the back side of the high-temperature melt attached to the main chill roll 20 are synchronously cooled by the main chill roll 20 and the auxiliary chill roll 30 respectively; then, the cooling water runs for a certain distance along with the main chill roll 20 and is immersed into the cooling tank 40, the cooling tank 40 is filled with water cooling liquid, and the temperature of the cooling liquid is controlled at 25 ℃, so that the cooling liquid is cooled by the cooling tank 40, and a cast sheet 70 is prepared; the main chill roll 20 is provided with an oil scraper 21 in a matching way, and the oil scraper 21 is arranged opposite to the roll surface of the main chill roll 20; after passing through the cooling tank 40, the cast slab 70 is drawn out through the peeling roller 50; in addition, a press roll 60 can be arranged at the opposite position of the stripping roll 50, the cast sheet 70 is wound through the gap between the press roll 60 and the stripping roll 50, and residual cooling liquid on the cast sheet 70 is removed through the squeezing action of the two;
conveying the cast sheet into a stretching unit for biaxial stretching, wherein the longitudinal stretching temperature is 90 ℃, and the longitudinal stretching ratio is 4.5 times; the transverse drawing temperature is 125 ℃, and the transverse drawing ratio is 5.5 times;
sending the stretched film into an extraction tank for extraction and drying, extracting white oil from the stretched film, and drying at 60 ℃ to obtain a dried film; the extractant in the extraction tank adopts Dichloromethane (DCM); and then carrying out heat setting on the obtained film, removing stress through an oven system, and then sending the film to an online winding machine for winding to obtain the lithium ion battery diaphragm.
Example 2
A production process of a lithium ion battery diaphragm comprises the following steps:
uniformly mixing the ultrahigh molecular weight polyethylene powder and the white oil in a mass ratio of 1:5 to obtain a mixture A; uniformly mixing high-density polyethylene (HDPE) powder and white oil in a mass ratio of 1:5 to obtain a mixture B; the mass ratio of the mixture A to the mixture B is 1: 3;
conveying the high-temperature melt A obtained by the mixture A through an extruder to a first discharge channel of a die head at the temperature of 200 ℃; conveying the high-temperature melt B obtained by the mixture B through an extruder to a second discharge channel of a die head at the temperature of 200 ℃;
the high-temperature melt A and the high-temperature melt B simultaneously flow out of discharge ports of a first discharge channel and a second discharge channel of the die head and are overlapped on the main chilling roller, the auxiliary chilling roller is synchronously operated to be attached to the other side of the high-temperature melt on the main chilling roller, the temperatures of the main chilling roller and the auxiliary chilling roller are controlled to be 25 ℃, and the rotation directions of the auxiliary chilling roller and the main chilling roller are opposite, so that the front side and the back side of the high-temperature melt attached to the main chilling roller are synchronously cooled by the main chilling roller and the auxiliary chilling roller respectively; then, the cast piece moves for a certain distance along with the main chilling roller and is immersed into a cooling tank, water cooling liquid is filled in the cooling tank, the temperature of the cooling liquid is controlled at 23 ℃, so that the cooling liquid is cooled by the cooling tank and then is led out by a stripping roller and a compression roller, and the cast piece with a double-layer structure is prepared;
conveying the cast sheet into a stretching unit for biaxial stretching, wherein the longitudinal stretching temperature is 90 ℃, and the longitudinal stretching ratio is 7 times; the transverse drawing temperature is 115 ℃, and the transverse drawing ratio is 9 times;
sending the stretched film into an extraction tank for extraction and drying, extracting white oil from the stretched film, and drying at 80 ℃ to obtain a dried film; the extractant in the extraction tank adopts Dichloromethane (DCM); and then carrying out heat setting on the obtained film, removing stress through an oven system, and then sending the film to an online winding machine for winding to obtain the lithium ion battery diaphragm.
Example 3
A production process of a lithium ion battery diaphragm comprises the following steps:
mixing ultra-high molecular weight polyethylene powder and white oil according to a mass ratio of 1:4, uniformly mixing to obtain a mixture A; uniformly mixing polypropylene powder and white oil in a mass ratio of 1:4 to obtain a mixture B; the mass ratio of the mixture A to the mixture B is 2: 1;
extruding the mixture A through an extruder to obtain a high-temperature melt A, and conveying the high-temperature melt A to a first discharge channel of a die head at the temperature of 200 ℃; extruding the mixture B through an extruder to obtain a high-temperature melt B, and conveying the high-temperature melt B to a second discharge channel of the die head at the temperature of above 200 ℃; extruding the mixture A through an extruder to obtain a high-temperature melt A, and conveying the high-temperature melt A to a third discharge channel of the die head at the temperature of above 200 ℃;
the high-temperature melt flows out of the discharge ports of the first discharge channel, the second discharge channel and the third discharge channel of the die head at the same time, and is attached to the main chill roll in an A/B/A (alternating/alternating) mode, the auxiliary chill roll is synchronously operated to be attached to the other side of the high-temperature melt on the main chill roll, the temperatures of the main chill roll and the auxiliary chill roll are controlled to be 25 ℃, and the rotation directions of the auxiliary chill roll and the main chill roll are opposite, so that the front side and the back side of the high-temperature melt attached to the main chill roll are synchronously cooled by the main chill roll and the auxiliary chill roll respectively; then, the cast piece moves for a certain distance along with the main chilling roller and is immersed into a cooling tank, water cooling liquid is filled in the cooling tank, the temperature of the cooling liquid is controlled at 23 ℃, so that the cooling liquid is cooled by the cooling tank and then is led out by a stripping roller and a compression roller, and the cast piece with a three-layer structure is prepared;
conveying the cast sheet into a stretching unit for biaxial stretching, wherein the longitudinal stretching temperature is 75 ℃, and the longitudinal stretching ratio is 7 times; the transverse drawing temperature is 115 ℃, and the transverse drawing ratio is 9 times;
sending the stretched film into an extraction tank for extraction and drying, extracting white oil from the stretched film, and drying at 80 ℃ to obtain a dried film; the extractant in the extraction tank adopts Dichloromethane (DCM); and then carrying out heat setting on the obtained film, removing stress through an oven system, and then sending the film to an online winding machine for winding to obtain the lithium ion battery diaphragm.
Comparative example 1
A production process of a lithium ion battery diaphragm comprises the following steps:
uniformly mixing ultrahigh molecular weight polyethylene powder, High Density Polyethylene (HDPE) powder and white oil in a mass ratio of 1:2:7 to obtain a mixture; extruding the mixture by an extruder to obtain a high-temperature melt, and conveying the high-temperature melt into a die head at 200 ℃; the high-temperature melt flows out of a discharge hole of the die head and is attached to a main chilling roller, the temperature of the main chilling roller is controlled to be 30 ℃, the main chilling roller runs along with the main chilling roller and is immersed into a cooling tank, water cooling liquid is contained in the cooling tank, and the temperature of the cooling liquid is controlled to be 25 ℃, so that the cooling liquid is cooled by the cooling tank, and a cast piece is prepared;
conveying the cast sheet into a stretching unit for biaxial stretching, wherein the longitudinal stretching temperature is 90 ℃, and the longitudinal stretching ratio is 4.5 times; the transverse drawing temperature is 125 ℃, and the transverse drawing ratio is 5.5 times;
sending the stretched film into an extraction tank for extraction and drying, extracting white oil from the stretched film, and drying at 60 ℃ to obtain a dried film; the extractant in the extraction tank adopts Dichloromethane (DCM); and then carrying out heat setting on the obtained film, removing stress through an oven system, and then sending the film to an online winding machine for winding to obtain the lithium ion battery diaphragm.
Comparative example 2
A production process of a lithium ion battery diaphragm comprises the following steps:
uniformly mixing ultrahigh molecular weight polyethylene powder, High Density Polyethylene (HDPE) powder and white oil in a mass ratio of 1:2:7 to obtain a mixture;
extruding the mixture by an extruder to obtain a high-temperature melt, and conveying the high-temperature melt into a die head at 200 ℃; the high-temperature melt flows out of a discharge hole of the die head and is attached to a main chilling roller, the temperature of the main chilling roller is controlled to be 30 ℃, the high-temperature melt runs for a certain distance along with the main chilling roller, so that the front side of the high-temperature melt is cooled by the main chilling roller, and the back side of the high-temperature melt is in contact with air for cooling, so that a cast piece is prepared;
conveying the cast sheet into a stretching unit for biaxial stretching, wherein the longitudinal stretching temperature is 75 ℃, and the longitudinal stretching ratio is 4.5 times; the transverse drawing temperature is 125 ℃, and the transverse drawing ratio is 5.5 times;
sending the stretched film into an extraction tank for extraction and drying, extracting white oil from the stretched film, and drying at 60 ℃ to obtain a dried film; the extractant in the extraction tank adopts Dichloromethane (DCM); and then carrying out heat setting on the obtained film, removing stress through an oven system, and then sending the film to an online winding machine for winding to obtain the lithium ion battery diaphragm.
The lithium ion battery diaphragms prepared in the above examples 1-3 and comparative examples 1-2 were subjected to performance tests, and specific test indexes and test methods were as follows:
1. the front and back sides of the lithium ion battery separator prepared in example 1 were tested by using a Scanning Electron Microscope (SEM), and SEM images obtained are shown in fig. 2 and 3. Wherein, fig. 2 is a topographic map of the front side (x 5000) of the lithium ion battery separator, and fig. 3 is a topographic map of the back side (x 5000) of the lithium ion battery separator.
As can be seen from fig. 2 and 3, the original fibers and pores formed on the front and back surfaces of the lithium ion battery separator have uniform structure, moderate pore size, small difference in structural properties between the front and back surfaces, and good consistency in basic physical properties.
2. The lithium ion battery diaphragm prepared in the embodiment 1-3 and the comparative example 1-2 is subjected to performance test, and the specific test method comprises the following steps:
(1) thickness: reference is made to the provisions of GB/T6672-2001, wherein the resolution of the thickness gauge should not be greater than 0.1 μm, and no less than 3 points are measured at equal distances in the width direction, and the average value is taken.
(2) Air permeability: ventilating: according to the specification of GB/T36363-2018, the 100ml air passing area is 6.45cm under the pressure of 1.21KPa2The time required for the septum.
(3) Average pore diameter: mean pore size data were obtained using PMI instrument measurements, pore size expressed in nm.
(4) Coefficient of friction: the friction coefficient data are obtained by testing with a friction coefficient tester according to the specification of the friction coefficient measuring method of GB/T10006 plastic films and sheets.
The performance of the lithium ion battery separators of the examples 1 to 3 and the comparative examples 1 to 2 was tested according to the above method, and the results are shown in the following table 1:
table 1 properties of each example and comparative example lithium ion battery separator
As can be seen from the above Table 1, the lithium ion battery separators prepared in the embodiments 1 to 3 have high physical property consistency, the friction coefficient of the separator is within the range of 0.4 to 0.6, the deviation range of the friction coefficient of the front surface and the back surface of the separator is 0.01 to 0.05, the separator has physical property consistency, and the performance of the separator is superior to that of the lithium ion battery separators prepared in the production processes of the comparative examples 1 and 2.
Claims (10)
1. A production process of a lithium ion battery separator is characterized by comprising the following steps:
s1, mixing the olefin polymer with an organic solvent to prepare a mixture;
s2, enabling the mixture to pass through an extruder and a die head to form high-temperature melt to flow out, synchronously cooling the front and back surfaces of the high-temperature melt through a main chilling roller and an auxiliary chilling roller respectively, and cooling the high-temperature melt through a cooling tank to obtain a cast sheet;
and S3, stretching, extracting and heat setting the casting sheet to obtain the microporous diaphragm.
2. The production process of the lithium ion battery separator according to claim 1, wherein the step S2 specifically includes: the mixture passes through an extruder and a die head to form high-temperature melt to flow out, the high-temperature melt is attached to a main chilling roller, an auxiliary chilling roller is synchronously operated to be attached to the other side of the high-temperature melt on the main chilling roller, the temperature and the rotating speed of the auxiliary chilling roller are controlled to be the same as those of the main chilling roller, the rotating directions of the auxiliary chilling roller and the main chilling roller are opposite, and therefore the synchronous cooling of the front side and the back side of the high-temperature melt attached to the main chilling roller through the main chilling roller and the auxiliary chilling roller is achieved; the film sheet then travels a distance with the main chill roll and is immersed in a cooling bath so that it is cooled by the cooling bath.
3. The production process of the lithium ion battery separator according to claim 2, wherein the temperature of the die head is 140-280 ℃, and the temperature of the main chill roll and the auxiliary chill roll is 20-55 ℃.
4. The process for producing a lithium ion battery separator according to claim 2,
step S1 specifically includes: mixing an olefin polymer A with an organic solvent A to prepare a mixture A, and mixing an olefin polymer B with an organic solvent B to prepare a mixture B;
in step S2, the die head includes a first discharging channel and a second discharging channel arranged in a stacked manner; step S2 specifically includes: the mixture A forms a first high-temperature melt flow through a first extruder and a first discharge channel of the die head; the mixture B forms a second high-temperature melt outflow through a second discharge channel of the die head of a second extruder; the first high-temperature melt and the second high-temperature melt are stacked and attached to the main chilling roller, and the front and back surfaces of the first high-temperature melt and the second high-temperature melt are synchronously cooled by the main chilling roller and the auxiliary chilling roller respectively and then cooled by the cooling tank to obtain a cast sheet;
alternatively, step S2 specifically includes: forming a first high-temperature melt flow out of the mixture A through a first extruder and a first die head; the mixture B forms a second high-temperature melt through a second extruder and a second die head and flows out; the first high-temperature melt and the second high-temperature melt are stacked and attached to the main chilling roller, and the front and the back of the first high-temperature melt are synchronously cooled by the main chilling roller and the auxiliary chilling roller respectively and then cooled by the cooling tank to obtain the cast sheet.
5. The production process of the lithium ion battery separator according to claim 1, wherein in step S1, the content of the olefin polymer in the mixture is 15 to 30 wt%, and the content of the organic solvent is 70 to 85 wt%.
6. The process for producing a lithium ion battery separator according to claim 5, wherein the olefin polymer comprises polyethylene; preferably, the olefin polymer comprises ultra high molecular weight polyethylene and/or high density polyethylene.
7. The production process of the lithium ion battery separator according to claim 6, wherein the olefin polymer comprises a monomer having a mass ratio of 1: (1-4) an ultrahigh-molecular-weight polyethylene and a high-density polyethylene.
8. The process for producing a lithium ion battery separator according to any one of claims 1 to 7, wherein in step S3, the draw ratio is 4 to 8 times in the longitudinal direction and 5 to 10 times in the transverse direction.
9. The process for producing a lithium ion battery separator according to claim 8, wherein the stretching comprises a longitudinal stretching and a transverse stretching; and the temperature of the longitudinal drawing is 60-95 ℃; the temperature of the transverse drawing is 110-125 ℃.
10. The lithium ion battery separator is characterized by being prepared by the production process of the lithium ion battery separator as claimed in any one of claims 1 to 9, wherein the friction coefficient of the lithium ion battery separator is 0.4-0.7, and the deviation of the friction coefficient of the front side and the back side of the lithium ion battery separator is 0.03-0.06.
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